The Stress Sensitivity of Coal Bed Methane Wells and Impact on Production

Abstract Coal bed methane (CBM) significantly contributes to unconventional energy resources. With the development of the drilling technology, multi-branched horizontal wells (MBHWs) have been put into the exploitation of CBM. In this paper, a semi-analytical mathematical model is introduced to study the production characteristics of MBHWs in the composite CBM reservoir. Stress sensitivity, composite reservoir, and complex seepage mechanisms (desorption, diffusion, and Darcy flow) are taken into consideration. Through Pedrosa transformation, Perturbation transformation, Laplace transformation, Finite cosine transformation, element discretization, superposition principle, and Stehfest numerical inversion, pseudo-pressure dynamic curves and production decline curves are plotted and 13 flow regimes are divided. Then, the sensitivity analysis of related parameters is conducted to study the influences of these parameters based on these two type curves. Model verification and field application are introduced which shows that the model is reliable. The model proposed in this paper and relevant results analysis can provide some significant guidance for a better understanding of the production behavior of MBHWs in the composite CBM reservoir.

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

Energy Exploration & Exploitation ◽

10.1177/0144598719898537 ◽

2020 ◽

Vol 38 (4) ◽

pp. 1099-1117

Author(s):

Xiuqin Lu ◽

Zhiqi Wu ◽

Xuefei Li ◽

Chen Zhang ◽

Ning Wang ◽

...

Keyword(s):

Methane Production ◽

Single Phase ◽

Fluid Velocity ◽

Stress Sensitivity ◽

Initial Permeability ◽

Coal Bed ◽

Coal Bed Methane ◽

Bottom Hole ◽

Phase Water ◽

Pressure Propagation

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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The Optimization of Production and Drainage of CMB for Multi-Branch Horizontal Well

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.774-776.1446 ◽

2013 ◽

Vol 774-776 ◽

pp. 1446-1450 ◽

Cited By ~ 2

Author(s):

Lei An ◽

Zhenhua Cai ◽

Na Si ◽

Yu Jin Yuan

Keyword(s):

Horizontal Well ◽

Stress Sensitivity ◽

Coal Bed ◽

Coal Bed Methane ◽

Low Permeability ◽

Formation Pressure ◽

Unconventional Gas ◽

Fossil Resource ◽

Pressure Fall

The unconventional gas is the most available alternative fossil resource in China and coal bed methane is big part of it. The main characteristics of coal reservoirs are low permeability, thin formation and strong stress sensitivity. The multi-branch horizontal well is emerging technique for developing CMB and applied successfully in FanZhuang block etc. But a lot of problems need to be solved during production and drainage. Such as coal bed can easily collapse when formation pressure fall fast and strong sensitivity leads cheats system closing. In this paper the operation of CBM wells is discussed and optimized project of production drainage is presented to maximum the productivity of multi-branch horizontal well.

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