Low permeability coal seam gas productivity enhancement by cyclic nitrogen injection technique (an adsorption simulation study)
Hoa T. Nguyen A B , Mohammad Sayyafzadeh A and Manouchehr Haghighi AA The University of Adelaide, SA 5005, Australia.
B Corresponding author. Email: thuanhoa.nguyen@adelaide.edu.au
The APPEA Journal 58(1) 159-167 https://doi.org/10.1071/AJ17197
Submitted: 8 December 2017 Accepted: 30 January 2018 Published: 28 May 2018
Abstract
Coal seam gas (CSG) usually contains high levels of methane, which is mostly in the adsorbed state on micropores. For coal that is not highly permeable, stimulation may be required to enhance productivity. In this study, we propose a new technique to increase near wellbore productivity in tight CSG. This technique comprises three stages: injection, soaking and production. Firstly, nitrogen is introduced to the target formation while maintaining high reservoir pressure. Next, the well is shut for a period of time before the gases are flown back to the surface. The technique is based on competitive adsorption of methane and nitrogen during the shut-in period, which yields pressure build-up. Hence, with this combination of desorption, the coal matrix shrinks and permeability eventually increases. The proposed technique was tested by adsorption simulation at core scale. The model was constructed for crushed samples and the extended Langmuir isotherm and micro–macro kinetics models were applied in ASPEN adsorption software. Tight coal was then simulated with different porosity and sorption characteristics. Finally, we used the stress-sensitive permeability model Palmer–Mansoori to predict permeability changes. The results show that permeability is improved based on pressure variations. We observed 10% pressure increments with greater than 150% permeability enhancement. The model indicates the feasibility of the newly proposed technique to produce the ‘unproducible’. However, more experimental and simulation studies at a reservoir scale are needed to fully confirm the technique.
Keywords: core scale, diffusion, desorption, isotherm, Langmuir, nitrogen stimulation, Palmer–Mansoori, permeability enhancement.
Hoa Thuan Nguyen is a master of philosophy candidate at the Australian School of Petroleum (ASP) at the University of Adelaide. Before commencing his candidature, Hoa had worked on an honours project of deep CSG proposed by ASP and Santos Ltd. His research interests focus on unconventional resources such as CSG and gas hydrate. The aim of his current project is to enhance productivity in low permeable CSG. |
Mohammad Sayyafzadeh is a lecturer in Petroleum Engineering at the University of Adelaide. He holds a BSc in Chemical Engineering and MS. in Reservoir Engineering from Tehran Polytechnic and a PhD in Petroleum Engineering from the University of Adelaide. Mohammad’s research interest is Applied and Computational Mathematics targeting Reservoir and Production Engineering problems. He has contributed in publishing more than 20 papers in peer-reviewed journals and conferences, and serves as a reviewer for different journals and EAGE/SPE conferences. He is the lead investigator of a project on developing a computer-assisted history matching tool sponsored by Santos Ltd and participated as a co-investigator and research fellow in three other industrial projects. |
Manouchehr (Manny) Haghighi is an associate professor of petroleum engineering. His research and teaching focus is on unconventional reservoirs, reservoir simulation, well testing, and formation evaluation. He has supervised more than 40 MSc and 10 PhD students. Before joining the University of Adelaide in 2009, Manouchehr was associate professor of Petroleum Engineering at the University of Tehran (Iran). During 2000–07, he was the head of the Petroleum Engineering Program at the University of Tehran. In 2000, Manouchehr established Simtech, a consulting company for integrated reservoir simulation in which he has been project director of several full-field simulation projects for oil and gas reservoirs. Manouchehr has published more than 100 articles in peer-reviewed journals or presented in international conferences. He has served as a reviewer for various journals including the Journal of Petroleum Science and Engineering. |
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