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Simulation of GAGD Process to Study the Impact of Effective Parameters on Operability Range and Recovery Factor

Nasiri, Javad | 2011

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 41473 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Pishvaie, Mahmoud Reza; Bozorgmehry, Ramin
  7. Abstract:
  8. Gravity drainage is the self-propulsion of oil downward in the reservoir rock. Under favorable natural and operational conditions, it has been found to effect recoveries comparable to water displacement. With modern technical knowledge, the operator can often make a choice between dissolved gas drive, water drive and gravity drainage as the principal recovery agent in a reservoir. So far, gravity drainage has received less consideration than the other two. Gravity drainage is one of the most important processes taking place in fractured reservoirs and it plays a major role in oil recovery from low permeability matrix blocks during gas injection process. Gravity drainage is responsible for production from various gigantic reservoirs in southern part of Iran which are over half a century old. An endeavor is made to set forth some of the principles of gravity drainage using simulation first, to point out the types of reservoirs favorable for it, and second, to study the impact of effective parameters on operability range and recovery factor during gravity drainage process. Simulation study using oil-wet model yielded better oil recovery (of over 8%) than water-wet model test. This was attributed to the presence of oil-films on the rock surface which further aided the film-drainage of oil towards the horizontal producer at the bottom of the payzone. On the contrary, simulation study demonstrated that the highest oil recovery was obtained in water-wet sandstone porous media; whereas the lowest oil recovery was obtained in such oil-wet porous media. This poor recovery was attributed to the strong capillary retention (or surface) forces acting on the wetting phase films. This study clearly shows that the effects of injection rate on the gravity stable GAGD floods are minimal but the simulation results appear to indicate that there is a critical gas injection rate yielded higher ultimate oil recovery. In terms of re-infiltration, delay in production and lower recovery is observed. Exact estimation of matrix block size is a determinant parameter on GAGD oil recovery. That means as area of matrix blocks decreases, ultimate recovery increases and will be achieved at an earlier time. It has significant effect on the ultimate recovery time. Higher fracture permeability and lower matrix capillary pressure (capillary hold-up) have positive effect on GAGD recovery. In summary, the proposed GAGD process offers significant potential for increasing ultimate oil recovery in fractured reservoirs compared to that achievable by the conventional WAG process that is being widely applied in the oil fields four corner of the globe.
  9. Keywords:
  10. Simulation ; Critical Rate ; Fractured Reservoirs ; Wettability Alteration ; Enhanced Oil Recovery ; Gas-Assisted Gravity Drainage (GAGD)

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