渭河盆地固市凹陷生物气成藏要素评价

Evaluation of biogas reservoir forming factors in Gushi Sag,Weihe Basin

为明确渭河盆地生物气资源潜力,落实生物气勘探有利区,以渭河盆地固市凹陷张家坡组已发现生物气藏为研究对象,在区域地质背景分析基础上,通过烃源岩地质及地球化学评价、岩心薄片鉴定、铸体薄片鉴定及X-衍射分析等技术,结合野外地质观察及钻、测、录井资料,厘清了有效生物气源岩评价标准及优质储层类型,以生物气成藏动力学为指导,对张家坡组生物气成藏要素进行了分析。研究表明,固市凹陷沉积中心张家坡组未成熟-低成熟的灰色-灰黑色泥岩是生物气的主力烃源岩,张家坡组中孔中渗粉-细砂岩是较有利的生物气储层,储-盖层渗透率差异控制了盖层的封堵能力,近源分布的同沉积构造背景上的构造-岩性圈闭发育区是生物气勘探的有利目标;张家坡组生物气具有自生自储源内成藏的特征,利用“生气率法”,计算固市凹陷生物气资源量约为310×10^(8) m^(3)。

In order to clarify the potential of biogas resources in Weihe Basin and implement the favorable areas for biogas exploration,taking the discovered biogas reservoir in Zhangjiapo Formation of Gushi Sag in Weihe Basin as the research object,on the foundation of regional geological research,by the techniques of geological and geochemical evaluation of source rock,identification of core thin section,identification of cast thin section and X-diffraction analysis,combined with field geological observation,drilling,survey based on the logging data,the evaluation criteria of effective biogenic gas source rocks and high-quality reservoir types are clarified,and the biogas reservoir forming factors of Zhangjiapo Formation are analyzed under the guidance of biogas reservoir forming dynamics.The research shows that the immature-low mature gray-gray black mudstone of Zhangjiapo Formation in the sedimentary center of Gushi Sag is the main source rock of biogas,and the medium porosity and medium permeability siltstone and fine sandstone of Zhangjiapo Formation are more favorable biogas reservoir.The permeability difference between reservoir and caprock controls the sealing ability of caprock,the lithologic trap development area on the synsedimentary structural background of near source distribution is a favorable target for biogas exploration;On this basis,the lithologic structural biogas reservoir forming model of self generation and self storage is established,and the control of source rock,trap and preservation conditions on biogas reservoir formation is clarified.Using the“gas generation rate method”,the biogas resources in Gushi Sag are calculated to be about 310×10^(8) m^(3).