Kong Debin, Lian Peiqing, Zheng Rongchen, Li Yiqiang
School of Civil and Resource Engineering, University of Science and Technology Beijing Beijing 100083 China
State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum Beijing 102249 China.
RSC Adv. 2021 Sep 15;11(49):30610-30622. doi: 10.1039/d1ra03859a. eCollection 2021 Sep 14.
Gas-assisted gravity drainage (GAGD) is an effective method for oil recovery. Gravity increases the stability of the Gas-Oil Contact (GOC), thus delaying gas breakthrough and promoting crude oil production. Studying the effects of fluid and reservoir parameters on the stability of GOC could help understand the mechanism of GAGD. In this study, a series of high-pressure GAGD tests were conducted on a 3D heterogeneous scaled model established according to the heterogeneity of the oil reservoir. During the tests, GOC was monitored with electrical resistivity tomography (ERT) to study the effects of gas injection rate, gas type, and gas injection direction on GOC and oil recovery factor (RF). The results showed that N-GAGD achieved the most stable GOC, the largest sweep volume but a poor RF. CO-GAGD achieved the best RF of 63.33% at the injection rate of 0.15 m d under 15 MPa. CO and CH could interact with crude oil and reduce the advancing rate and transverse swept area of GOC. CO and CH could lead to a higher RF as they reduce the viscosity of crude oil, cause swelling when dissolved, and have low tension. Therefore, the effects of gas dissolution, swelling, and viscosity reduction must be considered in addition to those of gravity, viscous force, and the capillary force so that RF could be increased while ensuring the stability of the displacement front. Accordingly, a new non-dimensional number was proposed with comprehensive considerations of gravity, viscous force, capillary force, gas-oil viscosity ratio, the viscosity reduction by gas, and reservoir properties. Finally, a prediction model was proposed, which could accurately predict the RF of heterogeneous reservoirs applying GAGD.
气驱重力泄油（GAGD）是一种有效的采油方法。重力增加了气-油界面（GOC）的稳定性，从而延迟气突破并促进原油生产。研究流体和储层参数对GOC稳定性的影响有助于理解GAGD的机理。在本研究中，对根据油藏非均质性建立的三维非均质比例模型进行了一系列高压GAGD试验。试验过程中，采用电阻层析成像（ERT）监测GOC，以研究注气速率、气体类型和注气方向对GOC和采收率（RF）的影响。结果表明，氮气辅助重力泄油（N-GAGD）实现了最稳定的GOC，波及体积最大，但采收率较低。在15MPa压力下，二氧化碳辅助重力泄油（CO-GAGD）在注气速率为0.15m/d时采收率最高，达到63.33%。二氧化碳（CO）和甲烷（CH）可与原油相互作用，降低GOC的推进速率和横向波及面积。CO和CH可提高采收率，因为它们降低了原油粘度，溶解时会引起膨胀，且表面张力较低。因此，除了重力、粘性力和毛管力外，还必须考虑气体溶解、膨胀和粘度降低的影响，以便在确保驱替前缘稳定性的同时提高采收率。据此，综合考虑重力、粘性力、毛管力、气油粘度比、气体引起的粘度降低和储层性质，提出了一个新的无量纲数。最后，提出了一个预测模型，该模型可以准确预测应用GAGD的非均质油藏的采收率。
