A semi-analytical model for drainage and desorption area expansion during coal-bed methane production

Sun, Zheng; Li, Xiangfang; Shi, Juntai; Yu, Peimin; Huang, Liang; Xia, Junshi; Sun, Fengrui; Zhang, Tao; Feng, Dong

doi:10.1016/j.fuel.2017.05.047

Cited by 86 publications

(27 citation statements)

References 15 publications

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“…Although the measured total gas amount is less than the theoretical adsorption gas content estimated by the Langmuir equation at the initial reservoir pressure, few evidences indicate that all the measured gas amounts are in adsorbed state. In reality, the existence of free gas in undersaturated CBM reservoirs has already been proven through field applications (Sun et al 2017(Sun et al , 2018bShi et al 2018aShi et al , 2019b, such as the Muai CBM reservoir in the Junlian production area in the southern Sichuan Basin, the initial water saturation is fitted to be less than 1 during the history matching process, demonstrating there is a small amount of free gas in this undersaturated CBM reservoir. Furthermore, some researchers have concluded that there exist tight sandstone gas layers with free gas from nearby coal seams although these coal seams are measured and classified as undersaturated CBM reservoirs (Li et al 2018), indicating that there must exist free gas in these undersaturated CBM reservoirs in the past and there may still exist some free gas at the current state.…”

Section: Discussionmentioning

confidence: 96%

“…The CBM reservoir, as one of the unconventional gas reservoirs, has unique flow mechanism and production schedule (Aminian et al 2004;Clarkson and Salmachi 2017;Jenkins and Boyer 2008). CBM is produced through dewatering to make adsorbed gas desorb from the interface of coal matrix after the critical desorption pressure is achieved (Jenkins and Boyer 2008;Sun et al 2017Sun et al , 2018a. Before gas production, only water can flow in the cleat system, even though in some cases there is a small amount of free gas; but since its saturation is less than the critical flowing saturation, gas cannot flow but will expand in volume.…”

Section: Introductionmentioning

confidence: 99%

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Methods for simultaneously evaluating reserve and permeability of undersaturated coalbed methane reservoirs using production data during the dewatering stage

Shi

Sun

et al. 2020

Pet. Sci.

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In this work, a flowing material balance equation (FMBE) is established for undersaturated coalbed methane (CBM) reservoirs, which considers immobile free gas expansion effect at the dewatering stage. Based on the established FMBE, five straight-line methods are proposed to determine the control area, initial water reserve, initial free gas reserve, initial adsorbed gas reserve, original gas in place, as well as permeability at the same time. Subsequently, the proposed FMBE methods for undersaturated CBM reservoirs are validated against a reservoir simulation software with and without considering free gas expansion. Finally, the proposed methods are applied in a field case when considering free gas expansion effect. Validation cases show that the straight-line relationships for the proposed five FMBE methods are excellent, and good agreements are obtained among the actual reserves and permeabilities and those evaluated by the proposed five FMBE methods, indicating the proposed five FMBE methods are effective and rational for CBM reservoirs. Results show that a small amount of free gas will result in a great deviation in reserve evaluation; hence, the immobile free gas expansion effect should be considered when establishing the material balance equation of undersaturated CBM reservoirs at the dewatering stage.

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Section: Discussionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Methods for simultaneously evaluating reserve and permeability of undersaturated coalbed methane reservoirs using production data during the dewatering stage

Shi

Sun

et al. 2020

Pet. Sci.

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“…Xu等人 [19] 提出一种能简单预测煤层气井解吸区扩展规律的半解析模型, 考虑了不同生产阶段储层内部的压力展布, 但忽略了储层单元内流体饱和度分布. Clarkson和Qanbari [20] [10,19] :…”

Section: Clarkson模型仅能适用于煤层气井的生产早期和晚期unclassified

A mathematic model for characterizing the relationship between coal reservoir pressure and fluid saturation

Sun¹,

Li²,

Xu³

et al. 2018

Sci. Sin.-Tech.

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“…permeability reduction should be relatively less and the drainage area should be enough longer. From this point, some prediction models for drainage area and desorption area expansion have been proposed (Sun et al, 2017(Sun et al, , 2019aWan et al, 2016). These models require to combine with the actual water production to get the drainage radius, which is not suitable for the dewatering rate optimization in the early single-phase water.…”

Section: Introductionmentioning

confidence: 99%

Novel method for optimizing the dewatering rate of a coal-bed methane well

Wu²,

Li³

et al. 2020

Energy Exploration & Exploitation

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The reasonable dewatering rate in the single-phase water flow plays an essential role in pressure propagation and coal-bed methane production. However, current fluid velocity sensitivity experiments cannot provide an optimum dewatering rate for field coal-bed methane production. This study proposes a new method to optimize the dewatering rate for coal-bed methane wells by assuming the investigation distance reaches the well boundary when the bottom hole pressure declines to the critical desorption pressure. The effect of the stress sensitivity and fluid velocity sensitivity on pressure propagation was first simulated with COMSOL Multiphysics software. The results showed that the expansion area considering the stress sensitivity is shorter than that neglecting the stress sensitivity when the bottom hole pressure reached to the critical desorption pressure at 200 days. The expansion area with high dewatering rate will be shorter about 35 m than that with low dewatering rate at 200 days. The relationship between the maximum investigation distance and required time was established to optimize the dewatering rate by combining the pressure profile considering the influence of stress sensitivity with material balance equation. The new model indicates that the initial permeability, porosity, and cleat compressibility have an important effect on investigation distance. The simulation of these parameters’ sensitivity suggests that the bigger the ratio of initial permeability and porosity, the longer the investigation distance is, and the smaller the cleat compressibility is, the longer the expansion area is. According to this model, we need to take more than 600 days at 0.58 m/d constant dewatering rate to reach the maximum investigation distance of 0.67 mD initial permeability. This work can be conducive to choose reasonable dewatering rate in single-phase water flow for coal-bed methane well production.

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A semi-analytical model for drainage and desorption area expansion during coal-bed methane production

Cited by 86 publications

References 15 publications

Methods for simultaneously evaluating reserve and permeability of undersaturated coalbed methane reservoirs using production data during the dewatering stage

Methods for simultaneously evaluating reserve and permeability of undersaturated coalbed methane reservoirs using production data during the dewatering stage

A mathematic model for characterizing the relationship between coal reservoir pressure and fluid saturation

Novel method for optimizing the dewatering rate of a coal-bed methane well

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