莺琼盆地高温高压钻井工程风险定量评价方法

Drilling engineering risk quantitative assessment for HTHP exploration wells in Yingqiong basin

南海莺琼盆地具有温度高、压力高、压力台阶多、安全密度窗口窄等地质特性,钻井施工过程中工程风险事件发生概率较高、处理难度大,严重制约了高效、安全钻井。传统钻井工程风险评价结果多为定性或半定量,无法满足南海莺琼盆地高风险钻井施工作业的安全要求。本文建立了一套钻井工程风险定量评价方法,首先对地层压力和钻井液当量循环密度(ECD)的不确定性进行了分析,得到了地层压力和ECD的概率分布;在此基础上,基于广义应力与强度干涉可靠度理论推导了风险评价模型。莺琼盆地高温高压探井实例分析结果表明,本文提出的钻井工程风险评价模型计算得到的钻井风险概率结果与现场实际发生风险相吻合,可为该地区高温高压探井钻井安全作业提供指导。

Yingqiong basin in South China Sea shows the following geological characteristics, such as high temperature, high pressure, multiple pressure steps and narrow safety density window, which bring high occurrence probability of engineering risk events during drilling and difficulty in risk handling, seriously restricting the efficient and safe drilling. The results of conventional drilling risk assessment are mostly qualitative or semi-quantitative, which fail to satisfy the safety requirements of high risk drilling in Yingqiong basin, South China Sea. In this paper, the uncertainties in the formation pressure and the equivalent circulating density (ECD) of drilling fluid are analyzed firstly, and the probability distributions of formation pressure and ECD are obtained. On this basis, the generalized stress and strength interference reliability theory-based risk assessment model is derived. The analysis results of HTHP exploration wells in Yingqiong basin, South China Sea suggest that the drilling risk probability results calculated by this model are consistent with the actual risk occurrence in those wells, and this model can provide guidance for the safe operation of HTHP exploration wells in this area.