Study On The Effect Of Rock Fracture Morphology On Macro Scale Resistivity

Shale gas is a kind of unconventional natural gas which occurs in shale dominated reservoirs.Compared with conventional energy resources,shale gas has the advantages of larger recoverable reserves and longer production cycle.It is a hot spot of energy development in recent years.Due to shale reservoir porosity and permeability is low,hydraulic fracturing technology is generally adopted in industrial production,and the artificial fracture and the primary fracture of shale are combined with the primary fracture through the method of subsection fracturing in horizontal wells,so as to improve the productivity of the fracture network.Because of the current mechanism of hydraulic fracturing in the formation of cracks in deep rock is not clear,the study is more limited to the qualitative evaluation,it is difficult to find from the surface fracturing fractures caused by the shape and distribution,resulting in difficult to choose the appropriate oil and gas exploration point to maximize the efficiency of mining.How to quantitatively evaluate fractured reservoirs is also a difficult problem today.This paper examines the difference of apparent resistivity in the presence of cracks in the rock.Based on rock fracturing fracture can affect the resistivity of rock,the research designs shale fracturing test,measuring the resistivity of samples in different stages using four pole method,the relationship between the resistivity and the influence of the crack before and after fracturing fluid in the joint of rock resistivity.The mechanical experiment with standard specimens cannot meet the conditions of electrode resistivity test method of four pole spacing is much larger than the sample diameter,and destroy the integrity of rock fracturing,the relationship between resistivity and fracture morphology through experimental study in the laboratory is very difficult.In this paper,two reasons for measuring errors and their improvement methods are analyzed by using finite element numerical simulation method.In order to study how the crack shape in the rock will change the anisotropic of apparent resistivity of rock,rock model with crack is established with the method of finite element modeling,calculate the apparent resistivity of model at different angles and forms cracks under different conditions.By comparing and analyzing the calculated results,it is concluded that the resistivity of rock will change with the fracture angle and the connectivity of fracture,and the anisotropic coefficient of the model will be calculated.The low resistivity fracturing fluid used for hydraulic fracturing of shale gas will also change the apparent resistivity of rock formations,which provides the possibility to infer the shape of underground fractures through resistivity measurements.In order to verify the rock resistivity anisotropy can applied to surface exploration,this research established a large depth model and Simulation of electromagnetic method in measuring the surface electric field and magnetic field strength,and then calculate the apparent resistivity distribution of the surface geological model,and by comparing the horizontal and vertical resistivity measurement of resistivity measurement result analysis the relationship between surface resistivity distribution and fracture orientation.This dissertation and related research have been supported by the strategic pilot science and technology special category(B)(XDB10030500)of Chinese Academy of sciences.