Reservoir Candidate Screening: The SURE Way to Successful Underbalanced Drilling Projects - Case Study

Abstract Abu Dhabi National Oil Company (ADNOC) and its group of companies are considering adapting new technologies to ensure that strategic resources are optimally explored, developed and produced during the life cycle of their oil and gas fields. Underbalanced Drilling (UBD) technology, which can achieve these objectives effectively when applied in conjunction with horizontal drilling techniques, is being considered among various options. Abu Dhabi Company for Onshore Oil Operations-ADCO, decided to pioneer the introduction of the new technology. A systematic scientific approach was applied to screen thirty reservoirs for underbalanced drilling candidacy, in order to identify the best potential candidates from a given portfolio and to ensure a successful pilot application. The screening process incorporated reservoir, drilling, and operational data with risk analysis into a rigorous expert system aimed at maximizing the value of any UBD operation. The screening process was performed in two phases; Phase I comprised of: - Evaluating and ranking thirty reservoirs with respect to their risked probability of being successfully exploited with horizontal underbalanced drilling and completion techniques as opposed to conventional drilling and completion techniques. - Comparing candidate reservoirs against global database of analogues proven to be suitable with UBD. - Selecting the best three candidates for the Phase II detailed reservoir damage analysis and productivity forecast. Phase II comprised of: - Identifying the formation damage mechanisms that are expected to occur in each of the three reservoirs. - Comparing underbalanced and overbalanced costs, production rates, projected revenues and net present value. - Ranking the three candidates for UBD application. The paper describes the expert system methodology used in the screening process and the results obtained. The detailed economic analysis presented in Phase II of the study would help ADCO determine the benefit that underbalanced drilling could provide compared to competing conventional drilling & completion technologies.