Integrated Multidisciplinary Pore Pressure Prediction Leads to Accurate Casing Design: A Case Study

Abstract

Abstract The well design of LT- 4 and LT- 5 wells in the Niger delta is evidence that application of current 3-D seismic technology, accurate modelling and RFT data with inclusion of offset well information lead to improved pore pressure and fracture gradient predictions. The LT field had no cores, no PVT samples, nor production history. Seismic modelling by geologists and geophysicists observed a pressure trend above hydrostatic from 10, 600ftTVDSS which corresponds to the 17.4MFS. Pressure data (RFT) from offset wells and other drilling performance data (FIT, mud weight, kick pressure) from wells drilled in the wider area were used to constrain the pressure prediction. Two distinct pressure ramps were observed from the plot, coinciding with the base of the 17.4MFS and 19.4MFS respectively (fig. 2.1) which illustrates the geological control on overpressures. The kill mud weight data indicated from offset wells in which kicks occurred provided information on overpressures in the 8 ½” hole sections. The pore pressure evaluation over pressures in the deepest zones would not have been predicted based only on either the other pressure data (RFT) available or on the seismic velocity data. Sensitivity analysis of the pore pressure prediction with inclusion of the well kick data for the well planning and design provided a more robust basis for design resulting in selection of an appropriate intermediate casing weight and grade. This paper presents a case study of the LT- 4 and LT-5 wells showing how an effective casing design which depends on an accurate pore pressure prediction can be achieved through integration of seismic calibration and offset well information.