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中国陆相最大天然气田——克拉2气田经过10余年的高速开发后,目前面临气井快速见水和气水界面非均匀抬升等问题。为进一步明确复杂构造背景下的高压气田水侵机理,开展了气田内部基于断裂的地质力学活动性及其与气井见水之间的关联性研究。将气田四维地应力场建模和三维断裂力学分析相结合,建立了随气田开发的断裂力学活动性预测模型,研究了断裂活动性对气田水侵的影响。结果表明:(1)气井见水与井旁断裂力学特征变化有较好的关联性,随着气藏开采及现今地应力场的动态变化,断裂面受力状态也随之改变,从而使断裂带内部渗透性变强或变弱。(2)随气藏地层压力的下降,若井旁断层和裂缝活动性增加或保持较好,则气井见水较早,气水界面抬升较快。(3)由于气田内部应力场和断裂分布均较复杂,因此不同构造部位的断裂活动性差异较大,从而造成不同位置气水界面抬升不均匀且相差较大。研究进一步明确了克拉2气田的水侵机理,并利用断裂地质力学活动性指数将气藏划分为3个见水风险区,为气田开发方案优化提供依据。
After more than 10 years of high-speed development, the Kela-2 gas field, the largest continental natural gas field in the continental China, is facing problems such as rapid gas seepage and non-uniform gas-water interface uplift. In order to further clarify the mechanism of water intrusion in high-pressure gas fields under complicated structural background, the study on the relationship between fault-based geomechanical activities and water seepage in gas wells has been carried out. By combining the modeling of 4D ground stress field and 3-D fracture mechanics, the prediction model of fracture mechanics activity developed with the gas field was established and the influence of fault activity on water invasion of gas field was studied. The results show that: (1) There is a good correlation between gas seepage and mechanics characteristics of wellbore fracture. With the gas reservoir mining and the dynamic changes of the present geostress field, the stress state of the fracture surface also changes accordingly, With internal permeability becomes stronger or weaker. (2) With the decrease of gas reservoir pressure, gas wells see water earlier and gas-water interface lift faster if well faults and fracture activities increase or remain well. (3) Because of the complicated internal stress field and fracture distribution in the gas field, the fracture activity varies greatly between different tectonic parts, resulting in uneven elevation and large difference in gas-water interface at different positions. The study further clarified the mechanism of water intrusion in Kela-2 gas field, and divided the reservoir into three water-risk zones by using the fracture geomechanical activity index to provide the basis for gas field development plan optimization.