Subsurface process improvement to minimize subsurface uncertainties for workover optimization, a Case Study from Mature Waterflood Field, Central Sumatera Basin, Indonesia

Abstract

The workover (WO) opportunity identification in the complicated and mature field with over 40 years of the production and injection becoming very challenging. With the limited resources and high turnaround of staff in the organization, it creates the unique opportunity to focus on the high priority areas to maximize the production and arrest the field production decline. Internal brainstorming suggested that there are three areas need to be improved; (1) WO success rate, (2) healthy WO backlog and (3) accelerate the approval process to accelerate the program generation and reduce recycling. After further analysis, the root causes of the problem were; (1) No prioritization of areas of focus in which to deliver big opportunity, (2) Lack of big picture understanding of the remaining opportunity and producer-injector alignment and (3) late engagement of approver in the process. The major changes conducted is dividing the big field into smaller areas based on subsurface (G&G) closures or compartments. This new smaller area is a revision to existing areas that crossing geology compartments and dominantly based on surface facilities. Once the smaller areas (called “region”) established, then the next step is to prioritize region to be review that expected to have higher remaining oil accumulation. Typical crestal or attic closure area become higher priority to be review. Focusing on attic area will help to reduce remaining oil uncertainty as oil saturation log surveillance not give big benefit historically due to dynamic of reservoir. Shut-in attic injector and dedicated injector to flank area or to re-direct injection to individual sand that required injection also conducted to be align with waterflood management. WO proposal justified using good well analog, the analog help to reduce uncertainty on remaining oil, production allocation and whether Team can copy success from other area or play to current area. Preferable well analog are; (1) well with single sand production, (2) well with recent wireline log data, (3) commingle well but with production allocation from finger print analysis or (4) recently WO success at other area (for new play). Standard documentation is developed such as informative well cross section including both G&G and production information’s for helping better communication and engagement to the Approver. This engagement helps Approver understanding the WO proposal and the associated uncertainties. All the effort of subsurface prioritization and review give good result on better WO candidates selection, speed up the technical and cost approval process and good or healthy WO backlog. Ongoing WO execution also give good initial signpost of increasing WO success rate.

AAPG Datapages/Search and Discovery Article #90354 © 2019 AAPG Asia Pacific Technical Symposium, The Art of Hydrocarbon Prediction: Managing Uncertainties, Bogor, (Greater Jakarta), Indonesia, August 7-8, 2019