CO2 messes with rock physics

2021 ◽  
Vol 40 (6) ◽  
pp. 424-432
Author(s):  
Manika Prasad ◽  
Stanislav Glubokovskikh ◽  
Thomas Daley ◽  
Similoluwa Oduwole ◽  
William Harbert
Keyword(s):  
Pore Space ◽  
Rock Physics ◽  
Time Lapse ◽  
Saline Aquifers ◽  
Carbonate Cement ◽  
Monitoring Tools ◽  
Rock Physics Modeling ◽  
Physics Modeling ◽  
Seismic Anomalies ◽  
Wave Induced

Seismic techniques are the main monitoring tools for CO2 storage projects, especially in saline aquifers with good porosity. The majority of existing commercial and pilot CO2 injections have resulted in clear time-lapse seismic anomalies that can be used for leakage detection as well as refinement of the reservoir models to conform with the monitoring observations. Both tasks are legal requirements imposed on site operators. This paper revisits the rock-physics effects that may play an important role in the quantitative interpretation of seismic data. First, we briefly describe a standard approach to the rock-physics modeling of CO2 injections: Gassmann-type fluid substitution accounts for the presence of compressible CO2 in the pore space, and dissolution/precipitation of the minerals changes the pore volume. For many geologic conditions and injection scenarios, this approach is inadequate. For example, dissolution of the carbonate cement may weaken the rock frame, wave-induced fluid flow between CO2 patches can vary the magnitude of the seismic response significantly for the same saturation, the fluid itself might undergo change, and the seal might act as a sink for CO2. Hence, we critically review the effects of some recent advances in understanding CO2 behavior in the subsurface and associated rock-physics effects. Such a review should help researchers and practitioners navigate through the abundance of published work and design a rock-physics modeling workflow for their particular projects.

Quantifying hydraulically induced fracture height and density from rapid time-lapse DAS VSP

Geophysics ◽  
2020 ◽  
pp. 1-26
Author(s):  
Xiaomin Zhao ◽  
Mark E. Willis ◽  
Tanya Inks ◽  
Glenn A. Wilson
Keyword(s):  
Rock Physics ◽  
Horizontal Wells ◽  
Time Lapse ◽  
Seismic Profile ◽  
P Wave ◽  
Fracture Properties ◽  
Vsp Data ◽  
Rock Physics Modeling ◽  
Physics Modeling ◽  
Fracture Height

Several recent studies have advanced the use of time-lapse distributed acoustic sensing (DAS) vertical seismic profile (VSP) data in horizontal wells for determining hydraulically stimulated fracture properties. Hydraulic fracturing in a horizontal well typically generates vertical fractures in the rock medium around each stage. We model the hydraulically stimulated formation with vertical fracture sets about the lateral wellbore as a horizontally transverse isotropic (HTI) medium. Rock physics modeling is used to relate the anisotropy parameters to fracture properties. This modeling was used to develop an inversion for P-wave time delay to fracture height and density of each stage. Field data from two horizontal wells were analyzed, and fracture height evaluated using this technique agreed with microseismic analysis.

A new approach to petroelastic modeling of carbonate rocks using an extended pore-space stiffness method, with application to a carbonate reservoir in Central Luconia, Sarawak, Malaysia

2020 ◽  
Vol 39 (8) ◽  
pp. 592a1-592a10
Author(s):  
Amir Abbas Babasafari ◽  
Yasir Bashir ◽  
Deva Prasad Ghosh ◽  
Ahmed Mohammed Ahmed Salim ◽  
Hammad Tariq Janjuhah ◽  
...  
Keyword(s):  
Elastic Properties ◽  
Carbonate Rocks ◽  
Pore Space ◽  
Rock Physics ◽  
Carbonate Reservoir ◽  
Inclusion Model ◽  
Rock Physics Modeling ◽  
Physics Modeling ◽  
Central Luconia ◽  
Pore Types

Pore geometry plays an important role in the elastic response of carbonate rocks. Diagenetic processes in carbonate sediments generate a range of pore-type distributions. Hence, the petroelastic modeling (PEM) of carbonate rocks is more complex than for clastics. Petrophysical properties connect to elastic properties through PEM or, in general terms, rock-physics modeling. Pore types cause variation in P-wave velocity — up to 40% for a given porosity. A variety of pore types with different aspect ratios such as vuggy, moldic, interparticle, intraparticle, fracture, and crack makes the porosity-velocity relationship complex, and empirical models fail to handle it properly. We propose a new, easy-to-implement approach for PEM of carbonate rocks that leads to more accurate elastic properties estimation. It offers a novel PEM method that reduces the number of defined parameters and equations. In it, the Xu-Payne rock-physics modeling equations are replaced with an extended pore-space stiffness equation. Instead of including a pore's aspect ratio as is done when using the Xu-Payne inclusion model formulation, in our proposed technique only the appropriate value of pore-space stiffness for each pore type is considered, together with the corresponding volume fraction of pore types. However, parameters are optimized by calibrating the estimated elastic properties with corresponding information from well-log measurements. This inclusion model yields acceptable predictions of elastic properties at wells that do not have measured elastic logs. The method was tested using well data from a carbonate reservoir in Central Luconia, offshore Sarawak, Malaysia. Here, one well has a complete suite of log data needed to calibrate the model. The calibrated model was then used to predict the missing shear velocity log in the other well. Next, simultaneous elastic seismic inversion was performed on 3D seismic data covering the area of the carbonate reservoir, and elastic property volumes (acoustic impedance and VP/VS ratio) were estimated. From these results, a posterior probability distribution of stiff pore types was determined, which validated the outcome of this approach using a blind test.

Integrated VTI model building with seismic data, geologic information, and rock-physics modeling — Part 1: Theory and synthetic test

Geophysics ◽  
2016 ◽  
Vol 81 (5) ◽  
pp. C177-C191 ◽  
Author(s):  
Yunyue Li ◽  
Biondo Biondi ◽  
Robert Clapp ◽  
Dave Nichols
Keyword(s):  
Seismic Data ◽  
Seismic Anisotropy ◽  
Model Building ◽  
Rock Physics ◽  
Seismic Inversion ◽  
Additional Information ◽  
Synthetic Test ◽  
Rock Physics Modeling ◽  
Physics Modeling ◽  
Geologic Information

Seismic anisotropy plays an important role in structural imaging and lithologic interpretation. However, anisotropic model building is a challenging underdetermined inverse problem. It is well-understood that single component pressure wave seismic data recorded on the upper surface are insufficient to resolve a unique solution for velocity and anisotropy parameters. To overcome the limitations of seismic data, we have developed an integrated model building scheme based on Bayesian inference to consider seismic data, geologic information, and rock-physics knowledge simultaneously. We have performed the prestack seismic inversion using wave-equation migration velocity analysis (WEMVA) for vertical transverse isotropic (VTI) models. This image-space method enabled automatic geologic interpretation. We have integrated the geologic information as spatial model correlations, applied on each parameter individually. We integrate the rock-physics information as lithologic model correlations, bringing additional information, so that the parameters weakly constrained by seismic are updated as well as the strongly constrained parameters. The constraints provided by the additional information help the inversion converge faster, mitigate the ambiguities among the parameters, and yield VTI models that were consistent with the underlying geologic and lithologic assumptions. We have developed the theoretical framework for the proposed integrated WEMVA for VTI models and determined the added information contained in the regularization terms, especially the rock-physics constraints.

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