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Time-Pressure Correlation to Estimate Dewatering Time for Coalbed Methane Reservoir at Saturated and Undersaturated Condition

Permana, I Gde; Hutami, Dinar Citra Indar; Alhamzany, Isna Kamalia; Alam, Hudan Wira; Wicaksono, Sri Konsep Harum
Petroleum Engineering Master Program, Institute Technology of Bandung, Bandung, Indonesia.

In Coalbed Methane reservoir, while some free gas may exist in the coal deposits, the majority of the gas is adsorbed on the surface of the coal matrix. At undersaturated condition, when reservoir pressure is above critical desorption pressure, only water is produced.

Initially the natural fractures of the coal are typically water saturated. This water has to be removed in order to achieve any significant gas production. Dewatering of the coal seam reduces the reservoir pressure, which allows the gas to be desorbed from the coal matrix so that gas to flow to the wellbore. Proper dewatering of CBM wells is the key to efficient gas production from these reservoirs. Dewatering processing consumes much times and it is not effective for well development time. The problem encountered during dewatering process to determine the time of gas began to flow, where the reservoir is still undersaturated condition. In this paper, authors would like to recognize dewatering time using time-pressure correlation.

Therefore, in this paper, authors show correlations indicating the relationship between the initial pressures at saturated and undersaturated condition versus dewatering time. For saturated condition at typical condition for CBM reservoir, correlation by Thungsungtonkhum will be employed. At this condition, there will be two phase water and gas production. The correlation shows that gas flow rate and water flow rate will be calculated from the integral function of pressure as Darcy flow because it is assumed there is no diffusion while the cleat is filled by water. For undersaturated condition, King and Ertekin correlation will be employed by assuming there is diffusion phenomenon using Fick's Law.

Time-pressure correlation will show linear relationship for dewatering time. This correlation can be applied generally in similar CBM reservoir properties in this paper. Dimensionless correlation can also be generated from pressure and dewatering time.

 

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012