Research On Pore Characteristics Of Shale Gas In The Longmaxi Formation, Wulong-qianjiang District Of Southeast Sichuan

This paper systematically does research on Shale reservoir in the Longmaxi Formation, wulong-qianjiang district of southeast Sichuan, under the premise of the previous research on structural characteristics and sedimentary facies of the Longmaxi formation, through the combination of field investigation, sampling and experimental research method, doing research on lithological features, rock micro composition, organic matter characteristics, pore characteristics, physical characteristics of the Longmaxi formation and getting the following understanding.The Longmaxi formation in the study area is divided into two segments, and from the top to the lower, its rock color changes from shallow to deep, granularity changes from coarse to fine, and characterized by static water environment, belongs to shallow shelf-deep water shelf deposition. From the analysis of rock mineral composition, the Longmaxi formation is mainly composed of brittle minerals and clay minerals of the shale, the brittleness mineral is given priority to siliceous mineral, clay mineral surface samples mainly consists of illite and chlorite is second, samples of downhole clay minerals mainly illite and mixed layer. According to its mineral composition, rock in the Longmaxi formation is mainly divided into three types, the upper section of which are mainly composed of “quartz + clay + feldspar” and “quartz + clay + carbonate rocks”, and the lower section of which are mainly composed of “quartz + clay”.The organic matter type of the Longmaxi formation is given priority toⅠ type, its Total Organic Carbon(TOC) is on average 2.11%(field), 2.26%(underground), and its maturity of organic matter(Ro) averaged 2.26%(field), 2.65%(underground). Plane, according to the organic carbon content and organic hole maturity, the study area is divided into a ultra-high value area and a high value area; Vertically, with the increase of buried depth, organic carbon content increased, while the organic matter maturity kept at small changes between 2.5% ~ 3.0%; Overall performance of high organic carbon content and high- high evolution degree.The shale pore types of the Longmaxi Formation are intergranular pore, intragranular pore, intercrystalline pore, dissolution pore and organic hole; Its pore faces at a rate of 0.95%, which is given priority to pore between mineral and organic hole, the mineral of pore ranged from 0.05 to 10 microns, organic hole diameter between 0.002 ~ 1μm, mainly composed of nanoscale hole; The pore throat of the Longmaxi Formation are mainly the throat between organic matter and mineral throat, and throat between the mineral separation has coarser slanting degrees, distributed parallel plate and good connectivity. The main factors influencing shale pore structure in the Longmaxi Formation have diagenesis, organic carbon content and mineral content.The average porosity of the Longmaxi formation is 1.62%, the permeability is 0.58×10-3μm2,overall shows the characteristics of low porosity, low permeability, and factors that affect the porosity and permeability are mineral content and organic carbon content.According to the evaluation standard of shale reservoirs, making the composition of plane distribution maps of organic carbon content, organic maturity, porosity and permeability, then considering the influence of various factors on the reservoir, getting the understanding of that they are two good blocks of shale reservoir in the Longmaxi formation in the study area.