Investigation of pore pressure, in-situ stress state and borehole stability in the West and South Al-Khilala hydrocarbon fields, Nile Delta, Egypt

• Published in: Geomechanics and geophysics for geo-energy and geo-resources. Vol. 7; no. 3
• Main Authors: Leila, Mahmoud, Sen, Souvik, Abioui, Mohamed, Moscariello, Andrea
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01.08.2021; Springer Nature B.V
• Subjects: Boreholes; Collapse; Compaction; Drilling; Drilling muds; Energy; Engineering; Environmental Science and Engineering; Exploratory drilling; Foundations; Gas fields; Geoengineering; Geophysics/Geodesy; Geotechnical Engineering & Applied Earth Sciences; Hydraulics; Marine sediments; Messinian; Miocene; Motion stability; Mud; Neogene; Oil and gas exploration; Oil and gas fields; Orientation; Original Article; Overpressure; Photosystem I; Plates; Pliocene; Pore pressure; Pore water pressure; Porosity; Pressure distribution; Pressure gradients; Reservoir sedimentation; Reservoirs; Sea level changes; Sedimentary facies; Sedimentation rates; Sediments; Shales; Slip; Stability analysis; Stress; Stress concentration; Stress state; Weight; Wellbore stability; Nile Delta; Horizontal stress orientation; In-situ stress; Pore pressure; Al-Khilala field
• ISSN: 2363-8419; 2363-8427
• DOI: 10.1007/s40948-021-00256-3

This work interprets the pore pressure distribution and in-situ stress magnitudes in the ~ 10,600 feet thick Neogene succession of the West and South Al-Khilala gas fields, onshore Nile Delta. The Messinian incised valley-fill (IVF) fluvio-marine sediments host the principal gas-bearing zones having a 0.47 PSI/feet pore pressure gradient, as seen from the downhole measurements. Early Pliocene is marked by a dramatic regional sea-level rise which deposited thick marine shales unconformably above the Abu Madi IVF reservoir facies. A high sedimentation rate during Pliocene retained excess porosity and translated to a mild overpressure of around 0.55 PSI/feet in the Kafr El Sheikh Formation due to compaction disequilibrium. Vertical (S v ), minimum (S h ), and maximum (S H ) horizontal stress gradients are estimated as 0.97–0.98; 0.64–0.76, and 0.86–1 PSI/feet, respectively. Interpreted stress magnitudes decipher a normal to strike-slip stress state in the studied fields. B-Quality wellbore breakouts with ~ 600 feet cumulative length infer NNE-SSW S H orientation, almost parallel to the motion direction of the African plate. Wellbore stability analysis indicated a minimum mud weight of 11.45 PPG needs to be maintained against the Pliocene shales which exhibited major wellbore instability issues in the exploratory drilling campaign. Based on the interpreted pore pressure, S h, and collapse pressure gradients, a safe drilling mud window is proposed to ensure borehole stability. Article highlights Pliocene marine shales have mild overpressure resulting from disequilibrium compaction, while the Miocene Abu Madi reservoirs have 0.47 PSI/feet pore pressure gradient. Normal to strike-slip stress state in inferred in the West and South Al-Khilala gas fields. B-Quality wellbore breakouts infer NNE-SSW S H orientation. Collapse pressure and safe mud weight window are inferred to ensure borehole stability in the Miocene shales.