准南芦草沟组沉积特征及油气勘探前景

Depositional Characteristics and Petroleum Exploration Significance of Lucaogou Formation in South Junggar Basin

为了进一步促进芦草沟组非常规油气勘探,在详细的野外地质调查基础上,结合前人研究成果及已有页岩气调查井钻探成果对芦草沟组岩性岩相组合特征、沉积演化进行了深入研究,结果表明:芦草沟组岩性岩相组合特征所呈现出的三段性特征明显,因此,将芦草沟组分为上、中、下3个岩性组合段。芦草沟组包含了扇三角洲及湖相沉积体系。上段为前扇三角洲至半深湖-深湖亚相沉积,以灰黑色炭质泥页岩夹碳酸盐岩夹层为显著特征,是最优质的区域性重点烃源岩,具较好页岩气勘探潜力。中段为扇三角洲前缘-前扇三角洲沉积,以灰黑色炭质泥岩与灰色中厚层状粉砂岩互层为显著特征,可构成具良好勘探潜力的致密储层;下段为扇三角洲平原-前扇三角洲沉积,岩性组合横向变化较大,由砂砾岩、粗细砂岩过渡为粉砂岩及灰黑色炭质粉砂质泥岩,既是常规油气目标层,又具非常规勘探潜力。芦草沟组自下而上整体呈现为一个相对湖平面上升的湖扩过程。

In order to promote the exploration of the unconventional oil gas in Lucaogou Formation,the lithologic and lithofacies assemblage characteristics and the sedimentary evolution of Lucaogou Formation were studied based on the detailed geological survey,the previous research results and the shale gas well drilling results. It is shown that： the lithologic and lithofacies assemblage presents obvious three-segment feature,and therefore Lucaogou Formation can be divided into upper member,middle member and lower member. Lucaogou Formation includes fan delta and lacustrine depositional systems. There is pro-fan delta to semi-deep-deep lake sedimentary facies in upper member,the interlayer of carbonate rock in dark grey carbonaceous mudstone is the obvious feature of upper member,it is the best regional hydrocarbon source rock,and has good exploration potential to shale gas; there is fan delta front-pro-fan delta sedimentary facies in middle member,the interbed of dark grey carbonaceous mudstone with grey medium-thick layered siltstone is the obvious feature of middle member,which forms tight reservoir with good exploration potential; there is fan delta plain-pro-fan delta sedimentary facies in lower member,the lateral change of lithology combination of lower member is great,the lithology transits from sand conglomerate,coarse,fine sandstone to siltstone and dark grey carbonaceous silty mudstone,it is both conventional oil and gas target layer and has unconventional exploration potential. Lucaogou Formation presents a lake expansion process of lake level relatively rising from lower to upper.