Study On The Shale Reservoir Of The Lower Silurian Longmaxi Formation In The Changning Area, Southern Sichuan

Changning area, located in southern Sichuan Basin, is a part of national demonstration area for shale gas exploration and development. The study of shale gas geology in China has just started, and a unified evaluation parameters and standard for shale gas potential has not yet been established. This paper aims at the marine shale of lower Silurian Longmaxi Formation in Weiyuan-Changning district. Based on large amounts of relevant research results at home and abroad, guided by stratigraphy, paleontology, sedimentary petrology, geochemistry, unconventional oil and gas geology and petroleum geology, by outcrop data, core, logging and drilling, seismic materials and laboratory analysis, combined with regional background, this thesis has carried on detailed research on the potential and the favorable exploration area from the gas generation ability, reservoir capacity and exploitation probability.The thickness of Longmaxi Formation is very large and well N210 area is the thickest region,340 meters. Silty Mud Shelf microfacies and Mud Shelf microfacies are the dominant sedimentary facies in the study area, with Calcareous Silt Shelf and Muddy Silt Shelf microfacies.The kerogen type are mainly type ? in the study area, with little type ?1; the organic carbon content is from 0.07% to 8.35% and the average content is 2.46%; the maturity is already reach high-over-mature stage, with an average content of 1.62%.The effective thickness of shale gas in the Lower Silurian Longmaxi Formation is distributed between 20 to 60m; The burial depth of Longmaxi Formation is moderate and stably distributed. Most area is between 2000m and 4500m.The conventional microscope, scanning electron microscopy (SEM), X-ray diffraction analysis and Argon ion polishing method show that the mineral composition of the study area is mainly quartz, calcite and clay minerals, with some feldspar, dolomite and pyrite; the brittleness index is over 50%, which is benefit for later stimulation; the reservoir space is dominated by intergranular pore and organic pore; the porosity is from 0.5% to 8%, and the permeability is only dozen to hundreds of nanodarcy, belonging to low porosity, ultra-low permeability reservoir. The gas content obtained from direct method (desorption method) show that the gas content is similar to that of the five developed shale play in North America. The gas content has some relationship with total organic carbon, porosity, and quartz. Select the shale depth and effective thickness, organic carbon content, maturity, porosity, reservoir siliceous content and clay mineral content of seven parameters to evaluate the reservoir area of Changning.