Analysis Of The Accumulation Conditions Of Shale Gas In Jiaolai Basin

Jiaolai Basin has developed multi-segment dark shale. Shuinan Formation is the major shale gas producing reservoir section,which well-developed set of dark shale and has good geological conditions. This paper selects the Shuinan Formation shale as the research object in Jiaolai Basin. Data collection,geological investigation,experimental test and theory research are conducted in the study to analyze the core scientific issues of Shuinan Formation shale gas accumulation conditions. The results showed that:Shuinan Formation is formed in semi-deep and deep sedimentary environment,which is comprised by shale,siltstone and limestone,with a total thickness ranging from 50~200m and the depth from 1000~3000m up to 5000 m. The organic matter of shale is based type II,sub-type Ⅲ. The abundance of organic matter ranged from 0.15% to 4.0%. The thermal maturity ranged from 0.8 % to 1.6%,which mainly between 1.0 % to 1.4%,showing that it has achieved the mature stage. The main composition of mineral is clay and quartz. The friability is equaled to the lower Paleozoic marine shale of south China. The maximum adsorption capacity is between 1.34 ~2.09m3/t,with the average of 1.67m3/t.There are four pore types in the target strata:organic pore,intragranular pore,dissolution intergranular pore and intergranular pore. The porosity is generally range from 4% to 10%. Microporous and eyelet is the main pore diameter. Natural micro-cracks are well developed,which act as the main channel for adsorbed gas resolving to free,and benefit for gas storage and migration.Factors of controlling Shuinan Formation shale gas accumulation is summarized as follows:Firstly,it is the depositional environment that controlled the substances sources of hydrocarbon,effective thickness of hydrocarbon source rock and the abundance of organic matter. Secondly,the clay mineral offer the principle pore volume space and specific surface area,and brittle mineral can enhance the brittleness and the ability creating fracture.Besides,the structural transformation can promote the hydrocarbon generation of the organic matter,but at the same time,intense tectonic reconstruction would develop a large number fracture of the reservoir,made saved gas gathering and escaping. Finally,the pore structure and its type may affect the free and absorbed state of the shale gas,especially for the organic pore,which mostly affects the occurrence of shale gas.In short,Jiaolai basin is thought to have good prospects for shale gas resources.. The most prospective areas for shale gas exploring are situated at Taocun sag,the deep of Laiyang sag,the eastern of Xiagezhuang sag,the deep of Zhucheng sag and the northern of Pingdu sag,which hava a good condition for shale gas accumulation.