Empirical analysis for the characterization of geo-mechanical strength and pressure regime: Implications on hydraulic fracturing stimulation

J Petrol Explor Prod Technol

Oladunjoye

Olayinka

et al. 2020

Self Cite

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.

Section: Resultsmentioning

confidence: 77%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

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

J Petrol Explor Prod Technol

Oladunjoye

Olayinka

et al. 2020

Self Cite

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

J Petrol Explor Prod Technol

2021

Self Cite

Heat extraction from geothermal reservoir by circulating cold water into a hot rock requires an amount of fluid pressure, which is capable of inducing fault opening. Although stress change promotes the potential of fault failure and reactivation, the rate at which fluid pressurization within the fault zone generates variations in pore pressure as fault geometry changes during geothermal energy production have not been thoroughly addressed to include the effects of joint orientation. This study examines how different fault/joint models result in different tendency of injection-induced shear failure, and how this could influence the production rate. Here, a numerical simulation method is adopted to investigate the thermo-hydro-mechanical (THM) response of the various fault/joint models during production in a geothermal reservoir. The results indicate that pore pressure evolution has a direct relationship with the evolution of production rate for the three joint models examined, and the stress sensitivity of the individual fault/joint model also produced an effect on the production rate. Changing the position of the injection well revealed that the magnitude of shear failure on the fault plane could be controlled by the hydraulic diffusivity of fluid pressure, and the production rate is also influenced by the magnitude of stress change at the injection and production wells. Overall, the location of the injection well along with the fault damage zone significantly influenced the resulting production rate, but a more dominating factor is the joint orientation with respect to the maximum principal stress direction. Thus, the rate of thermal drawdown is affected by pore pressure elevation and stress change while the fault permeability and the production rate are enhanced when the joint’s frictional resistance is low.

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

Geomech. Geophys. Geo-energ. Geo-resour.

Gan

Oladunjoye

et al. 2021

Self Cite

A pre-existing plane of weakness along the fault is comprised of a particular pattern of joints dipping at different orientations. The fault stress state, partially defined by the orientation of fault, determines the potential of slip failure and hence the evolution of fault permeability. Here the influence of fault orientation on permeability evolution was investigated by direct fluid injection inside fault with three different sets of fault orientations (45°, 60° and 110°), through the coupled hydromechanical (H-M) model TOUGHREACT-FLAC3D. The influence of joints pattern on slip tendency and magnitude of potential induced seismicity was also evaluated by comparing the resulted slip distance and timing. The simulation results revealed that decreasing the dip angle of the fault increases the corresponding slip tendency in the normal fault circumstance. Also, with changing joints dip angle associated with the fault, the tendency of the fault slip changes concurrently with the permeability evolution in a noticeable manner. Permeability enhancement after the onset of fault slip was observed with the three sets of fault angles, while the condition of 60° dipping angle resulted in highest enhancement. Joints pattern with a dip angle of 145° (very high dip) and 30° (very low dip) did not trigger a shear slip with seismic permeability enhancement. However, high dip and intermediate dip angles (135°, 50° and 70°) yielded high permeability in varying orders of magnitude. The large stress excitation and increasing permeability during shear deformation was noticeably high in intermediate joint dip angles but decreases as the angle increases. Article highlights The magnitude of injection-induced permeability enhancement is largely influenced by the fault and joint spatial orientations. With a slight change in the joint direction, there is an increasing possibility for fault to approach a different critical state of failure. Stress elevation at the point of failure is controlled by the orientations of fault/joint planes with respect to the direction of maximum principal stress.