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13 Feb 2018

Gas Production Strategy of CBM Formation using Sacrifice Well

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Coal Bed Methane (CBM) is an unconventional resource that shows great promise, particularly in Indonesia, whose CBM reservoir is relatively thick. Gas reserves of CBM are estimated at 450 TSCF in Indonesia, which makes it, the 6th largest CBM-containing country in the world. However, regulatory and technical limitations slow the progression of the exploitation of this resource. One of the fundamental technical problems is related to the length of gas production due to the duration of the dewatering time. Many studies have been developed related to the production of CBM, and this paper discusses several characteristics, patterns and techniques regarding the production of methane gas from coal through the use of a sacrifice well.  Several scenarios are analyzed with the use of a simulator. The results show that the production of a thick CBM reservoir, with some sensitivity patterns of production through the use of a sacrifice well, have an influence on the production of gas and water for the exploitation of CBM resources. In other words, the use of new techniques that are discussed in this paper have an impact on reducing the dewatering time and are effectively implemented in Indonesia, which has thick CBM formations.

 

Based on the simulation result done on various sensitivities of CBM production patterns through sacrifice wells, hence can be concluded that the application of 3 horizontal wells at the bottom of the well is much more effective and efficient as a sacrifice well as well as production well from a technical point of view than the application of 6 vertical wells. The thicker a reservoir CBM, the gas rate will be and due to the influence of gravity, the faster the gas out of the CBM surface so that gas production is relatively easy. The thicker a reservoir CBM then the water rate on the sacrifice well and production well will be bigger, and dewatering time will also be longer. The use of wells at the top of the CBM reservoir and the opening of wells with different time with the opening of the sacrifice well will assist in accelerating the gas production that tend to have a low water content and also higher rate of gas. The application of two horizontal (T) wells is more effective and efficient in producing gas from technical point of view than the application of 2 cross horizontal wells (x). If a CBM well production uses sacrifice well at bottom reservoir, it is advisable to install a production well that is far enough from sacrifice well. And if possible, production well is installed on top reservoir only.