Characterization And Prediction Of Fractures In Low Permeability Reservoirs

Structural fractures are commonly developed in the low permeability reservoir of the Third Member of the Shahejie Formation of Niu 35 fault block in Niuzhuang depression,Dongying Sag.Their characteristics were characterized by core observation,thin section observation and CT scan.In the meanwhile,triaxial mechanical tests were used to study the mechanical properties and the factors affecting fracture development of the middle of the Third Member of the Shahejie Formation;Fracture occurrences,filling characteristics and rock acoustic emission tests are used to divide the fracture stages;Based on the strain energy theory,the composition of energy in rock deformation was studied and the fracture prediction formula was derived.The fracture prediction was carried out by finite element simulation.The study found that the low-angle and high-angle oblique fractures in the low-permeability reservoirs of the middle of the Third Member of Shahejie Formation of Niu-35 fault block were the most diversity and developed,and shear fractures were developed mainly.Micro-fractures were mainly through joins.The fractures were larger in scale and smaller in overall opening with low filling degree,resulting in the better effectiveness of the fractures.Controlled by the extensional and strike-slip stress field in Cenozoic Dongying Sag,three groups of structural fractures were mainly developed.Combined with the attitude of fractures,the characteristics of fillings and the Kessel point of the acoustic emission experiment,three stages of the fractures were concluded:the Third Member of Shahejie Formation to the Second Member of Shahejie Formation,the First Member of Shahejie Formation to Dongying Formation,Guantao Formation to Minghuazhen Formation.The characteristics of fracture development and triaxial mechanical tests were used to summarize the mechanical properties of the middle of the Third Member of the Shahejie Formation of the Niu 35 fault block reservoir rocks and their influencing factors.According to the triaxial mechanical tests,the relevant mechanical parameters were obtained.ANSYS software was used to simulate the stress field of the Niu 35 fault block during the Third Member of Shahejie Formation to the Second Member of Shahejie Formation.According to the prediction formula of fractures density based on the energy composition during the rock deformation process,the fractures of the Well N35 can be predicted quantitatively.Simulation result showed that the fracture volume density in Well N35 was 0.507 m~2/m~3,Well N104 and H125-1 was 0.1 m~2/m~3,which was in the same order of magnitude as the actual core observation fracture volume density,and the result was more accurate.Based on the fracture prediction results,combined with the Petrel geological model of porosity and permeability,the Fracman model of fractures,it was concluded that the potential oil and gas development in the study area should proceed along the NE-SW direction of Well N35.