塔里木盆地中下寒武统膏质白云岩盖层突破压力预测方法

Prediction method for breakthrough pressure capability of gypsum dolomite caprock of Middle and Lower Cambrian in Tarim Basin

针对塔里木盆地中下寒武统白云岩盖层层段不易精确厘定和物性变化复杂的问题,在运用岩性统计分析和实验测试手段的基础上,以优势盖层岩性膏质白云岩为主要研究对象,确定其具有不同物性特征的分散状、斑块状、裂缝分散状、裂缝斑块状4种微观结构,进而得到颗粒结构、石膏-黏土含量和裂缝发育程度是影响白云岩突破压力的3个主要因素。据此选取能够响应膏质白云岩岩性和物性特征的测井曲线,运用逐步线性回归分析,明确膏质白云岩突破压力与自然伽马和补偿中子测井数据相关性最强,进而构建其突破压力的预测公式。应用该方法可以准确地预测塔里木盆地中下寒武统膏质白云岩的突破压力,并通过单井分析和连井剖面初步确定巴楚-塔中隆起地区中下寒武统盖层发育特征为“横向上彼此相连,纵向上互相叠置”,对其下部储层内的油气封闭起着积极作用。研究结果与目前油气发现部位具有良好的一致性,可以为塔里木盆地中下寒武统天然气保存条件分析及明确下一步勘探层位提供指导。

Aiming at the challenge of determining caprock interval accurately and the complex property variation of Middle and Lower Cambrian dolomite in Tarim Basin,based on lithologic statistical analysis and experimental testing method,gypsum dolomite which is dominant lithology of caprock is taken as main research object,and is determined as 4 types with different microstructures including dispersed,patched,fractures dispersed and fractures patched structures,thus getting 3 main factors of grain structure,gypsum-clay content and fractures development af-fecting the brdakthrough pressure of gypsum dolomite.Accordingly,by selecting logging curves which can respond lithology and property of gypsum dolomite,it is determined that breakthrough pressure of gypsum dolomite has the strongest correlation with natural gamma ray and compensated neutron logging data by stepwise regression analysis,thus prediction formula for breakthrough pressure of gypsum dolomite is established.This method can be used to ac-curately analyze breakthrough pressure of Middle and Lower Cambrian gypsum dolomite in Tarim Basin,and single well analysis and well tie section preliminarily determine that the development characteristics of Middle and Lower Cambrian caprock in Bachu-Tazhong Uplift area are“horizontally connected to each other,and vertically stacked with each other”,which plays positive role in oil and gas sealing in the lower reservoir.The research results have good consistehcy with current oil and gas discovery and provide guidance for analysis of natural gas preservation conditions and determination of next exploration interval of Middle and Lower Cambrian in Tarim Basin.