Method of predicting soil mechanical parameters in shallow formation while jetting process in deep-water drilling

The mechanical properties of shallow soils in deep water play an important role in drilling design and construction as well as later oil and gas development. Since it is difficult to collect soil samples from layers deeper than 10 m below the sea floor, the acquisition of shallow soil mechanics, based on the variation of drilling parameters in the deep-water drilling process, is not only economical but also reliable. In this article, we analyze the variation of subsea soil properties based on the variation of deep-water jet-drilling construction parameters, calculate the lateral friction resistance of conductor by use of weight-on-bit (WOB) and displacement parameters in the jetting process, and determine the drilled formation’s shear strength and internal friction angle in consideration of restored friction resistance. To verify the accuracy of the prediction-while-drilling model on seabed shallow soil mechanics, indoor unit and field simulation experiments were separately conducted. Moreover, the calculations from field application examples indicate that the prediction-while-drilling of deep-water seabed shallow soil mechanics achieves high conformity with the local practice results, which also indicates that this method could effectively guide field construction operations.深水浅层土体的力学特性，在钻井设计与施工以及后续油气开发中均发挥着重要作用。由于难以从海床以下10米深度的土层中采集土体样本，基于深水钻井过程中钻井参数变化来获取浅层土体力学特性的方法，不仅经济可行，且结果可靠。本文基于深水射流钻井（jet-drilling）施工参数的变化规律，分析海床土体特性的演化特征；利用射流过程中的钻压（weight-on-bit, WOB）与位移参数，计算导管（conductor）的侧向摩阻力，并结合恢复摩阻力确定钻进地层的抗剪强度与内摩擦角。为验证海床浅层土体力学随钻预测（prediction-while-drilling）模型的准确性，本文分别开展了室内单元试验与现场模拟试验。此外，现场应用案例的计算结果表明，深水海床浅层土体力学随钻预测结果与现场实测结果具有较高的吻合度，同时证明该方法可有效指导现场施工作业。