Integrated pre-drill and real-time geomechanical modelling brings significant benefits to deepwater wildcat exploration drilling campaign – a case study

Abstract

This case study demonstrates the significance of integrated pre-drill geomechanical modelling and real-time monitoring for drilling wildcat exploratory wells in the deepwater settings of an offshore field in South-East Asia. The key challenges in the area include deeper water depths (1.6 km), lack of relevant offset well information and a complex geological setting. In this project, the primary input data for the pre-drill geomechanical model were low resolution 2D seismic velocities derived from an un-calibrated velocity model and petrophysical data from an offset well located in shallow waters, 100 km away from the deepwater prospect. During pre-drill planning, a contingency casing plan was put in place to consider the uncertainties in the model and cover the worst-case scenario of high pore pressure (PP). To reduce the uncertainty during drilling, the well was monitored in real-time and the pre-drill predictions improved whenever new information or data became available. The objective was to have good data coverage to assist in real-time geomechanical modelling for operational decision making. Real-time wellbore stability monitoring was carried out by utilising all available drilling and logging data as well as logging while drilling (LWD), pressure measurements and seismic while drilling (SWD) velocities. Wellsite interpretation on cuttings, cavings and formation gases were also integrated into the model predictions. Based on real-time monitoring, pre-drill predictions and model parameters were continuously updated for the next planned section at the end of each section target depth (TD). Interactive real-time monitoring with continuous pre-drill model updates before drilling the subsequent sections helped to not only deepen the intermediate hole sections, but also to drill efficiently with proper mud weight management and without any significant wellbore instability issues. This integrated workflow helped to successfully drill two exploratory wells, with the major benefit of eliminating the contingency 6ʹʹ slim-hole section.