Optimization Of Complex Fracture Conductivity Created By Acid Fracturing In Carbonate Reservoir Located At The 4th Part Of Dengying Formation In Gao-mo Area

Marine carbonate reservoirs are important parts of global oil and gas resources reservoirs,which contain about 70%oil and gas resources of the total resources,while the explored and producible reserve is around 50%.Recently,significant oil and gas resource exploration discovery has been made about carbonates in the 4th member of Sinian Dengying formation in the middle of Sichuan Basin.Acid fracturing is a crucial stimulation treatment and access to get stable production.But carbonate reservoirs in the 4th member of Sinian Dengying formation in the middle of Sichuan Basin are in deep depth and high temperature,of which the main rocks are dolomites with intrinsic fractures,while the reservoirs have high closed pressure and poor level of uneven etching.Thus,it is difficult to estimate the fracture conditions and conductivities under varied support states after acid fracturing for stimulation in the reservoirs.The paper focuses on the development of intrinsic fractures based on essential characteristics of carbonates in the 4th member of Sinian Dengying formation,and finishes 3D numerical reconstruction for fracture systems inside rocks by CT scanning and recognize the features of intrinsic fractures spreading.Then,true triaxial hydraulic fracturing tests are carried out according to features of intrinsic fractures spreading.After that,fracture systems are reconstructed,while propagation paths and patterns of hydraulic fractures and impact of intrinsic fractures on propagations of hydraulic fractures are analyzed.Furthermore,feasibilities of complicated patterns formations of fractures are analyzed.Meanwhile,based on the geological characteristics of the 4th member of Sinian Dengying formation,the dual porosity media model of single well reservoir is established.The effect of different fracture length and conductivity on the productivity of a fracturing well are studied,optimizing fracture conductivity under the economic productivity.According to the feasibility of forming complicated fractures,the fracture states,and the optimized fracture conductivities,experiments are designed to study the fracture conductivities under different closed pressures,acid concentration,proppant particle size and sand concentration in the state of three different fractures,including self-supporting fracture,acid etching fracture and sand-adding acid fracture.The study shows that the fourth Member of Deng formation in Gao-Mo area will induce nature fracture to open,and produce some shear slip fractures.The large-scale ture triaxial physical simulation test indicates that a certain degree of complex fractures can be formed,but the conductivity of self-supporting fractures in the complex fracture system is limited,acid treatment is still needed to meet productivity requirements.With the increase of acid injection rate,the surface morphology of acid etching fracture is more complex.For sand-adding acid fracture,the conductivity increases with the increase of proppant loading concentration.However,at low proppant concentration(<2kg/m2),the conductivity of sand-adding acid fracture is lower than the acid etching fracture conductivity,sand-adding acid fracture exists a critical sand-adding concentration.In addition,the proppant size effect on conductivity is not obvious.The experimental means to characterize fracture is established to provide new ideas for analyzing feasibility of forming complex fractures.At the same time,the results of the three-stage supporting fracture conductivity of acid fracturing can provide guidance for reconstruction of carbonate reservoirs in Sichuan Basin.