酒泉盆地长沙岭构造带下沟组一段油藏圈闭特征及形成机理

Characteristics and Formation Mechanism of Traps in K_(1)g_(1) Reservoir in Changshaling Structural Zone,Jiuquan Basin

通过岩心观察、铸体薄片鉴定、扫描电镜成像等手段,在剖析砂岩特征、成岩作用、孔隙类型、溶蚀流体来源等基础上,开展圈闭形成机理研究。结果表明,酒泉盆地长沙岭构造带白垩系下沟组一段砂岩油藏圈闭为成岩圈闭,储集空间主要为次生孔隙,遮挡层为成岩早期方解石胶结致密砂岩;携带蒙皂石微粒的大气淡水通过断层下渗,溶蚀致密砂岩方解石胶结物和长石颗粒,产生次生粒间孔隙和粒内孔隙,形成富黏土矿物储集层,远离断层而未接触到大气淡水的致密砂岩则成为遮挡层;圈闭呈长条状沿断层走向展布,具“大砂体、小圈闭”的特征;研究区下沟组一段砂岩油藏应优先勘探断层控制的成岩圈闭,且井位应部署在靠近断层的区域。

With the meanings such as core observation,casting thin section identification and scanning electron microscope imaging,and based on the analysis of sandstone in light of petrological characteristics,diagenesis,pore types and dissolution fluid sources,the trap formation mechanism was investigated.The results show that the traps in the sandstone reservoir of the first member of the Cretaceous Xiagou formation(K_(1)g_(1))in the Changshaling structural zone,Jiuquan basin,are diagenetic traps,the reservoir space is dominated by secondary pores,and the barrier is tight sandstone cemented by calcite in the early diagenetic stage.Atmospheric fresh water carrying smectite particles infiltrates through faults and dissolves the calcite cements and feldspar particles in tight sandstone,creating secondary intergranular pores and intragranular pores and clay-rich reservoir forms.The tight sandstone which is far from faults and has non-contact with atmospheric fresh water becomes the barrier.The traps are elongated and distributed along the fault trend,with the characteristics of“large sand bodies and small traps”.For the K_(1)g_(1) sandstone reservoir,the diagenetic traps controlled by faults should be preferentially explored and wells should be deployed in the areas close to faults.