Study On Fracture Propagation Of Sandy Conglomerate Reservoir

In the Mahu Oilfield,the conglomerate reservoir has a thick oil layer,deep burial,micro-fractures,high gravel content,and serious reservoir heterogeneity.Fracturing reconstruction is difficult,with complex fracture shapes,high tortuosity,easy sand plugging,and short support crack lengths.In order to improve the effect of fracturing reconstruction,it is necessary to study the physical and mechanical characteristics of the target reservoir,as well as the law of crack propagation in the conglomerate reservoir.In this paper,through the on-site data analysis,the physical properties,fluids and in-situ stress characteristics of the target block are clarified;the microscopic pore characteristics of the target reservoir are analyzed by means of core observation,microscope observation and scanning electron microscope;the target reservoir mechanical parameters are obtained through the laboratory rock mechanical parameter test experiment;The triaxial compression experiment was used to initially understand the fracture propagation behavior in the sandstone conglomerate reservoir;based on numerical simulation methods to systematically study the influence of the gravel content,particle size and modulus on the fracture propagation morphology,the main understandings obtained in this paper are as follows:(1)The abnormal high pressure and normal temperature system of the target block,the preliminary oil test has no bottom water,and has good large-scale fracturing conditions;the whole reservoir has low porosity and low permeability characteristics,and the layer has strong heterogeneity The pore structure is complicated,and the pore type is mainly composed of residual intergranular pores and intragranular dissolved pores,and shrinkage cracks are developed locally.(2)Triaxial compression test results show that the crack propagation modes under the influence of gravel mainly include three types: penetrating gravel,winding gravel and stopping gravel.(3)When the gravel content is less than 20%,the fracture encounters gravel mainly through the gravel and around the gravel,resulting in a single long slit;when the gravel content exceeds 30%,due to the shielding and blocking effect of the gravel,it is easy to produce complex micro crack.(4)When the particle size of the gravel is less than 10 mm,the fractures are mainly through and around the gravel.The particle size of the gravel is small.The energy required for the fracture to pass through a single gravel is low,and it can spread through multiple gravels to a distance.When the particle size of the gravel is between 15 and25 mm,the fracture will penetrate through the gravel,turn around and stop the gravel when it encounters the gravel;the particle size of the gravel is large,the energy consumption of the fracture through a single gravel is high,and the ends of the upper and lower branches of the fracture are mostly stopped at Gravel interior.(5)When the ratio of the Young’s modulus of the gravel to the Young’s modulus of the sandstone matrix is less than 1.5,the fracture propagation is mainly through the gravel,and the presence of gravel has no obvious effect on the fracture propagation morphology;when the gravel Young’s modulus and the sandstone When the ratio of matrix Young’s modulus is between 1.75 and 2.25,the crack propagation is mainly around the gravel,the cracks formed have a large tortuosity,and the presence of gravel has a significant effect on the direction of crack propagation;when the crack initiation point is inside the gravel,the crack The expansion resistance is large,the energy consumption is high,and a short thick seam is formed.