潜江凹陷页岩油储层储量丰富,其孔隙中富含多种可溶性矿物,采用CO2-纯水吞吐进行开发,不仅能利用CO2的超临界特性驱油,而且有利于提高CO2在目的储层中的埋存,有效减少CO2排放。但CO2-纯水体系能否进入页岩微纳米孔隙,并有效动用孔隙中的原油是该方法能否实施的关键。通过设计CO2、CO2-纯水和CO2-地层水的吞吐实验,基于核磁共振方法,明确了注CO2、注CO2-纯水和注CO2-地层水组合的吞吐特征,总结了不同孔隙的原油动用规律和作用机理。实验结果表明:注CO2-纯水体系比纯CO2吞吐效率高8.62个百分点,比CO2-地层水组合高12.66个百分点,CO2-纯水组合形成的酸性流体会溶蚀孔隙表面的可溶性矿物,改善孔隙连通性,提高储层渗流能力,并且能有效提高小于0.01 μm、0.01~0.10 μm孔隙中的原油动用程度。多周期吞吐后,产出液中的离子物质的量浓度明显下降,表明后续注入纯水并未扩大波及体积,只是提高原油动用效率。该研究证实注CO2-纯水体系可以有效提高页岩油藏采收率,为陆相页岩油有效开发提供新思路。
The shale oil reservoirs in Qianjiang Sag are of abundant reserves, and their pores are rich in a variety of soluble minerals. In the development with CO2 - pure water stimulation, the supercritical characteristics of CO2 can be utilized for oil displacement and the CO2 sequestration in the target reservoirs also can be improved, which effectively reduce CO2 emissions. However, the key to implementation of this method lies in whether the CO2- pure water system can enter the shale micro-nano pores and effectively drive the crude oil in the pores. Experiments of stimulation with CO2, CO2- pure water and CO2- formation water were designed, the stimulation characteristics of CO2 injection, CO2- pure water injection and CO2- formation water injection were clarified based on NMR method, and the law and mechanism of crude oil production in different pores were summarized. The experimental results showed that the stimulation efficiency of CO2- pure water injection was 8.62 percentage points higher than that of CO2 injection, and 12.66 percentage points higher than that of CO2- formation water injection, and the acidic fluid formed by the combination of CO2- pure water could dissolve the soluble minerals on the pore surface, improve the pore connectivity and enhance the reservoir permeability, and effectively increase the production of crude oil in pores smaller than 0.01 μm and 0.01 to 0.10 μm. After multiple cycles of stimulation, the volumetric solubility of ionic substances in the produced liquid was decreased significantly, indicating that the subsequent injection of pure water failed to expand the swept volume, but only improved the production of crude oil. This study proves that the CO2- pure water injection can effectively improve the recovery rate of shale reservoirs, and provides a new idea for the effective development of onshore shale oil.
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