A State-Of-Art Study on Solution to Liquid Hold-Up and Back-Pressure Management in Long Tieback Deepwater Gas Pipeline Network in Indian Offshore

Abstract

Abstract Deepwater long tie back subsea gas pipelines poses a critical operational challenge with declining pressure and production over the field life, the problem will further aggravate if early water breakthrough encountered. The pipeline networks exposed to such a low producing early water cut fields for long period of time will lead to accumulation of high liquid resulting in creation of additional backpressure which affect the well deliverability. The increase in water production in gas wells were started to cause unstable flow in one of the complex Deepwater (1300m) dual 14"x58 km subsea (with U loop) to shore network from Eastern offshore of India due to liquid loading, making flow assurance a challenge to daily operations. An innovative liquid management strategy has been developed through extensive analysis and devised the methodology by Flow Assurance team in association with an integrated Operations team, in order to address the liquid loading issues by effectively utilizing the limited available resources and surface handling facilities. Continuous monitoring and dynamic simulation tools have helped to understand flow stability in the subsea network for minimizing liquid holdup which have significantly reduced the back pressure and resulted in enhanced production. An integrated dynamic multiphase flow model used to optimize operating philosophy after validation with field parameters and accounted for the uncertainty of the associated controlling parameters, and accordingly devised the sequence of steps for dynamic pigging to minimize liquid holdup. The sequential methodology comprises of reduction of operating pressure at process end for partial liquid knockout; optimized diversion of selective wells to maintain the hydrodynamic slugging within handling limit; flowing all wells via U loop to knock out rest of the liquid to the possible extent. Successfully mitigated the issue by effective implementation of innovative strategy which proved to be highly efficient in maintaining production in a sustainable mannerly minimizing the liquid holdup and significant back pressure reduction. This paper presents the details of the innovative methodology, devised and successfully implemented using state-of-the-art dynamic simulation tools. These steps were proved to be effective in field without need of any additional operational/capital cost in safe operating conditions. The framework presented here can be applied to any similar deepwater field with subsea long tie-back. This model is a handy tool not only for engineering simulation but for operator training and real-time surveillance as well.