Reservoir Characterization And Evalution Of Paleozoic Shale In Fenggang Guizhou And Surrounding Areas

Fenggang and the surrounding area which belong to the north Guizhou Province is one of the main battlefield of the shale gas exploration.The observations and sampling for shale outcrops in the study area have been done systematically.The organic geochemical characteristics of shale reservoirs have been analyzed by organic geochemistry test.Using X-ray diffraction and clay mineral analysis,the characteristics of rock mineral composition of shale reservoir have been researched.The thin section,scanning electron microscopy,argon ion polishing-field emission microscopy experiments and technology have been used to divide the reservoir space of the marine shale reservoirs in the study area,pointing out the effects of different types of reservoir space for shale gas formation.N2 adsorption method,NMR,porosity and permeability testing,rock mechanics analysis,experimental adsorption isotherm and other methods have been used to analyze shale pore structure,pore size distribution,reservoir properties,rock mechanics and adsorption characteristics.The idea of combinations of macro and micro,qualitative and quantitative analysis of observation,theory and applied research is used to comprehensively study of the characteristics of shale reservoirs,including the shale reservoir system on organic geochemistry,rock and mineral composition,reservoir space,pores and fractures,reservoir properties,rock mechanical properties and adsorption and other features comprehensive characterization.Through the comprehensive anlysis,controlling factors for shale pore structure,fractures,and other aspects of adsorption properties have been discussed.Then,the formation conditions of quality marine shale reservoir in have been analyzed and a comprehensive evaluation for Niutitang shale reservoirs has been carried out in the study area.The results of comprehensive analysis are as belows:In the study area,Niutitang Cambrian sedimentary period witnessed massive transgression and its sedimentary facies are mainly deep water shelf,semi-deep water shelf and shallow shelf.The environment of Longmaxi shale formation for Lower Silurian is semi-deep water shelf,shallow shelf and the local tidal conditions.The shales have excellent capacity of generating gas.Niutitang shale has high content of quartz mineral with high brittleness.Reservoir pore space can be divided into organic,inorganic holes and fractures.The most important reservoir spaces are clay floc pores,pore clay mineral collection of the body between the film grain dissolution pores and fractures in Nano-micron.Shale reservoir porosity and permeability is very low,with a variety of pore types and mesoporous(2-50nm)is the main adsorption sites and reservoir space of shale gas.TOC and mineral components on the nanoscale pores of shale reservoir development has control action.The gas adsorption of Niutitang and Longmaxi black shale formation are 4.48m3/t and 0.72m3/t.The main factors controlling the gas adsorption capacity of the shale reservoir are maceral,organic carbon content,maturity,mineral components and pore structure.The features The segment of quality marine shale reservoirs are "seven high and one low" with high percentage of organic carbon(TOC),a high percentage of quartz mineral,low percentage of clay minerals,high brittleness index(BRI),high fracture development,high porosity,high permeability,a high adsorption gas.Quality marine shale reservoir formation conditions were high abundance of organic matter,moderate maturity,high quartz low clay mineral assemblages,abnormal formation pressure and good preservation conditions.