This study has been focusing on planning wells, which target lower Pleistocene reservoirs below a depleted Ha'py gas field. Many Non Productive time events (NPT) have been anticipated, and the challenges of losing wells and running over budget have been considered as major risks in targeting the deeper prospects.
Years of production from the main Pleistocene A20 reservoir has resulted in significant pressure depletion, while underlying largely-undeveloped Pleistocene reservoirs appear to be very promising they remain at or close to virgin conditions. In addition, the position of the platform at the centre of the field has made it necessary to drill highly-deviated wells to access remaining reserves at the crest of the field.
Detailed planning and close collaboration between the PhPC (Pharaonic Petroleum Company) subsurface and drilling teams has been necessary to understand the geological and geomechanical properties of the key formations. This has helped in selecting appropriate mud rheology and mud additives in addition to ensuring good drilling practices that maximise safety and success. The combined effects of depletion and low rock strength make it effectively impossible to drill the A20 interval with the mud weights required to minimize well bore instability. As a result, stress cage additives were employed in the drilling mud in order to reduce the potential for losses due to the large overbalance against the depleted sand. Modeling prior to drilling suggested this application lay close to the technical limit of the stress cage methodology, and was beyond anything previously attempted within the Pleistocene reservoirs in the offshore Nile Delta.
Careful execution meant we were able to successfully drill through the depleted zone, and as a result of this work, we have been able to deepen recent wells to access underlying gas resources. This success has allowed us to reduce NPT while ensuring safe well operations.