The horizontal stress profile plays a key role in managing the wellbore from drilling to well completion in unconventional reservoirs. A robust prediction of the stress profile and fracture initiation values in vertical wells is required to identify sweet zones and fracture height barriers to design a successful hydro-fracturing job. In this paper, we provide the details of a workflow adopted for building a pre-fracture geomechanical models using breakouts and advanced acoustic data to further history match post-fracture results. The analysis involves the effects of filter cake around permeable sandstone, variation in tensile strength, and quantification of horizontal stress contrast in the different clusters. Different reservoirs have been analyzed across multiple wells to map the variations in geological, petrophysical, and geomechanical parameters. Core test data was used to build dynamic-to-static rock elastic and mechanical properties, both of which reduced uncertainty in the model. The poroelastic horizontal strain met hod was used to estimate the horizontal stress profile. The aeolian deposits have a wide variation in horizontal stress, and fracture height is typically governed by the stiffness of the layers. The study shows that the geometry of hydraulic fractures in the area is strongly controlled by the in-situ stress state. The ratio of maximum horizontal stress-to-minimum horizontal stress varies between 1.18 and 1.28 based on the post-fracture analysis, which correlates well with the regional geological setting. Predrill models have been extremely useful for perforation design in different wells with a maximum deviation of 6% from the actual values for one set of reservoirs. Geomechanical analysis helped to optimize well drilling and hydro-fracture campaigns with cost savings.
The hydraulic fracturing process in a low permeability unconventional reservoir involves the creation of new flow channels where the downhole fluid pressure exceeds the minimum principal stress value plus the tensile strength near the wellbore. Hydro-fracturing is intended to stimulate fractures within a target hydrocarbon zone with proper containment around the stress barrier. Inputs from three different domains, i.e., geomechanics, petrophysics, and geology, are crucial for successful hydrofracturing jobs.
