地层孔隙压力的精确预测及其应用

Accurate prediction of formation pore pressure and its application

在钻井设计中 ,国内外多数教科书遵循的地层孔隙压力预测准则是依据某一裸眼段的最高孔隙压力设计该井段的钻井液密度。作者提出了地层孔隙压力精确预测的新准则 ,并成功运用于大港油田板深 7井。关于新准则及其相关技术 ,作者已发表过论文 ,出版过专著 ,并申请了国家专利。本文主要是关于这项技术的理论上的探讨。通过严格的数学证明 ,指出从出现井喷迹象到发生井喷 ,其所需时间比人们原来想象的要长 ;并认为 ,随着目前钻井中各种先进的井控及录井监控装置的引入 ,可以运用新的数学方法 ,忽略所占比例不大的少数高孔隙压力井段 ,来进行地层孔隙压力预测。这样预测的结果 ,可大大降低钻井设计中钻井液的密度 ,不仅可以加快钻井速度 ,降低钻井成本 ,而且可以有效地解决钻井过程中的油气层保护问题。文中导出了一套新的钻井过程井涌微分方程 ,给出了相关的函数曲线图 ,并且利用概率论的方法 ,给出了在现场应用的有关数据 ,为在更大范围内应用这一方法提供了方便条件。

A new principle to predict formation pore pressure for drilling design has been proposed and successfully applied to well BS 7 in Dagang oilfield. This principle is different from the traditional one described on most textbooks in China and abroad that the mud density is designed according to the highest pore pressure of a section to be drilled. For the new principle, the authors have published technical papers and a special book, and have applied a patent in China. A theoretical discussion of the principle is presented in the paper. The strict mathematical justification has indicated that the time lag from having blowout signs to making a real blowout during drilling is longer than that conceived previously. The designers could ignore a few thinner formations with high pressure and use some new mathematical methods to predict formation pressure as various advanced control equipments are introduced for drilling and logging. Such prediction of formation pressure can result in a significant drop of mud density in drilling design, thus accelerating drilling process, reducing cost and effectively improving reservoir protection. This technique can be applied easily elsewhere in terms of a set of new differential equations of well kick, their plotted curves and the field data from probability theory, which are given in the paper.