Geomechanical Properties Estimation for Marginal Oil Field Development at Onshore Niger Delta, Nigeria

Abstract

Rock geomechanical properties were estimated for an onshore marginal field in Niger Delta with the aim of boosting hydrocarbon production in the field. Rock elastic properties and rock strength properties revealed bulk modulus ranged from 1.45 to 1.73 Mpsi, young’s modulus from 1.01 to 1.58 Mpsi, shear modulus from 0.37 to 0.59 Mpsi and Poisson’s ratio from 0.35 to 0.39. These results indicate that the shales are very stiff and harder to fracture, making them very good caprocks. Unconfined Compressive Strength ranged from 785.80 to 1357.65 psi, angle of internal friction ranged from 28.92 to 29.87 deg and cohesion ranged from 232.09 to 393.67 psi respectively. Results of shale geomechanics revealed overburden pressure (vertical stress) ranged from 1648.99 to 5652.36 psi, formation pore pressure from 2083.75 to 3277.22 psi, fracture pressure from 1648.99 to 4821.53 psi, hydrostatic pressure from 2025.10 to 3159.94 psi, maximum horizontal stress from 1648.99 to 11205.70 psi and minimum horizontal stress from 1648.99 to 4507.96 psi. Two under-pressure zones were identified across the entire field at depths ranging from 7000 to 8500 ft in UPX-01 well and 7000 to 9000 ft in UPX-05. Safe drilling mud pressures for maintaining a stable borehole in UPX field should not exceed fracture pressures of 1648.99 psi at shallow depths and 4821.53 psi at deeper depths to prevent loss in circulation. Similarly, drilling mud pressures should not be less than formation’s pore pressure of 2083.75 psi at shallow depths and 3277.22 psi at deeper depths to prevent a kick and blow-out from occurring in the field. This study recommends well break-outs be acquired in order to determine the directions of horizontal principal stresses for geosteering.