基于"扩缝串洞"理念的超深层小缝洞群碳酸盐岩储层改造数值模拟OA北大核心CSTPCDEI

As the exploration and development of carbonate oil and gas reservoirs in the Sichuan Basin and the Tarim Basin steps into ultra-deep field,the ultra-deep geological conditions lead to the reservoirs transforming from large-scale fractured-vuggy type to small-scale(centimeter to millimeter scale)fractured-vuggy type.However,the previous acid fracturing technologies for the stimulation of large-scale fractured-vuggy reservoirs are not suitable for small-scale fractured-vuggy reservoirs.In order to sufficiently give full play to the natural gas productivity of ultra-deep small-scale fractured-vuggy carbonate reservoirs,this paper establishes a multi-scale discrete fracture-vug method based on the characteristics of small-scale fractured-vuggy carbonate reservoirs.Then,a thermal-hydraulic-mechanical-chemical field coupling numerical model is established,which takes into account rock deformation,fracture propagation,acid flow and reaction,and temperature change.Finally,the"fracture expanding and vug connecting"concept with multi-stage diversion for expanding area,accurate viscosity controlling for connecting fractures and vugs,and fixed-point acid etching for increasing fracture length as the cores is put forward,and the fracture controlled stimulation mode of"fracture expanding and vug connecting"for small-scale fractured-vuggy carbonate reservoirs is optimized and analyzed.And the following research results are obtained.First,viscous fingering caused by multi-stage alternative injection can promote the increase of fracture controlled stimulation area and the non-uniform etching of fracture,thus increasing the dimensionless productivity index and achieving the best fracture controlled stimulation effect.Second,as the acid injection viscosity ratio increases,the dimensionless productivity index of fracture controlled stimulation increases first and then decreases.When the viscosity ratio exceeds 30,the dimensionless productivity index begins to decrease rapidly.Therefore,the alternation viscosity ratio of acid in fracture controlled stimulation shall be controlled between 25 and 35.Third,the larger the acid consumption,the greater the fracture controlled stimulation area and dimensionless productivity index.For certain reservoir parameters and single well controlled area,however,there is an acid consumption limit for fracture controlled stimulation.When acid consumption exceeds this limit,the fracture controlled stimulation area approaches to a limit value,but steady increase is still observed in dimensionless productivity index.In conclusion,the key to stimulate small-scale fractured-vuggy carbonate reservoirs is to increase the fracture controlled stimulation area and activate small fractures and vugs.The research results provide a theoretical guidance for the efficient development of ultra-deep small-scale fractured-vuggy carbonate gas reservoirs.