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Numerical Investigation of the Extraction-induced Change in Total Stress Field in Oil and Gas Reservoirs

Sharifi, Barzin | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56929 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Pak, Ali
  7. Abstract:
  8. As a result of extraction from underground oil and gas reservoirs, the pore pressure in the reservoir decreases and the effective stress increases accordingly. Although the gradual consolidation of underground reservoirs and their compaction due to the extraction can improve the production process (Compaction Drive) and facilitate the release of hydrocarbon fluid, it may cause some problems. Field measurements in the past two decades have shown that in addition to the change of effective stress, the total horizontal and vertical stress field can also change in and around the reservoir. As a result of the settlement that occurs at the upper part of the reservoir due to the consolidation phenomenon, the stability of this area is reduced and it causes “Stress Redistribution” inside and around the reservoir. The mechanism of stress redistribution is attributed to the “Stress Arching” phenomenon. By the stability reduction at the roof of the reservoir due to the compaction, this area will no longer bear the whole over-burden weight. As a result, a part of the over-burden is transferred to more stable areas such as the regions adjacent to the sides of the reservoir. In addition, the mechanism of “constraining effect” from the surrounding rock, which is triggered by the compaction of the reservoir during the production operation, and due to the elastic coupling (Interactive Effect) between two rock media, can play an important role in changing the total stresses of the entire area affected by extraction. The purpose of this research is investigating the occurrence and the involving mechanisms of changes in the total vertical and horizontal stresses in and around the oil and gas reservoirs under the effect of extraction, identifying the conditions under which these changes become significant, and also knowing the side effects of this phenomenon on the production process, by numerical modeling. The 3D Simulation of the extraction from the reservoir is done with a fully coupled hydro-mechanical analysis using Abaqus FEA software. In order to better simulate the process of fluid extraction from the reservoir and consider the effect of production operation on the hydro-mechanical properties of the depleting zone, a non-linear poroelastic constitutive model is used. The results based on the assumptions considered in this research show that following the extraction of pore fluid from the reservoir, there is a possibility of significant change in total vertical and horizontal stresses of the reservoir and a more considerable change of these stress components in the peripheral rock adjacent to the reservoir boundaries. Factors such as the difference in elastic properties between the reservoir and the surrounding rock (Elastic Contrast), and the distance between the boundaries of the reservoir from the extraction point (the smaller lateral extent, and the greater thickness of the reservoir), can play an important role in the more severe change of the total vertical stress of the reservoir. The results of this study show the importance of considering the effect of changes in the total stress field caused by extraction operation in different aspects of production and field development
  9. Keywords:
  10. Nonlinear Elastic Behavior ; Peripheral Rock Constraining Effect ; Stress Redistribution ; Stress Arching ; Coupled Hydro-Mechanical Simulation ; Total Stresses Change

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