砂岩储层射孔压实带孔隙度与渗透率损伤研究

Study of porosity and permeability damage of perforation compaction zone in sandstone reservoir

射孔孔眼是储层油气进入生产井筒的通道,聚能射孔过程会在孔眼周围砂岩储层产生不同程度的损伤。基于射孔效能物理试验和数值模拟,提出了一种用于定量评价射孔压实带孔隙度和渗透率损伤程度的方法。应用塑性随动强化材料模型表征高应变率冲击载荷下的砂岩形变特性,通过显式动力分析程序LS-DYNA数值模拟孔眼压实区域的砂岩动力学响应,获得了砂岩骨架应力、塑性应变、体积应变等关键数据,结合射孔压实带孔隙度与渗透率演化模型,量化分析了砂岩射孔压实带损伤程度。以胜利油田粒间孔隙砂岩靶为例,数值结果与靶心流动效能测试、CT扫描数据能够较好地吻合,验证了定量评价方法的有效性。结果表明,聚能射孔对压实区域砂岩的损伤主要表现为塑性挤压和剪胀两种机制。在孔道内壁区域,砂岩骨架主要受剪胀作用,孔隙度增加;但塑性挤压又改变了原始孔隙结构,造成流动通道阻塞,渗透率降低。

The perforation tunnel is the channel for transporting the hydrocarbon to the well bore. The shaped charge perforation operation, however, usually leads to some damage to the surrounding sandstone. Based on the perforation efficiency tests and numerical simulations, a new method is developed to quantitatively evaluate the porosity and permeability damage degree of the compacted zone. The kinematic-hardening plastic flow law is used to describe the sandstone deformation under high strain rate loading. Then dynamic responses of near-tunnel sandstone during perforation process are simulated by using the explicit dynamic analysis code LS-DYNA. Some key data, such as the sandstone matrix stress, plastic strain and volumetric strain are obtained. Subsequently, the damage degree of compacted zone is quantitatively analyzed by using these data together with the porosity and permeability evolution models. By comparing numerical results with the experimental results of core flow efficiency and CT scanning data from the interparticle pore Sandstone targets in Shengli oil field; good agreements are achieved, the validaty of the proposed method is verified. It is shown that, during shaped charge perforation, there are two major damage mechanisms for the compacted zone, namely, the plastic squeezing and shear swelling. Near the tunnel＇s inner wall, the sandstone matrix mainly suffers dilatancy actions, which enhances the porosity; meanwhile, the original structure of pore are changed due to plastic squeezing, which brings a jam to the tunnels, resulting in a reduction in permeability.