Reservoir Features and Influential Factors of Lucaogou Formation Shale in Jimusaer Sag

Wei Cui, Gang Gao, Dou Chen, and Chengyun Wang
College of Geosciences, China University of Petroleum, Beijing, China

The Jimusaer Sag lies in western of east slope region of the Junggar Basin, and Lucaogou formation develops in salty lacustrine sedimentary environment, development is rich in carbonate mineral with high organic matter abundance of mudstone/shale formation. The shale thichness ranges from 20m to 120m, the total thickness distribute from 30m to 250m, and gradually thickens from north to south. Lucaogou formation lithofacies include massive grey or black mudstone/shale, laminated dolomitic mudstone/shale, laminated and silty mudstone/shale. The average content of quartz, feldspar and pyrite of this formation is 55.9%, the average content of clay mineral is 11.5%, and the average content of calcite and dolomite is 31.3%. Most of porosity in different rock core is mainly less than 6%, the permeability is dominately from 0.01mD to 0.1mD. Pore type of this formation include pore and crack; Crack, suture and bedding fissure grow in rock core; the micropores in the shale observed in the SEM are dominated the minerals intergranular(dissolution)pores, intergranular gaps, intragranular pores, the organic matter micro-pores and micro-fractures. The development of pores in lacustrine shale is controlled by lithology, mineral composition, diagenetic evolution and the characteristic of organic matter. Primary pores of mudstone/shale are charged by coarse minerals composed of quartz and feldspar with high capability of anti-compaction. Unstable minerals such as carbonate and feldspar are beneficial to the development of dissolved pores. Physical properties of laminated dolomitic mudstone/shale are better than those of grey or black mudstone/shale and silty mudstone/shale; In the late diagenetic stage, arrangement of clay minerals is changed, the montmorillonite changes to chlorite and illite in different formation, which is good for pores preservation and forms new micro-pores to increase the effective porosity. In the process of thermal evolution of organic matter, hydrocarbon generation of solid kerogen formates new pores and with shrinkage joint. Both increase the micro-pores. Acidic fluid generated by hydrocarbon generation can enhance unstable mine dissolution, inorganic mineral evolution can promote the Reservoir capability effectively. With rich organic matter (TOC>3%), TOC and porosity has a positive correlation.

AAPG Datapages/Search and Discovery Article #90180©AAPG/SEPM/China University of Petroleum/PetroChina-RIPED Joint Research Conference, Beijing, China, September 23-28, 2013