Rock physics and geomechanical application in the interpretation of rock property trends for overpressure detection

Abstract

One of the complexities of geomechanical study is in the classification of rock’s properties and overpressured intervals—a knowledge which is not only essential for well safety and cost-effective drilling, but crucial in evaluating exploration risk factors and ensuring a successful hydraulic fracturing program. In this study, a more robust prediction of reservoir pressure regime is presented, where the geomechanical distributions of the rock give a distinct correlation. Three wells from the Niger Delta Basin were studied using empirical equations to estimate the elastic properties, wave velocities and the rock physics parameters for each well. From the results obtained, the velocities of compressional wave (Vp) and shear wave (Vs) decrease as porosity increases. Also, a linear correlation exists between Poisson’s ratio and Vp/Vs, where both variables showed distinct behavior and similar trend serving as useful tools for lithology identification. Another significant observation is the acoustic impedance of the materials which decreases with increasing porosity. Meanwhile, the depth plot of the impedance showed divergence and scattering away from the supposed linear trend. While inhomogeneity of the rock materials and disequilibrium compaction of sediments may account for this scattering, the variation of geomechanical distributions in this study revealed that pore pressure has a first order effect on the elastic strength of formations, also, under normal pore pressure conditions, acoustic impedance increases linearly with depth.

Numerical investigation of the influence of discontinuity orientations on fault permeability evolution and slip displacement

“…Table 1 shows the assumed material properties for the fault zone and host rock, derived from laboratory measurements and previously published data from the study area (Eyinla and Oladunjoye 2019;Chukwu 2017;Nwozor et al 2017;Emudianughe and Ogagarue 2018;Ichenwo and Olatunji 2018;Ogunsakin et al 2019;Eyinla et al 2020Eyinla et al , 2021. The constitutive mechanical properties for the model were derived from the work of Gan and Lei (2020).…”

“…From reports (e.g. Shrivastava and Lawatia 2011;Xue et al 2014;Wang et al 2016;Feng et al 2018;Eyinla et al 2021), tight reservoirs have specific variations from the conventional reservoirs because of certain factors which include high heterogeneity, their deeper depth of burial, diagenetic properties, low porosities, very low permeability, poorly developed fracture system and abnormal pressure with. While rocks contain different forms of discontinuities which play an inevitable role in the overall mechanical and elastoplastic behaviour, the most significant types of discontinuities in rocks include faults, fractures, weak planes/joints, shear zones, planes of foliation, bedding planes and planes of cleavage (Eshiet and Sheng 2017).…”

“…Thus, this study explores the roles of fault geometry and associated joints, using data from tight shale reservoir from Akas field of the Niger Delta Basin as a case study. Studies from this field have been discussed in previous reports (Eyinla and Oladunjoye 2019;Eyinla et al 2020Eyinla et al , 2021. The reservoir model is presented as a finite medium with a hydraulically induced normal fault, and the overall mechanical behaviour of fault is represented by a set of solid elements with ubiquitous joints which are oriented as weak planes in the fault zone as described by Cappa and Rutqvist (2011).…”

Fracture Gradient Analysis for Lockhart Formation at Kohat–Potwar and Nizampur Sub-Basins, Pakistan

“…The pressure exerted by the weight of the rock formations and fluid columns above the point of interest is called overburden pressure and is always in the vertical direction (Eyinla et al, 2021). The higher the rock and the fluids densities, the greater the overburden pressure will be over the reservoir (Green et al, 2016).…”

Analysis of the influence of joint direction on production optimization in enhanced geothermal systems

“…Generally, rocks contain different geomechanical properties which change as the pore pressure changes (Eyinla and Oladunjoye 2019;Eyinla et al, 2021b). However, discontinuities also play an inevitable role in the overall mechanical and elastoplastic behaviour.…”