Characteristics of Jurassic shales and potential of shale gas in Southwest Depression of Tarim Basin

Based on outcrops, drilling data, combining with the analysis of Rock-Eval pyrolysis, X-ray diffraction, SEM and isothermal adsorption measurement, the current study was designed to characterize geological and geochemical properties, mineral composition, pore structure as well as gas adsorption capacity. The results show that the thickness of Jurassic shales is large in this research area, about 60-300 m, because of continuous changes in sedimentary environment, it has three small depositional centers with NW-SE strike on the plane; the abundance of organic matters is high, its average value reaches up to 2.09%, the organic material primarily consists of type III terrestrial kerogen (gas-prone); the temperature of maximum pyrolysis output Tmax (400-590℃) and vitrinite reflectance Ro (1.4%-2.4%) indicate that the shale is in the post-mature stage and in the gas window of hydrocarbon generation; clay minerals dominates the mineralogy followed by quartz minerals, and clay minerals are dominated by illite-montmorillonite mixed-layer, which contributes to the accumulation of adsorption gas, meanwhile, the isothermal adsorption test shows that the adsorbed gas is 0.8-1.6 m3/t, which proves that the shale has a strong ability of gas adsorption; the various types of pores and fractures in nanometer-micrometer level provide space for shale gas; in contrast to the typical marine and continental shales, the main assessment indicators of the shale in the research area is similar to (even better than) typical continental shales and marine-continental transitional Lewis shale in the San Juan basin. A comprehensive analysis indicates that Jurassic shales in Southwest Depression of the Tarim Basin could tentatively be regarded as a potential shale gas exploration target. © 2016, Editorial Office of Journal of China Coal Society. All right reserved.