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Fourth EAGE Workshop on Rock Physics
- Conference date: November 11-13, 2017
- Location: Abu Dhabi, United Arab Emirates
- Published: 11 November 2017
1 - 20 of 25 results
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Effect of Rock Physics Uncertainties on Reservoir Flow Simulations
By T. MukerjiSummaryThis talk will explore the link between seismic rock physics and reservoir flow simulation models. How does rock physics interpretation uncertainty affect the flow simulator response? What are the sensitivities between rock physics model parameters and flow simulations? Two cases will be discussed: one where the well-log rock physics interpretation of facies can affect the static model that goes into the simulator, and another where the dynamic time-response of the simulator is influenced by the rock physics model parameters, thus impacting the interpretation of time-lapse seismic data used in seismic history matching.
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Facies-based Reservoir Characterisation Through the Asset Lifecycle
By M. KemperSummaryReservoir characterisation is essentially the process of getting as much valuable information as possible out of a variety of data sources (wells, seismic, …) so that geological modelling and subsequent flow simulation, the main thrusts of this workshop, are optimally underpinned by that information.
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Trends in Micro-Crack Properties of Sedimentary Rocks in Loading and Unloading Mechanism
More LessSummaryAnalysis of trends in micro-crack properties such as crack density and aspect ratio of sedimentary rocks in loading and unloading mechanism.
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Prediction of Reservoir Properties for North Sea Chalk by Inverse Rock Physics Modelling
Authors A.H. Drottning, T.A. Johansen and E.H. JensenSummaryThe elastic properties of North Sea chalk formations are controlled by porosity, matrix properties (though mostly pure calcite), rock texture, pore fluids and pressure, where porosity is expected to be the dominant factor. Lithology and fluid characterization is more challenging as their elastic signature may be diffuse and ambiguous. In this paper we present a first application of the IRPM method for predicting the PLF properties of a North Sea chalk reservoir, and discuss the requirement to data quality needed to make such predictions.
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Carbonates: Rock Physics Models in the Context of Experimental-Derived Seismic Rock Properties
By G. BaechleSummaryIn this core study, we show the similarities and difference of the two rock physics models. Our motivation is to determine which of the two models is preferred to understand the rock’s pore structure.
First we revisit how the effective medium model and an image analysis procedure can be used to determine the rock’s pore structure. Next, we compare two different approaches which have been utilized in the past to predict carbonate rock properties: the dry rock approximation (DRA) of the DEM model and the Extended Biot Theory (EBT). Finally, we compare the derived model parameters back to the pore types observed thin section.
Using a differential effective medium (DEM) model with a dual porosity approach, a conceptual aspect ratio of 0.1 for micropores and a measured aspect ratio of 0.5 for macropores results in a good prediction of elastic properties of carbonate rocks using image analysis. We conclude that compliant micropores have dominant effects on the velocity of the rock, whereas stiffer macropores show a negligible effect on the stiffness of the rock. Both methods, the DRA and the EBT, are successful utilized to approximate the DEM trendlines of the two endmember conceptual aspect ratios for macropores and micropores.
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An Integrated Approach for Carbonate Pore Systems Acoustic Characterization: Application to Late Paleozoic Carbonates
Authors D. Mastellone, O. Borromeo, G. Mastellone, S. Duca and A. OrtenziSummaryThe pore space and acoustic properties of Late Paleozoic carbonates have been analysed to investigate relationships between geological factors and acoustic behaviour of a sample dataset comprising limestone, dolostone, spiculitic cherts and carbonate-rich sandstones.
Each sample was classified by lithology, pore type and geometry, to investigate geological controls in the Velocity/Porosity domain.
Lithology produces a clustering in the velocity/porosity domain: for a given porosity, dolostone samples show higher velocity than limestone samples.
Considering pore types, rocks dominated by vugs and molds show generally higher Vp and Vs in contrast to rocks dominated by interparticle and micropores.
Petrophysical and acoustic data allowed calculation of the Frame Flexibility factor γk to characterize the flexibility of the rock frame as a result of the pore structure. Above a porosity threshold of about 10%, two clusters are detectable: one marked by low γk reflecting a stiffer rock frame, another marked by high γk reflecting a weaker rock frame.
The clustering reflects mostly a mineralogy control with dolostones generally stiffer than limestones, however a minor influence of the dominant pore type is detectable in the limestone samples.
These results suggest that diagenetic drivers like dolomitization, should be considered when interpreting seismic facies.
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AVO Analysis Constrained by Burial History
Authors P. Avseth, I. Lehocki and P. AbrahamsonSummaryWe have demonstrated how burial history and modeling of compaction and diagenesis can be combined with rock physics modeling in order to predict expected AVO signatures for a given reservoir. This method can be used in a forward modeling way to predict seismic signatures given a known burial history. We show examples from the Barents Sea, offshore Norway, and demonstrate that the proposed methodology can be useful to screen for hydrocarbons from seismic AVO data if knowledge/information about net erosion (uplift) is available.
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Geologically Consistent Rock Physics- and AVA Depth Trends in Siliciclastic Rocks
By A.D. DraegeSummaryRock physics depth trends is a powerful tool for estimating changes in reservoir properties and seismic response for various depths, pressures and temperatures. Recorded subsurface properties at a given depth can be extrapolated up and down in the lithological column. Traditionally, rock physics depth trends are estimated for an “average” or representative homogeneous sand and shale without honoring the internal cyclicity in the sediments. The traditional method therefore results in smooth sand and shale trends, with only small variations in properties within small depth intervals. A heterogeneous sandstone will for instance be approximated with a homogeneous sandstone with representative properties when depth trend modeling is performed. This will lead to information loss and increase the uncertainty of the results. It can be of large importance for seismic and amplitude versus angle (AVA) response if a heterogeneous sand is more dirty in the top or the base, and this information will not be included when making traditional smooth depth trends.
This study demonstrates a workflow for modeling rock physics depth trends where internal geological variations in sands and shales are included. The estimated depth trends of elastic properties and density are used to model AVA responses versus depth for a shale – sand interface while honoring geology.
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Carbonate Rocks: A case Study to Evaluate Rock Properties Using Digital Rock Physics
Authors H. Sun, G. Tao, S. Vega, E. Saenger and X. JingSummaryAccurate knowledge of petrophysical parameters plays a significant role in effective characterization of hydrocarbon reservoir. Only using experimental methods is difficult to get detailed knowledge of the factors that affect rock properties, such as pore geometry, cementation state, and pore morphology. Digital Rock Physics (DRP) techniques relying on imaging technologies can be used to obtain estimates for various macroscopic rock properties from digital rock images. But DRP study in carbonates is always a challenge due to their complex pore structures and heterogeneity. Single resolution image cannot be used to address all issues of the calculations of rock properties, thus, multi-scale image fusion technique is needed. In this paper, we present a case study on calculation of rock properties with multi-scale image fusion method for five carbonate rock samples. Both 2D Scanning Electron Microscope (SEM) images and 3D X-ray Computed Tomography (XCT) images are used to do the simulations of rock properties, such as porosity, permeability, P- and S-wave velocities. By analyzing the simulations and the lab measurements, the rock properties of carbonates can be evaluated.
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A Pore Network Model for Evaluation of Permeability, Relative Permeability, Recovery Factor and Sealing Capacity from Pore Size Distribution
By Y. YangSummaryPermeability, relative permeability, recovery factor and caprock sealing capacity are among the most fundamental petrophysical properties in reservoir characterization, evaluation and modelling. These properties are difficult to measure, whereas pore size distributions are routinely measured by using mercury intrusion. This work presents a newly developed pore network model for evaluation of these petrophysical properties from pore size distributions.
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Characterization and Modelling of a Naturally Fractured Reservoir-Caprock Unit Targeted for CO2 Storage in Arctic Norway
Authors K. Senger, M. Mulrooney, N. Schaaf, J. Tveranger, A. Braathen, K. Ogata and S. OlaussenSummarySuccessfully storing CO2 underground requires a good understanding of the subsurface at the storage site, and its robust representation in geological models. Geological models, and related simulations, provide important quantitative information on critical parameters for the optimal utilisation of the subsurface, such as storage capacity, fracturing pressure, optimal injection rates and drilling strategy. In the majority of cases, such models are constructed on the basis of seismic and well data, and history matched using production and injection data. On the Arctic archipelago of Svalbard, however, a siliciclastic unit ca. 700–1000 m deep is considered for CO2 storage, and its outcrop equivalents are exposed 15–20 km from the planned injection site. These outcrops provide an important insight into the structural and sedimentological heterogeneity of the target reservoir. The use of modern tools such as photogrammetric digital outcrops enhances our ability to obtain relevant quantitative data for the geomodel. We here present an integrated characterization of the UNIS CO2 project target reservoir, combining well, core, seismic, EM and outcrop data, to build a realistic model of the planned CO2 storage site.
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An Analytical Workflow to Predict Geomechanical Well Behaviour from Seismic
Authors S.S. Payne and J. MeyerSummaryThe successful exploitation of unconventional resource plays requires an understanding of the subsurface geology, natural fracture network and present day stress regime. Each play has its own unique combination of these factors that control the response to fracture stimulation and ultimately impact productivity. New borehole datasets and interpretation techniques have provided methods to appraise target formations at well locations. However, seismic reflection data remains the most viable source of spatial information away from well locations. We describe an analytical geomechanical workflow that is constructed using elastic property volumes from a pre-stack seismic inversion. The seismic inversion used in the workflow is an innovative Bayesian pre-stack approach that simultaneously inverts for both impedances and facies. The inversion is grounded in a comprehensive well-based rock physics analysis of the formations’ elastic properties. The geomechanical analysis uses the seismic property volumes from the inversion to generate an analytical prediction of the horizontal stresses. The stress field is then solved around a vertical cylindrical borehole to make predictions of the fracture initiation pressure. The results can be used to understand fracture behavior - including stress anisotropy, initiation pressures, fracture barriers, and potential height growth – at any potential well location within the data volume.
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Rock Physics Modeling in Frontier Areas: An AVO Case Study in the Layered Evaporite Sequence
Authors R. Lubbe, M. Widatalla, H. Sibon and A. AlhaniSummaryA rock physics forward-modeling study was carried out to investigate the Direct Hydrocarbon Indicator (DHI) potential of a prospect resembling the Layered Evaporite Sequence (LES) in the Red Sea (Saudi Arabia). Various workflows were designed based on the Amplitude Versus Offset (AVO) behavior observed at the closest offset well penetrating the LES. The anomaly observed at the prospect was at the same depth interval as that of the LES encountered in the offset well, but unfortunately this well was located a few hundred kilometers away from the actual prospect. The workflows presented in this study can be applied directly to the Intercept/Gradient seismic reflectivity, or inverted pre- or post-stack elastic volumes, in the absence of a well within the inverted seismic volume
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Validation by Pre-stack Inversion of an Optimized Seismic Data Pre-conditioning Processing Sequence-Case Study from UAE
Authors A. Mukherjee, G. Nyein, K. Elsadany, I. Kiyotaka, E. Shimpei and I. ShunsukeSummaryAdvancements in seismic data acquisition techniques and processing algorithms in the last decade have made it possible to establish quantitative links between surface seismic data and reservoir properties. In carbonate reservoirs the imaging and reservoir quality can be negatively impacted by the presence of strong interbedded multiples. This motivates us to select and validate a seismic pre-conditioning processing sequence by testing on a pilot dataset. Our tests suggest options for multiple generator identification, optimization of multiple model parameterization, prediction, and subtraction, optimal angle selection and event alignment prior to inversion. Application of these and other processes can have a significant contribution to improving seismic reservoir imaging quality, resulting in substantial improvement in inversion to reservoir properties.
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Characterization of the Lower Cretaceous Thamama Group Reservoirs through Stochastic Inversion and Rock Physics Modeling
Authors K. Havelia, O. Aly, A. Mukherjee, R. Zeng, G. Nyein, L.G. Figuera, M. Aamir, K.M. Al Hosani, F. Alkatheeri, M. Al Raeesi, A. Al Hamedi, S. Khan and H. SudiroSummaryThe Lower Cretaceous Thamama Group is one of the most productive group of formations in the Middle East, containing large hydrocarbon accumulations. Thamama Group deposited along a gently sloping carbonate platform, is a thick sequence of limestone and dolomite with minor shales, with alternating reservoir and tight zones.
The reservoir characterization study encompassed classification of Thamama A-H zones and Habshan zones. As most of the Thamama reservoirs were beyond seismic resolution, Pre-stack High-Resolution Geostatistical inversion (Stochastic inversion) was performed after the deterministic AVO Pre-stack Inversion, in order to improve the understanding of heterogeneities and vertical/lateral correlation of reservoir properties (e.g. Porosity) in areas of interest under sub-seismic scales.
Geostatistical inversion could successfully separate out the thick reservoirs as well as the thin reservoirs, and capture the uncertainty associated in the model. Multiple realizations were output and the P10, P50 and P90 cases can be used as separate volume scenarios. The rock physics model predicted porosity with high confidence, using acoustic impedance and Vp/Vs. The model, generated from 31 wells, was validated using ∼600 wells and showed a good match with the well porosity.
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Reviving the Icon: Dammam Dome Seismic to Simulation Case Study
By M. AhmedSummaryField Development Case Study for Carbonate Field.
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Ultrasonic Velocities of Unconsolidated Sand: Evaluating the Microstructure and Contact Based Models
Authors Z. Ahmed and M. LebedevSummaryMicrostructure and grain shape factors largely affect the seismic velocities through unconsolidated sands. Moreover, parameters such as coordination number (CN) and contact surface area are dependent on the grain sorting and grains shape factors. We use 3D micro-CT images to quantify the microstructure in terms of CN and contact surface area, and grain shape factors in terms of sphericity and roundness to understand the results of the laboratory experiments on the ultrasonic wave propagation through four different sorted unconsolidated sand samples. We have found that sample with a higher CN and large total contact surface area has higher ultrasonic velocities (both compressional VP and shear VS). CNs calculated for all samples provide a good match between contact based model for effective bulk modulus and dynamic effective bulk modulus obtained from measured velocities. Following the contact based effective elasticity models that incorporate fraction of no slip contacts between the grains, we analyze the relationship of it with porosity and compaction stress.
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Experimental System for Seismic Dynamic Elastic Property Measurements under Elevated Temperature and Shear Deformation
Authors R.J. Chalaturnyk, C. Lu and G. ZambranoSummaryA new experimental system has been designed and commissioned to measure dynamic elastic properties at seismic frequencies under deviatoric stress. A specialized servo-hydraulic load frame with a pair of laser displacement sensor is applied in this research. Calibration has been completed using aluminum, which has well-known properties. The results show the stability and accuracy from 0.001 Hz to 1Hz and the system performance has been tested using 3D printed sandstone specimens (using sand as the print medium) that provide an unparalleled opportunity to remove inter-specimen variability in the testing. The results show the frequency dependence of elastic moduli.
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Variations of Acoustic Velocity as Function of Brine and Oil Saturation in Carbonates
Authors A. El-Husseiny, S. Vega, O. Raheem and S. NizamuddinSummaryThis study aims to improve our understanding of the seismic signature (i.e., variations in acoustic velocity) as a result of variations in the brine and oil saturation. To this scope, we utilized a customized core flooding system and measured P- and S-wave velocity (Vp and Vs respectively) under reservoir pressure and as function of brine and oil saturation during drainage and imbibition, in three carbonate samples.
Our results show that both Vp and Vs decrease as oil displaces brine (imbibition) and then increase as brine displaces oil (drainage). The Vp-saturation trend during imbibition followed the lower bound predicted by Gassmann theory assuming uniform fluid distribution, while drainage data followed the upper bound assuming patchy fluid distribution. Since oil production or EOR processes can be represented by the drainage process (i.e., gas or brine displacing oil), patchy fluid distribution should be considered in Gassmann theory when performing feasibility studies to predict changes in Vp as function of saturation changes. Despite the success of Gassmann theory in predicting Vp here, the results obtained for Vs show that Gassmann theory fails significantly to predict Vs as function of saturation. This suggests that the constant-shear-modulus condition in Gassmann is violated as fluid saturation changes.
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Improved Transition Zone Identification Using Relations Between Shear Wave Velocity and Density
Authors J.A. Hansen, N.H. Mondol, F. Tsikalas and S. DoeringSummaryIn this study, we present a method for identification of the transition zone between mechanical and chemical compaction in data from shaly lithologies. By utilizing crossplots of wireline log-measured shear wave velocity (Vs) and bulk density (ρb), we observe an increased sensitivity compared to compressional wave velocity (Vp) to the onset of chemical compaction/cementation, while eliminating uncertainties related to porosity estimations. A clear change in the velocity (Vs) gradient with increasing density is shown to occur in data from eight exploration wells. Data above and below a certain velocity value (Vs = 1350 m/s) show substantially different behavior which is expected to be a result of cementation. A linear relation in the Vs –density domain is derived from the data and suggested as a representative trend for mechanical compaction in the study area. Our suggestion is that whenever recorded with sufficient vertical coverage, direct measurements of Vs and density are trust-worthy parameters for identifying the transition zone between mechanical and chemical compaction.
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