Sukowati field is a prolific carbonate oil and gas field located at East Java operated by Joint Operating Body of Pertamina PetroChina East Java (JOB PPEJ). The field produces the hydrocarbon since 2004. This paper briefly explains the principles of the inversion technique to correct the orientation of horizontal in-situ stresses that was applied in our recent multi-well study with JOB PPEJ because of high-angle wells deviation. The deviated wells were commonly drilled to avoid land clearance issue in a densely populated island like in Java as it happens in Sukowati field. Knowing the horizontal in-situ present day stresses orientation is important to be used for further application in building mechanical earth model (MEM) for many geomechanics applications such as wellbore stability analysis in drilling and designing hydraulic fracturing for well stimulation purpose.
The study used wireline borehole image logs data acquired for 6 wells in Sukowati field to identify two borehole failure features due to drilling process, such as breakout and drilling induced fractures. Regions within earth's crust are normally in a state of stress imbalance with magnitudes of stress components along three principal directions being unequal. Wells drilled within such deviatoric stress regime with prominent stress inequilibrium, experience brittle failure on borehole walls in the form of breakouts and induced fractures. These as a general rule develop along minimum and maximum horizontal principal stress respectively. Borehole images provide accurate orientations of these features. These orientations combined with the general rule can be used to determine in situ stress geometry. The general rule holds true for vertical wells where the plane perpendicular to borehole axis contains the two horizontal principal stress directions. In deviated wells principal stresses are neither along the borehole axis, nor are contained by the plane perpendicular to borehole axis thereby making the relation between the brittle failures and the stress directions more complex. So, in deviated wells determination of stress geometry directly from breakout and induced fracture orientations may provide erroneous results. Inversion techniques are used to handle this complex relationship. Breakout and induced fracture orientations obtained from images in deviated wells are fed into the inversion along with wellbore profile to generate exact directions of minimum and maximum stresses. In addition to stress directions, inversion also outputs relative magnitude of principal stresses from which the stress state can be deduced.
