川西坳陷中部现今地应力纵向分布规律研究及应用

STUDY AND APPLICATION OF LONGITUDINAL DISTRIBUTION LAW OF IN-SITU STRESS IN THE MIDDLE OF WEST SICHUAN DEPRESSION

川西新场和洛带气藏储产层是典型的低渗透致密砂岩,气藏开发绝大多数要经过压裂改造才具有工业产能,而认识该区应力场纵向分布规律对正确选择压裂层位有着重要的指导意义。文章利用测井资料和水力压裂资料计算现今地应力值,通过相关分析建立校正关系式,对测井计算值进行校正。计算结果的统计分析表明,水平主应力随地层深度加深而增加的趋势减小,垂直应力增加趋势加大,上层蓬莱镇组偏应力值大而下层沙溪庙组值小,导致破裂压力由上至下逐渐增大而压裂施工变难。通过计算临界井深得到本区应力关系在约250m和1100m发生转变,这种应力状态的改变可以导致压裂缝延伸方向转变,从而影响压后增产效果。综合分析单井应力分层剖面特点和应力纵向分布规律以及已进行压裂施工井的压后效果,提出了适合本区的压裂选层标准,并为相邻区块的勘探开发提供了参考依据。

The gas reservoirs of Xinchang and Luodai structures in west Sichuan depression belong to typical compacted sandstone with low permeability. Only by using hydraulic fracture can most of them be put into commercial production. And so, it is of important realistic significance to study longitudinal distribution law of stress for correctly selecting the layers to hydraulic fracture. In this paper, the stress values are calculated by using logging and hydraulic fracture data; the formulas for rectifying result are set up by correlation analysis and then put into rectifying data from logging calculation. Statistical and analytical result indicate that increasing tendency of horizontal principle in-situ stress will decrease with well-depth increasing but increasing tendency of vertical stress will increase. Discrepancy between two horizontal principle stress is larger at Penglaizhen Formation than that at Shaximiao Formation, which leads fracturing pressure increasing from upper to lower to make hydraulic fracture operation become more difficulty. By calculating, it can be known that stress characteristic will change at 250 m and 1100 m well-depth, which will change the extended direction of hydraulic fracture to influence the increase production effects after fracturing. Combined stress distribution characteristic in stress section maps of different layers with production effects of hydraulic fracture, the standard of selecting layer to do hydraulic fracture is finally established.