Research On The Effect Of Tectonic Stress Field On The Fracture Distribution And Permeability Of Niutitang Shale Reservoir In Northern Guizho

There are complex geological and tectonic conditions in Guizhou area.As a shale gas reservoir,shale is very different from conventional reservoirs.The transformation and control mechanism of the formation will provide a theoretical basis for the evaluation of shale gas exploration prospects in northern Guizhou.This paper studies the fracture distribution and permeability of shale reservoirs in the study area by using the research methods of data collection,field investigation and sampling,physical experiments,theoretical analysis and numerical experiments.The main research contents are as follows:(1)Based on geological data and field investigation,the geological background,structural evolution characteristics and stratigraphic distribution characteristics of northern Guizhou were analyzed.(2)Based on a lot of shale-related data,it is believed that the natural fracture system in shale reservoirs is the direct cause of permeability.Through outcrop observation,core observation and electron microscope scanning test methods,the development characteristics of macro and micro pores and fissures in Niutitang Formation shale were qualitatively analyzed.The mineral composition,porosity and permeability distribution of the Niutitang Formation shale reservoirs were quantitatively analyzed by XRD diffraction analysis and porosity and permeability tests.And the main controlling factors of shale reservoir permeability are analyzed.(3)The core samples from the northern Guizhou area were sampled,and the Brazilian splitting,uniaxial compression,triaxial permeability tests,the In-Situ tectonic stress test by the inelastic strain method and the numerical test of the rock fracture process were carried out.The physical and mechanical characteristics of shale are studied,the evolution law of permeability and the evolution mechanism of fracture damage are analyzed,and the magnitude and direction of In-Situ tectonic stress are obtained.(4)A geomechanical model of the Niutitang Formation shale reservoir in the northern Guizhou area was established by numerical simulation.Using the theory of fracture mechanics,the Yanshanian paleo-tectonic movement in the northern Guizhou region is inverted,and the stress distribution law and the semi-quantitative characteristics of the fractures in the Yanshanian period(key fracture formation period)are analyzed.(5)Numerical model of the Niutitang Formation shale reservoir in northern Guizhou area was established by numerical simulation.The regional characteristics of the present tectonic stress field of the Niutitang Formation in the northern Guizhou region are inverted using the thin plate bending model theory,the permeability stress sensitivity analysis of the shale in Well Fengcan 1 is carried out.,and the In-Situ tectonic stress distribution characteristics and permeability distribution law of the Niutitang Formation in northern Guizhou area are obtained.