Hydraulic fracturing is the industry-proven technology for efficient exploitation of tight reservoirs.Thisstudy evaluated the technology by drilling horizontal wells through acid fracturing the low permeabilitygas reservoirs of a lower cretaceous carbonate formation,located onshore Abu Dhabi.1D Geomechanicalmodeling was critical in determining fracturing strategy.Containment of fracture height growth was the mostcritical aspect of the fracturing process,as the target units were stacked within heavily depleted reservoirs.The challenge was that the rock strength,poroelastic behavior and stress paths vary significantly throughthe various formations overlying/underlying to target reservoirs.In addition,the depositional nature of thetarget reservoirs meant inherent variations in rock mechanical properties.Hence,a continuous profile of in-situ stresses and other rock mechanical properties was essentially mandatory for addressing the challengesfor optimal placement of the horizontal drain hole and assessing fracture height growth.Existing rock mechanical measurements,dipole sonic and image logs,as well as in-situ stressmeasurements were reviewed for 400ft(TVD)interval above and below the target reservoirs.Significantdata gathering was managed in the vertical pilot hole of the first well to fill data gaps.A custom-builtworkflow was performed for 1D Geomechanical modeling in the first well,integrating poroelastic modellingwith failure models.The study integrated drilling-induced and production-induced Geomechanical aspectsinto the 1D stress profile,including depletion-induced poroelasticity,shear anisotropy,and rock mechanicalheterogeneity.Wellbore failures observed in vertical pilot hole and the in-situ stress measurements fromoffset wells were used for validating 1D Geomechanical model.This work resulted in a rigorous 1D-stress profile that contributed to initial fracture modelling,whilstde-risking the fracture height growth into the depleted reservoirs and optimizing the choice of drain holelocation within sub-units of the target reservoirs.The fracture gradient and breakdown pressures derivedfrom 1D stress profile were found to be in very close agreement with that measured from the minifracconducted in vertical pilot hole of the first well.This paper presents a purpose-driven workflow designed specifically for these circumstances.Themerit of the workflow lies in its systematic and methodical approach,providing solutions to variousGeomechanical problems relevant to the target reservoirs,as well as the depleted reservoirs above and below.The results are beneficial for analogous fields where hydraulic fracturing is required to improverecovery of low permeability reservoirs in mature fields.
展开▼
