二氧化碳在砂岩透镜体中充注封存的盖层岩石抗断裂性能分析

把CO2这一主要的温室气体注入到地下深处具有适当封闭条件的地层中进行封存和隔离,已被公认为是有效减少CO2排放量的一种比较安全的技术途径。砂岩透镜体油气藏具有良好的圈闭构造和储层物性,油气濒临枯竭的砂岩透镜体是较理想的CO2地质封存箱。基于币形裂纹模型和水力致裂原理,将纵向厚度和横向展布长度均远小于盖层岩石尺度的水平产状砂岩透镜体简化为盖层岩石中的I型币形裂纹,从岩石断裂力学角度分析封存箱盖层岩石的抗断裂性能。采用叠加原理给出了盖层岩石币形裂纹尖端(砂岩透镜体尖灭部位)应力强度因子的计算公式,在此基础上提出了断裂力学判别准则(K=KIC)和临界有效压应力判别准则(P=PC),从岩石断裂力学角度为砂岩透镜体封存箱盖层岩石抗断裂性能分析和评价提供了一种新的研究思路。

FRACTURE RESISTANCE ANALYSIS ON THE CAP ROCK OF THE SAND LENS RESERVOIR DUE TO CARBON DIOXIDE INJECTION AND STOR AGE

Injecting the CO2 into deep underground formations with the appropriate closure for isolated storage has been recognized as a possible effective technical approach in reducing CO2 emissions. The sand lens reservoir trap has a good structure and reservoir properties for the storage. The sand lens reservoirs with depletion of oil and gas are better CO2 geological storage boxes. Based on the penny shaped crack model and the hydraulic fracturing principle，the sand lens reservoir of horizontal occurrence is simplified as a type-I penny shaped crack of the cap rock. It is due to the fact that the thickness and horizontal distribution length of the reservoir are much smaller than the global cap rock scale. The cap rock fracture resistance of the storage box is analyzed from the view of rock fracture mechanics. The stress intensity factor of the penny shaped crack tip (corresponding to the tip of sand lens reservoir) for the cap rock is calculated by the superposition principle. And then the fracture mechanics criteria (K=KIC) and the critical effective compressive stress criteria (P=PC) are concluded as the basic principle to evaluate the fracture resistance of the cap rock of the sand lens reservoir. The findings in the paper can provide a new way for the evaluation of cap rock fracture resistance capability of sand lens reservoir.