莺琼盆地高温超压地层钻前压力预测面临的问题与对策

南海莺琼盆地的中深层普遍具有高温超压特征,基于近几年的研究成果,将总结出的地层孔隙压力预测模型应用到目标井的钻前压力预测时准确率一直较高。但是,在2013年的探井钻探时又遇到了新的问题,即钻前预测压力和实钻计算压力都与实际测试压力存在较大误差,高温超压地层压力预测技术遇到了新的挑战。为此,依据DF1-A、DF13-B、LS13-C井3口井钻后的压力计算结果,分析了误差产生的原因。结果认为问题主要出在对储层连通性、流体性质、断层封堵性以及卸压通道等方面的认识不足。进而提出了该区地层孔隙压力预测的改进方法,即在以往压力预测模型的基础上,结合砂体展布和断层分析结果,考虑压力传递作用,并确定压力传递点来进行钻前压力预测。将此方法应用于LS13-D井,计算的地层压力系数为1.936,与实际测压点吻合程度非常高,证实了改进后的预测压力方法的有效性和准确性。

Pre-drilling pressure prediction problems and solutions in the HTHP strata of the Yinggehai-Qiongdongnan Basin

The middle and deep sequences in the Yinggehai-Qiongdongnan Basin are generally characterized by high temperature and high pressure (HTHP). Research on pressure prediction models in recent years revealed that the porosity pressure prediction model can make relatively accurate pre-drilling pressure prediction. However, a new problem occurred when this model was applied to the exploratory well drilled in 2013. Both the pre-drilling predicted pressure and post-drilling calculated pressure by using the drilling data were quite different with the actual measured pressures, indicating that pressure prediction of HTHP strata was faced with a new challenge. In view of this, the post-drilling calculated pressures of DF1-A, DF13-B and LS13-C wells were thoroughly analyzed. The results revealed that the errors were mainly caused by poor understandings of reservoir connectivity, fluid property, fault sealing capacity and pressure-relief channels. The pore pressure prediction model was improved accordingly, with additional factors integrated such as sandbody distribution, fault sealing capacity, pressure transmission. The modified model was applied to LS13-D well and the predicted pressure coefficient was 1.936, which is highly concordant with the measured pressure, verifying the effectiveness and accuracy of the modified pressure prediction method.