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鄂尔多斯盆地上三叠统延长组张家滩页岩为一套湖相富有机质页岩,已在其中发现了工业性页岩气。张家滩页岩的有机质成熟度相对较低(Ro为0.7%~1.3%),页岩中滞留有大量液态烃,其对页岩气的赋存状态和原地气量的估算具有重要影响。利用荧光显微镜、扫描电镜和能谱分析技术,结合索式抽提、热解和甲烷等温吸附测试等手段分析了张家滩页岩中液态烃的赋存状态及含量,研究了液态烃对页岩气赋存状态、含气量的影响。结果表明,张家滩页岩中液态烃含量高,氯仿沥青“A”含量介于0.2%~1.2%,平均0.72%;热解S1含量主要变化在1.00~7.00 mg/g,平均3.87 mg/g。显微观察与测试结果表明,液态烃主要以游离态赋存于页岩的孔隙、裂缝中,或吸附于有机质及黏土矿物表面。进一步研究发现,液态烃的存在会导致页岩的甲烷吸附能力明显降低,降低程度达35%~57%,平均约45%。在地层温度、压力条件下,张家滩页岩的液态烃中会溶解大量的天然气,溶解气量变化在0.21~1.21 mL/g,平均0.65 mL/g,约占总含气量的20%。如果考虑损失的轻烃部分,溶解气含气量还会更高,平均约0.91 mL/g,约占总含气量的28%。此外,张家滩页岩中的液态烃还影响到了各种赋存状态页岩气的含气量。在评价类似延长组张家滩页岩这类较低成熟度的页岩气资源量时,除了需要对液态烃含量进行轻烃校正和重烃补偿外,还需要考虑液态烃中的溶解气含量、液态烃所占据的孔隙空间大小、液态烃对吸附气量及游离气量的影响,这样获得的页岩气资源评价结果才更为客观、可靠。
The Upper Triassic Yanchang Formation Zhangjiatan Shale in the Ordos Basin is a lacustrine organic-rich shale where industrial shale gas has been discovered. The maturity of Zhangjiathan shale is relatively low (Ro is 0.7% -1.3%). Large amounts of liquid hydrocarbons remain in the shale, which have an important influence on the occurrence status of shale gas and the estimation of in situ gas. The occurrence and content of liquid hydrocarbons in Zhangjiadan shale were analyzed by fluorescence microscopy, scanning electron microscopy and energy dispersive spectroscopy combined with Soxhlet extraction, pyrolysis and methane isothermal adsorption test. Rock status, gas content. The results show that the content of liquid hydrocarbon in Zhangjiatan shale is high, the content of chloroform bitumen “A ” is 0.2% -1.2% with an average of 0.72%, and the content of pyrolysis S1 is 1.00-7.00 mg / g with an average of 3.87 mg / g. Microscopic observation and test results show that the liquid hydrocarbons mainly occur in the pores and cracks in the shale, or adsorbed on the surface of organic matter and clay minerals. Further study found that the presence of liquid hydrocarbons will lead to shale methane adsorption capacity decreased significantly, the degree of reduction of 35% to 57%, an average of about 45%. Under the conditions of formation temperature and pressure, a large amount of natural gas is dissolved in the liquid hydrocarbons of Zhangjiatan shale. The dissolved gas volume varies from 0.21 to 1.21 mL / g with an average of 0.65 mL / g, accounting for about 20% of the total gas content. The dissolved gas content will also be higher if the light hydrocarbon fraction lost is considered, averaging about 0.91 mL / g, accounting for about 28% of the total gas content. In addition, the liquid hydrocarbons in Zhangjiatan shale also affect the gas content of various occurrence shale gas. In evaluating the amount of shale gas of lower maturity such as Zhangjiatan shale in the Yanchang Formation, in addition to light hydrocarbon correction and heavy hydrocarbon compensation for liquid hydrocarbon content, dissolved gas content in liquid hydrocarbons needs to be considered , The size of the pore space occupied by liquid hydrocarbons, and the effect of liquid hydrocarbons on the amount of adsorbed gas and the amount of free gas. The shale gas resource evaluation results thus obtained are more objective and reliable.