新的地层压力系数预测方法及在板深7井的应用

以往在钻井设计中，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。提出了新的地层孔隙压力系数预测方法：考虑到目前钻井设备中的井控装置，各种先进的录井监测装置，以及各种业已成熟的录井计算机预测算法等，可以忽略占比例较小的高孔隙压力井段，对地层孔隙压力梯度进行预测。使用该方法得到的从出现井喷迹象到井喷发生的时间化使用以往预测方法得到的时间长，归纳了一套描述井涌过程的数学方法（线性函数，非线性函数，特殊的非线性函数），回顾了人们以前对井涌过程的解释，并提出了笔者的新见解。非线性函数模型认为井涌过程中，地层向井筒内注气的速率不是随时间线性增加的，气体体积增加的速率与当时气体的体积成正比；特殊的非线性函数模型则认为井眼内注入气体的速度并不是与气体量成正比，而是与此时气体量与液体量的乘积成正比，该模型能够解释井喷现象，并提出了预测地层压力新方法的有关数学方法，分析了新方法与以往方法的关系，并根据具体情况对新的观测模型进行了修正，这一新方法在1998年大港油田板深7井的钻井设计及钻井中试用，使钻井液密度大幅度降低，不仅加快了钻井速度，还很好地保护了油气层，使板深7井成为大港油田历史上第一口“千吨井”，为国家发现了一个大气田。

A new predicting method of formation pore pressure indexes and its application in well BS-7

In conventional drilling design, the drilling fluid density is determined according to the highest formation pore pressure of a certain open hole section. A new method of predicting the formation pore pressure indexes is presented. As the time from the show of blowout signal to the well actually blows out is longer than expected traditionally, and with the help of efficient well control equipment and advanced logging instruments, the section with high pressure that account for only a small percentage can be eliminated when predicting the formation pore pressure. By using the new method, the drilling fluiddensity could be dropped remarkably, ROP is increased and formation damage is minimized during drilling. Mathematics methods describing the well kick process (linear function, non-linear function and special non-linear function) are presented and the conventional interpretations to well kick are reviewed. For the non-linear function model, the gas invasion rate from formation to the hole does not increase linearly during well kick; the gas volume increasing rate is proportional to the existing volume. While it is vice versa for the special non-linear function, it is proportional to the produce of gas and fluid volume. This model can explain well blowing out. The mathematics models of the new predicting method are proposed, and the relationship between the new method and the conventional ones is investigated, and the new method is revised accordingly. This method is adopted in the drilling design and field drilling of well BS-7 in Dagang Oilfield in 1998, and remarkable economic benefits are obtained.