致密碳酸盐岩酸蚀蚓孔研究

Study on acidizing wormhole of tight carbonate reservoir

基质酸化是碳酸盐岩储层最早使用的解除储层污染的增产技术之一。但现场实践表明,对于微裂缝不发育的致密碳酸盐岩储层,基质酸化效果往往不佳。该文利用压裂酸化工作液动态滤失实验系统,进行了系统的岩心驱替实验。通过改变酸液注入速率、实验温度及使用不同酸液体系等方法,对致密碳酸盐岩储层孔隙基质在酸化过程中蚓孔产生的可能性进行了实验研究。研究表明:对于致密碳酸盐岩,由于基质渗透率非常低,在10 MPa的驱替压差下,酸液仍然很难进入岩心基质,所以酸岩反应仅能在岩石表面进行,即使部分酸液进入基质孔隙内,由于残酸难以快速滤失,所以鲜酸难以迅速补充,使得酸岩反应的类型仅能停留在密集型溶蚀阶段,难以形成深穿透的酸蚀蚓孔。此外,通过岩心流动实验对比,分析了高渗露头及致密岩心的流动反应特点,证实酸液在高渗透岩心表面及天然裂缝发育处能形成酸蚀蚓孔。最后,通过理论分析认为,对于致密碳酸盐岩储层基质酸化很难形成深穿透的酸蚀蚓孔。

Matrix acidizing is one of the oldest well-stimulation techniques used to remove the damage for carbonate reservoir. However, field practice shows that the effectiveness of matrix aeidizing is not very well for tight carbonate reservoir, in which the microfractures have not been well developed. The dynamic filtration apparatus of acid fracturing fluid is used to conduct a systemic core displacement test. Many experiments have been taken in order to determine the possibility of wormhole presence during matrix acidizing in tight carbonate reservoir through the way of changing the injection rate of acidizing fluid, test temperature and utilizing the different acidizing fluid systems. Study result shows that the acidizing fluid is hard to enter into the core at the pressure differential of IOMPa for tight carbonate rock because of its low permeability. The acid-rock reaction can be taken at rock surface. Even when partial acid fluid enters into the rock pores, the fresh acid fluid is difficult to add quickly because the spent acid can not leak off rapidly, which makes the acid reaction only stay at the stage of compression corrosion, being difficult to create the deeppenetrating wormhole. In addition, the features of high-permeability outcrop and flow reaction in tight core are analyzed through core flow test, which confirms that the acidizing wormholes can be created for high-permeability core surface and the area of developed natural fracture. Finally, theoretical analysis indicates that the matrix acidizing treatment of tight carbonate reservoir can hardly form the deep-penetrating acidizing wormholes.