Planning and Preparation of a Viable Pore Pressure Prediction in a Wild Cat High Pressure, High Temperature HPHT Exploration Well in Offshore Sarawak, Malaysia
Authors: Chatterjee Avirup , Ghosh Amitava , Bordoloi Sanjeev , Mustapha Anifadora Bt. 
Published: October 2017

As the industry is facing continued low oil price and exploration targets deeper overpressured reservoirs, proper well planning is the key to lowering the cost of drilling. Pore pressure prediction is an important part of an asset team's planning process from assessing the seal integrity to delivering the pressure profiles to the drilling engineer. A precise prediction requires a multidisciplinary approach to address the challenges and uncertainties which in turn needs to be transferred to the drilling engineer while designing the well. This paper focuses on different aspects to be considered while planning and preparing a viable pore pressure analysis which has resulted in successful drilling of a wild cat HPHT exploration well in Offshore Sarawak, Malaysia. A predrill pore pressure prediction study was initiated involving three offset wells in Central Luconia Province Offshore Sarawak. Firstly, the uncertainties in prediction models arise from the quality and relevance of offset well control. In the study area, the two offset wells penetrated thick carbonate sequence and one offset well encountered thick sand-shale sequence with carbonate stringers. The variation in lithologies has to be considered while selecting the relevant offset well. Secondly, understanding the drilling challenges in offset wells related to pore pressure is key to design the planned well. All the offset wells drilled encountered significant challenges in terms of pore pressure. Similar drilling challenges were expected at the proposed location. However, the offset wells didn't penetrate the deeper cycles and as such there were no calibration in deeper undrilled section at the proposed location. The third aspect is the complexity of the geological and structural conditions around the well. The proposed well was planned to be drilled in a structure which was formed on the footwall block for the shallow targets and crossing the fault to hanging wall block to hit the main target in deeper cycles. The fourth one deals with overpressure generation mechanism and prediction methodologies. A conventional workflow to plan a wild cat exploration well makes a precise prediction almost impossible until the overpressure generation mechanism is well understood in the study area. Such analysis were carried out in offset wells to carry a fit for purpose prediction at the proposed location. The fifth aspect covers the seismic velocities in terms of quality and calibration. A very coarse 2D seismic velocities were available with very poor quality of seismic reflections along the proposed well path. The errors that are inherently present in such velocities from different sources has to be considered for determining the quality of the seismic based pore pressure calibration. Considering all the above aspects and the associated uncertainties, a fit for purpose pore pressure model was adopted. The paper explains how all the challenges were addressed to reduce the uncertainty and a three case scenario for pore pressure was proposed for well design. Based on postdrill analysis, the actual pore pressure was within the uncertainty model which helped to make decisions on well design in realtime.