RICHARD SWARBRICK, STEPHEN O’CONNOR, and RICHARD LAHANN, IKON-GeoPressure
High-pressure sediments in which oil and gas are generated and accumulate in traps are proven in many operating areas along the entire West African margin. Although classic areas for high pressure are found in Tertiary deltas, such as the Niger Delta, other types of basins in which young clastic sediments have accumulated also create the environment for high pressure and drilling challenges. The BP Macondo oil spill in the Gulf of Mexico has highlighted the technical challenge of drilling for oil in deep water, and the high pressures there added complexity to the control incident and the high volumes of fluids which blew out to the seabed.
Understanding mechanisms which create high pressure, the context for pressure prediction, using all available data including seismic, and quantifying uncertainty are all required for successful, safe drilling in these challenging subsurface environments. Where there are many well penetrations with appropriate data, compilation of relevant data and their analysis within an integrated basin-scale pressure study allows the whole area to be contextualized for pressure studies have been completed in Europe and North America, but along the West African margin so far only in the Niger providing understanding of pressure distributions in the main reservoirs as well as relationships concerning seal breach and lateral drainage.
This article places into context the reasons why and where high pressures are expected in drilling operations along the West African Margin and focuses on the challenges that come with it. Particular attention is paid to the Niger Delta where a major new regional initiative, in conjunction with DPR and NAPIMS and industry sponsors in Nigeria, is leading the way in regional interpretation of pressures leading to reduced drilling risk as well as new exploration opportunities.