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82nd EAGE Annual Conference & Exhibition
- Conference date: October 18-21, 2021
- Location: Amsterdam, The Netherlands
- Published: 18 October 2021
151 - 200 of 1137 results
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GPOS Evaluation For Geothermal Projects in the Netherlands
More LessSummaryEvery subsurface project has the risk of failure or disappointment if the predictions made by the subsurface evaluation team are incorrect. In some cases the reality is so much different from the expected that no production is possible or allowed. This is well known for hydrocarbon wells, but also in geothermal projects prediction errors are possible that could result in a total write off of the well or the project. To cater for these risks a fit-for-purpose GPOS evaluation scheme for geothermal projects has been developed within EBN. A consistent GPOS evaluation will help EBN to determine the correct usage of funds in its mission to explore for and accelerate the use of geothermal energy in the Netherlands. Five subsurface aspects are seen as the main parameters determining the technical success of a geothermal project in the Netherlands: Aquifer, Permeability, Fluid Compatibility, Temperature and Connectivity. These five parameters constituting GPOS are estimated by different techniques. The main data and evaluation techniques, both for the pre-drilling estimate of GPOS and the post-drilling evaluation of the project are discussed.
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While Drilling Checkshots and Prediction Ahead of the Bit Using a Drill Bit As a Source
Authors A. Aldawood, I. Silvestrov, E. Hemyari and A. BakulinSummaryDrillCAM is a fully integrated real-time system for predicting and imaging ahead of and around the drill bit by utilizing seismic-while-drilling data (SWD) as well as assisting with drilling optimization and automation. We present results and analysis of several SWD applications from the first field trial in an onshore well in a desert environment. Data was recorded with an adaptable grid of wireless geophones and top drive sensor using depth range of 0–10,000 ft. DrillCAM delivered robust checkshots while drilling down to a depth of 7300 ft that included a combination of roller cone and PDC bits. The obtained velocity profile was found in good agreement with three nearby offset wells. VSP reflection data were successfully processed and delivered a more accurate estimate of over-pressured formation about 2000 ft ahead of the bit. Finally, a reliable VSP corridor stack was generated and shown to tie the surface-seismic data.
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Applying the Synergistic Effect of Chemically Low Salinity Water Flooding Assisted Fines Migration in Coated Micromodel
Authors A. Maghsoudian, A. Esfandiarian, A. Izadpanahi, M. Hasanzadeh and F. FamooriSummaryOne of the important subjects in enhanced oil recovery (EOR) is low salinity water (LSW) flooding and it has been performed as the secondary oil recovery. Many studies have reported that LSW flooding can increase recovery in sandstone and carbonate reservoirs. The main goal of this investigation is comparing the synergistic effect of polymer, water salinity and the presence of fines migration on final recovery which have rarely investigated before. A series of experiments have been done at high temperature (80 °C), including fluid-fluid interaction tests, rock-fluid interaction tests, and micromodel flooding tests. Six aqueous solutions that have been applied for EOR purposes include sea water (SW), ten times diluted sea water (LSW), SW+ hydrolyzed polyacrylamide (HPAM), LSW+HPAM, deionized water (DW), and DW+HPAM. The results show that the high concentration of cations caused the best efficiency in interfacial tension reduction by SW+HPAM. LSW+HPAM has the highest recovery due to the high performance of HPAM, suitable wettability alteration, and better emulsification. Moreover, it was observed in the sandstone coated micromodel flooding test that fine migration has a positive impact on recovery in the case of LSW+HPAM. However, in the case of DW+HPAM, recovery slightly dwindled due to the pore blocking.
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Microseismic Signal Recognition Based on a Single Channel Psr-Ica Method
More LessSummaryThe signal-to-noise (S/N) ratio of the microseismic data is very low and the energy of the effective signal is also weak. In addition, due to complex noise, the effective signal is usually overwhelmed by the random noise. So it is important to improve the S/N ratio of the microseismic data for recognising the effective signal. However, conventional denoising methods may not be fully qualified to remove the noise and improve the S/N ratio. In this paper, we propose a single channel independent component analysis (ICA) method based on phase space reconstruction (PSR) for noise attenuation. Through PSR, the one-dimensional signal is reconstructed into a high-dimensional phase space without destroying the dynamic characteristics of the original data, while meeting the condition of the ICA algorithm. Combine the dynamic and higher statistical characteristics, the single channel PSR-ICA algorithm can effectively separate the noise and improve S/N ratio of the microseismic data, so that the effective signal can be recognised easily.
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Regional Geological Evaluation for the Scan Geothermal Exploration Campaign, the Netherlands
Authors H. van Lochem, M. Ter Borgh and H. MijnlieffSummaryIn 2018 a geothermal exploration campaign named SCAN was started to decrease the subsurface uncertainties in the less explored areas of the Netherlands. This program includes the reprocessing of vintage seismic and the acquisition of new 2D seismic lines. Finally, the intention is to drill geothermal research wells. In order to focus the SCAN research and exploration activities a regional geological study was embarked upon to define the plays and map geothermal leads. Some new or improved geological concepts can be envisaged. One is based on the observation that below unconformity surfaces improved reservoir quality is often found in the subcropping formations. This difference in reservoir quality can be explained by the leaching of unstable minerals and cements due to infiltration of fresh surface water. Secondly, exploration in the Dutch offshore has shown that the facies and thickness of the Rotliegend sandstone reservoir is highly dependent on paleotopography, which was formed after the Hercynian tectonic phase. In the SCAN areas a conceptual model for the Rotliegend thickness and facies trends can be made. This model could help to target areas where the Rotliegend reservoir may be thicker and thus more attractive to drill.
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Fracture Characterization and Dfn Modelling of the El Gueria Carbonate Reservoir in Zarat Field
Authors D. Bouthaina, M. Saoussen, K. Samir and B. NoureddineSummaryThe Zarat field (offshore Tunisia in the Gulf of Gabes) is a large gas condensate field underlied by a thin oil rim, producing from fractured limestone reservoir of the ypresian Nummulitic El Gueria formation. The development plan of the Zarat field was prepared through a simulation study, based on a 3D static matrix model combined to a fracture model representing the fracture network in the reservoir. The main objective of the fracture modeling is the assessment of the permeability distribution to allow the simulation of the well production, the flow behavior and the prediction of the early water and or the gas breakthrough.
Te fracture intensity of the reservoir represents the major uncertainty in this field where a Discrete Fracture Networks model was constructed based on sismic and well data (core and Image). This model will be used for the fracture network prediction, the assessment of the fracture porosity and permeability distribution that have to be used on the simulation study.
Additional input data such as the results of new wells, analogues outcroup inputs such fracture lenghth, fracture aperature and fracture intensity around fault systems using, by direct measurements or remoted technics, should really improved the current model.
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Material Balance Equation of Foamy Extra-Heavy Oil Reservoirs
By Z. YangSummaryThis study provides a material balance equation for foamy extra-heavy oil reservoirs, which helps to yield performance predictions and potential evaluations of these foamy oil heavy oil reservoirs.
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Mitigating Cycle Skipping in Full-Waveform Inversion Using Partial Matching Filters
Authors J. Cooper, A. Ratcliffe and G. PooleSummaryExisting methods for addressing cycle skipping in full-waveform inversion (FWI) typically involve either a modification of one of the data sets used to compute the least-squares objective function, or a reformulation of the objective function itself, often in terms of a traveltime (or equivalent) misfit. Both approaches can be successful, but they are reliant to varying extents on the notion of event similarity – that is, the requirement that the observed and modeled data contain the same, distinct, seismic events, even if the corresponding kinematics are different. We introduce a new technique for mitigating cycle skipping in FWI based on partial matching filters. The method accommodates amplitude differences between observed and modeled data, and does not require any major modification to an existing inversion engine. The proposed approach is validated on synthetic and real data sets, including an example where we observe a reduced reliance on event similarity compared to an established cycle skipping mitigation technique.
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Saline Environment Source Rocks Evaluation of Continental Rift Basin: A Case Study in Lzw Depression, China
More LessSummaryBohai Bay Basin is a petroliferous basin located on the east coast of China. Generally, three organic rich layers (Es3, Es1 and Ed members) have been proved to be the main sources of oil accumulation. The fourth member of the Shahejie Formation (E2s4) was previously paid little attention as it is featured with deep burial depths of more than 3500m (11483ft) and few source rocks were discovered. However, in our recent investigation, regionally extensive evaporites were discovered in E2s4 Formation of LZW depression during the Early Eocene when the Bohai Bay Basin was developing as a rift basin. The E2s4 strata is featured with gypsum, halite, mudstone and carbonates deposits. Influence by Tan-Lu fault activities, a salt arch structure was formed. By means of a large amount of geochemical analysis, we studied the characteristics of source rocks in the saline lacustrine basin and analyzed the origin of source rocks in saline environment. Theory of transgression, deep brine and closed evaporation were proposed, of which closed evaporation theory is the most probable origin, we finally find evaporation is greater than the injection in the enclosed environment and deposits overlying evaporites are often of high quality.
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Multi-Wave and Full-Waveform Inversion in Southern Oman
Authors S. Masclet, G. Bouquard and H. PrigentSummaryWith a shallow anhydrite layer, strong multiples and converted wave contamination, Southern Oman represents an outstanding challenge for land velocity model building and imaging. While acoustic land full-waveform inversion (FWI) has proved successful on new broadband datasets in Northern Oman, no successful application has been reported for Southern Oman. We show here that the challenge of acoustic FWI in South Oman can be overcome using a dedicated workflow combining Multi-Wave Inversion (MWI) and multi-Dimensional Optimal Transport FWI (multiD OT-FWI). The key component of the workflow is the very near surface characterization provided by surface wave dispersion curves, which allows delineation of the Rus layer in the initial FWI model. MultiD OT-FWI is then used to mitigate amplitude issues in the presence of short period multiples and reduce cycle skipping beyond the depth of penetration of diving waves.
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Structural Restoration of Geological Structures With Viscous Stokes Flow - Principle and First Results
Authors M. Schuh-senlis, C. Thieulot, P. Cupillard and G. CaumonSummaryRestoration of geological structures is commonly used to assess past basin geometry from present-day structures. In geomechanical restoration, numerical methods to date consider the rock properties as fully elastic and the faults as frictionless contact surfaces. However, salt bodies have been proven to behave as Stokes viscous fluids in geomechanics, and faults appear in rocks reaching a plastic limit inside a shear zone.
In order to take these behaviours into account, we introduce a new geomechanical restoration scheme based on Stokes equations. Such a strategy seems reasonable for three main reasons. First, rocks have been found to be mainly ductile in large deformations under long time periods (1e5 to 1e9 years). Second, these equations allow the modelling of other rheologies and boundary conditions closer to natural ones. Third, the reversibility of the Stokes equations can be used to compute the reverse motion of a geological domain.
Our restoration scheme is implemented in a software called FAIStokes. The classic forward modelling part of this software is validated through relevant benchmarks. First tests, including van Keken (1997) &s benchmark, on the more innovative backward modelling part, show the great potential of the proposed scheme for restoration using only mechanical (i.e. no geometrical) conditions.
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Analysis of Geological Susceptibility to Induced Seismicity in the Montney Formation Using Supervised Machine Learning
Authors P. Wozniakowska and D. EatonSummaryThis project aims to determine the most important geological factors influencing the susceptibility to induced seismicity in the Montney Formation geological and geomechanical characteristics including pressure gradient, distance to the Cordilleran foreland thrust and fold belt and known lineaments, proximity to the Precambrian basement and Debolt formation, variation of maximum horizontal stress direction and depth factor were investigated. Supervised machine learning methods including four different Tree-based methods (Decision Tree, Bagging, Random Forest and Gradient Boosting) were used to calculate the feature importance. Geological susceptibility analysis was performed using Logistic Regression, commonly used for the probability estimation.
The analysis of the Tree-based algorithms suggests three types of characteristics having the biggest impact on the geological susceptibility to induced seismicity in the Montney Formation: (1) variance of the SHmax direction from the regional trend, (2) vertical distance to Precambrian basement and (3) depth of the injection relative to the Montney top. Pore pressure gradient and distance to the Debolt Formation were interpreted as least influencing the geological susceptibility distribution. The highest discrepancy in geological susceptibility levels was observed in the northern part of the formation. Moreover, the Lower Montney was determined as most susceptible to induced seismic activity of all units.
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Seismic Interpolation Based on the Random Forest Method
More LessSummaryIn course of any seismic data acquisition, one inevitably encounters instances of empty seismic traces or insufficient spatial sampling, which results in bad sectors and can greatly affect seismic data quality. It is therefore often necessary to undertake seismic trace interpolation to solve this problem. In this paper, a machine learning based method is proposed and applied. This approach requires that the statistical relationship between the amplitude of each trace at each time point and the amplitude of the adjacent trace and time window be derived using a random forest regression prediction algorithm, then the empty trace can be populated according to the adjacent trace data. The method proposed in this paper has achieved good results in the derivation of empty trace values when applied to both model data and actual data, thus proving its validity and effectiveness.
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Eigenray in 3d Heterogeneous General Anisotropic Media: Kinematics
More LessSummaryConsidering 3D heterogeneous media and general anisotropy, the kinematic Eigenray is an original finite-element optimization method for obtaining stationary ray paths (minimum traveltime or saddle point solutions due to caustics) between two fixed endpoints in cases where conventional two-point ray tracing methods are challenging. Based on Fermat’s principle, we introduce an original Lagrangian that we consider the most convenient for our finite-element solver. For the minimum traveltime, the target function includes the traveltime and two essential penalty functions, and it is optimized with the Newton method. For the saddle point, the traveltime in the target function is replaced by the traveltime gradient squared and a gradient optimization method is used. In each iteration, the trajectory is optimally discretized by a number of nodes and segments, with the Hermite interpolation. The degrees of freedom are node locations along the path and the nodal ray (or ray velocity) directions. In either case, both the global gradient and Hessian of the traveltime are needed and computed. The traveltime Hessian of the stationary path is then used to compute the relative geometric spreading between the source and receiver. Finally, we introduce the normalized relative geometric spreading to be used as a propagation complexity criterion.
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Eigenray in 3d Heterogeneous General Anisotropic Media: Dynamics
More LessSummaryConsidering 3D heterogeneous media and general anisotropy, and a parameterized stationary ray path obtained by the kinematic Eigenray, we analyse the second traveltime variation and derive the linear, second-order, vector-form Jacobi dynamic ray tracing (DRT) ODE. It delivers paraxial rays defined by shift vectors normal to the ray direction in its vicinity. The solution is obtained by applying the same finite element scheme (with the Hermite polynomial interpolation) used in the kinematic Eigenray. The resolving matrix of the linear algebraic DRT equation set coincides with the global traveltime Hessian already computed in the kinematic Eigenray stage. Two different solutions of the Jacobi DRT ODE with their corresponding point-source initial conditions, related to the chosen ray coordinates (RC), are needed to compute the ray Jacobian representing to the signed cross-area of the corresponding ray tube. For the chosen RC, we derive an original relationship between the ray Jacobian and the relative geometric spreading. The proposed Eigenray method has been tested using a benchmark numerical example with orthorhombic elliptic factorized inhomogeneous anisotropy. This model has an analytic solution for the ray path configuration, traveltime, arclength, and parameter sigma. The results demonstrate the high accuracy obtained by the proposed method.
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Vwgradient Picking – An Approach to Resolve the Near-Surface in the Presence of Velocity Inversions
Authors C. Diggins and G. HampsonSummaryRefractor shingling is a common geophysical response to thin high-velocity layers called “stringers” embedded in the near-surface of many geological basins. Between stringers are low-velocity inversions. Refractor shingling precludes turning-ray tomography which assumes a monotonic increase in weathering velocity from the surface.
This paper introduces a new strategy to creating tomographic models in the presence of refractor shingling. We recommend picking a continuous weatheringvelocity gradient that starts at zero time at the surface and follows a continuous velocity until it merges with a deeper refractor. In this way, we pick inside the shingling, picking instead the velocity gradient consistent with a steadily increasing weathering velocity. We call this strategy “VwGradient Picking”.
We mathematically model a near-surface stringer in a slow-velocity medium, verifying the existence of the VwGradient in the presence of refractor shingling. We show various examples of shingling and VwGradient picking in several planes. Stacks with VwGradient-derived turning-ray tomo statics compared to other refraction statics approaches show the efficacy of this novel picking strategy.
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The Dutch Scan Geothermal Seismic Exploration Program – Current Status and Future Plans
Authors J. Rehling, E. Siemerink, M. Ter Borgh and G. Zaalberg-MetselaarSummaryTo achieve the Dutch policy objective to reduce carbon emissions by 49% in 2030, a shift from fossil towards renewable energy resources is required. Within the Netherlands, Geothermal Energy is a proven renewable energy resource, but currently only with a limited number of operating installations, which are located in areas of good subsurface data coverage.
However, subsurface data coverage is poor in roughly half of the country, including major residential and industrial areas with high heat demand. Improving the data coverage in these areas would increase the benefit-risk ratio of geothermal projects, which would greatly support the development of these projects.
To address these data shortcomings, Energie Beheer Nederland B.V. (EBN) and the TNO Advisory Group for Economic Affairs (TNO-AGE) have embarked on a geothermal exploration campaign, which includes reprocessing of vintage data as well as the acquisition of new, long-offset 2D seismic to improve the subsurface imaging and allow reliable interpretation to a depth of at least 6km. At a later stage deep research wells will be drilled and all subsurface data will be made public.
This paper will give an update regarding the geophysical work program, discuss results achieved by June 2020 and outline further plans.
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Partial Fraction Signal Decomposition and Time-Frequency Representation
Authors B. Ursin and M. PorsaniSummaryWe present a new method for obtaining the time-frequency decomposition of a non-stationary signal. The input signal is modeled as a dynamic short-time autoregressive process. From the analytic signal or complex trace, we compute the AR coefficients or prediction error operator (PEO), in sliding time windows. The inverse of the Z-transform of the PEOs can be represented by a sum of partial fractions, each one related to a single pole. Each pole may be used to deflate the PEO, allowing us to rewrite the AR representation of the signal as a sum of signal components. Also, the position of each pole provides the dominant frequency, which is useful to distribute the signal component in the time-frequency domain. The signal components are obtained by convolving the input signal with the reduced PEOs, scaled by the partial fractions coefficients. The new time-frequency signal decomposition method is demonstrated on synthetic data.
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Evaluation of the Unconventional Gas Potential of Diyab in West Uae and Exploration Effectiveness
Authors D. Xiao, D. Mao, L. Wang, X. Hu, M. Lv, Abdulla Al Blooshi, Maryam Al Shehhi, W. Zhao, Ashis Shashanka, M. Jia and J. YangSummaryWith advancement of drill and hydraulic fracturing technologies, shale gas are blooming in recent years. The Middle East also pays high attention to unconventional plays. The Diyab source in western UAE deposited in an intra-shelf basin with mudstone, wackestone, and high argillaceous-carbonaceous matters in the low section. This set is widely developed with high TOC, thickness, maturity and is evaluated to be the main unconventional play of gas bearing.
Based on data of wells, cores and seismic, a procedure of basin modelling was implemented to regionally evaluate the Diyab. Generally, good source of the Diyab performs TOC 2-4%, with maximum of 5.2%. Thickness of net play ranges around 100-150ft. This formation has high maturity of Ro 1-1.4. Hydrocarbon generation and expulsion intensity from basin modelling are 25bcf/km2,20bcf/km2 respectively.
Focusing on the most favorable area, sweet spot was predicted to capture key parameters of TOC, brittleness, porosity, fracture and strain & stress. Based on evaluation from the factors, one well was drilled in 2019 and yielded gas in vertical borehole after hydraulic fracturing. The result is encouraging and indicates unconventional gas potential in the Diyab.
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Dispersion Coefficient Inferred from Convection Dynamics of CO2 in Brine Saturated Porous Media
Authors S. Mahmoodpour, B. Rostami, S. Omrani and M. Salehi SedehSummaryMass transfer rate estimation is an important aspect of the dissolution trapping mechanism analysis during CO2 sequestration in saline aquifers which has been studied extensively in recent years. Based on laboratory experiments or direct numerical simulation tools, scaling relationships have been introduced for the mass transfer rate estimation. However, there are discrepancies between these results. To investigate the discrepancies between experimental and direct numerical simulation results, we carried out a series of experiments to quantify dispersion during CO2 convective mixing, which enabled us to obtain robust scaling relationships. Two brine compositions including sodium chloride (NaCl) and a mixture of NaCl and calcium chloride (CaCl2) are separately considered in two levels with two levels of permeability to encompass the applicable range of the Peclet number (Pe). Furthermore, we conducted a series of high resolution direct numerical simulations to show the applicability of the proposed relationship in simulation. Our analysis of results reveals that a power-law scaling relationship based on the Pe best fits the dispersion values. Furthermore, numerical simulation results show that dispersion has a considerable impact on the pattern and amount of CO2 dissolution in brine.
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Optimization of Two Simultaneous Water and Gas Injection Scenarios in a High GOR Iranian Oil Field
Authors A. Izadpanahi, R. Azin, S. Osfouri and R. MalakootiSummaryGas Oil Ratio (GOR) is one of the most important production parameters in oil reservoirs. GOR increase may lead to shutting-in the wells due to being uneconomic. The main goal of this study is to investigate two simultaneous water and gas injection scenario in a real fractured oil field with high producing GOR. This field is located in the south-west of Iran and the production from this field was started in 2013. A dynamic reservoir model was built by using the reservoir properties, reservoir fluid model, reservoir geometry, relative permeability and production data. A history match was conducted to validate the reservoir model for future forecasts. After validating the model, two scenarios were investigated including 1) one water injection well and two gas injection wells and 2) one gas injection well and two water injection wells. Then, an optimization study was conducted on each scenario. Production rate, water and gas injection rate, status of the wells were optimized. This optimization caused improved oil recovery of each scenario. The scenario with two water injection wells has better results than the other one due to the controlling gas oil ratio and preventing of production wells shut-in.
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PS Converted-Wave NMO Correction and its Application to Improve PS Reflection Imaging Quality of VSP Data
Authors M. Lou and H. SimpsonSummaryWe have developed a new three-term formulation of normal moveout (NMO) correction for PS converted reflection waves in VSP data. The formulation is accurate for multi-layered media with a large source offset (up to a ratio of ∼2.5 of offset to reflector depth) in VSP survey. Based on the new NMO correction formulation, we also developed a new methodology to improve signal to noise (S/N) ratio and the final imaging quality of PS converted reflection waves in VSP data. The methodology consists of three major processing steps in the common receiver gather domain: NMO correction for flattening/aligning PS converted wave reflection events, median filtering for attenuating coherent and incoherent noise, and reverse PS NMO correction for migrating PS converted reflection waves. The processing of a field walkaway VSP dataset with our methodology demonstrates the effectiveness of the methodology in improving the imaging quality of PS converted reflection waves.
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Geochron-Based Restoration Workflow Applied to Clyde Seismic Dataset
Authors A. Tertois and J. MalletSummaryGeomechanical restoration helps validate seismic data interpretation and check structural model consistency. Most current methods are mechanically-based and thus require knowledge of rock properties and geological boundary conditions which can be difficult to assess and tedious to input. Furthermore, the finite element codes used to solve the systems of mechanical equations can be slow. As a consequence, these useful and valuable methods are not used as often as they should be in modelling workflows.
Last year, we proposed a geometric restoration method based on the GeoChron mathematical framework. Our method is simple and fast, requiring no prior knowledge about rock properties or boundary conditions. Starting from an initial GeoChron model, we compute restoration transformations by solving a set of equations with strong theoretical roots which ensure the consistency of restored models at each restored stage and with the initial model.
The present paper complements the theory by showing results of this GeoChron-Based Restoration method applied to a complex structural model. We show results at different restoration stages and discuss potential benefits for further interpretation of this data set.
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Frequency-Dependent Inversion Using Spherical-Wave Reflection Coefficient with Critical and Post-Critical Offsets
More LessSummaryAs an zero-order approximation of spherical wave theory, plane wave theory based on the Zoepprtiz equations and various linear approximations has been widely used in seismic exploration, such as prestack inversion, deconvolution and Q compensation. Since localized sources excited in field acquisition usually produce spherical wavefront, the plane wave approximation fail to correctly utilize post-critical information and frequency-dependent characteristics have been completely neglected. Unlike conventional inversion using multiple offsets, the existence of frequency-dependence makes the inversion using reflected record of single offset possible. Therefore, the feasibility of frequency-dependent inversion using one offset is analyzed and investigated in this paper. The sensitivity, resolution matrix and objective function are adopted to analyze the coupled relationship between different parameters and to determine proper parameters to be inverted. Combining a global optimal algorithm, the effectiveness of frequency-dependent inversion is verified in both synthetic data. The velocity and density parameters with acceptable error are well-inverted, especially when critical offset is included. Moreover, the inversion uniting frequency-dependent feature with multiple offsets offers more accurate and concentrated estimations for both density and velocity parameters.
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Effects of Cable Deployment Method on Das VSP Data Quality: Study at CO2CRC Otway in-situ Laboratory
Authors R. Pevzner, K. Tertyshnikov, E. Sidenko and S. YavuzSummaryDistributed acoustic sensing provides a unique opportunity to deploy massive seismic receiver arrays on the surface and in downhole environments. For downhole installation several options including temporary wireline deployment or more permanent setups such as cementing behind the casing, strapping to production tubing or cementing inside the casing during the abandonment operations.
CO2CRC Otway project was the first Australian demonstration of CO2 geosequestration commenced in 2006. Stage 3 of the project is focused on the downhole monitoring of a small scale (15,000 t) CO2-rich gas injection utilising a borehole array. This array comprises of existing and several new 1.5-1.7 km deep wells drilled within approximately 1 km2 area and all instrumented with optical fibres. The wells have a combination of fibre optic cables deployed using different approaches, in some cases – one well can have several cables deployed differently.
Prior to completion of the wells, we acquired a set of zero-offset VSP surveys using conventional 3C geophones in the four new wells drilled in 2019. A series of DAS tests focusing on the effects of deployment methods on DAS VSP data quality were also performed. In this presentation, we share findings from these experiments.
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Q-Compensated Fourier Finite-Difference Wave-Equation Migration in Tilted Transversely Isotropic Media
More LessSummaryAttenuation has an influence on a seismic wavefield’s amplitude and phase. Because the Q effect strongly relates to the frequency, it is natural to include Q compensation in the one-way Fourier finite-difference wave-equation migration (FFD WEM) that can produce images with high quality and resolution, with a much lower cost than reverse time migration when there are no steeply dipping structures (e.g., above 75°). FFD WEM propagator involves three components: 1) a phase-shift term, 2) a thin-lens term, and 3) an FFD term. The complicated FFD term has a large impact on the accuracy of imaging structures with relatively large dips. We propose an improved Q compensation scheme for FFD WEM in tilted transversely isotropic media. Analogous to frequency-dependent phase velocity, we use a group of coefficients at each frequency, which are calculated by combining linear and nonlinear inversions to increase the accuracy of the least-squares estimation. By approximately including the Q effect in all three components of the FFD WEM, we increase the simulation accuracy for the wave propagation in relatively large dip angles. Both synthetic and field data examples show the validity of the proposed methodology in producing Q-compensated images.
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Trialling Passive Seismic with Das in CO2CRC Otway Project: Ambient Noise Composition and Prospects for Utilisation
Authors R. Pevzner, K. Tertyshnikov, E. Sidenko, S. Glubokovskikh and B. GurevichSummaryTime-lapse seismic is the standard technique for monitoring changes in the subsurface. This technique has great spatial resolution and sensitivity to changes in fluid saturation. However it has certain drawbacks related to relatively high cost, temporal sparseness of the data and risk of disruption to other land use activities. Opportunity to permanently deploy large receiver arrays in the subsurface, made particularly feasible by recent advances in Distributed Acoustic Sensing (DAS) using optical fibre, leaves most of the cost and disruption to seismic sources. Better utilisation of the active seismic source energy and deriving as much information from ambient noise by literally “recycling” elastic energy emitted by both human-related and natural sources is likely to extend applicability and possibly revolutionise the use of the seismic monitoring.
In this presentation we summarize findings of an initial feasibility study conducted using passive downhole seismic recorded in several wells in 2018-2019 as a preparation for Stage 3 of the CO2CRC Otway Project. We demonstrate that there is enough detectable ambient energy that can be recorded by DAS, perform initial analysis of the wave field composition and identify prospective approaches for data utilisation.
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An Adaptive Finite Element Method for Calculating the Stress Field of Reservoir
More LessSummaryThe study of crustal stress is one of the important links in oil and gas exploration and development system engineering. In view of the problems of high cost and few data points in actual stress testing of ground stress, the adaptive finite element method is used to simulate the distribution of the actual reservoir ground stress. The simulation results show that the adaptive finite element method can adapt to the calculation of the ground stress field in the complex geometric area, which has the advantages of high precision and fast speed, and the calculation results accord with the general geological knowledge.
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Seismic Flownet: Using Optical Flow Field for Dense Horizon Interpretation
Authors Z. Li and A. AbubakarSummaryWe developed a FlowNet based deep learning workflow, to produce flow field cube from a seismic survey. Based on the flow field, stratigraphic sequence information such as horizons can be densely extracted given any seed point. Training of the network is performed on image and distorted image pairs generated by applying elastic deformation with random flow field without manual labeling. A multiscale horizon tracking method was developed to incorporate flow fields from different resolutions.
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Multichannel Reflectivity Inversion Using an Adaptive Lateral Amplitude Perturbation Constraint
More LessSummaryWe propose a lateral amplitude perturbation (LAP) estimation to regularize the multichannel reflectivity inversion procedure. In our algorithm, the LAP estimation, characterizes the lateral structural variation at individual pixel, is converted to a lateral constraint term by exploiting the shaping regularization method. The constraint is imposed along horizontal direction and can be achieved easily. By this way, this adaptive constraint maps the spatial dependence in data into the estimated result, and reaches a balance between guaranteeing lateral continuities of structures and alleviating blurring of the geological detailed information. Model and field data examples confirm the merits of our algorithm compared to the sparse spike inversion (SSI) approach.
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The Journey of Lang Lebah Discovery and Multidisciplinary Approaches for Carbonate Sweet Spot Targeting
SummarySarawak exploration is dominated by the Late Miocene platform carbonates and pinnacle reefs discovery of Central Luconia sub-basin, Sarawak Basin, offshore northwest Borneo. The basin formed in Late Eocene to Oligocene extends over 40,000 sq.km and developed more than 200 carbonate build-ups. Since 1950s, all large structure of carbonate pinnacles has been explored and left with uneconomical prospects and high geological risk. In 2019, PTTEP together with KUFPEC and PETRONAS Carigali has revived the Sarawak exploration activities and discovered a multi-TCF gas field of Lang Lebah Carbonate Pinnacle, which became a world top rank and the largest hydrocarbon resources of Malaysia in 2019. In order to successfully explore remaining hydrocarbon potential in a mature basin, comprehensive exploration approach in carbonate reef was established. The approach requires integration of reservoir characterization (seismic inversion) and carbonate growth architecture identification. The multidisciplinary approach then alluded to the sweet-spot target for carbonate build-up appraisal program. This paper will discuss on the journey of Lang Lebah discovery, guided by the novel multidisciplinary technical approaches and new exploration concepts.
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Separating and Sparse Imaging of GPR Diffractions by Dictionary Learning and Least-Squares Migration
More LessSummaryTo efficiently separate weak diffractions from the GPR data, which usually has a single coverage and is easily contaminated with noise, we formulate a GPR diffraction separation method by incorporating the plane-wave destruction method and online dictionary learning technique. To promote the focusing ability of diffractions, a reweighted L2-norm and L1-norm minimization model is also introduced for accomplishing high-resolution GPR images, which has potential in focusing diffractions and reducing migration noise. The results obtained in our provided field example illustrates its good performance in separating and imaging of GPR diffractions and its potential value in illuminating fractures and the broken conditions.
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Oriented Inverse Q Filtering Using Prestack Data
More LessSummaryAttenuation is the main factors responsible for degrading the resolution of seismic data. It seriously decreases the energy of signal components especially those with higher frequency. The attenuation-induced energy loss can be partially compensated via inverse Q filtering. However, inverse Q filtering is inherently not stable, which suffers from overcompensation and noise burst. Among the existing compensation methods, poststack data are used more frequently. Nevertheless, poststack compensation can’t provide us with compensated prestack seismic data directly, which are commonly used in prestack impedance inversion and other prestack processing. We have developed an oriented and stable method by introducing plane-wave destruction (PWD), predictive painting and stable division based on Taylor expansion for compensation of attenuating common midpoint (CMP) gathers. We call it warped mapping (WP). The compensation of synthetic data is carried out to illustrate the well performance of the proposed method even though in the presence of ambient noise.
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Inversion-Based Multitrace Absorption Compensation with Lateral Regularization
More LessSummaryThe presence of seismic absorption distorts seismic record and reduces seismogram resolution, which can be partially compensated by application of absorption compensation algorithms. Conventional absorption compensation techniques are based on 1D forward model with each seismic trace being compensated independently. Therefore, the 2D results combined by each compensation trace may be noisy and discontinuity. To eliminate this issue, we extend the 1D forward model to the 2D forward system and further add an additional lateral constraint to the compensation algorithm for enforcing the lateral continuity of the compensated section. By solving the proposed laterally constrained absorption compensation (LCAC) algorithm, we simultaneously obtain the multiple compensated traces with lateral smoother transition and higher signal-to-noise ratio (S/N). We testify the effectiveness of the proposed method by applying both synthetic and field data. Synthetic data examples demonstrate the superior performance of the LCAC algorithm in terms of improving algorithmic stability and protecting lateral continuity. The field data tests further indicate its ability to not only improve seismic resolution, but also maintain the S/N of compensated data.
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Origin and Evolution of Paleofluid of the Middle Permian Maokou Formation in Southern Sichuan Basin
More LessSummaryBased on petrology, rare earth elements, carbon and oxygen isotopes and fluid inclusions analysis, paleofluid origin and evolution of carbonate rocks in diffenert diagenetic stages of Maokou Formation are discussed. The results show that: (1) Maokou Formation was occurred “penecontemporaneous seawater cementation→ -eogenetic mixed water cementation→ epigenetic atmospheric freshwater dissolution→phyllomorphic formation water cementation, metasomatism and acidic-fluid dissolution”; (2) origins of sedimentary and diagenetic fluid include seawater, atmospheric freshwater, hydrocarbon fluids and thermal fluids: the oxidized seawater is characterized by the left-lead limestone REE, and similar the δ13C characteristics with the global paleo-seawater, the acidic hydrothermal fluid is mainfested Eu positive anomaly and obvious negative δ13C, atmospheric freshwater is conducted obviously negative δ18O in carbonate cement; (3) Maokou Formation was experienced multi-phase oil and gas charge: the Late Permian-Early Triassic Maokou Formation was exposed to leaching, and the anomalous thermal of the Emei mantle plume caused dolomitization and hydrocarbon charge. Meteoric water , organic acid dissolution, dolomitization and fracture play constructive roles in Maokou Formation reservoir. Dissolution and coarse-grained calcite cementation damaged the Maokou Formation since the Jurassic, karst reservoirs associated with structural fractures are more conducive to later gas accumulation.
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A Mathematical Model of Water Spontaneous Imbibition into Oil-Saturated Fractures in Unconventional Reservoirs
More LessSummarySpontaneous imbibition is an important EOR mechanism in unconventional oil reservoirs. Lots of attentions have been paid on spontaneous imbibition in tight matrix, but studying the mechanism of spontaneous imbibition in nano/micro fractures is of great significance to EOR in unconventional oil reservoirs. In this paper, an implicit analytical solution of water spontaneous imbibition into an oil-saturated fracture with the effects of gravity and oil viscosity is firstly developed, and verified with numerical simulation. With the function of fracture distribution, a core-scale spontaneous imbibition model in fractured porous media is proposed. The key parameters influencing spontaneous imbibition in fractures are investigated. The research results show that the inertia force (acceleration term) only affects imbibition velocity at the initial stage of imbibition and can be ignored. In large fractures, such as with 10 μm of fracture aperture, the gravity effect cannot be ignored. Viscous force is the resistance of spontaneous imbibition, and the imbibition velocity increases with the increase in water-oil interface location due to the reduction in oil viscous force. For the core-scale fractured porous media, the imbibition rate is more dominated by the distribution of fracture apertures.
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Characteristics and Controlling Factors of Deep Buried Reservoir in the Southern Margin of Junggar Basin
More LessSummaryThe Junggar basin is a large petroliferous, superimposed basin in Northwest China. The burial depth of Cretaceous Qingshuihe Formation sandstone reservoirs in the southern margin is 5500-7000m.Although the burial depth is large, the sandstone reservoirs are of good physical properties. The Qingshuihe reservoirs have mineralogical immaturity and moderate textural maturity. The pore system is mainly primary intergranular pore and a few secondary dissolution pore. Microfractures are developed in some grains. More initial porosity lost by compaction than cementation. Eodiagenesis in Qingshuihe sandstones is dominated by mechanical compaction, cementation by calcite and analcime. Mesodiagenesis mainly consist of further mechanical compaction, dissolution of feldspars and cements, formation of illite and mixed-layered I/S, Fe-calcite cementation. The formation of deeply buried high-quality reservoirs in the Qingshuihe Formation is controlled by four key factors. Firstly, grain size and rock composition played a significant role on initial porosity. Secondly, early long⁃term shallow burial and late rapid deep burial is conducive to the preservation of primary pores in the reservoir. Another factor is intragranular micro-fractures, which can increase the permeability of the reservoir and the overpressure also is an important factor for the formation of high-quality reservoirs.
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Reflection Raytracing Using Snell’s Law in Multi-Stage Fast Marching Method
More LessSummaryReflection traveltime tomography needs accurate calculation of reflection traveltime and reflection angle. The multi-stage fast marching method (MFMM) is widely used in reflection raytracing, which performed well in reflection traveltime calculation, but the reflection angle has pretty large error since the reflected ray does not follow the Snell’s law strictly nearby the reflector. Here, we developed a modified multi-stage fast marching method that use Snell’s law to compute the reflection traveltime of grid points just above the reflector and the corresponding reflection point at the reflector to improve the accuracy of reflection angle. The numerical examples show the reflection angle improved a large scale.
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Combining Edge Enhancement Images for More Reliable Detection of Magnetic Features: A Python Implementation
Authors V. Ribeiro and J. MarkovSummaryThe most common use of aeromagnetic data is the identification of magnetic bodies and contacts. Edge enhancement techniques are crucial to the interpretation process because they allow more accurate mapping of these key features. However, most techniques used to enhance magnetic features have disadvantages of one type or another. The algorithm presented here allows the user to apply any combination of fourteen different enhancement filter techniques. This strategy has the advantage of letting the interpreter to compare the noise-to-signal ratio obtained for different methods and chose only the better results for a specific study case. We also included two different options to combine the results: a simple stacking approach where all filters considered have the same weight to compose the final map and one that divides the solutions in four different groups, according with the number of results obtained. By stacking the solutions obtained by different filters it is possible to enhance true edges while minimizing false peaks and mathematical artefacts. The method was tested on a synthetic data set and one real case to demonstrate the methods performance. The synthetic case was designed to simulate the presence of three sources at different depths with a strong unknown remanent component.
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Improved Signal to Noise Ratio Estimation Based on Edge-Preserving Method
More LessSummarySignal-to-noise ratio (SNR) is an important evaluation standard for measuring data quality in seismic data processing and interpretation. However, it is too one-sided to evaluate the SNR with only one value for the whole data, so it is proposed to retain the partial SNR distribution. In this paper, we propose an improved method based on the seismic disorder attribute to estimate the randomness of post-stack data, which mainly modify the smoothing method by using the edge-preserving smoothing (EPS). We test the method on the post-stack synthetic seismic data and field seismic data. It is proved that the proposed method can be applicable to the structural shape change, retain the structure information and the spatial distribution of data quality, and estimate SNR more accurately.
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Modelling the Effect of Fracture Density and Saturation on S-Wave Radiation from Vertical Sources
By J. GaiserSummaryRecent investigations in shear waves (S-waves) that convert to compressional waves (P-waves) as primary reflections (SP-waves) model S-wave radiation from vertical sources. These have been to understand the effect of isotropic heterogeneities near the source, and the influence of anisotropy on generating different S-wave modes, and to assess the subsurface illumination of these modes. In this study I model the effect of different fracture properties, density and saturation, on the radiated S-wave properties of amplitude and azimuthal illumination relative to fracture orientation. The primary influence of increasing fracture density and saturation is to reduce displacement amplitude of slow S2-waves that are polarized perpendicular to fractures relative to amplitude of fast S1-waves that are polarized parallel to fractures. This low amplitude behaviour is expressed as a reduction in azimuthal subsurface illumination. However, the opposite is true for unsaturated or nearly dry fractures where S1-wave amplitude is reduced relative to S2-wave amplitude. Uneven azimuthal illumination of S1- and S2-waves may pose additional challenges for using converted SP-waves to characterize oil and gas fractured reservoirs.
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Improving Seismic Resolution by a Sequential Convolutional Neural Network
More LessSummarySeismic data with high resolution provides better insights for extracting geological information. Due to the earth filtering, gathered seismic data are band limited. As a routine operation in seismic processing, high resolution processing involves multiple techniques. Some commonly-used methods are theory-based, demonstrating both advantages and disadvantages due to the assumptions and theories governing their issues. Besides, some data-driven methods have been introduced to perform high-resolution processing. Inspired by the encoder-decoder network and residual network, a sequential convolutional neural network was developed to improve seismic resolution. The encoder-decoder architecture works well for sequence to sequence transformation and contributes to extracting high-hierarchy features. The usage of residual learning is good for accelerating convergence and improving generalization. Taking 1D low-resolution and high-resolution time series pairs as training data, the proposed sequential convolutional neural network is trained by deep learning. Considering the limitation of acquiring actual high-resolution seismic, synthetic seismic traces are generated with separate low-resolution and high-resolution wavelets to prepare realistic and correlative input feature and output label pairs. Experiments on raw seismic data demonstrate the efficiency and generalization of the proposed method.
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Convertible Geometry Studies
More LessSummaryFor the seismic acquisition equipment tech to develop, and the great progress in nodes technology, the cost of acquisition equipment is continuously decreasing, so that it is possible to apply the large-scale application of acquisition equipment for geophysical exploration. This seismic acquisition method will become a seismic data acquisition trend. How to fully utilize a large number of acquisitions equipment to obtain large scale offsets, full azimuth angle seismic data is a new challenge. It can provide sufficient raw seismic data by using Convertible Geometry in seismic acquisition. In the follow-up seismic data processing, according to different geological targets, the relevant processing methods are applied to the acquired seismic data, and those seismic data has gotten by convertible geometry, which can get higher quality seismic images. For seismic data acquired by simultaneous multi-source with convertible geometry, simultaneous multi-source acquisition deblending separation technique and seismic wavelet inversion will be used in seismic data processing. Compared the seismic data by different geometries, the images of geological structures by convertible-geometry will be more accurate. The convertible geometry acquisition method is highly efficient, cost-effective, full azimuth. It can bring high-quality image of underground geological structures.
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Evaluation of Reservoir Compartmentalization Using Seismic Pore Pressure Modeling in an Oil Field in Persian Gulf
Authors P. Adabnezhad, A. Mollajan and F. ForghaniSummaryPore pressure prediction is a key necessity for successful drilling operation during exploration phase. Unexpected changes in pore pressure may increase all risks related to drilling operation. The aim of this study is to introduce pore pressure gradient model as a useful tool for investigating geomechanical reservoir compartmentalization in Mishrif carbonate reservoir from an oil field located in Persian Gulf. In this regard, simultaneous inversion algorithm is used to generate a high definition velocity model. Inverted velocity model is then converted to a 3D pore pressure model using velocity-based version of Eaton’s equation. Analyzing created pore pressure model shows a sharp discontinuity crossing central part of reservoir under study that reflects the presence of two different geomechanical zones in the region. A strong geological evidence that confirms one old major fault divided Mishrif reservoir into two different blocks in the region proves this idea.
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Reservoir Productivity Prediction Based on a Hybrid Deep Neural Network
More LessSummaryFor productivity prediction, physics-based methods generally depend on some hypotheses and are confined to certain types of reservoirs. Some machine learning methods take statistic average as input feature when utilizing log curves, which discards the spatial correlation of reservoir formation contained in log curves. By means of deep learning, we develop a productivity prediction method based on a hybrid deep neural network with mixed inputs. The hybrid deep neural network is composed of a multilayer perceptron network and a convolutional neural network, adding some fully-connected layers. The multilayer perceptron network is used to process numerical and quantified categorical data. The convolutional neural network is adopted to make full use of structural data, such as log curves. Structural log curves reflect the spatial variation of reservoir formations, containing more details. Further consideration of numerical or categorical data insures the comprehensiveness and diversity of machine learning dataset. The hybrid architecture is the key to establish complex nonlinear relationship between target productivity and mixed inputs. Applied to a development oil block and compared with typical multilayer perceptron model and convolutional neural network model, the proposed hybrid deep neural network model stands out with high accuracy and good generalization.
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Temperature Dependence of Ultrasonic Velocities in Fluid-Saturated Rocks: Experiments and Modelling
More LessSummaryUnderstanding the effect of temperature on the physical properties of rocks is important to develop deep oil, gas and geothermal resources. However, relatively little effort has thus far been made to capture the temperature effect on velocity in fluid saturated rocks. To overcome this limitation, a double-porosity medium model is developed, which incorporates the Batzle-Wang empirical equations for the pressure and temperature dependence of the pore fluid, as well as the David and Zimmerman models to quantify temperature-dependent micro-crack density. This model is tested on samples of carbonate, for which the variation of ultrasonic P-wave velocity with temperature has been measured. Modeling and experimental data show that the proposed model is versatile enough to quantitively describe the velocity-temperature relation. It turns out that for these rock samples the temperature-dependent fluid properties dominate the velocity-temperature relations.
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Optimization of Cold Production with Horizontal Wells in Foamy Extra-Heavy Oil Reservoirs
By Z. YangSummaryThis research provides a more profitable development plan for improving cold recovery of foamy extra-heavy oil reservoirs in the Eastern Orinoco Belt.
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Shallow Water Delta Reservoir Configuration Analysis In Qk Oilfield, Bohai Bay Basin
More LessSummaryAffected by complex contact relationships between single distributary channels and reservoir heterogeneity, the distribution of remaining oil is complex and the shallow water delta oilfield development effect becomes worse at the late stage of waterflooding development. Taking QK oilfield as an example, the reservoir configuration of shallow water delta sand body is studied by using core, well logging and production dynamic data. The classification of shallow water delta sand body configuration, interface identification and spatial structure model are established. Combined with the actual development of the oilfields, the shallow water delta sandbodies in the study area can be classified into 4 levels of reservoir configuration. The longitudinal interfaces of single distributary channel include mudstone interface of sediment origin, calcium interface of carbonate cementation origin and physical interface of erosion origin. The lateral interfaces includes three types of qualitative identification methods which are overflow sediment, lacustrine mudstone and abandoned channel deposits, and one quantitative method of thickness model. Spatially, affected by the decline of lake level, the plane shape of sand bodies changes from sheet to strip, and the connectivity of reservoirs becomes worse, which makes remaining oil mainly distribute on the top of composite channel sand bodies.
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Efficient Clock Drift Corrections and Self-Surveys for Nimble Nodes
Authors A. Crosby, D. Dieulangard, A. Ourabah, C. Brooks, T. Manning, J. Quigley, K. O’Connell, C. Vasile and D. AblyazinaSummaryAlthough a GNSS chip remains an essential component of the next generation of small land seismic recording nodes, their power consumption is high compared to other aspects of the electronics. To maximize the lifetime of the battery and minimize node size and weight, GNSS use should be optimized. We use two field trial examples from the development of the latest generation of land seismic receivers to show how GNSS usage can be optimized without compromising on timing accuracy or the ability of the nodes to self-survey to an accuracy sufficient for seismic processing. Without temperature calibration, we find that as few as four time-checks per day are sufficient to ensure that sample time errors are less than ±1ms. With temperature calibration, GNSS hiatuses of up to several days can be corrected. For short surveys, the lower limit on the number of fixes may be set by positional requirements, with at least 60 measurements being required to measure X, Y and Z to within ±2m.
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Avo Sparklines
By A. CrosbySummaryThorough quality control of AVO or other multi-volume attributes across 3D seismic volumes is difficult using current workflows without sacrificing detail or becoming laborious, especially given the recent trend towards high-density, rich-azimuth acquisition. Using examples, we introduce the concept of “AVO sparklines” to enable rapid yet detailed screening of pre-stack AVO behaviour across large volumes. Sparklines are small, minimally adorned, generated automatically and positioned alongside the input seismic gathers, and are designed so that several hundred can be viewed at once. They may be encoded in the seismic data file itself. AVO sparkline displays are designed to be platform-independent and take advantage of high-resolution monitors and natural human skill in pattern recognition and anomaly detection. The sparkline concept can be extended to many other quality control and assurance problems in seismic processing and analysis.
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