Abstract
Sustainable and clean production of natural gas is of paramount importance in transitioning to a low-emission economy. Gas production in an unconventional well such as a coal seam gas (CSG) relies on continuous dewatering, commonly performed through a progressive cavity pump (PCP). PCPs are susceptible to failure for different reasons, primarily the interference of solid particles. This results in interruptions, pump replacement, well cleaning and recommissioning which pose long downtimes (i.e., reduced well deliverability), work-over at substantial costs, along with environmental impacts such as increased methane emissions to the atmosphere.This paper aims to demonstrate and assess the performance and suitability of a sustainable dewatering technique, referred to as foam-assisted gas lift (FAGL) which offers uninterrupted dewatering, minimal downtime and minimised environmental impacts. FAGL is capable of maintaining the gas well deliverability by replacing the downhole pump with a gas compressor at the surface and an engineered gas-liquid-solid flow dynamics by injecting foamers and a small amount of surplus gas into the wellbore.The performance of FAGL is evaluated in 45 vertical CSG wells in Australia under different operating conditions and depths ranging between 400 and 1050 m and is compared with well data using PCPs. The flowing bottomhole pressure (FBHP) is calculated to assess the suitability of FAGL under different operating conditions. The results from this study show that FAGL outperforms PCPs in more than 50% of the cases under this study, offering on average 34% lower FBHP. The FAGL's capability in lifting solid particles is demonstrated using solids taken from gas wells in Queensland, showing a reliable and continuous lift of particles. In addition, chemical defoaming of the foam at the surface is demonstrated to avoid re-foaming in the downstream and mitigate the risk of contamination of the surrounding area.
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