柴达木盆地西部古近系储层裂缝有效性的影响因素

古近系盐湖相裂缝性泥灰岩储层是柴达木盆地西部地区的重要储层类型,储层中发育剪切裂缝、纵张裂缝、顺层滑动裂缝和成岩裂缝4种类型。裂缝普遍被方解石、石膏或钙芒硝等充填,裂缝的有效性对储层评价十分重要。有效裂缝不仅提供了储层的重要储集空间和主要渗流通道,还决定了油气的富集规律和储层的潜在生产能力。裂缝的有效性主要受裂缝形成时间、溶蚀作用、第四纪以来的构造抬升剥蚀作用、异常流体高压作用、膏盐层分布和断层的活动性等因素控制。晚期形成的裂缝有效性更好;溶蚀作用可明显地增加裂缝的有效性;第四纪以来的构造抬升剥蚀作用和异常流体高压作用可使裂缝重新裂开,使裂缝的有效性变好;离膏盐层越远,裂缝的有效性越好。裂缝的有效性与现今地应力方向关系不密切,主要受断层活动的影响,与主断层平行的裂缝有效性最好。

Influence factor of validity of fractures in the Palaeogene reservoirs, western Qaidam Basin

The Palaeogene fractured saline muddy limestones are the important reservoir in the western Qaidam Basin. There are shear fracture, tensional fracture, sliding fracture and diagenesis fracture in the Palaeogene reservoirs. Fractures are generally filled with calcite, gypsum and glauberite. The validity of fracture is very important to reservoir evaluation. Effective fractures not only provide storage spaces and channels for fluid flow, but also determine enrichment rule and potential throughput of oil and gas. The validity of fracture is controlled by forming time, solution, uplift and denudation, abnormal fluid high pressure and distribution of gypsum and salt beds. Late fractures are more effective than early fractures. Solution can obviously increase the validity of filled fractures. Uplift and denudation from Quaternary and abnormal fluid high pressure can make filled fractures reopen and have good validity. Fractures distributed far away gypsum and salt beds have better validity. The effective fractures influenced by fault activity are not necessarily aligned with the maximum horizontal stress. Fractures parallel to main faults have the best validity.