柴达木盆地鱼卡地区中侏罗统页岩气成藏条件

通过地质钻井、野外现场解吸、样品实验分析等,对柴达木盆地鱼卡地区中侏罗统页岩气成藏条件进行了研究。结果表明,鱼卡地区中侏罗统泥页岩主要发育于大煤沟组第五段和石门沟组,是一套以辫状河三角洲间湾、辫状河三角洲平原和湖泊相为主的优质烃源岩,累计厚度38~300m,TOC为0.12%~13.23%,Ro为0.29%~0.89%。石英含量为18.0%~63.3%,粘土矿物含量为10.1%~55.6%,孔隙度为1.53%~14.92%,渗透率为0.007×10-3~6.24×10-3μm2。微孔隙发育,主要有粒间孔、溶蚀孔、粒内孔,孔隙直径多为0.3~3μm。泥页岩含气量为0.42~0.83m3/t,解吸气CH4含量8.6%~64.9%,δ13C1为-80.59‰~-63.32‰。与国内外含气泥页岩对比发现,研究区中侏罗统泥页岩具有厚度大、TOC高、石英含量居中的特点,但分布面积小、成熟度低、含气量小,且自中、新生代以来经历了多期次构造运动,对页岩气的保存影响较大。预测鱼卡地区中侏罗统页岩气勘探前景,还需重点加强构造作用对页岩气保存的影响及页岩气成因类型、资源量评估等方面的研究。

An analysis of reservoir-forming conditions of shale gas in Middle Jurassic strata of Yuqia area,Qaidam Basin

According to geological drilling, field desorption, and experimental sample analysis, the authors studied the reservoir-form-ing conditions of shale gas in Middle Jurassic strata of Yuqia area. The results show that the shale in Middle Jurassic strata of Yuqia area is a set of high-quality hydrocarbon source rocks comprising mainly braided river delta, braided river plain and lake facies. It is mainly developed in Dameigou(J2d5) and Shimengou formations. The cumulative thickness is 38~300m, TOC is 0.12%~13.23%, Ro is 0.29%~0.89%, quartz content is 18.0%~63.3%, clay mineral content is 10.1%~55.6%, porosity is 1.53%~14.92% and permeability is 0.007×10-3~6.24×10-3μm2. Scanning electron microscope analysis has revealed micro pores consisting mainly of intergranular pore, dissolved pore, grain pore, with pore diameter being more than 0.3~3μm. Shale gas content is 0.42~0.83m3/t, desorption gas CH4 content is 8.6%~64.9%, and δ13C1 is -80.59‰~-63.32‰. A comparison with domestic and foreign gas shales shows that the Middle Jurassic shale in the study area is characterized by large thickness, high TOC and medium quartz content; nevertheless, there also exists some disadvantages in the study area such as small distribution area, low maturity and low gas content in addition, the study area has experienced repeated tectonic movement since Cenozoic, which exerted a considerable impact on shale gas. For the exploration prospect of Middle Jurassic shale gas in Yuqia area, much attention should be paid to the study of tectonic preservation of shale gas and shale gas genetic types as well as resource assessment.