Unlocking Potential of Billion Barrels in the Largest Mature of 99% Water Cut's Field by Developing Thin - Low Quality Reservoir with HAZZ Methodology

Abstract For over 70 years, Natinah, the biggest oil field discovered in Southeast Asia, has remained the backbone of Indonesia's oil production with recovery factor ~56%. Unfortunately, the current water cut (WC) is 99.4% and remaining oil opportunity left is Low Quality Reservoir (LQR) with <5% WC, which has not been well-developed since 1952 due to its complexity. This challenges the engineers to find the best approach to unlock over 2 billion barrels oil of LQR amidst many obstacles. With current limitations in reservoir model, surveillance, forecast methodology, limited surface well pads, thin LQR sand (8-15 ft.) and low permeability, a strategic LQR maturation methodology has been proposed for better horizontal well candidacy and execution. This methodology starts with subsurface candidate maturation including LQR thickness mapping, focus area determination, opportunity validation process, high-resolution sector-3D model, trajectory well design, completion design, until new analytical approach of horizontal inflow calculation using the "HAZZ" equation and its digital "HAZZ" forecast tool equipped with "Monte Carlo" simulation to mitigate risk of subsurface uncertainty, which has been developed to improve the forecast of LQR horizontal well production. By adopting this comprehensive approach, successfully narrowing the subsurface uncertainty risk in LQR development. Mapping high accumulated oil left in low-permeability zone, grouped into focus areas by sand and characterized into play types: fining upward, sandwich and full body. These efforts resulted in a better subsurface understanding for having high grade LQR candidacy that will be followed by the next maturation process. "HAZZ" equation, as new technical approach in horizontal well forecasting which embe dded in "HAZZ" forecast tool, is one of the big improvements in managing LQR development to have better LQR forecasting that drive in project's decision, both technical and economical. Moreover, the new workflow of decision-making during drilling (especially determining landing point, lateral section, and total depth that one of the keys is utilizing azimuthal-deep-resistivity) and well completion selection has been implemented to have smooth well execution and final completion. These comprehensive improvements have not only succeeded in delivering high quality of LQR horizontal well candidates, but also succeed in having better and smooth project execution until put-on-production. In actual, the project team succeeded in delivering high profile of LQR production with 5-10% WC and increase success rate of LQR horizontal well execution from 0% to 100%. This paper introduces a new way of reservoir development that offers a better success rate and economical in mature field, especially with high water cut condition where further development might seem unlikely except for EOR. A new comprehensive workflow for unlocking billion barrels of LQR, which includes a new maturation methodology, new forecast analytical approach and new workflow in decision-making during execution, will be benefited to seek new hope for majority of mature/marginal/brown field before deciding to shut-down the field.