AAPG/SPE Africa Energy and Technology Conference

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Wellbore Strengthening in Narrow Margin Drilling

Abstract

Natural gas is one of the cleanest energy sources, its uses range from fueling power stations to cooking and heating. Global demand for natural gas is expected to rise in the coming years. Meeting these energy demands means drilling deeper exploration and development wells to access huge volumes of gas present under high pressure and high temperature (HPHT) conditions. Despite the attractiveness of the reward, managing the narrow drilling window between the reservoir pore pressure and the formation fracture gradient has remained a major source of cost escalation and non-productive time on HPHT projects. In order to improve the economics of HPHT projects, technologies like Managed Pressure Drilling and borehole strengthening have been used as a means of mitigating the risks associated with narrow margin drilling, thus enabling a paradigm shift from traditional casing seat selection methodology. In the Niger Delta, it is not uncommon to observe significant jumps in pore pressure values in proximate high pressure formations. The simplification of well designs and successful drilling operations are often challenged by the need to navigate through series of high pressured reservoirs in narrow margin windows. Compliance with process safety requirements requires selection of mud weight that is low enough to prevent mud loss and high enough to overbalance the reservoir pressure. Mud loss induced by formation fracture is often encountered in tight margin drilling, and when this happens, the focus shifts to strengthening the damaged wellbore using various techniques such as pumping chemical resins to seal off the loss zones. Various degrees of results have been achieved when borehole strengthening techniques are deployed with the objective of restoring wellbore integrity in both permeable and non-permeable formations. Successful deployments have resulted in achieving the well objectives safely and cost effectively. This paper details loss of wellbore integrity experienced on an HPHT well in the Niger delta and the wellbore strengthening strategy that was used to restore the strength in a non-permeable formation. It sheds light on how understanding the nature of the fracture, rock lithology as well as proper job execution can restore a damaged wellbore to its previous strengths. A Cost reduction approach to the execution of the strategy is also discussed.