Novel Approach for Selecting Well Candidates and Appropriate Design of Hydraulic Fracturing in Challenging Reservoirs

Abstract

Karim and Haradh reservoirs within the Karim Small Fields (KSF) cluster in the South of the Sultanate of Oman are characterized by low to medium permeability and significant heterogeneity and contain medium to heavy crude oil. Reservoir depths are in the range of 1500 to 2000 m and productive areas are relatively small (around 2 km2 per field). Over the past 10 years, fields development did not result in sustained oil production despite the close well spacing. Geological and reservoir studies indicated that this is mainly due to the heterogeneity, lack of reservoir continuity and presence of significant wellbore damage in most wells. Accordingly, the KSF operator initiated an appraisal campaign focusing on hydraulic fracturing to stimulate the producing wells and improve the extension of their drainage areas. This campaign resulted in significant improvement in well productivity and the analysis of results indicates good potential for improving the ultimate oil recovery from these reservoirs. Although the results from hydraulic fracturing campaign are encouraging, they also indicate that appropriate selection of well candidates, key parameters in the fracturing procedure, effects of well completion and impact of well age are very important for successful oil gain. As a result, a comprehensive procedure for selecting and ranking candidate wells for hydraulic fracturing in Karim and Haradh formations has been developed. The procedure includes assessing the impacts of key properties such as fracture height, depth of oil-water contact, thickness of oil column, and distance to faults. In addition, the lessons learned from the previous appraisal campaign will contribute to achieving optimum fracture geometry in future campaigns. The candidate selection workflow involves understanding the geology, geomechanics, and petrophysics of the wells in which a fracturing operation was performed previously in different formations in KSF. More than 20 existing wells were screened through the candidate selection process using a clear workflow to incorporate all the relevant aspects of the selection criteria. The outcome of the candidate selection phase led to selection of the best wells for fracturing operations in the Karim and Haradh formations. The improvements on the fracturing design have been followed to obtain the optimum fracturing design for the selected wells.