Reservoir Geomechanics in Carbonates

Abstract

Abstract Development of formations with stress sensitivity is raising awareness that Geomechanics is a vital aspect of future management. Understanding geomechanical behavior is becoming more and more important for the petroleum industry. It has been reported by many authors (e.g. Herwanger and Koutsableloulis 2011) that, significant changes in pore pressure (ΔP) due to depletion or injection in weak formation might lead to increase in effective stress, compaction, reduction in porosity and permeability, casing deformation, failure and subsidence, challenges in fracturing the formation, closing and opening pre-existing fracture fault re-activation and bedding parallel slippage. The deformations affect the apparent time-shifts from seismic surveys of under- and overburden. The changes in stresses/strain affect the formation of interest as well as the overburden layers and directly affect all operations such as drilling, completion and production strategies because of permeability reduction. Stress affects nearly all petrophysical properties. Compaction, shear casing and well damage, cap-rock integrity, fault reactivation and sand production can occur during Formation depletion. A coupled Finite Element approach is taken for modeling Geomechanical effects induced by production/injection and the cycle dependence between pore fluid flow and def of the tight carbonate, which impact hydrocarbon production. Using Visage, the finite element analysis model for the geomechanical analysis and the fluid flow simulator Eclipse for ΔP determination, this work looks at ΔP – stress coupling, which has significant implications for porosity/permeability reduction. To address these issues, a conceptual two-way coupling model has been constructed using Finite Element method and Eclipse; the results show that, change in pressure has some implications on porosity and pereability. Both 3D and 4D Geomechanical models were developed that describe the state of stresses in the weak formation and overburden as well as changes in stress over time with either production or injection.