鄂尔多斯盆地盒8段致密砂岩气藏储层特征及地质工程一体化对策

Characteristics of He 8th member tight sandstone gas reservoir and solution based on geology-engineering integration in Ordos Basin

为明确致密砂岩气藏储层特征、低产原因及提高单井产量对策,应用铸体薄片、恒速压汞、高压压汞、低温液氮吸附、应力敏感、水锁伤害等分析测试手段,对鄂尔多斯盆地上古生界二叠系石盒子组盒8段致密砂岩储层微观孔隙结构特征和气藏低产原因进行深入分析;结合气藏特征,明确了提高单井产量的地质工程一体化对策。研究认为,盒8段致密砂岩储层以岩屑溶孔、晶间孔等次生溶蚀孔隙为主,裂缝不发育,为单一孔隙介质储层;喉道半径分布曲线主峰为0.2~2.2μm,渗透率小于1mD的储层中近纳米级喉道连通的孔隙体积大于38%,为微细喉储层,微细喉道控制了储层的渗流能力;应力作用下微细喉道易发生缩颈、闭合,遇水快速自吸引发喉道缩颈、堵塞,应力敏感伤害和水锁伤害强。加之单砂体规模小、储量丰度低,单井普遍低产。地质工程一体化提高单井产量的对策:一是优选含气富集的物性"甜点"和储层易改造的工程"甜点",降本增效;二是精细方案设计,强化储层保护,依据储层特征设计针对性改造方案;三是通过体积压裂加大储层改造规模,将单一孔隙介质储层改造成孔隙-裂缝双介质储层,减弱微细喉道对储层渗流能力的控制,优选垂向连通性较好的主河道部署水平井,扩大泄流面积;四是多层动用、多层合采,提高单井产量。

Several analytical methods,including casting thin sections,constant-rate mercury intrusion,high-pressure mercury intrusion,low-temperature liquid nitrogen adsorption,stress sensitivity,and water locking damage,were used to investigate the microscopic pore structures and causes for low production of tight sandstone gas reservoirs in the 8th member of Shihezi Formation,Permian,Upper Paleozoic("He 8th member"),Ordos Basin.Then,a solution based on geology-engineering integration was proposed for increasing single-well production.The study shows that the He 8th member tight sandstone reservoir comprises secondary dissolved pores such as lithic dissolved pores and intercrystal pores,without fractures,indicative of a single-porosity reservoir.The peak throat radius is 0.2-2.2μm.The pore volume communicated by nearly nano-throats in the reservoir with permeability less than 1 mD is greater than 38%,suggesting as micro-throat reservoir where the micro-throats control the permeability.Under the action of stress,micro-throats are prone to shrinking,closing and quickly absorbing when exposing to water,so that they are stress-sensitive and likely induce water locking damage.In addition,the single sand body is small in scale and low in abundance,so the single-well production is generally low.The solution based on geology-engineering integration for increasing single-well production mainly involves four aspects.First,geologic sweet spots with rich gas and engineering sweet spots in fracturable reservoirs are preferred for development with lower cost and higher efficiency.Second,a specific and customized stimulation program is designed depending on the reservoir characteristics.Third,volume fracturing is applied to increase the stimulated reservoir volume(SRV)through changing the single-porosity reservoir to a dual-porosity(pore-fracture)reservoir and weakening the control of micro-throats on the permeability.Horizontal wells are preferentially deployed along primary channels with ideal vertical connectivity to expand the drainage area.Fourth,multi-layer/zone commingled production is adopted to enhance the single-well productivity.