Single-Trip Multizone in Challenging Highly Deviated Wells - Case Study from Natuna Sea

Abstract An operator in Natuna Sea needed to fast-track three highly deviated wells in unconsolidated Arang and Udang Formations. Sand control was key and Single-Trip Multi-Zone (STMZ) was deemed the most appropriate approach for the wells. A suite of critical characteristics, including inclination greater than 70° across all treated intervals, small casing (7"), low fracture gradient, high permeability, etc., complicated operations. However, all three wells were completed without significant issues, production exceeded target, and costs were below planned. A system was progressed to complete three wells in the unconsolidated Formations; primarily selected because of cost effectiveness, equipment availability, and selective capability to open or close any interval. While it was appreciated that the system was less suited to higher deviations; it was agreed to manage these risks through operational decision making. The main challenges were the high inclinations (70-73° across targets), high permeabilities, and high friction pressure from small production casing (7"). While the boundary condition of equipment selection was pre-ordained, close collaboration in a multi-disciplinary manner meant that the risks could be identified and managed. Consideration began with which completion system would meet the critical delivery timetable and minimum functional requirements. Existing inventory was available and restrictions that this would place on completion and production capability was fully assessed. Close collaboration between Completions, Subsurface, Drilling, and Service Providers was fundamental to deliver success. The nature and approach to final completion intervals were decided after detailed discussion with the Subsurface Team. On occasion, the number and length of intervals to be completed were reduced or restricted to fit with limitations, including when high permeability contrast existed within a single zone. Friction simulation and torque and drag modelling were performed across multiple scenarios to avoid tool failures due to long interval lengths and high inclinations. Actual parameters were then closely compared to the model during the tool deployment and fluid pumping, to calibrate for accuracy. Proppant pumping selection methodology was determined during a pre-job workshop based on fracture simulation and re-confirmed after performing the mini-frac operation. All these steps and contingencies worked together to deliver a highly successful completion campaign, and post-completion production exceeded the target. This paper outlines the completion of three sand-control wells, starting from an aggressive timeline (around 6 months) that constrained optimum equipment selection. However, early appreciation of this and close collaboration and integration across all Teams resulted in highly successful execution. The approach demonstrated that cross-functional appreciation, compromise, and learning could result in selection, mitigation, and contingency that fully addressed potential risks.