Modelling of High Point Vents in water gathering systems – a new approach using Simcenter Flomaster

Abstract

The cost-efficient extraction of coal seam gas (CSG) is the ultimate objective of every CSG project. One challenge is that gas holdups in water gathering lines can significantly obstruct water removal by causing higher back pressure on the wells, thus resulting in lower dewatering rates with subsequent delays in expected gas production. Gas holdups originate from entrained gas entering the wellhead pumps and from dissolved gas bubbling off in water gathering pipelines. Gas holdups are mechanically removed by High Point Vents (HPVs) installed at pipeline high points, with the efficiency of gas removal directly impacting project economics. A new hydraulic modelling approach enables the realistic simulation of two-phase flow regimes in a single-phase solver by utilising hydraulic components designed to separate gas and water. This modelling process offers major advantages over the traditional gas water ratio approach, as it enables the addition of individual HPVs to be analysed for their impact on the pressure reduction in water gathering pipelines. Modelling can be performed for any network complexity in either steady-state or transient simulation, enabling the analysis of the entire water gathering network over its life span of several decades. An operating envelope of well and pipeline pressure can be generated for an idealistic gas-free network, showing the lowest pressure and a network with fully developed gas holdups and resulting in the maximum possible back pressure. The paper includes a benchmarking study of an existing complex water gathering system confirming the practicality and accuracy of this game changing modelling approach.