柴达木盆地英西地区下干柴沟组上段超压孔缝型储层特征及形成机理

柴达木盆地英西地区深层的油气勘探在下干柴沟组上段取得重大突破，获得了一批中-高产井，发现了特殊的咸化湖盆超压孔缝型储层。通过岩心和薄片观察，结合扫描电镜和孔、渗资料的统计与分析，系统总结了超压孔缝型储层的特征。超压孔缝型储层的主要储集空间为基质微孔和残余孔洞，而不同级别的网状裂缝作为输导通道，将普遍发育的基质微孔连通起来，形成孔-洞-缝三位一体的储集-输导体系。裂缝和残余孔洞是初期高产的关键因素，而普遍发育的基质微孔是稳产的基础条件。英西地区下干柴沟组上段超压孔缝型储层的发育受沉积作用、成岩演化、构造运动和流体活动的综合控制。沉积-准同生期的成岩环境控制了基质孔隙的发育，其中，准同生白云石化作用形成的大量晶间孔不仅是重要的储集空间，还为后期溶蚀改造提供了基础条件；构造-压力耦合控制了裂缝体系发育，目的层段受快速沉降-沉积、长期构造活动和良好的盐层封盖等因素的综合影响形成异常高压，并在构造应力诱导下形成网状裂缝体系；流体-岩石相互作用控制了溶蚀作用的发生，受其影响，英西地区下干柴沟组上段作为柴达木盆地西部最好的烃源岩之一，在达到生、排烃高峰后，排出的酸性流体可改善储层的物性，增加基质微孔的有效性和连通性。

Characteristics and formation mechanism of overpressure pore-fracture reservoirs for Upper Member of Xiaganchaigou Formation in the west of Yingxiong ridge,Qaidam Basin

In recent years, major breakthroughs have been made in the deep oil and gas exploration of Upper Member of Xiaganchaigou Formation, the west of Yingxiong ridge, Qaidam Basin. Multiple medium-high yield wells have been discovered in the overpressure pore-fracture reservoir of the special saline lake basin. Based on the observation of cores and thin section, in combination with the statistics and analyses of scanning electron microscope and the porosity-permeability data, the characteristics of overpressure pore-fracture reservoirs are systematically summarized. The main reserving spaces of these high-quality reservoirs are matrix micropores and residual holes, while the net-like fractures at different levels are transport channels to connect the widely developed matrix micropores, thus forming a triune reservoir-transport system of pores, holes and fractures. Among them, fractures and residual holes are the key factors controlling high yield in the initial stage, while the widely-developed matrix micropores are the basic conditions for stable production. The development of overpressure pore-fracture reservoir for Upper Member of Xiaganchaigou Formation in the west of Yingxiong ridge is jointly controlled by sedimentation, diagenetic evolution, tectonic movement and fluid activity. The sedimentary-penecontemporaneous diagenetic environments control the development of matrix pores. The large number of intercrystalline pores formed by penecontemporaneous dolomitization is not only an important reserving space, but also provides basic conditions for the later dissolution. The tectionic stress controls the development of fracture systems. Under the comprehensive influences of rapid subsidence-sedimentation, long-term tectonic activities and good sealing of salt layers, abnormal overpressure occurs in the target layer of the study area; induced by tectonic stress, net-like fractures are thus formed. The fluid-rock interaction controls the occurrence of dissolution. Under this influence, the Upper Member of Xiaganchaigou Formation in the west of Yingxiong ridge is one of the best source rocks in the western Qaidam Basin. After reaching the peak of hydrocarbon generation, the discharged acidic-fluid improves the reservoir properties and increases the effectiveness and connectivity of matrix micropores.