刘洪林 王红岩 张建博
摘要：煤层气吸附时间是煤层气生产的一个重要参数 ,它直接影响煤层气井的产气速度和产气高峰到来的早晚。通过对影响吸附时间的因素的分析 ,作者认为 :煤阶、灰分、温度、显微煤岩类型、割理发育程度及煤样粒度等参数是影响吸附时间长短的最重要的因素。我国主要煤层气盆地的吸附时间一般为 0 .17～ 2 7.42d。吸附时间对产量的敏感性表明 ,中国的煤层气吸附时间对煤层气单井产量影响不大。
王可新 傅雪海 权彪 王继尧 申建
Influence of sorption time in CO2-ECBM process in Indian coals using coupled numerical simulation
V. Vishal T.N. Singh P.G. Ranjith
Abstract: Production of coal-bed methane from a reservoir is a function of several parameters, including in situ gas content, the permeability of the coal, and the thickness of the coal seams. Such coal seams usually have low sorption time and there is an easy release of methane from coal upon pressure depletion due to water extraction. Coals with high sorption time are usually not suitable from an economical point of view. This study investigates the role of sorption time in the production behavior of coal under carbon dioxide injection using numerical simulation. A thick coal seam at an intermediate depth of 1600 ft was modeled with two production wells and one injection well between them. Sorption time was varied and the water/methane production and CO2 injection behavior were monitored up to a period of 4000 days. It was found that coals with non-equilibrium sorption time have high CO2 adsorption capacity. Therefore, they can be considered for the enhanced recovery of methane with gas injection. A large quantity of water is released from this type of coal until the start of methane desorption, and despite CO2 injection the onset of gas release remains delayed. At the end of the first year, a reduction of nearly 50% water production was computed for coal with sorption time τ = 0.1 day, while water release reduced by only 23.5% for coal with τ = 50 days. The rate of CO2 injection after six months duration increased to 41.6 mscfd in the case of high sorption time coal, while it rose to only 20 mscfd for low sorption time coal, indicating almost double the rate of gas injection in the former case. The first year methane production from a coal with τ = 0.1 day was 90 mscf, and that for τ = 300 days was 42 mscf. At the end of the fifth year, the cumulative gas production was 842 mscf and 613 mscf respectively for the respective varieties, showing that the difference slowly reduced. Possible mechanisms to understand the behavior of coals with different sorption times are proposed. It is also established that coals with sorption time less than 10 days follow an equilibrium trend in typical Indian Gondwana settings.
Investigating the effect of sorption time on coalbed methane recovery through numerical simulation
Ali S.Ziarani Roberto Aguilera Chris R.Clarkson
Abstract: The objective of this work is to study the effect of non-equilibrium sorption time on the gas production rate in coalbed methane (CBM) reservoirs. Numerical simulation is employed to investigate this phenomenon in coal seams with single-phase flow of methane and two-phase flow of methane and water. Radial and rectangular models with vertical and horizontal wells are considered. A multi-layered model is also generated with properties similar to the Horseshoe Canyon (HSCN) formation in Alberta. The results indicate that the sorption time affects the production rate in the early production phase, namely a few months to a few years depending on how slow the desorption/diffusion process is, but this depends on the magnitude of the sorption time. This is valid both for dry and initially water saturated coalbed methane reservoirs. However, in the latter case, the effect lasts longer since the dewatering must occur first for desorption/diffusion process to start. The type of wellbore also influences the dynamics of sorption/diffusion effects. For smaller diffusion coefficients (larger sorption times), the gas decline rate in horizontal wells is larger relative to vertical wells. The results of the multi-layer study indicate that when sorption time is smaller than 10 days, the effect of sorption/diffusion phenomena on total commingled production rate is negligible. In general, we recommend non-equilibrium models for early-time production when diffusion flow from matrix to fracture is still in transient state. For late-time production, when steady-state diffusion flow has been established between matrix and fracture, equilibrium models can be used.
Desorption Behavior of Coalbed Gas and its Anisotropy Within High Rank Coal Reservoir in the Zhengzhuang Block of the Southern Qinshui Basin, China
Junqian LI, Shuangfang LU, Pengfei ZHANG, Ping ZHANG, Jianjun CHEN