青藏高原羌塘盆地中生界主要烃源层分布特征

DISTRIBUTIONS OF THE MAIN MESOZOIC HYDROCARBON SOURCE ROCKS IN THE QIANGTANG BASIN OF THE QINGHAI-TIBET PLATEAU

青藏高原羌塘盆地是一个中生界海相残余盆地．根据地质调查和3850块烃源岩样品29个分析项目23976块次约200000个原始基础数据的分析、筛选、整理统计和综合研究得出．纵向上发育J3s、J2x、J2b和T2x 4套主要烃源层．不同坳陷或凹陷内主要烃源层有所差别。南羌塘坳陷东部为J3s，J2b和J2q-T3x．中西部为J2x，J2b和T3x；北羌塘坳陷东部为J2b．T3x西部为J3S．J2x，J2b和T3x。侏罗系有效泥质烃源岩厚度一般在100～500m．有效碳酸盐烃源岩厚度一般在200～600m，J2x和J3S局部地区发育有200～400m的富烃源岩；T3x一般厚500～700m，北羌塘坳陷T3x也发育100～300m的优质好烃源岩。J2T页岩残余总有机碳含量平均最高达4．15％，J3s泥灰岩残余总有机碳含量平均最高达1．26％；T3x页岩残余总有机碳含量平均最高大于1．5％，但T3x海相页岩残余总有机碳含量一般在0．5％～1％之间。J2x灰色及灰绿色泥岩残余总有机碳含量多小于0．5％．J3s和J2b灰岩残余总有机碳含量多小于0．2％。

Qiangtang Basin in Qinghai-Tibet plateau is a Mesozoic marine residual basin. Geologic survey and analysis of the hydrocarbon source rock samples show that there are four hyddrocarbon source rocks longitudinally developing in T3x, J2b, J2x and J3s formations in Qiangtang Basin. The main hydrocarbon source rocks in the different depressions or sags are different. The hydrocarbon source rocks develop in J3s, Jeb and J2q-T3x formations in the east of South Qiangtang Depression and in J2x, J2b and T3x formations in the centre and west of South Qiangtang Depression. In North Qiangtang Depression, the hydrocarbon source rocks develop in T3x and J2b formations in the east and in J2er, T3x, J2b and J3s formations in the west. The thicknesses of the effective Jurassic muddy hydrocarbon source rock and carbonate hydrocarbon source rock are generally 100 to 500 meters and 200 to 600 meters, respectively. There are hydrocarbon-rich rocks with 200 to 400 meters thick devceloping in J2x and J3s formations. The thickness of the good-quality hydrocarbon source rock developing in Taer formation is generally 500 to 700 meters. And in North Qiangtang Depression, 100 to 300 meters thick of good-quality hydrocarbon sourck rock developing in T3x formation. The maxima of residual TOC of the Jeer shale, J3s marl and T3x shale are 4.15%, 1.26% and 〉1.5%, respectively. However, the values of residual TOC of the Jeer gray and gray-green mudstone as well as J3s and J2b limestone are mostly less than 0.5% and 0.2%, respectively. The value of residual TOC of the T3x marine shale is generally in the range of 0.5% to 1%.