渤海稠油蒸汽吞吐井扩容降压增注机理研究与矿场实践

Mechanism of hydraulic dilation,pressure reduction,and enhanced liquid injection in heavy oil cyclic steam stimulated wells and field practice in Bohai Oilfield

在渤海油田稠油的热采过程中,由于储层物性较差或井周堵塞,蒸汽吞吐井通常面临蒸汽注入困难的问题。岩石力学扩容作为一项新技术,能够有效解决常规增产措施存在的有效期短和作业成本高等问题。然而,目前针对储层水力扩容特性的实验研究仍然很少,特别是在考虑蒸汽吞吐开发初期或实际地层所处的真三轴应力环境下的实验。以渤海L稠油油田为例,对注蒸汽开发前的稠油油层岩心进行了粒径分析,以及电镜扫描与能谱分析等微观物理性质观测,并研究了真三轴应力条件下岩心的力学与高温水力扩容特性。实验结果表明,岩心粒径平均为225μm,属于细—中粒径;岩心微观结构较为松散,颗粒之间存在沥青胶结物,疏松程度高;岩心元素中Si含量与C含量最高。岩心在单轴应力下会迅速出现剪切膨胀现象,但在真三轴应力条件下由于水平应力的限制岩心体积持续被压缩,未出现扩容现象,且强度较低。真三轴高温水力扩容实验中岩心流体压力波动较大,说明在水力扩容阶段内部裂缝不断产生、发育及扩展,导致岩心体积膨胀,在到达破裂压力后岩心仍具有较强的承载能力。CT扫描表明,岩心在水力扩容后体积膨胀明显,在水平方向表现出了较大变形,内部出现了次生复杂缝网,扩容效果良好。最后,通过现场扩容施工实例展示了渤海稠油吞吐井扩容作业的效果,以期为水力扩容与安全连通高效开采稠油提供可行性分析。

In the process of thermal recovery of heavy oil in Bohai Oilfield,cyclic steam stimulated wells often face problems of difficult steam injection due to poor reservoir physical properties or blockage of the circumferential borehole.Hydraulic dilation,an innovative technology,effectively solves the problems of short effective period and high operational costs by applying conventional well stimulation methods.However,there are few experimental studies on the characteristics of reservoir hydraulic dilation,especially those considering the initial cyclic steam stimulation stage or the true triaxial stress field in actual formation conditions.Taking Bohai L heavy oilfield as an example,the grain size of core sample has been analyzed and the microscopic physical properties of heavy oil layer before steam injection development have been observed,including microscopic scanning and energy spectrum analysis.In addition,the mechanical and high-temperature hydraulic dilation features of core samples have been studied in the true triaxial stress conditions.The experimental results indicate that the average grain size of core sample is 225μm,which shows fine-medium grain size.The microstructure of core sample is relatively loose,and there are asphalt cements among grains.The silicon and carbon contents are the highest in core sample.The shear dilation rapidly occurs in the uniaxial stress of core sample,but the core volume continues to be compressed due to the restriction of horizontal stress in the true triaxial stress conditions,without any dilation,showing low rock strength.In the true triaxial high-temperature hydraulic dilation experiment,the fluid pressure in core sample showed significant fluctuation,which indicated that the internal fractures continued to initiate,develop,and propagate during the hydraulic dilation stage,leading to the volume dilation of core sample,and the core sample still had strong bearing capacity after reaching the fracture pressure.CT scanning showed that the core volume expanded significantly after hydraulic dilation,significant deformation occurred in the horizontal direction,and secondary complex fracture network appeared inside,indicating superior dilation effect.Finally,a field case is studied to demonstrate the good results of hydraulic dilation construction in heavy oil cyclic steam stimulated wells in Bohai Oilfield.The study results provide feasibility analysis for hydraulic dilation and safe connection and high-efficiency development of heavy oil.