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78th EAGE Conference and Exhibition 2016
- Conference date: May 30, 2016 - June 2, 2016
- Location: Online
- Published: 30 May 2016
101 - 150 of 1034 results
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Numerical Study of Thermohydrodynamic Processes in Inclined Wells with Variable Trajectory
Authors R.F. Sharafutdinov, R.A. Valiullin, A.S. Ramazanov, A. Sharipov and T.R. KhabirovSummaryHorizontal wells is effective method of oil and gas development. One of the important tasks is production control of horizontal wells. At this case, interpretation of logging data is a very difficult task. First problem is uneven trajectory because horizontal well typically have ascending, horizontal and descending sections, in which the phase velocity and fluid holdup is changed (in this paper consider oil and water stratified flows). Secondly, in the ascending section of horizontal well can occurs countercurrent flow. Thirdly, the heat exchange between fluid phases and the surrounding rocks take place and it influence on temperature distribution.
The paper discusses a mathematical model for the calculation of fluids holdup, velocities and temperature distribution along horizontal wells with countercurrent flow. The calculation results of fluids holdup, velocities and temperature distribution are shown in paper and analysis of countercurrent flow influence are made.
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A New Correlation for Prediction of Critical Two-phase Flow through Wellhead Chokes
Authors H.R. Nasriani, M. MoradiDowlatAbad and A. KalantariaslSummaryThe first scope of this study is to develop a new accurate empirical Gilbert type critical flow correlation based on 361 actual production tests data from Middle Eastern oil fields by means of non-linear regression analysis. The second scope is to study the impact of temperature on Gilbert type critical flow correlation for these data sets.
In order to modify the Gilbert type critical flow correlation for these data sets, correlations are tuned based on available field data points using nonlinear regression method. in this study, generalized reduced gradient (GRG) algorithm of iteration was used to find the correlation coefficients based on available field data and the convergence criteria is to minimize the value of the squared sum, SS, of the difference between the real data and the estimated one.
Based on error analysis, for the oil fields, liquid flow rate prediction is improved when new approaches (including/excluding temperature) are used. It is also concluded that the accuracy of new approach to predict production rate is not expressively improved by including the temperature in choke performance correlation for this data set compared to the case without temperature.
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Case Study of Asphaltene Flow Assurance Risk Mitigation - Emerging Numerical Model to Evaluate Inhibitor Efficiency
More LessSummaryThis work was motivated for establishing a robust asphaltene flow assurance engineering in an onshore oil field that has a high risk of asphaltene precipitation in tubing. A typical counter measure was considered to apply asphaltene inhibitor, therefore, the best candidate IB-23 was selected through the two staged asphaltene dispersant test (ADT) from total nineteen samples. The IB-23 revealed high inhibiting efficiency more than 80 % at 200 ppm concentration and maintained its efficiency more than 70 % even at 10 ppm. For further evaluating persistent of inhibiting efficiency during entire field life in which operating condition in tubing is varied, an emerging technique was developed to numerically model inhibitor. Currently, any commercial software is not available for allowing such modelling of asphaltene inhibitor due to confidentiality for inhibitor’s physical data. This study achieved to model inhibiting efficiency by treating inhibitor as pseudo-resin. It could be defined using limited physical data that was available in public accessible material safety data sheet (MSDS). Consequently, the inhibiting efficiency was expressed as size-reduction of asphaltene precipitation envelope (APE) on thermodynamic plot. Comparison between APEs and vertical lift curves could provide a comprehensive prediction of the inhibitor effect at early and late field life.
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Dual and Intelligent Completions Optimize Producing Gas Wells
By M BoussaSummaryAt Hassi R’Mel field, dual completions could significantly improve output from multi-zone gas wells, but results from intelligent completions look even better.
Dual completions were used for a long time to produce wells perforated in several zones, mostly for oil wells and rarely for gas wells. To improve production in the upper zones of Algerian gas wells, a study was conducted on producing gas wells with two and three zones in Hassi-R’Mel field. Discovered in 1956, this field is 500 km south of Algiers in the Sahara Desert and is one of the world’s largest wet gas reservoirs.
Engineers at the operator, Sonatrach, studied the choice of completion method and suggested installing dual completions for wells with several zones. This study would demonstrate the necessity of using dual completions in gas producers with several reservoirs, to improve upper-zone production and avoid cross-flow from one zone to another. Initial results made it possible to conduct a technical/economic study that showed the effects on the reservoir, well equipment and investment costs.
This article discusses the advantages and disadvantages of dual completions on gas wells, and shows the profit ratio on capital costs after these completions.
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Acid Matrix Stimulation to Reveal Formation Damage in Greater Burgan Oilfield Clastic Reservoir
Authors B.S Alshammari, N.M. Rane, D.S. Almatar and A.K. AlrabahSummaryEvaluation and classification of formation damage type and magnitude is critical exercise in oil industry. Formation damage around wellbore can be evaluated from various well testing techniques, that can provide amount of the total skin factor as an overall measurement of the formation damage. This paper focus on acid matrix stimulation in a clastic reservoir in Burgan field to remove formation damage formed around well bore by drilling and completion operations in a newly drilled well. Matrix stimulation encompasses pumping processes used to improve the connection between wellbore and reservoir to remove formation damage caused by factors such as: drilling mud, cementing operation, completion fluid and perforation. Consequently, this will dominates permeability reduction in the porous media in the invaded zone. As a result of this skin damage, oil production rate will be affected and reduced, high decline rate in production, short production life time and extra pressure drawdown will be required for production. Therefore, planning a proper acid matrix stimulation treatment is essential to increase revenue from oil well by removing and overcoming skin damage resulted from drilling fluids, enhance well productivity to increase oil production rate and meet the target rate and KPI especially for newly drilled well.
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Development of a Comprehensive Well Performance Assessment in a Giant Gas Condensate Field
Authors M. Sheydaeemehr, S. Dowlati and M. PasdarSummaryProductivity loss due to condensate blockage is the main and common problem in gas condensate reservoirs around the world. In this paper, a comprehensive framework is developed to assess the performances of the different well trajectories in a giant field. The studied field is one of the world’s largest gas condensate fields located in the Middle East and has been produced for more than ten years from four non-communicating layers in Kangan-Dalan formations.
A comprehensive comparison between the vertical well and the deviated well was performed using surface testing, production history, and reservoir simulation data.
Based on the surface well testing, IPR curves show the better performance of the deviated well. It is concluded from the simulation results that, on the one hand, development of a deviated well in the gas condensate field delays the emergence of the dew point pressure, results in longer production plateau period, and delivers more cumulative production of the gas and the condensate in the life of the well. On the other hand, the vertical well causes higher condensate saturation around the well and more severe reduction in relative permeability of gas phase and productivity index of the well below the dew point pressure.
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Parametric Study of Condensate Bank Development and Well Productivity Loss in Gas Condensate Wells
Authors A. Sheikhoushaghi, M. Ghoroori and M. RasaeiSummaryCondensate bank is formed near the wellbore after bottom-hole pressure is dropped below the dew point pressure. Based on Fevang theory (1995), the main source of productivity loss in gas condensate (GC) wells is region 1 (the closet region to the wellbore), where condensate saturation exceeded critical value. The size of region 1 increases with time. The maximum condensate saturation and development of condensate bank depends on a combination of different parameters.
In this study, a parametric analysis was carried out to investigate the development of region 1 and productivity loss in the GC wells. It was found that production rate impacts the formation time of region 1, while its development with respect to pressure depletion is identical for various production rates. Increasing fluid richness results in faster development of region 1, while the effect of critical condensate saturation is in reverse.
The degree of productivity loss is mainly a function of SCAL data rather than fluid type and production rate. The maximum condensate saturation in the vicinity of wellbore is higher than PVT test condensate dropout, and depends on SCAL data. The degree and time of productivity loss can be estimated by a simple method proposed in this study.
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Porosity Calculation of Horizontal Wells when Acoustic Slowness Is Abnormal - A Case Study in Northern Ordos Basin, China
More LessSummaryOwing to the complicated borehole environment and detection characteristics of acoustic log, acoustic slowness is always partial distortion in the horizontal wells. Besides, the logging data is sometimes insufficient due to the expensive cost and imperfect technology. Therefore the porosity calculation with insufficient and partial wrong horizontal logging data becomes one of the big challenges. Such as in the Shiguhao Area which is located in northern Ordos basin, only several logs have been measured. Through the horizontal well log interpretation and formation evaluation work, we found that the acoustic slowness was abnormal in some formations by the stratigraphic correlation. Then, several factors which lead to the high acoustic slowness are summarized in this paper. For the porosity calculation in the horizontal wells, the abnormal acoustic slowness is not recommended to be used because it can be so hardly corrected that may reduce the accuracy of the calculation since others always get the defective result by acoustic correction. Meanwhile, due to the lack of density log, we propose the use of compensated neutron log instead of abnormal acoustic log to calculate porosity. Several case studies are in great consistent with oil test results which confirm the feasibility of our method.
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Geophysical Characterization of Landslides in Serbia and Bosnia and Hercegovina – A GWB Project
Authors M. Urosevic, S. Komatina, M. Burazer, K. Suto, S. Arsenovic, D. Milosevic, S. Ziramov and F. CorenSummaryContinuous, heavy rainfall commencing in May 2014 has resulted in extensive flooding in Serbia, Bosnia and Herzegovina (BiH). Thousands of landslides developed rapidly after several days of torrential rain.
Shortly after a diverse group of geophysicists and geologists got together and set out a project to investigate these landslides. The main objective was to characterize and categorize landslides and provide results that could help devise an optimum mitigation program. Prediction of the reactivation potential of landslides was also of direct interest to the investigations. In the first phase of the project investigations included simultaneous acquisition of reflection, refraction, MASW and resistivity data along 17 profiles, distributed over six different localities. In addition, a mini 3D survey was successfully recorded along steep slope. These measurements were supported by sparse drilling, logging, coring, geotechnical analysis and the airborne laser scans.
Very good agreement was achieved between different methods, despite vastly different geometry and composition of landslides. Joint analysis of resistivity images, reflection data, and P and S-velocity fields, obtained from refraction tomography and inversion of surface waves, provide new geological insights that are important for understanding the mechanism of a landslide. This will provide valuable input for a mitigation program.
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Euler Deconvolution of the Analytic Signals of Gravity Gradient Tensor for Underground Horizontal Pipeline
More LessSummaryAt present, there are few inversion methods for horizontal pipelines. In this paper, a data interpretation approach is applied to estimate the source parameters of underground horizontal ferromagnetic pipeline. The horizontal pipeline is divided into small pieces, and every piece can be regarded as a point mass to calculate the corresponding gravity gradient tensor. By superposition principle, the gravity gradient tensor of the whole pipeline is obtained. Euler deconvolution of the analytic signal of gravity gradient tensor can be solved by analytic signal instead of gravity field derivatives. The result shows that this method can estimate the source location accurately and draw the outline of horizontal pipeline effectively. Depending on high resolution and high sensitivity of gravity gradient tensor data, analytic signal has the advantage of determining the location of anomalies bodies. Euler deconvolution of the analytic signals of gravity gradient tensor is a geophysical inversion method which can estimate the boundary position of the source automatically or semi-automatically without a priori information, and eliminate the influences of structural index and background field.
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Application of In-mine Geoelectric Methods for Detecting Tectonic Disturbances of the Coal Seam Structure
Authors A. Gyulai, T. Ormos, M. Dobroka and J. Somogyi MolnárSummaryIn-mine geoelectric methods – the geoelectric seam-sounding and geoelectric transillumination – were applied for detection of fault zones in a coal mine. To determine the model parameters of the coal seam structure seam- and drift-sounding measurement were carried out along the boundary of the coal layer (roof sounding) and that of the floor (floor sounding). From the measured apparent resistivities the model parameters of the structure were determined using a joint inversion procedure ( Dobróka et al., 1991 ).The measured data were interpreted using geoelectric tomography procedure. Good agreements were found between the location of tectonic zones predicted by the interpretation and those observed during the mining extraction.
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Near-surface Seismic Interpretation to Reduce the Loss of Water Resources
Authors O.K. Tiapkin, S.A. Onyshchenko and I. MendriiSummaryNow some economically developed regions is almost exhausted the opportunity to develop their fresh water resources. The main reserve of this resource is only the decrease (liquidation) the loss of the water of the main water consumer – agriculture. First of all it’s reconstruction of irrigation systems. The results of research of humidity inhomogeneities of the upper part of a geological section may be the spatial basis of this reconstruction. The solution to this problem with near-surface velocity mapping (the determination of average velocity of this part of a geological section for any seismic systems and energy sources – up to depth of tens of meters) is shown. The maps of this velocity characteristic are easily recalculated to the density and humidity and further may be used for the spatial prognostication of near-surface humidity inhomogeneities. The tectonic origin of some of these inhomogeneities according to the results of near-surface seismic interpretation is illustrated by the example of the steppe zone area in the southwest of Russia.
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Analysis of Selected Aromatic Hydrocarbons from Drinking Water and Natural Water Potentially Affected by Shale Gas Production
Authors A.-M. Tugulea, J. Hnatiw, C. Kubwabo, R. Charon and R. StrathernSummaryIn Canada, shale gas exploration is underway in several provinces, with most of the production currently on-going in the western provinces. Public concern is growing with regard to potential impacts on the quality and quantity of water resources, most importantly drinking water. Water impact assessment requires extensive collection of baseline data sets. Re-use of produced water for hydraulic fracturing is being encouraged and knowledge of organic impurities present is important in optimising treatment processes.
Developing analytical methods for chemical indicators of shale gas exploitation impact on water sources is key for future monitoring studies. An automated SPME-GC-MS method for the quantitation of 22 aromatic hydrocarbons (BTEX, trimethylbenzenes, naphthalene, methyl and dimethylnaphthalenes) with adequate sensitivity for drinking water impact studies is described here. Drinking water samples were quenched with 0.114 M ascorbic acid, extracted using a CombiPAL autosampler equipped with a PDMS fibre and analysed using a GC-MS/MS instrument. The method was tested on untreated and treated water samples. Method sensitivity was adequate for drinking water quality testing. All analytes were stable for 14 days in all tested samples. Analyte recovery ranged from 78% for benzene to 116 % for 1,2,3-trimethylbenzene and was independent of the characteristics of the water.
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Comparative Evaluation of Ground Water Storage Using GRACE-GPS Data in Highly Urbanized Region in Uttar Pradesh, India
Authors S Arora and P.K.R. GautamSummaryIn the present effort we have tried to evaluate the Ground Water Storage (GWS) in the highly populated and industrial region of India. With this goal we selected two districts Meerut and Lucknow of Uttar Pradesh (UP) state in India.
Meerut region is highly populated and industrial compare to Lucknow. To achieve the goal, ten years data of Gravity Recovery and Climate Experiment Satellites (GRACE), Soil Moisture Contents (SMC), Rain Fall (RF) from 2003 to 2012, bore-hole data of 42 wells from May 2005 to November 2010 and one year Global Positioning System (GPS) data of the year 2012 of International GNSS Service (IGS) station LCKI of Lucknow region have been included in the study.The Meerut region which is relatively highly urbanized shows more depletion rate -2.76±0.87 cm/yr compare to the depletion rate of -1.46±0.74 cm/yr at Lucknow. After all we found that the over extraction of the groundwater due to the continuous urbanization is the major factor, which was more responsible for the depletion of ground water resource compared to the meteorological effect. If proper measurements are not taken soon to ensure sustainable ground water usage, that day is not far away when Uttar Pradesh will face a severe shortage of ground water.
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Comparison of Microtremor and Electrical Resistivity in Detecting Sliding Surface
Authors M. Kazemnia Kakhki, W. Joao Mansur and B. BamaniSummaryReconnaissance of sliding surface has always been the challenge.
Microtremor measurement is one of the most useful methods which can be applied in landslide studies. For this, Nakamura approach have been applied for detecting the subsurface conditions on a big landslide surface in NargesChal, a village in north of Iran in Golestan province.to verify the Microtremor results, Electrical resistivity method was also applied.
Therefore based on processed data, the slide surface was detected and it is distinguished that the studied region has experienced several landslides.
Processed sections show the presence of slip zones at different depth ranges on landslide face of ground surface to 30 m. The Geotechnical logs and resistivity measurements clearly outline the importance of Microtremor measurements in landslide studies for mapping bedrock depth and shear wave velocity. The present study has utilized low cost and fast field survey procedures with high resolution imaging of electrical properties of subsurface and Microtremore. The obtained results clearly display the importance of Microtremore in landslide hazard investigations. The results were controlled by geotechnical logs and Geoelectric profiles and the extracted slide surfaces were confirmed by direct subsurface information. The geology conditions were mapped during the electrical measurements. Combinations of geological information, Microtremore and Electrical resistivity results have proved to be a powerful tool for the investigation of landslides in areas of complex geology. According to SPT tests and the mentioned methods, three sliding surface was determined, one in the depth 5m, the other one in 12m and the last in the depth 25m.
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A Link between the Pressure Dependency of Elastic and Electrical Properties of Porous Rocks
Authors T. Han, B. Gurevich, M. Pervukhina and M.B. ClennellSummaryWe present a technique to invert for the stiff and compliant porosity from velocity measurements made as a function of differential pressure on saturated sandstones. A dual porosity concept is used for dry rock compressibility and a squirt model is employed for the pressure and frequency dependent elastic properties of the rocks when saturated. The total porosity obtained from inversion shows satisfactory agreement with experimental results. The electrical cementation factor was determined using the inverted porosity in combination with measured electrical conductivity. It was found that cementation factor increased exponentially with increasing differential pressure during isostatic loading. Elastic compressibility, electrical cementation factor and electrical conductivity of the saturated rocks correlate linearly with compliant porosity, and electrical cementation factor and electrical conductivity exhibit linear correlations with elastic compressibility of the saturated rocks under loading. The results show that the dual porosity concept is sufficient to explain the pressure dependency of elastic, electrical and joint elastic-electrical properties of saturated porous sandstones.
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Application of Fine Rock Physical Modeling Techniques in High-quality Reservoir Prediction of Glutenite
More LessSummaryThe Triassic Baikouquan Group in Mahu slope area has massive accumulation characteristics, and the reservoir is sandy-conglomeratic deposits of the fan delta front facies with the low porosity and permeability, and high quality reservoirs control the oil and gas distribution. Through geophysical responses and pre-stack sensitive parameters analysis, it is considered that P-wave impedance can not distinguish the effective reservoir from tight reservoirs and pre-stack inversion is an effective way to solve this problem. Because of the lack of shear wave logging data, which makes difficulty to optimize parameters and build high-precision petrophysical model to obtain high-quality shear wave data for carrying out pre-stack inversion. Through accurate calculation of shale content, porosity, fluid saturation and other parameters, we construct a reasonable petrophysical model and effectively improve the estimation accuracy of shear-wave velocity for pre-stack inversion. And through pre-stack inversion of Vp/Vs ratio, the distribution of high quality reservoir of glutenite is effectively implemented, which provides a favorable basis for well deployment and reserve confirmation and achieves excellent effects. This study is funded by the research of “Xinjiang-Daqing” and “high-density and wide-azimuth seismic exploration supporting technology research”
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Capillary Pressure as a Source for Brie’s Fluid Mixing Law
Authors G Papageorgiou, K. Amalokwu and M. ChapmanSummaryThe need to accurately predict acoustic velocities has resulted in a widespread popularity of Brie’s
effective fluid mixing law. This empirical model together with Gassmann’s
formula are used routinely in fluid substitution problems in
petroleum geophysics and seismic monitoring of carbon capture and
storage. Most attempts to justify Brie’s
model have been focused on interpretation in terms of patchy
saturation models and attaching meaning to the Brie parameter in
terms of the patch size. In this paper, using a microstructural
description of the rock and a parameter relating to capillary
pressure, we calculate an effective fluid modulus
that is very similar to Brie’s law. The fluid mixing law we propose is
independent of frequency and has a solid theoretical foundation. This
proposed law produces analytically harmonic and
arithmetic averaging at the endpoints. Our results indicate Brie-like
behaviour may not
necessarily be related to frequency and patch-size dependent phenomena.
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Study on Anisotropy Affection Factors of Longmaxi Formation Shale
More LessSummaryThe Silurian Longmaxi Formation shale in Sichuan Basin is an important shale gas reservoir for shale gas exploration in China, but the anisotropy of Longmaxi shale is not studied sufficiently. In this case, the velocity anisotropy is examined under the reservoir pressure conditions by ultrasonic testing method. The variation patterns of wave velocity in different directions as a function of confining pressure are also presented. Mineral analysis and X-Ray scanning techniques are applied to reveal the affection factors in Longmaxi shale, the result shows the mineral layer and micro-bedding are the mainly factors of anisotropy.
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A Decoupling Approach for Differential Equivalent Equations Based on Linear Approximation
More LessSummaryBulk and shear moduli of dry rocks are two key parameters for fluid substitutions and S- wave velocity predictions. Differential equivalent medium (DEM) theory is an important method to determine the effective elastic properties of dry rocks. But the differential equations for bulk and shear moduli are coupled. Based on the approximate linear relation between dry-frame modulus ratio and porosity, this paper proposes a new method to decouple the differential equations and obtain the analytic expressions for dry rock frame modulus. The applications of experiment and logging data both show the validity of the new analytic solutions in estimating P- and S-wave velocities of clastic reservoirs.
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An Experimental Evidence of the Squirt-flow Effect in Glycerol-saturated Berea Sandstone at Seismic Frequencies
Authors V. Mikhaltsevitch, M. Lebedev and B. GurevichSummaryIn sedimentary rocks saturated with fluid characterized by low mobility, which can be determined by low intrinsic permeability or high fluid viscosity, relative motion between pore fluid and rock skeleton may produce a significant impact on acoustic wave attenuation and dispersion of the elastic moduli of rocks at seismic frequencies. To investigate the influence of low-mobility pore fluid on elastic and anelastic parameters of sedimentary rock, the seismic-frequency laboratory measurements on dry and glycerol saturated Berea sandstone were carried out. The elastic moduli and extensional attenuation of the sandstone were measured at differential pressures of 5 MPa and 10 MPa under temperatures of 23 and 31 °C. Noticeable peaks of attenuation and significant dispersion of the moduli were detected for the glycerol-saturated sample. It was found that the frequencies of the peaks increase approximately twofold when the viscosity of glycerol was reduced by half with the temperature changing from 23 °C to 31 °C. Our analysis shows that the quantitative relationship between the extensional attenuation and the Young’s modulus measured for the glycerol-saturated sandstone is consistent with the causality principle presented by the Kramers-Kronig relationship.
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Low-frequency Seismic Reflection from a Fractured Layer
Authors A.G. Krylova and G.M. GoloshubinSummaryWe make use of the averaging of the elastic properties of the fluid-filled fractured rock with consideration of the extremely slow and dispersive Krauklis wave propagation within individual fractures. The presence of Krauklis wave tends to the high dispersion of the effective velocity and remarkably increases the amplitude of the reflection from the fractured medium as a layer, in particular at low frequencies.
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Laser Doppler Interferometer Waveform Enhancement Using a Space-varying Median Filter along the Structural Direction
More LessSummaryLaser Doppler interferometer can be used to measure the diagonal group velocities and further help to obtain the anisotropic parameters (especially for δ) on shale. It has many advantages over the commonly used transducer-based approaches. However, the strong erratic noise introduced during the excitation, transmission and receiving processes will decrease the quality of recorded waveform. We propose a novel median filtering based approach for removing such erratic noise. Instead of directly applying the median filter along the spatial direction, we apply median filter along the structural direction of the waveforms. The principle of such median filtering is to apply a median filter along the spatial direction in a locally flattened processing window. Considering that the structural-oriented median filter will require an accurate estimation of local slope of waveforms, in the case of imperfect slope estimation, the local processing window cannot be flattened well, which will still make the traditional median filter fail. To deal with this problem, we propose to apply a space-varying median filter along the structural direction to mitigate the influence caused from imperfect flattening. We apply the proposed algorithm onto one synthetic example and real recorded data from the Laser Doppler interferometer to show a successful performance.
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Is There Value in Highly Spatially Sampled Zero-offset Vertical Seismic Profiles?
More LessSummaryDistributed vibration sensing (DVS) involves using a fibre optic cable to record seismic data with sub-metre spatial sampling. The results presented here, however, show that there is little point in recording highly sampled VSP data to obtain detailed interval velocity profiles due to the high sensitivity of the velocity estimation to very small errors in the pick times. Highly sampled data therefore requires the application of a pick smoothing algorithm which results in a profile that is generally consistent with that obtained from raw data with a larger spatial interval. In velocity profiles generated for DVS data, the smoothing effect of the gauge length further reduces the value of high spatial sampling.
If a corridor stack is required, acceptable results, for high SNR data, can be obtained even when the minimum sampling criteria are not met if median filters are used for wavefield separation. If significant shear- or tube-wave noise is present in the data, this noise may be difficult to remove if the spatial sampling criteria is relaxed. If the SNR is low, as it generally is for DVS surveys, then acceptable corridor stacks can be obtained if the data is highly sampled.
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Traveltime Inversion of 3D or Multi-azimuthal Walkaway VSP Data for a Model with Dipping Tilted Orthorhombic Layers
By E. BliasSummaryIn this paper, I present a new methodology to estimate interval orthorhombic parameters in a 3D model with curvilinear orthorhombic layers. This methodology includes (i) pre-work survey design for interval orthorhombic parameter estimates, (ii) the non-linear constrained first break inversion and (iii) uncertainty analysis of estimated anisotropic parameters. To estimate interval orthorhombic parameters and symmetry plane direction, connected with fracture orientation, we use the non-linear adaptive constrained optimization with applying the Levenberg-Marquardt method. Dipping boundaries, interval velocities and anisotropic parameters are simultaneously estimated through the least squares method with adaptive stabilizing weights. Model tests show that we do not need expensive 3D vertical seismic profile (3DVSP) survey for building an accurate 3D multi-layered orthorhombic model. This approach was applied to a 3DVSP dataset.
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Vertical Seismic Profiling (VSP) Survey Optimization for Imaging Fracture Zones over Geothermal Areas
Authors F. Reiser, C. Schmelzbach, H. Maurer and S. GreenhalghSummaryA primary focus of geothermal seismic imaging is to map dipping faults and fracture zones that control the permeability and fluid flow. We simulated and processed acoustic synthetic data to optimize VSP survey layouts for mapping moderately to steeply dipping fracture zones over geothermal reservoirs. The geophysical models were based on the geothermal site at Soultz-sous-Forêts (France). It was found that fracture zones located at a borehole offset distance of about 300 m can be imaged accurately for a range of the different dips. Only 8 to 12 source positions were required for obtaining very good results. Adding further sources did not necessarily improve the results, but rather resulted in image distortions. Generally, large offsets between sources and the borehole are required for imaging steeply dipping interfaces. When such features cross-cut the borehole, they are particularly difficult to image.
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Reduction of Fault Uncertainties Using Vertical Seismic Profiling Data
Authors M. Irakarama, P. Cupillard and G. CaumonSummaryDue to the limited resolution of seismic reflection data in imaging near vertical structures, structural models can have significant uncertainties related to fault geometries and position. These uncertainties can be reduced by performing a history matching analysis on a large number of structural models generated stochastically. This work investigates about the integration of vertical seismic profiling data as another way to constrain and reduce such uncertainties. Because travel-times are not sufficiently sensitive to fault geometry perturbations and because we cannot model amplitudes accurately, we rely on phase distortion of seismograms as they propagate through the faulted models.
To extract instantaneous phase information from seismograms, we used the empirical mode decomposition algorithm. This approach offers several advantageous properties compared to computing the instantaneous phase by analytic signal transformation. An instantaneous phase misfit was then defined as the L2 norm of two instantaneous phase functions.
A numerical experiment was carried out in which 60 fault networks were generated stochastically from a single 3D interpretation of multiple cross sections; the 60 models were then ranked from the most similar up to the most dissimilar from a randomly chosen reference model. Results show that the proposed misfit can successfully constrain fault geometry.
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Target-oriented Imaging Using Active and Passive Interferometry
Authors M. Karrenbach and S. ColeSummaryTarget oriented imaging uses seismic interferometry to suppress overburden effects, improving resolution and image quality. Interferometry can be used to construct data that can be processed by standard imaging algorithms or it can be included as part of the depth imaging operator. When these approaches are applied to active source and passively recorded data, the resulting images show the target in high resolution. Although the image extent is limited in 2D or 3D to a small target zone, the added resolution allows detailed interpretations that are difficult to achieve with non-interferometric methods. This approach is illustrated with two real data examples. In a microseismic monitoring project from West Texas, images derived from microseismic events have energy in excess of 400 Hz giving resolution of a few feet. In a VSP salt flank imaging example from the Texas Gulf Coast, virtual shot gathers derived from single shots are used to delineate the salt flank with improved resolution over other methods.
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Auto-estimation of Up-down Wavefields in a Horizontal Borehole using Single Component Data
Authors Y. Liu, B. Arntsen, J. van der Neut and K. WapenaarSummaryThe standard requirement for up-down wavefield separation in seismic data is to use multi-component data. An important application for such separation is to remove the interference from multiple reflections from either the free surface or the internal subsurface structures. As an alternative, we propose an automatic scheme of estimating the up-down wavefields in a horizontal borehole using only single component measurements. The scheme builds upon recent developments of the Marchenko method. The up-down fields are constructed essentially from the surface reflection response (surface seismic data), together with the direct waves’ travel time from the borehole data. No prior information of the subsurface is needed, and an automatic working flow is suggested. The numerical test using a synthetic field model shows good results compared to that from a conventional multi-component approach.
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The Effects of Pulse Width on Fibre-optic Distributed Vibration Sensing Data
Authors T. Dean, A. Hartog, T. Cuny and F. EnglichSummarySystems for distributed vibration sensing (DVS), also known as distributed acoustic sensing (DAS), use a fibre-optic cable as the sensor, rather than the discrete point sensors used in conventional systems. Theoretically, they measure strain, which is the change in the length of the section of fibre divided by the gauge length. In reality, they measure the change in phase of the backscattered light which is directly proportional to strain. However, the phase is not measured at a single position along the fibre; instead, the value is a result of the application of a Gaussian window.
The results included here indicate that the laser pulse width used during DVS acquisition can have a significant effect on the quality of the data acquired. As shown previously, the gauge length must be carefully selected due to its strong frequency response, but due to the Gaussian nature of the pulses, their associated frequency response is more muted. The point at which the effect of the pulse width becomes larger than the gauge length is half the gauge length, allowing considerable scope for it to be increased, and thus the SNR of the data improved.
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The Use of Multi-frequency Acquisition to Significantly Improve the Quality of Fibre-optic Distributed Vibration Sensing
Authors A. Hartog, L.B. Liokumovich, N.A. Ushakov, O.I. Kotov, T. Dean, T. Cuny and A. ConstantinouSummaryUnlike conventional sensors that measure the passage of seismic waves at a single position, distributed vibration sensing (DVS) systems, also known as distributed acoustic sensing (DAS) systems, detect the passage of seismic waves by averaging a measurement of strain over a section of fibre optic cable. DVS systems work by transmitting pulses of light down the fibre and measuring the phase of the Rayleigh backscatter. At random positions along the fibre, however, fading occurs; this is where the amplitude of the backscattered signal is very small due to cancellation of the scattered electric fields, resulting in anomalously noisy traces.
The appearance of fading is dependent on the frequency of the laser pulse used to interrogate the fibre; thus, by transmitting a number of different frequencies, we can avoid its effects as well as reduce the overall noise of the system. Once the noisy traces are removed, the results of our experimentation and modelling suggest that the improvement is approximately √n where n is the number of frequencies being stacked.
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Unified Suppression of Surface-related Multiple and Ghost in Local Plane Wave Domain
More LessSummaryDeghosting and multiple suppression are crucial tasks in marine data processing. SRME has been proven effective in surface-related multiple suppression through large volume dataset processing, whereas a deghosting process should be applied beforehand. The absence of ghosts makes multiples predicted by SRME less accurate. Besides ghosts, multiple contribution gather is another important aspect that directly affects the accuracy of multiple prediction. In the local plane wave domain, we propose a method called USMG for unified suppression of surface-related multiples and ghosts. USMG takes into account ghosts and multiple contribution gather as two factors that affect the multiple prediction. Firstly, the ghosting operator is incorporated as part of the multiple prediction operator, instead of discarding the ghosts in multiple prediction. USMG simultaneously predicts the surface-related multiples and ghosts. And the multiples are more accurately predicted due to the introduction of the ghosting operator. Secondly, USMG automatically optimizes the multiple contribution gather through the exploitation of Snell’s law, and thus the precision of multiple and ghost prediction is further improved. Meanwhile, ghosts are suppressed, and the frequency bandwidth of the resulting wavefields is broadened. Tests on both synthetic and field dataset prove the effectiveness and feasibility of this method.
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Breakthrough of Internal Multiple Attenuation with XIMP Technology in Tarim Basin
More LessSummaryInternal multiples, which mainly contaminate land datasets, are more difficult to address than surface-related multiples. Internal multiples generally appear to be very similar to the primaries because of their comparable velocities; they are therefore difficult to differentiate, especially in areas with relatively flat geology. In northern Tarim basin of China, most surveys have this type of flat geology and internal multiple problem. Traditional event discrimination methods, such as multi-channel dip filter, Radon transform, and inside mute, have failed to effectively remove the multiples. We show recent results using a prediction based framework using the extended internal multiple prediction (XIMP) followed by adaptive subtraction, where encouraging results show a clear removal of internal multiples in Northern Tarim basin.
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Apex-shifted Sparse Parabolic Radon Transform in Mixed Frequency-time Domain with Alternating Split Bregman Algorithm
More LessSummaryMixed frequency-time domain sparse parabolic Radon transform (MSPRT) exploits the frequency domain Radon transformation operator to conduct Radon transform and imposes sparse constraint along the time and curvature direction. MSPRT combines advantages of the frequency domain sparse PRT (FSPRT) and time domain sparse PRT (TSPRT), i.e., high-resolution of the Radon model and high computation efficiency. However, standard 2D MSPRT cannot cope with diffracted multiples with their minimum travel time away from the zero offset. In this paper we extend the standard 2D MSPRT to the apex-shifted mode. Furthermore, to solve the sparse optimization problem of apex-shifted MSPRT we introduce the alternating split Bregman (ASB) algorithm, which is computationally economic. Synthetic and field data examples demonstrate the proposed apex-shifted MSPRT outperforms the traditional apex-shifted FSPRT and apex-shifted least-squares PRT for diffracted multiple removal.
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Random Noise Attenuation by Learning-type Overcomplete Dictionary Based on K-singular Value Decomposition Algorithm
More LessSummaryThe transformation of basic function is one of the most commonly used techniques for seismic denoising, which employs sparse representation of seismic data in the transform domain. The choice of transform base functions has an influence on denoising results. A learning-type overcomplete dictionary based on the K-singular value decomposition (K-SVD) algorithm is proposed. To construct the dictionary and use it for random seismic noise attenuation, we replace the fixed transform base functions with an overcomplete redundancy function library. Owing to the adaptability to data characteristics, the learning-type dictionary describes essential data characteristics much better than conventional denoising methods. Therefore, the sparsest representation of signals is obtained by the learning and training of seismic data. By comparing the same seismic data obtained using the learning-type overcomplete dictionary based on K-SVD and other denoising methods, we find that the learning-type overcomplete dictionary based on the K-SVD algorithm is able to represent seismic data more sparsely and suppress the random noise more effectively.
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Seismic In the Arctic - Suppressing Seismic Noise Due to Vibrating Ice
Authors K. Jensen, B.O. Ruud, T.A. Johansen and M. LandschulzeSummaryA common problem encountered when processing seismic data obtained in Arctic environments is the presence of dispersive flexural wave noise on the data. Flexural wave noise is generated when seismic sources are detonated near, or at, ice sheets overlying shallow water in the transition zone from land to sea. As the waves are highly dispersive, have high magnitude and propagate with low velocities, processing of the data remains challenging due to frequent spatial aliasing effects.
Seismic processing was performed on two separate shot gathers: a real shot gather obtained during a test survey on Svalbard, Norway, and a full-waveform synthetic shot gather based on the same experiment. A processing work flow which suppressed the flexural wave noise, while preserving signals initially obscured, was developed. The work flow combines conventional τ-p filtering with the more unconventional radial trace (RT) filtering, and successfully increases the signal-to-noise ratio.
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Noise Attenuation of Seismic Data Using Anisotropic Diffusion Method
Authors Y. Moradi Chaleshtori, A. Kiani and K. NajafzadehSummaryHaving high quality images of seismic sections is one of the most important issues for interpreters. In order to delineate geological features and sedimentary packages such as faults, channels and etc., many attempts carried out to attenuate unwanted noises which caused by improper environmental and acquisition parameters and processing artifacts.
In this paper, we propose a method based on Anisotropic Diffusion which is aiming at reducing noise without destroying significant parts of the image content, typically edges or other details that are important for the interpretation. Anisotropic diffusion is a process that produces a family of parameterized images. Each resulting image is a convolution between the original image and a 2D isotropic Gaussian filter that depends on the local content of the original image. Accordingly, anisotropic diffusion is a non-linear and space-variant transformation of the basic image. As this technique has special abilities in noise attenuation and preserve structures in the filtered image as well, it can be utilized for seismic data enhancement. Efficacy of this method in enhancing data quality and in highlighting small features is presented using synthetic and real data examples.
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Targeted Noise Attenuation - A Method to Suppress High Amplitude Noise in Seismic Data
Authors H. Alee Daneshvar, M. Emami Niri and Y. Moradi ChaleshtoriSummarySeismic data are always contaminated with noise. An essential stage of any seismic processing sequence is to detect and suppress noise from the seismic data. Several processing methods have been proposed to attenuate high energy coherent noise such as ground roll. However, its adverse effects are still frequently observed in the seismic processing products, which can adversely affect subsequent signal processing steps. In this paper, we present a simple and robust technique, called Targeted Noise Attenuation (TNA), to detect and suppress high energy coherent noise from the seismic data. The TNA filtering consists of several stages including (1) data conditioning to ensure the reliability of the amplitudes, (2) high amplitude noise detection by the means of the trace envelope, (3) blind de-noising, and (4) merging of the original data and the blind de-noised data to reconstruct the final filtered product. The approach presented in this paper is effective not only to suppress the ground roll noise, but also to attenuate noise generated from water pumps, powerline, airwaves. Our numerous applications of TNA to real 2D and 3D seismic data from different areas have proved the effectiveness of TNA in suppressing high amplitude localized noise in seismic data.
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A Case Study on Multiple Stratigraphic Reservoirs Related with Weathered Granite Buried-hill
More LessSummaryThe Betara buried-hill is located at the northern margin of South Sumatra back-arc rift basin in Indonesia. Its basement lithology is composed of phyllite, granite and metaquartzite. It is a mature area with six condensate and/or gas fields discovered. The new challenges meet with hydrocarbon exploration. Based on the integrated geological and geophysical study, Betara granite buried-hill geological model is established, which the granitic weathered rind and granite leached fracture zone formed at the basement, and the alluvial fans on the ramp from in rift stage from Eocene to Oligocene. They are effective factors of the model that three plays of the multiple stratigraphic reservoirs formed in Betara complex. A patch of new prospects are identified. The multiple stratigraphic reservoir model of granite buried-hill is a good petroleum exploration reference in South Sumatra basin.
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Dynamic FIeld Division of Hydrocarbon Migration - Accumulation in Dongpu Depression, Bohai Bay Basin, China
More LessSummaryThis paper introduces a concept of dynamic field division of hydrocarbon in petroliferous basins, which will divide the basin into 3 parts:free fluid dynamic field, restricted fluid dynamic field, irreducible fluid dynamic field.And mechanisms of hydrocarbon migration and accumulation in each field is different. Geological and statistical methods have been integrated to make it clear that the boundary between free fluid dynamic field and restricted fluid is about 3580m, and the boundary between restricted fluid dynamic field and irreducible fluid dynamic field is 5922.3m in Dongpu Depression, Bohai Bay Basin, China.
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A High-resolution Facies Model of Pre-salt Lacustrine Carbonates Reservoirs. Morro do Chaves Fm. Example, Brazil
Authors P. T. L. Menezes, J.M. Travassos and M.A.M. MedeirosSummaryBarremian lacustrine carbonates, essentially coquinas, are the reservoir rocks of the large pre-salt petroleum findings in deep to ultra--deep waters of Santos, Campos and Espirito Santo basins. The complicated geological setting of those discoveries, with the massive overburden of salt bodies, makes the seismic imaging of the carbonate reservoirs an expensive and challenging matter. In this setting, accurate facies models are a demand for the predictability of the carbonate reservoir intervals.
This work shows an analogue high-resolution coquinas facies model based on an interpretation of a pseudo--3--D Ground Penetrating Radar (GPR) survey. We rely not only on the trace amplitude analysis but mainly on trace attributes to diminish the ambiguity of the interpretation due to potential visual biases. We have used the dip and texture attributes to help us better understand the subsurface and to focus on the main stratigraphic features of the reservoir analogue. Then we have produced a joint interpretation, based on three trace attributes: i.e., amplitude, dip and texture to highlight the main radar facies. That resulted in a facies model in which three SW-NE striking coquina bars (reservoir facies), correlated with transgressive systems tract (TST) interbedded with shales (nonreservoir facies) of highstand systems tract (HST), are identified.
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Non-hydrocarbon Migration Model in Petroleum System Analysis - An Integrated Procedure for Accurate Risk Assessment
Authors C. Geloni, A. Consonni, M. Dalla Rosa, A. Battistelli, V. Bortolotti, S. Bonduà, M.E. Vasini and C. CormioSummaryHow to estimate the risk of the occurrence of non-hydrocarbon components (nonHC) such as carbon dioxide (CO2), hydrogen sulfide (H2S) or nitrogen (N2), is one of the main issues in the field of petroleum exploration. Numerical models can provide valuable tools to predict the occurrence and distribution of such components. Different approaches exists to this end, starting from the simplest ones, relying onto geometrical considerations, up to those based on a fully physical description of the migration and accumulation processes.In this work, a procedure for efficient coupling of petroleum system analysis withmultiphase Darcy flow simulations is developed to obtain 3D time dependent representation of the migration paths and accumulation volumes of nonHC at basin scale on a geological timescale.
We focus on the tests carried out to prove that is technically feasible to run simulations of very deep geological formations (high P, T, salinity) even if considering a very detailed picture of the transport phenomena (buoyant, viscous and capillary forces). The challenge is to find the right compromise between the needs to honor fine-scale hydrostratigraphic details of the structure and the size of the numerical model in its discretized form.
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Light Hydrocarbons Geochemistry of Oils Trapped in the Austrian Foreland Basin
Authors L. Pytlak, D. Gross, R.F. Sachsenhofer and H.G. LinzerSummaryThe Alpine foreland basin is a minor oil and moderate gas province in central Europe and is considered as mature in terms of hydrocarbon exploration. During this time many studies have been performed to understand the petroleum system in the basin. Within this context, organic geochemical, biomarker and stable isotope data have been used to characterize potential source rocks and their lateral variability in facies and maturity, as well as in oil-source rock correlations. However, till now all studies have focused on the C15+ hydrocarbon fraction of oil samples. Hence, the aim of the present study is to explore the information provided by the light hydrocarbon fraction with respect to maturity, kerogen type and hydrocarbons alteration. Results from the Austrian foreland basin reveal that hydrocarbons are derived from kerogen type II, which is in agreement with results from “classical” biomarkers studies. Maturity estimates based on the light hydrocarbon fraction correlate very well with estimates based on aromatic hydrocarbons. Water washing, which is difficult to trace using higher hydrocarbons fraction, can be clearly identified applying light hydrocarbons. Oil-water interaction yields information on hydrodynamic mechanisms in active aquifers, which are important for drilling issues, oil production as well as hydrothermal potential estimations.
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A Discussion on the Hydrocarbon Generation Lower Limit of Source Rocks at Shahejie iormation In Dongpu Depression Bohai
Authors L. Tang, P. Xiongqi, H. Tao and P. ZhihongSummaryThis article uses four categories of seven methods to determine the hydrocarbon generation lower limit of source rocks at Shahejie Formation in Dongpu Depression Bohai Bay Basin.It is of great significance to determine the lower limit of hydrocarbon generation since it can promote evaluation of oil and gas resources, calculation of oil and gas reserves and planning of oil and gas exploration.
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Facies Characteristic, Paleoenvironmental Reconstruction, and Reservoir Characterization of the Dariyan Formation, Lower
Authors M. Jamalian, D. Amirsardari, M. Fathi, M. Goodarzi and M. JamalianSummaryThe Dariyan Formation, with the age of lower Cretaceous, is one of the important hydrocarbon reservoir rocks of Khami Group in the Persian Gulf.
This reservoir was evaluated through studying microfacies, sedimentary environment, diagenesis processes, and reservoir characterization analyses.
Microfacies study led to the recognition of eight microfacies that are pertinent to three facies belts: lagoon, platform margin, and shallow open-marine. Gradual facies changes and absence of turbidite deposits indicate that the Dariyan Formation was deposited in a carbonate ramp environment.
Assessment of porosity and permeability according to microfacies, SEM, and conventional core analysis indicates that microfacies Dr-MF4, DR-MF3, and DR-MF2, related to proximal part of shallow open marine and platform margin facies belts, have good reservoir quality. Microporosity is dominant in most of the studied samples. The samples with this pore type do not have enough permeability to make a good reservoir zone unless another pore type (such as interparticle and vuggy porosities) enhances the reservoir characteristics.
This formation mainly consists of allochemical porous limestone with high oil-show in upper parts (i.e. above oil water contact), while the strata are composed of white chalky limestone with no oil-show below oil water contact.
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Preservation of Reservoir Quality in Sandstones by Chlorite Coats - Insights from Viewing Ion-Milled Samples in SEM
Authors S.P. Dutton, R.G. Loucks and W.A. AmbroseSummaryThe presence of continuous chlorite coats on detrital grains can preserve anomalously good reservoir quality in deeply buried sandstones by inhibiting quartz cementation. Two sandstones in the Gulf of Mexico basin—Upper Cretaceous Tuscaloosa sandstone in central and eastern Louisiana and Eocene Upper Wilcox sandstone in south Texas—have intervals that retain high porosity and permeability at temperatures >175°C because of extensive chlorite coats. However, significant variation exists in the morphology and orientation of the chlorite cement on detrital grains in these sandstones. Scanning electron microscope (SEM) observation of chlorite-cemented sandstone samples prepared by argon-ion-beam milling provides excellent views of grain/chlorite boundaries. This technique gives insight into the formation of the chlorite and development of quartz overgrowths within chlorite coats. Quartz overgrowths formed in gaps between chlorite crystals oriented perpendicular to detrital grains in Tuscaloosa sandstones of central Louisiana. In contrast, densely packed chlorite crystals oriented parallel to the detrital grains, such as those observed in Wilcox sandstones in south Texas, prevented precipitation of quartz overgrowths within the chlorite coats. Viewing ion-milled sandstone samples in SEM is a useful technique that can provide new insights into formation of diagenetic cements and preservation of reservoir quality in deeply buried sandstones.
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Diagenesis in Cenomanian Clastic Reservoir Rocks of the Alpine Foreland Basin (Austria)
Authors M.-L. Grundtner, D. Gross, A.S. Samsu, H.G. Linzer, D. Misch, R. Sachsenhofer, L. Scheucher and S. SchnitzerSummaryThe North Alpine Foreland Basin is a minor oil and moderate gas province. It´s major Reservoir horizons are for oil Cenomanian and Eocene non- and shallow marine sandstones, while mainly Oligo-/Miocene deep water sediments comprise gas.
In this contribution, the diagenetic history of Cenomanian reservoir sandstones is presented. Commonly, facies and primary mineralogy controls diagenesis. The lower units of the Cenomanian green-sandstones are poorly cemented and clay minerals (illite, kaolinite) prevail as pore filling. On the contrary, the upper unit is enriched in carbonate cement, identified as pure calcite. Occasionally clay minerals have been replaced by carbonate cement and are therefore interpreted as primary matrix or very early cement phase. Carbonate cements of Cenomanian sandstones exhibit isotope values of about d13C: -13.6 to +3.3‰ and d18O: -23.9 to -4.2‰ [PDB]. The trend of d18O towards lighter isotope ratios relative to sea water is attributed to a meteoric flush. Within one well, biogenic influence is indicated by light d13C ratios of -32.7 to -25.0‰.
Reservoir quality is affected by carbonate cementation. High porosity values are caused by poor cementation, whereas permeability is decreased by the presence of clay minerals.
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Distribution of Coatings in Fluvio-eolian Red Beds and Their Impact on Reservoir Quality Modeling
Authors B. Busch, C. Hilgers, C. Schmidt and D. AdelmannSummaryReservoir quality in siliciclastic reservoirs is generally impacted by the depositional environment and the presence of authigenic components. However, the distribution of clay coatings within depositional environments is unclear, although they are a main controlling factor in porosity preservation.
We show that the distribution and clay coat coverage is not purely dependant on the depositional environment, the grain size, sorting and the stratigraphic position.
The application of generalized correlations to reservoir quality modeling highlights the necessity for a purpose-built database, calibrated by analog samples from core material.
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Prediction of Diagenetic Facies Using Well Logs in Tight Sandstone Reservoir - A Case from Chang 7 in Ordos Basin, China
More LessSummaryUnderstanding diagenetic heterogeneity in tight sandstones is important for prediction of reservoir quality and further for economic success in hydrocarbon exploration. The seventh member of the Upper Triassic Yanchang formation in the Ordos Basin (Chang 7), central China, is an important oil-producing interval characterized by low porosity and low permeability. This study suggests that diagenetic facies identified from petrographic observations can be upscaled by correlation with log responses, which can facilitate prediction of reservoir quality in field-scale. Four diagenetic facies are determined based on pertrographic features including intensity of compaction, cement types and content, and degree of dissolution. Log characteristics of each diagenetic facies are summarized. However, because of overlaps in all well logs crossplots, it is difficult to discriminate these diagenetic facies. To further delineate these diagenetic facies, principal components are calculated using log values and a better model predicting diagenetic facies based on principal component analysis is built. The model is validated by blind testing log-predicted diagenetic facies against petrographic features from core samples in well Cheng 96, which shows it is a viable predictive model.
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Pore-preserving Mechanism of Chlorite Rims in Sandstone-example from the P3w Formation of Jinlong Area, Junggar Basin
By X. ShanSummaryDeeply buried sandstone reservoir in the Jinlong area, northwestern Junggar Basin is characterized by high porosity and well developed grain-coating chlorite. However, relationships between the two characteristics are still understudied. The goal of this study are: (1) examining the composition, structure, and distribution of the authigenic chlorite; (2) timing of chlorite growth; and (3) relationships between grain-coating authigennic chlorite and reservoir evolution. The results of the research are shown as followings: (1) The grain-coating chlorite of sandstone in upper Urho formation in the study area is Fe-rich chlorite which has the same component as that of marine sandstone. (2) Petrographic relationships indicated grain-coating chlorite grew mainly before the beginning of quartz cementation, laumotite cementation and feldspar grain dissolution but after mechanical compaction.(3) It can be inferred that chlorite coatings inhibit quartz cementation by reducing the number of individual growth sites present per sand grain.
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