A Holistic Approach to Rank Unconventional Reservoir Prospects led to Pakistan's First Successful Shale Formation Testing

Abstract

Pakistan holds significant volumes of unconventional hydrocarbon reserves. In 2013 EIA report, the Sembar Formation of the Lower Indus Basin has 101 Tcf shale gas with 5.8 billion barrels shale oil resource as the risked & technically recoverable hydrocarbons over an area of about 81,000 km². However, the EIA report has highly risked the prospective areas and the likelihood of development success. Thus, the main barrier for unconventional reservoirs development in the country is to reduce the associated uncertainty in a more rigorous manner and to decide, if and where to plant a flag in this vast area. A robust integrated approach was used to delineate and rank the unconventional reservoir prospect of Shale Gas, Shale Oil, and Tight Gas of Upper, Middle, and Lower Indus Basin of Pakistan by using multi hierarchy Shale Analysis Framework. This workflow spans the lifecycle of unconventional resource development by integrating petrophysical modeling, lab data, geologic and geophysical modeling, geomechanical modeling, stimulation modeling, drilling, reservoir and production engineering, and project management. Each of the workflow components is weighted as a function of their relative importance, and prospects in the study area are preliminary ranked according to how well they fulfill the criteria. Finally, the pilot area was selected/ranked by exhaustive uncertainty analysis using reservoir simulation and integrated with economic indicators such as Net Present Value (NPV), Return on Investment (ROI) & Rate of Return (ROR).

Initially, 27 prospective unconventional focused areas were identified and ranked among Upper, Middle & Lower Indus Basin. The top-ranked areas belong to the Sembar Formation of the Lower Indus Basin, in which further detailed assessment was carried out by extensive Shale Analysis Framework. Finally, the pilot areas were categorized based on integrated uncertainty and techno-economic evaluation. Based on outcomes, the top pilot area was tested by a mini-frac job as the first step. The Formation was successfully broken down within the estimated pressure range and produced hydrocarbons during the flow back period. The adopted framework proved to be successful in Pakistan's first shale formation testing and helps to reduce the number of appraisal or experimental wells needed to evaluate the resource potential and shorten the field development planning cycle and/or maximize the economic value of the resource via an efficient integrated approach.