Abstract
Coalbed methane (CBM) has been exploited in the deep area of the coal reservoir (>1000 m). The production of CBM vertical wells is low because of the high in situ stress, large buried depth, and low permeability of the coal reservoir. In this paper, efficient and advanced CBM development technology has been applied in the Libi Block of the Qinshui Basin. According to the characteristics of the coal reservoir in the Libi Block, the coiled tubing fracturing technology has been implemented in four cluster horizontal wells. Staged fracturing of horizontal wells can link more natural fracture networks. It could also expand the pressure drop range and control area of the single well. This fracturing technology has achieved good economic results in the Libi Block, with the maximum production of a single horizontal well being 25313 m3/d and the average single well production having increased by more than 60% from 5000 m3/d to 8000 m3/d. Based on the data regarding the bottom hole pressure, water production, and gas production, the production curves of four wells, namely, Z5P-01L, Z5P-02L, Z5P-03L, and Z5P-04L, were investigated. Furthermore, a production system with slow and stable depressurization was obtained. The bottom hole pressure drops too fast, which results in decreasing permeability and productivity. In this work, a special jet pump and an intelligent remote production control system for the CBM wells were developed; hence, a CBM production technology suitable for the Libi Block was established. The maximum release for the CBM well productivity was obtained, thus providing theoretical and technical support for CBM development with geological and engineering challenges.
Highlights
Coalbed methane (CBM) is an unconventional natural gas generated by geological and biological processes in coal seams [1, 2]
In the CBM development of the Libi Block, coiled tubing driven fracturing technology is used in cluster horizontal wells for hydraulic sand blasting perforation, which can be completed in a single operation. e fracturing technology in the Libi area will be implemented in accordance with the CBM industry standard “technical specification for CBM well fracturing.” e proppant combination consists of 40–70 mesh, 16–30 mesh quartz sand, and 12–20 mesh lowtemperature curable coated sand. e fracturing fluid is composed of clean water and 2% KCl
All horizontal wells that have been put into operation have achieved high and stable production. e Libi Block set a record for the highest gas production of a coal reservoir with high stress, large buried depth, and low permeability on July 31, 2015. e maximum production of a single horizontal well is 25313 m3/d, and the average stable production of a single well is 8100 m3/d. e average production of a single vertical well in the area around is less than 600 m3/d
Summary
Coalbed methane (CBM) is an unconventional natural gas generated by geological and biological processes in coal seams [1, 2]. 3. Influence of In Situ Stress on Hydraulic Fracturing Fractures e hydraulic fracturing technology can improve the seepage channel and enhance the permeability of the coal reservoir, providing the most effective means to improve the production of the CBM well. Since coal reservoirs in China are generally characterized by low pressure, low permeability, low gas saturation, and strong heterogeneity, hydraulic fracturing stimulations are required in order to provide guidance for CBM exploration. Where σv is the vertical stress, MPa; D is the buried depth of the formation, D > 300 m; pp is the pore pressure, MPa; σh is the minimum horizontal stress, MPa; v is Poisson’s ratio; b is minimum stress coefficient, b 0.035; and σH is the maximum horizontal stress, MPa. Horizontal well fracturing is an effective technology for complex geological conditions with high in situ stress and low permeability [40]. (1) Hydraulic fracturing of a single vertical well is developed to the staged fracturing of horizontal wells (2) Based on the active water, multifracturing fluid gradually becomes favored (3) e single primary fracturing develops to the deplugging fracturing and re-fracturing (4) e scale of fracturing increases, and the trend towards fracturing factory is observed
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