Zhou Xianmin, AlOtaibi Fawaz M, Kamal Muhammad Shahzad, Kokal Sunil L
Center for Integrative Petroleum Research, King Fahd University of Petroleum & Minerals, Dhahran 31261, Kingdom of Saudi Arabia.
Saudi Arabian Oil Company, Dhahran 31311, Kingdom of Saudi Arabia.
ACS Omega. 2020 Dec 15;5(51):33395-33405. doi: 10.1021/acsomega.0c05356. eCollection 2020 Dec 29.
The reservoir heterogeneity is the major cause of poor volumetric sweep efficiency in sandstone and carbonate reservoirs. Displacing fluids (water, chemical solution, gas, and supercritical CO (sc-CO)) flow toward the high permeable zone. A significant fraction of oil remains in the low permeable zone due to the permeability contrast. This study used in situ sc-CO emulsion as a conformance control agent to plug the high permeable zone and improve the low permeable zone's volumetric sweep efficiency in carbonate formation. We investigated the effect of two types of conformance control patterns and the size of sc-CO emulsion on tertiary oil recovery performance by sc-CO miscible injection for carbonate reservoirs at reservoir conditions. The conformance control patterns are achieved using two different approaches. In the first approach, the low permeable zone was isolated, and the diverting gel system, a 0.4 pore volume slug, was injected into a high permeable zone. In the second approach, the simultaneous injection of the diverting gel system, a 0.2 pore volume slug, was done on both the low and high permeable zones. The first sc-CO injection was conducted as a tertiary oil recovery mode to recover the remaining oil after water flooding. The diverting gel system was injected after the first sc-CO flood for the conformance control. The second or post sc-CO injection was conducted after the diverting gel system injection. The diverting gel system used in this study consisted of a polymer and a surfactant. An in situ emulsion was generated when the injected diverting gel system interacts with the sc-CO in the core plug. Results obtained from dual-core core flooding experiments suggested that the in situ sc-CO emulsion was generated successfully in the formation based on the different pressure increases and observation of the dual-core core flooding experiments. The volumetric sweep efficiency and oil recovery in both conformance control patterns were improved. The production performances were also compared for both conformance control models before and after the diverting gel system injection. The conformance control model 2 (simultaneous injection of the diverting gel system into low and high permeability cores) has a better choice to be applied in field application due to high recovery with a small sc-CO2 emulsion easy operation in the field.
储层非均质性是砂岩和碳酸盐岩储层体积波及效率低下的主要原因。驱替流体（水、化学溶液、气体和超临界CO₂（sc-CO₂））流向高渗透区。由于渗透率差异，很大一部分油残留在低渗透区。本研究使用原位sc-CO₂乳液作为调剖剂，封堵高渗透区，提高碳酸盐岩地层低渗透区的体积波及效率。我们通过在油藏条件下对碳酸盐岩储层进行sc-CO₂混相注入，研究了两种调剖方式和sc-CO₂乳液尺寸对三次采油性能的影响。调剖方式通过两种不同方法实现。第一种方法是隔离低渗透区，将0.4孔隙体积段塞的转向凝胶体系注入高渗透区。第二种方法是在低渗透区和高渗透区同时注入0.2孔隙体积段塞的转向凝胶体系。第一次sc-CO₂注入作为三次采油方式，用于水驱后采收剩余油。第一次sc-CO₂驱替后注入转向凝胶体系进行调剖。第二次或sc-CO₂后注入在转向凝胶体系注入之后进行。本研究中使用的转向凝胶体系由聚合物和表面活性剂组成。当注入的转向凝胶体系与岩心塞中的sc-CO₂相互作用时，会生成原位乳液。从双岩心驱替实验获得的结果表明，基于双岩心驱替实验中不同的压力升高和观察结果，在地层中成功生成了原位sc-CO₂乳液。两种调剖方式的体积波及效率和采收率均得到提高。还比较了两种调剖模型在注入转向凝胶体系前后的生产性能。调剖模型2（同时向低渗透和高渗透岩心中注入转向凝胶体系）由于采收率高、sc-CO₂乳液用量小且现场操作简便，在现场应用中是更好的选择。
