基于模糊数学的防气窜能力评价新方法及应用

摘要

Gas channeling in annular spaces is a difficult problem seriously harmful to cementing almost all gas wells.Accurate evaluation of cement slurry's anti-channeling performance is one of the key technologies for the prevention of gas channeling in annular spaces. There are several factors which affect gas channeling in annular spaces in a combined way, while the evaluation methods presently in use do not take them all in consideration and have limited accuracy, and hence they cannot give a full view of the problem they are trying to reveal. In this study, fuzzy mathematics has been used in establishing a model used in predicting comprehensively the anti-channeling performance of a cement slurry. This model takes into account the characteristics of gas channeling in annular spaces. Five commonly used evaluation methods, such as GFP method and SPN method etc., are integrated into an evaluation factor set,"good", "medium" and "poor" anti-channeling capacity are used as an evaluation set. Based on the characteristics of each factor, a corresponding membership function is determined. Use the principles of analytic hierarchy process, the weighted fuzzy set of each factor is calculated, and according to the "maximum subordination principle", the overall risk of sand production is determined. It has been proved that this evaluation method can be used to effectively predict gas channeling in well cementing. It provides a more comprehensive and integrated evaluation method for optimizing cement slurry formulation to prevent pressurized wellhead after well cementing, thereby to ensure the quality and safety of a cemented well.%环空气窜现象是几乎所有天然气井固井存在的难题,危害十分严重,准确评价水泥浆防气窜能力是有效预防环空气窜现象的关键技术手段之一.固井环空气窜受多种因素综合影响,现有评价预测方法考虑因素较单一,准确度有限,缺乏更为全面综合的预判结果.结合环空气窜特点,采用模糊数学理论建立了水泥浆防气窜能力综合判断模型,以潜气窜因子法、水泥浆性能系数法等5种常用方法为评价因素集,以防气窜能力"好"、"中等"和"差"3种情况为评价集,结合各因素特点确定对应的隶属函数,采用层次分析法原理计算各因素权重模糊集,按"最大隶属原则"判断水泥浆防气窜能力评价结果.应用表明,该评价方法可有效预测固井气窜问题,为针对性地优化水泥浆体系,避免固井后井口带压,保证油气井固井质量和安全提供了更为全面、综合的评价方法.