Pore-pressure prediction plays an important role in well planning as exploration targets shift to deeper, overpressured reservoirs. Pressure-related problems in such zones are mainly associated with narrow operating windows, resulting in severe well-control incidents, sometimes even leading to early abandonment. Uncertainties in prediction models arise from input data, assumptions used in the work flow, and the complexity of the geological or structural conditions. It is important to analyze these uncertainties and develop an understanding of them before drilling.
Central Luconia is a geological province of the Sarawak Basin characterized by extensive development of Miocene to Holocene carbonate buildups. The buildups reveal complex seismic geomorphologies, facies, and structural setting. There have been several discoveries in the shallow-water (approximately 90-m depth) area of central Luconia province offshore Sarawak. A predrill pore-pressure- and fracture-gradient-prediction study was initiated for a planned high-pressure/high-temperature (HP/HT) well with three offset wells (Offsets 1, 2, and 3) drilled in the vicinity of the study area. The objective of the study was to help in well design to reach desired deeper target reservoirs. The prospect is situated in a structure characterized by a northwest/southeast normal fault. It was formed on the foot wall block for the shallow (post-carbonate clastic) reservoirs and crossing the fault to the hanging wall block to hit the main targets in deeper (precarbonate clastic) cycles. The lithology for the shallow cycles is interbedded fine-grained siliciclastic shale and sand with limestone streaks. The deeper cycles consist of predominantly sandstones with interbedded shales. Two offset wells (Offsets 2 and 3) penetrated a thick carbonate sequence, and the other offset well (Offset 1) encountered a thick sand/shale sequence with interbedded carbonate stringers, which is similar to the prognosed-well result. Therefore, in the predrill modeling, there was only one relevant offset well (Offset 1) available in the study area that penetrated similar lithostratigraphic units....
Integrated Approach for Overpressure Prediction in an HP/HT Well Offshore Malaysia
01 April 2017