东海西湖凹陷致密砂岩气压裂改造层优选因素与方法

Optimization Factors and Method of Fracturing Tight Sandstone Gas Layer in Xihu Sag of East China Sea

致密砂岩气探明储量的猛增正逐步成为西湖凹陷乃至东海盆地勘探开发的主体。致密砂岩气储层具有复杂的岩性、孔隙结构、非均质性、泥浆深侵以及气水分布复杂多变的特点,致使其评价的难度大增。致密砂岩气储层常规测试一般无法获得自然产能,只能进行压裂改造,而海上压裂测试效果影响因素非常多,给压裂层的选取带来很大困难。此文在岩心分析的基础上,综合各类测井、录井和钻杆地层测试(DST)资料,总结出影响海上压裂层改造效果的五大类核心因素,构建致密储层可改造性判别指数,提出海上致密砂岩层压裂层优选方法,该技术在东海西湖凹陷得到广泛应用,降低了压裂风险,指导了海上压裂改造选井、选层工作。

With the sharp increase in the proven reserve of tight sandstone gas, the tight sandstone gas has become the major target in exploration and development in Xihu Sag, and even East China Sea Basin. The tight sandstone gas reservoirs are characterized by complex lithology, complex pore structure and reservoir heterogeneity, irregular mud invasion and the unclear distribution of water and gas, which made it difficult to evaluate tight sandstone reservoir correctly and quantitively. The fracturing technique is needed for testing the production ability, because the production ability is limited with conventional formation test. However many factors would affect the test resulting during the fracturing process, these uncertain factors bring difficulties in selecting the target layers. In this paper, on the basis of core analysis, combined with various logging data, DST testing data, five major factors that influence the offshore fracturing result have been proposed. In addition, the diagnostic index for fracturing the tight reservoir have been made, and a method to optimize the fracturing layer of the tight sandstone layer in the sea has been put forward. This optimization method has been widely used in the Xihu Sag and the goals to reduce the risks of fracturing has been achieved.