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RESEARCH PAPERS

# Damage Tolerance of Well-Completion and Stimulation Techniques in Coalbed Methane Reservoirs

[+] Author and Article Information
Hossein Jahediesfanjani1

Mewbourne School of Petroleum and Geological Engineering, the University of Oklahoma, Norman, Oklahoma, 73019 USA

Faruk Civan

Mewbourne School of Petroleum and Geological Engineering, the University of Oklahoma, Norman, Oklahoma, 73019 USA

1

T-301 Sarkeys Energy Center, 100 Boyd St. Norman, OK, 73019-1003; electronic mail:Hossein@ou.edu

J. Energy Resour. Technol 127(3), 248-256 (Jan 19, 2005) (9 pages) doi:10.1115/1.1875554 History: Received October 27, 2004; Revised January 19, 2005

## Abstract

Coalbed methane (CBM) reservoirs are characterized as naturally fractured, dual porosity, low permeability, and water saturated gas reservoirs. Initially, the gas, water, and coal are at thermodynamic equilibrium under prevailing reservoir conditions. Dewatering is essential to promote gas production. This can be accomplished by suitable completion and stimulation techniques. This paper investigates the efficiency and performance of the openhole cavity, hydraulic fractures, frack and packs, and horizontal wells as potential completion methods which may reduce formation damage and increase the productivity in coalbed methane reservoirs. Considering the dual porosity nature of CBM reservoirs, numerical simulations have been carried out to determine the formation damage tolerance of each completion and stimulation approach. A new comparison parameter, named as the normalized productivity index $Jnp(t)$ is defined as the ratio of the productivity index of a stimulated well to that of a nondamaged vertical well as a function of time. Typical scenarios have been considered to evaluate the CBM properties, including reservoir heterogeneity, anisotropy, and formation damage, for their effects on $Jnp(t)$ over the production time. The results for each stimulation technique show that the value of $Jnp(t)$ declines over the time of production with a rate which depends upon the applied technique and the prevailing reservoir conditions. The results also show that horizontal wells have the best performance if drilled orthogonal to the butt cleats. Long horizontal fractures improve reservoir productivity more than short vertical ones. Open-hole cavity completions outperform vertical fractures if the fracture conductivity is reduced by any damage process. When vertical permeability is much lower than horizontal permeability, production of vertical wells will improve while productivity of horizontal wells will decrease. Finally, pressure distribution of the reservoir under each scenario is strongly dependent upon the reservoir characteristics, including the hydraulic diffusivity of methane, and the porosity and permeability distributions in the reservoir.

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## Figures

Figure 1

Model for fluid flow through a hydraulically fractured reservoir according to Soliman (38)

Figure 2

Effect of skin factor on productivity of a vertical well

Figure 3

Effect of reduction in near-wellbore methane diffusivity on productivity of a vertical well in compared to a nondamaged well

Figure 4

Effect of changes in the Langmuir pressure constant PL on gas productivity of a vertical well placed in the middle of a CBM reservoir

Figure 5

Effect of changes in the Langmuir volume constant VL on gas productivity of a vertical well placed in the middle of a CBM reservoir

Figure 6

Effect of reservoir anisotropy on productivity index of a vertical well in a CBM reservoir

Figure 7

Effect of cavity radius when permeability of the near-welbore zone doubles to its original value

Figure 8

Effect of cavity radius when permeability of the near-welbore zone is three times of its original value

Figure 9

Effect of cavity near wellbore zone doubles to its original value when permeability of the

Figure 10

Effect of fracture conductivity on productivity of CBM reservoir

Figure 11

Effect of fracture length on productivity of CBM reservoir

Figure 12

Effect of fracture length and height on productivity of CBM reservoir

Figure 13

Effect of reservoir anisotropy and a fracture

Figure 14

Effect of reservoir anisotropy and a fracture with high Conductivity on productivity of CBM reservoir

Figure 15

Effect of damaged conductivity on fracture productivity

Figure 16

Effect of reduced diffusivity on fracture productivity

Figure 17

Productivity of horizontal wells with various lengths

Figure 18

Effect of reservoir anisotropy on horizontal well productivity

Figure 19

Productivity of different completion and stimulation techniques

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