Mechanical Layering:Implications for Hydraulic Fracturing in an Unconventional Tight Carbonate Reservoir in Abu Dhabi,UAE

摘要

The tight-carbonate gas reservoir of Onshore Abu Dhabi,UAE,is characterized by having alternating thin and dense reservoir and none-reservoir units,where hydraulic fracturing is the most effective way to increase the productivity by creating the maximal areal contact with the wellbore.The most significant operational constraint associated with hydraulic fracturing is the containment of the produced hydro-fractures,which might extend beyond the reservoir units.To avoid this problem,which is a function of the mechanical and elastic properties of its reservoir rocks and the type of existing stress regimes,these attributes within the reservoir units and the surrounding cap-rocks should be understood. The 1D Mechanical Earth Models(MEMs),which involve constructing the three principal in situ stresses’profiles with depth together with the elastic and strength properties of the tight carbonate units with their cap rocks have been carried out using different data along 12 wells such as sonic logs,full-bore microimage(s),and rock mechanics testing. The results of these twelve 1D MEMs in the field indicate that the three principal in situ stresses’axes swap directions and magnitudes at different depths giving rise to identifying different mechanical bedrocks with different mechanical properties corresponding to different stress regimes(normal and strike-slip)at different depths. The implications of these results suggest that it is likely that the produced hydraulic fractures are mainly vertical to sub-vertical under both normal and strike-slip stress regimes.Further,depending on the stress regime,the propagation of the hydraulic fractures would likely be into the horizontal in case of strike-slip regime compared to vertical propagation within the normal stress regime.Further,longer hydro-fractures are expected to be developed in stiffer layers.