Integrity Analysis of Cement Sheath in Tight Gas Reservoir Formations in Changqing
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摘要: 长庆致密油气藏的压裂压力较高,对水泥环力学性能提出较高要求,通过建立的套管-水泥环-地层组合体模型和组合体密封性能评价方法(密封安全系数法),对长庆一种典型井身结构(φ152.4 mm井眼φ114.3 mm套管)进行水泥环完整性分析。结合现场数据分析认为:①随着水泥环弹性模量的降低,水泥环的受力明显降低,安全系数明显增大;②随着压裂压力的升高,安全系数降低;③随着水泥体积收缩率的增大,水泥环的安全系数显著降低。根据该井计算结果,提出了水平段保障密封的水泥力学性能需求,该项研究成果可为长庆致密气藏或类似区块固井水泥环完整性提供理论支持。Abstract: The tight gas reservoirs in Changqing Oilfield have high fracturing pressures, imposing high requirements on the mechanical property of cement sheath. The integrity of cement sheath of a typical hole interval (φ152.4 mm hole size×φ114.3 mm casing size) of a well was analyzed using the established casing-cement sheath-formation combination model and the method for evaluating the sealing performance of a combination (sealing safety factor method). The analyses, taking account of the data gathered from field operations, showed that:① when the elastic modulus of a cement sheath was decreased, forces acting on the cement sheath was reduced, resulting in increased safety factor; ②when fracturing pressure was increased, the safety factor was reduced; ③ when the rate of volumetric contraction of cement was increased, the safety factor of the cement sheath was reduced remarkably. Based on the results calculated using the data gathered from the well, the mechanical property of cement sheath having good sealing performance in horizontal section of a well was presented. This study will provide theoretical support for analyzing the integrity of cement sheath in the tight gas reservoirs in Changqing Oilfield or other similar reservoirs.
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