| The object of this paper is the organic rich mud shale section in Longmaxi Formation of lower silurian series which was lacated in southern Sichuannorthern guizhou area. On the basis of predecessors’ research results, we collect the related geollgical data in research area, combining with the measurements of our field profile and drilling cores observation, analyzing several important shale gas geological conditions such as the basis of regional geological background, sedimentary facies-to suck, organic geochemical characteristics, the rich organic matter mud shale thickness, buried depth, brittleness mineral content, physical characteristics and gas-bearing characteristics and preservation conditions and so on, and came to some conclusions:In the settlement center of Yibin-Luzhou–Hejiang-Qijiang regions, the organic carbon content at around 5% of organic rich mud shale section, and since the settlement center, respectively, to the north near the upper uplift siltstones, and to be near the south Guizhou uplift in the organic carbon content gradually reduce in turn. In the deep-water shelf the content of organic carbon in rich organic matter of mud shale has a great value, and the kerogen type is given priority to with type I, II1 type, organic matter maturity is in 2.0% to 3.3%; Near the uplift is shallow water shelf sedimentary environment, the organic carbon content less than 2% generally lower, the kerogen type is given priority to with type I, II1 type and some type II2, organic matter maturity is 1.0% to 2.0%.The organic shales which distribute stable in Longmaxi group in lower silurian of South Sichuan-North Guizhou area belong to marine deposit.The center of subsidence which spread from Yibin-Luzhou to Hejiang-Qijiang area has large thickness of organic shale that can up to hundreds of meters. The thickness of organic shales in north area such as Zigong-Neijiang-Dazu areas goes down to 60 m, and in Chuanzhong uplift the organic shale disapears. In the south areas such as Changning-Qijiang area the thickness goes down to 80 m, and the thickness is around 60 m in Junlian-Xuyong-Daozhen areas. In Weixin-Gulin-Xishui-Zheng’an areas the thickness goes down to 40 m and in Qianzhong uplift the organic shale dispear All these areas except areas that near Chuanzhong uplift and Qianzhong uplift acquire favorable conditions that shale gas can accumulate.Longmaxi Formation in lower silurian of South Sichuan-North Guizhou area is spread 553 m to 5000 m underground. The buried depth of the center of subsidence which spread from Yibin-Luzhou to Hejiang-Qijiang area is relatively deep, which is about 3000 m to 4500 m.The buried depth of Xishui-Zheng’an area is relatively shallow, which is about 1000 m to 2000 m.The buried depth of Weixin-XuyongRenhuan areas are around 1000 m to 1500 m. The favorable area is mainly distributed in Weiyuan-Zigong-Neijiang areas and Changning-Xingwen areas, which has the buried depth of 1500 m to 3500 m.In the study area, the mineral composition of organic rich mud shale section in Longmaxi Formation of lower silurian series is given priority to with brittle mineral, detrital minerals and clay minerals as the secondary, and quartz and feldspar content is between 34% and 90%( the average of 51.1%); carbonate mineral content is less, content is between 0 to 53%, the average is 16.95%; Longitudinally the Longmaxi group brittleness mineral content gradually reduce from bottom to top, clay mineral gradually rise. In the research area of rich organic matter in Longmaxi Formation of lower silurian series, brittle mineral of the shale content is higher, and has good potential of fracturing.Within the in Longmaxi Formation of lower silurian series rich organic matter mud shale’s porosity is in commonly 1.5% to 10.1%, average 4.16%. Permeability are mainly distributed in 0.0014 × 10-3μm2~0.52× 10-3μm2, permeability of the average of 0.028 × 10-3μm2, pore throat diameter are mainly distributed in 20 nm to 110 nm. Reservoir space types mainly include two kinds of pore and micro cracks, Pore types mainly include mineral grains(intergranular) pores between seam, mineral particle dissolution pore, micro pore formed by organic matter hydrocarbon generation and matrix dissolution pore, etc.In Changning area, in Longmaxi Formation of lower silurian series of nearly 300 m segment of the shale’s air content figure is 0.5m3/t to 6.5m3/t, and 2363 m to 2396 m air content 3.5m3/t to 6.5m3/t(Weiyuan only 2.8m3/t), the gas analysis was 2.4m3/t to 4m3/t. Daoye well at the scene of the 553 m to 597 m hydrocarbon content parsing also shows better, and the total air content is in 1.84m3/t to 2.69m3/t, and Close to Ohio, New Albany. Compared with north American shale gas accumulation conditions, in Longmaxi Formation of lower silurian series study area has good shale gas exploration potential.In the study area, the advantage area’s distribution is given priority to Yibin-Luzhou–Hejiang-Qijiang and other areas as the center, and north to Weiyuan-Rong county–Neijiang, etc;south to Junlian-Gulin-Xishui-Daozhen, etc. Prospect areas are mainly distributed in near the upper uplift and guizhou uplift siltstones. |
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