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Abstract

The paper discusses a field case involving the transportation of ethane-rich gas streams. The streams were re-routed using an extensive pipeline network system with the objective of increasing ethane recovery. The changes presented significant operational challenges for managing large amounts of liquids accumulated in the pipeline system and delivering production smoothly to process.

Prior to re-routing the gas streams, transient multiphase flow simulations were performed to establish pipeline liquid accumulation, minimum and maximum allowable rates, pressure losses, and pipe scraping operations at different velocities. A later comparison between calculations and actual field performance showed a good match.

Dropping the planned refrigeration system for the gas pipeline system achieved significant capital savings. Ultimately, re-routing of the ethane rich gas allowed additional recovery equivalent to approximately 20 mmscfd with no additional capital investment.

A modern transient multiphase flow simulator proved useful in testing and setting up field operational changes prior to implementation, and managing extensive pipeline systems with severe liquid accumulation.

Introduction

Crude oil free flows from wells to four Gas Oil Separator Plants (GOSPs) and an in-field gas plant complex. Associated gas is separated from the crude oil in three stages: High Pressure Production Trap (HPPT) at 450 psig, Intermediate Pressure Production Trap (IPPT) at 250 psig, and Low Pressure Production Trap (LPPT) at 50 psig.

GOSP-5 and GOSP-6's IPPT and LPPT gas flows to the in-field plant. The IPPT and LPPT gas from GOSP-2 and 3 and HPPT gas from GOSP-2, 3, and 6 are refrigerated at GOSP-3 for liquids removal.

The IPPT and LPPT gases are compressed to 450 psig, and shipped together with the gas separated at the HPPTs to the North and South Gas Plant.

The system studied (Figure No. 1) is capable of delivering up to 440 mmscfd with maximum inlet pressure of 450 psig.

The study was originated to determine the correct allocation of associated gas to the North Gas Plant (NGP) and South Gas Plant (SGP). Higher ethane recovery is feasible at the NGP. Gas re-routing to the NGP results in 20 mmscfd additional ethane recovered for petrochemical feedstock, thereby increasing corporate profitability.

The NGP Pipeline is 36-inch, 127 km long (Figure No. 2), and overlays undulating terrain with a 20 meter net elevation. The SGP Pipeline is 42-inch, 68 km long (Figure No. 3), and traverses hilly terrain with a 260 meter net elevation.