Well Placement Optimization through the Triple-Completion Gas and Downhole Water Sink-Assisted Gravity Drainage (TC-GDWS-AGD) EOR Process

气体和井下水汇辅助重力驱油(GDWS-AGD)是一种在含有大底水的储层中提高油藏采收率(EOR)的新工艺。传统的GDWS-AGD工艺需要 建两口井用用于产油和排水,还需要额外的多个垂直注气井,成本高昂。然而,通过消除注气井并使用三井式多功能油井(TC-GDWS-AGD),可以大幅降低成本。




Gas and downhole water sink-assisted gravity drainage (GDWS-AGD) is a new process of enhanced oil recovery (EOR) in oil reservoirs underlain by large bottom aquifers. The process is capital intensive as it requires the construction of dual-completed wells for oil production and water drainage and additional multiple vertical gas-injection wells. The costs could be substantially reduced by eliminating the gas-injection wells and using triple-completed multi-functional wells. These wells are dubbed triple-completion-GDWS-AGD (TC-GDWS-AGD).

In this work, we design and optimize the TC-GDWS-AGD oil recovery process in a fictitious oil reservoir (Punq-S3) that emulates a real North Sea oil field. The design aims at maximum oil recovery using a minimum number of triple-completed wells with a gas-injection completion in the vertical section of the well, and two horizontal well sections—the upper section for producing oil (from above the oil/water contact) and the lower section for draining water below the oil/water contact. The three well completions are isolated with hydraulic packers and water is drained from below the oil–water contact using the electric submersible pump. Well placement is optimized using the particle swarm optimization (PSO) technique by considering only 1 or 2 TC-GDWS-AGD wells to maximize a 12-year oil recovery with a minimum volume of produced water. The best well placement was found by considering hundreds of possible well locations throughout the reservoir for the single-well and two-well scenarios. The results show 58% oil recovery and 0.28 water cut for the single-well scenario and 63.5% oil recovery and 0.45 water cut for the two-well scenario. Interestingly, the base-case scenario using two wells without the TC-GDWS-AGD process would give the smallest oil recovery of 55.5% and the largest 70% water cut. The study indicates that the TC-GDWS-AGD process could be more productive by reducing the number of wells and increasing recovery with less water production.

Keywords: gas injection; downhole water sink; assisted gravity drainage; particle swarm optimization; well placement optimization; enhanced oil recovery

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7. Summary and Conclusions

In this study, a black-oil reservoir simulation was conducted on the Punq-S3 heterogeneous reservoir to evaluate and determine the optimal setting of the triple-completion gas and downhole water sink-assisted gravity drainage (TC-GDWS-AGD) process. The evaluation and well placement optimization procedures of the TC-GDWS-AGD process were conducted to achieve maximum oil production with minimum water cut through a 12-year prediction period in a comparison with GDWS-AGD and GAGD processes. The operational decision parameters that were included in the well placement optimization along with the potential well locations included maximum surface oil rate and minimum bottom hole pressure of oil producers; maximum surface water rate and minimum bottomhole pressure of water producers; and maximum surface gas rate and maximum bottom hole pressure in gas injectors. The following points are the main conclusions retrieved from the evaluation and optimization procedures:

_ The effectiveness of the TC-GDWS-AGD enhanced oil recovery (EOR) technique was confirmed by this simulation study in terms of its ability to increase oil recovery and decrease water cut compared with applying gas-assisted gravity drainage (GAGD) and gas-downhole water sink (GDWS) EOR processes to the Punq-S3 synthetic reservoir.

_ The TC-GDWS-AGD completions are effective in reducing water cut and increasing cumulative oil production. Cumulative oil was increased from 1.47 _ 106 m3 from the primary process to 1.6 _ 106 m3 from the best TC-GDWS-AGD case with an oil recovery factor of 0.58, whereas water cut decreased from 70% in the GAGD process to 57% in the best TC-GDWS-AGD case.

_ As the TC-GDWS-AGD gas-injection rate was enhanced from350,000m3 to 500,000m3, the water cut decreased from 0.57 to 0.50. When the maximum surface-water-production rate (STW) constraint was raised to 20,000 m3/day, the PSO algorithm was able to find locations that achieved high oil recovery with the lowest overall water cut (0.45) for the two-TC-well cases.

_ The PSO algorithm was highly effective at identifying the optimum well completion locations for maximizing oil recovery and minimizing water cut in the studied reservoir. To achieve maximum reservoir coverage, for each simulated scenario, one well completion was placed to the right side of a surface location and one well to the left side.

_ The gas injection rate (STG) had only a minor impact on oil recovery volumes because the permeability of the reservoir layer two was very low. In fact, the transfer of gas from reservoir layer one to reservoir layer three was found to decrease as the gas injection rate increased.