Tangguh Big Gas Well Choke Re-evaluation: Cost Effective Problem Solution Boosting Deliverability

Abstract

Tangguh big gas wells are flowed with high gas flowrates and typically having significant daily production swing. Post operation, we experienced choke valve issues related to unsuitable initial design: (a) oversized trim, (b) pinching erosion even without sand
production, (c) unfavorable operating envelope where small opening produced excessively high flowrate, (d) undersized vendor recommended trim replacement.
Thus, a proper trim sizing and characteristic selection have been pursued intensively, -evaluation process used inputs from each well productivity relationship calibrated by available well production data. Petroleum engineers carefully calculated valve sizing and exercised the best choke opening characteristic by doing sensitivities against all possible well operating scenarios.
As the results, team successfully identified the best debottlenecked trim selections with equal percentage feature. This recommendation allows wide operating ranges produced with favorable operating envelope. Positive results obtained from applying this cost effective (0.02$mm/mboed) and low risk approach, where field deliverability increased by: +20 MMscfd (2014), +70 MMscfd (2015/2016), and +30 MMscfd (2016). The selected equal percentage trim provides more proportional operating curve, ensuring that high gas rate would only be achieved through big opening. This also prevents trim erosion due to pinching as in the past cases. The process then developed into daily choke surveillance techniques, where all well choke performances are monitored. Case examples demonstrate the robustness of this surveillance in pinpointing trim damage possibility, effectively  revented potential safety incidents.