青藏高原羌塘盆地中生界主要烃源层分布特征

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3 850块烃源岩样品29个分析项目23 976块次约200 000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T₃x4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100~500 m,有效碳酸盐烃源岩厚度一般在200~600 m,J₂x和J₃s局部地区发育有200~400 m的富烃源岩;T₃x一般厚500~700 m,北羌塘坳陷T₃x也发育100~300 m的优质好烃源岩。J₂x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%。 

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

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 T_3x,J_2b,J_2x and J_3s formations in Qiangtang Basin.The main hydrocarbonsource rocks in the different depressions or sags are different.The hydrocarbon source rocks develop in J_3s,J_2b and J_2q-T_3x formations in the east of South Qiangtang Depression and in J_2x,J_2b and T_3x formations in the centre and west of South Qiangtang Depression.In North Qiangtang Depression,the hydrocarbon source rocks develop in T_3x and J_2b formations in the east and in J_2x,T_3x,J_2b and J_3s 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 J_2x and J_3s formations.The thickness of the good-quality hydrocarbon source rock developing in T_3x 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 T_3x formation.The maxima of residual TOC of the J_2x shale,J_3s marl and T_3x shale are 4.15%,1.26% and >1.5%,respectively.However,the values of residual TOC of the J_2x gray and gray-green mudstone as well as J_3s and J_2b limestone are mostly less than 0.5% and 0.2%, respectively.The value of residual TOC of the T_3x marine shale is generally in the range of 0.5% to 1%.