Geo-pressure and geo-mechanical models for the Late Messinian Abu Madi reservoir in the Nidoco and Baltim gas fields, offshore Nile Delta Basin, Egypt

The young Nile Delta Basin of Egypt (Plio-Pleistocene) exhibits compaction disequilibrium, as the rate of sedimentation exceeds the rate of subsidence. This represents the main cause of the overpressure regime encountered in this basin. This condition presents a very challenging problem when adjusting the mud weight (MW) window with respect to the pore pressure (PP) and the fracture pressure (FP) to avoid possible crises (a blowout or lost circulation). This paper considers a scientific approach for constructing and interpreting geo-pressure and geo-mechanical models for the Late Miocene (Messinian) Abu Madi gas and condensate reservoirs (level II and III sands) in eight wells (BS-1, BE-2, BE-3, BN-1, BN-2, Nidoco-9, Nidoco-10 and Nidoco-7) distributed in the Baltim (South, East and North) and Nidoco fields, offshore Nile Delta, Egypt. The available data are in the form of repeat formation tester (RFT) data and well logs (sonic and resistivity) in addition to drill stem test (DST) data. Through the interpretation of pressure–depth (P-D) plots, two major geo-pressure regimes (abnormal and subnormal) were detected for the Abu Madi reservoir in the study area. The deduced fluid densities ranged between 0.5 and 0.71 g/cc, indicating the presence of gas and condensate. The gas–water contact (GWC) is located above the free-water level (FWL), indicating a water-wet reservoir. The geomechanical models were constructed based on the calculated Poisson ratios ( γ ) , which ranged from 0.22 for clean sand intervals and increase with increasing shale content to a maximum value of 0.34. Using this model, the calculated pore pressure (PP), mud weight (MW), overburden (σOB), and fracture (FP) and hydrostatic (Phyd) pressure gradients were obtained and compared graphically. Most of the pore pressures are mild to subnormal overpressures corresponding to the safe mud weight window between 8 and 9.5 ppg. The effective stresses (ESs) are generally high and can reach 10.5 ppg, which leaves room to house hydrocarbons and makes the examined fields suitable for future exploration.