Geomechanical analysis is an essential aspect of modeling reservoir deformation induced by changes in pressure, temperature, and saturation, as well as stresses in the surrounding geology brought about by production. Critically, changes in the overburden can lead to infrastructure damage or well failure.
Accurate modeling of the geomechanical changes in a reservoir during production, and the effect on surrounding rocks, is critical to both well planning and ongoing assessment of reservoir performance. However, modeling complex reservoir and overburden changes using finite element models can be time-consuming and costly. Alternative, less computationally intensive methods of geomechanical analysis allow geophysicists to quickly obtain an understanding of reservoir deformation, and its effects, before deciding if additional finite element modeling is warranted.
Geomechanical Analysis for Well Planning and Production
Geomechanical analysis and data visualization helps well planners optimize wellbore location and determine more optimum drilling strategies.
Modeling changes in porosity and permeability, their interdependencies, and their effects on subsurface structures can give engineers greater confidence in how they approach drilling and reservoir development. Understanding and modelling fluid migration allows teams to develop well planning strategies which, for example, avoid certain critical faults, that minimize risk and assess whether the planning is feasible.
Geomechanical analysis is critically important during the production phase. By combining geophysical data with production data reservoir engineers can model the effects of changes in pressure and temperature on reservoir stability. Shallow reservoirs present a greater risk of subsidence. In faulted reservoirs, changes can result in rock displacement that shears a wellbore, bringing production to a halt.
Workflows for Synthetic Seismic Volume Generation and Geomechanical Analysis
Dynamic Graphics, Inc. is the leader in 3D and 4D visualization and data analysis for reservoir management. As part of its CoVIz 4D software suite, DGI offers two optional workflows to help management teams gain a better understanding of changing geologic and reservoir conditions. The Sim2Seis workflow creates synthetic seismic volumes from predictive models which can be quantitatively compared with observed data. The Geomechanics workflow calculates strain, stress, displacement, and seismic time-shifts in the overburden due to reservoir changes during production.
1. Synthetic Seismic Volume Generation
The Sim2Seis workflow begins by creating a petroelastic model using a reservoir simulation model. The petroelastic model is then convolved with a wavelet to create 4D synthetic seismic volumes. The workflow then supports qualitative and quantitative comparisons of the synthetic volumes using the field-measured seismic and reservoir simulation inputs. Based on the comparisons, reservoir simulation models can be updated to improve the seismic history match. The Sim2Seis workflow facilitates better, faster seismic history matching, and 4D seismic feasibility studies.
2. Assess Reservoir Deformation
The Geomechanics workflow uses well-known published relationships and formulas (e.g. Geertsma) to derive volume change, uniaxial thickness change, deformation, stress, velocity change, and 4D seismic time-shifts from reservoir pressure changes. Beginning with a reservoir simulation cellular grid, the workflow uses first-order computation of deformation based on parameterized inputs to calculate the outputs mentioned above.
The workflow is multi-threaded and makes full use of all cores and GPU resources for rapid analytic computations. In cases where finite element modeling could be prohibitively time-consuming and expensive to compute vertical and horizontal stress and strain components, CoViz 4D geomechanics workflow provides a practical solution.
3. Visualize the Results to Obtain a Detailed Understanding of Seismic Changes
After completing the Geomechanics workflow geophysicists can visualize the results in a 4D environment to understand areas where there are thickness changes and displacement.
Time series analysis of seismic data can provide a more detailed understanding of seismic velocity changes and time-shifts that occur due to the effects of production, reservoir compaction, and overburden deformation. By animating reservoir evolution, engineers gain a far better understanding of the interplay between production, geomechanics, and reservoir integrity.
Changes in velocity in the overburden and subsequent time-shifts, as indicated in the Geomechanics output, could potentially be included in the Synthetic Seismic Volume process resulting in a collaborative approach, better understanding and improved models.
CoViz 4D: Efficient Geomechanics Analysis for Better Understanding of Deformation
Geophysicists and engineers responsible for reservoir development can gain a better understanding of reservoir deformation using the synthetic volume generation and geomechanics workflows and visualization capabilities of CoViz 4D. Members of the reservoir management team can simultaneously view and interrogate a wide range of subsurface datasets, regardless of the original data source. Geomechanics analysis (an extra cost option for Coviz 4D) allows engineers to explore and visualize the geomechanical effects produced by changes in pressure, saturation, and temperature over time.
Geomechanics analysis (an extra cost option for Coviz 4D) allows engineers to explore and visualize the geomechanical effects produced by changes in pressure, saturation, and temperature over time.
The exceptional ability to easily integrate a wide variety of subsurface datasets, apply tools and techniques to explore and visualize data relationships leads to more accurate geomechanical analysis. With these capabilities and the insights they deliver, engineers can collaboratively determine the best reservoir development and production decisions.