Uncertainties in the subsurface evaluations magnify in heterogenous naturally fractured reservoirs. The chances to leave the hydrocarbon in the subsurface are high if we look at one piece of the puzzle. The critical analysis of high frequency data, problem specific methodologies & engineering workflows, experience and multidisciplinary integration are key parameters of success to delineate the true potential of such complex fields. This paper presents a case study of a highly complex naturally fractured field, in which initially, the G&G and engineering data suggested challenges with respect to field extension and reserves but the critical well monitoring and updated seismic interpretation led to resolution of structural extension which paved way for further field development decisions.
The field located in the TAL block, is one of the Pakistan's highly tectonically challenging area and having complicated naturally fractured reservoirs. The field was discovered in 2016 and production started in 2017. After reviewing available historical data, the project began with the in-depth scrutiny of the exploration well production & pressure behavior, which led to improvised data acquisition. The evaluation of new static and dynamic data confirmed the understanding and indicated higher volumes associated as compared to volumes seen by the first well, highlighting the possibility of an additional well to improve overall structure recovery. However, there were critical concerns due to unexpected experiences in first well which are: 1) The structural uncertainty due to low resolution seismic data quality which posed challenge to identify the sweet spot for 2nd well. 2) Lower productivity of first well as compared to expectations. Possible reasons were, did we cut maximum fractures? Improvement in completion strategy? & Minimize drilling damage? 3) Any potential in other formations that didn't flow in first well 4) Aquifer Influx and its effect on new well location. These uncertainties were captured/studied by building the high-resolution Geo Cellular model followed by detailed numerical reservoir simulation and running the multiple realizations of best well location, well bore trajectory to cut maximum fractures, optimized completion strategy and jewelry. The result was the ability to maximize the probability of success with maximum rate of return on investment while keeping probabilistic weightage to multiple uncertainties.
There were number of milestones achieved in the project execution. In-house reservoir simulation study saved considerable cost for Tal JVPs. Drilling optimization resulted in final well cost & time savings of 34% & 40% respectively through multiple stakeholders’ proactive communication and knowledge sharing. Additionally, the rigorous designing of the Wellbore Trajectory resulted in maximum natural fractures intersection with wellbore yielded maximum productivity.
The multidisciplinary team efforts are well paid by achieving ~50% incremental production rate as compared to the estimated potential in normal development target, as well as fast tie-in and discovery of two additional reservoirs due to up-dip location of new well. The success proves the power of multidisciplinary integration that started just from apparent data validity, turned into breakthrough of additional reserves and matured by rigorous realizations of number of uncertainties in complex heterogenous natural fractured reservoir.
