基于安全风险评价的深探井井身结构设计方法研究

A METHOD TO DESIGN CASING PROGRAM FOR DEEP EXPLORATION WELLS BASED ON SAFETY RISK ASSESSMENT

由于对地层压力的预测准确性较低,采用传统的井身结构设计方法不能设计出合理的深探井井身结构,致使井涌、井塌、井漏及压差卡套管等井下复杂情况频频发生。首先采用三角分布概率密度法分析了深探井所钻区块地层压力的不确定性,介绍了建立含可信度地层三压力剖面的方法;然后结合工程数据确定了预防井下复杂情况的钻井液密度,建立了含安全度的安全钻井液密度窗口;最后提出了一套基于安全风险评价的自上而下、由外向内的井身结构设计方法,并进行了实例设计与分析。实例设计与分析结果表明,采用该方法设计出的深探井井身结构能有效降低钻进过程中发生井下复杂情况的可能性,比常规方法更具合理性。

Due to poor accuracy to predict formation pressure, conventional methods can not design a reasonable casing program for deep exploration well, resulting in frequent downhole complications such as well kick, hole collapse, lost circulation, and casing sticking under pressure difference. At first, the uncertainty of formation pressure from some drilled deep exploration wells is analyzed using triangular distribution probability density method; the method for establishing triformation-pressures profile with reliablity is also presented. Then, the drilling-fluid density,which may prevent downhole complications, is determined by combining with engineering data,and safe drilling-fluid density window with safety degree is established. Finally, based on safety risk assessment, an overall method to design casing program is proposed. Results show that for deep exploration wells, this method can effectively reduce the possibility of downhole complications, and it is more reasonable than other conventional methods.