High-efficiency coalbed methane extraction method by staged fracturing in multi-bottom horizontal wells in thin coal seam groups with large spacing

Abstract

A method for efficiently extracting coalbed methane by staged fracturing of multi-bottom horizontal wells in large-spacing thin coal seam groups, comprising combining factors such as coal mining planning and coalbed methane resources, forming 2-3 target production layers in layers with enriched coal seams According to the target production layer group, set the layout of each lateral wellbore of the multi-bottom horizontal well, determine the structure of the U-shaped or L-shaped multi-bottom horizontal well, carry out drilling, casing and cementing construction, and the multi-bottom casing respectively. The wellbore of each branch of the horizontal well is perforated, staged through multi-layer fracturing, pressure drop after fracturing, blowout, sand flushing, and well flushing to meet the running requirements of drainage equipment, install drainage equipment, and carry out Fine drainage and construction of cluster-type U-shaped or L-shaped multi-bottom casing horizontal well groups; the invention can overcome the problems of insufficient thickness of the current target production layer, small influence range of hydraulic fracturing and poor stimulation effect, etc. The rapid and efficient extraction of coalbed methane in thin-spaced coal seam groups can significantly improve the single-well coalbed methane production and recovery rate, meet the requirements of mine gas control standards, and solve the problem of unbalanced extraction and mining.

Description

technical field [0001] The invention relates to the technical field of high-efficiency extraction of coalbed methane (gas), in particular to a method for efficient extraction of coalbed methane by staged fracturing of multi-bottom horizontal wells in thin coal seam groups with large intervals. Background technique [0002] In coal-bearing areas such as the Permian in southwest my country and the Cretaceous in northeast China, the thickness of the coal-bearing strata is relatively large, and the coal seam group is developed. There are many coal seams and small thickness of coal seams. The distance span between the coal seam and the bottom coal seam is very large. In addition, many coal seams are broken and soft with low permeability. Usually, the conventional development methods of surface vertical wells, cluster wells or horizontal wells are used in the development of coalbed methane in such areas, and the gas production effect is not ideal, and the input-output ratio is ver...

AI Technical Summary

Problems solved by technology

[0003] (1) Conventional development methods such as surface vertical wells or cluster wells, single-layer or multi-layer composite layer hydraulic fracturing, and composite layer drainage are adopted. First, due to the small thickness of a single layer of coal seam, the cumulative thickness of the produced target production layer is insufficient; Second, because the coal seam is broken and soft, and the permeability is low, hydraulic fracturing fractures do not extend long in relatively plastic coal seams, and the scope of influence is limited, and the effect of fracturing stimulation is not good; , due to the large span between the upper coal seam and the lower part, as the dynamic liquid level decreases, the upper broken soft low-permeability coal seam will be exposed above the dynamic liquid level, the effective stress will increase too much, and the pores in the coal will lose the flow pressure support of the fluid However, it tends to be closed and the permeability tends to zero, resulting in a sharp decrease in the gas production of the upper coal seam, or even no gas production. The gas production of a single well decays rapidly, and it is impossible to achieve multi-layer commingled production, each layer contributes to gas production, and the gas production superimposes to increase effect

[0004] (2) Conventional horizontal well development method is adopted. Due to the insufficient thickness of the target production layer in the single coal seam drilled, the construction of horizontal wells in the broken soft coal seam is prone to hole collapse and buried drilling accidents, and it is difficult to complete the well, and the permeability of the broken soft coal seam is low. and other problems, the gas production rate of a single well is not high

The horizontal well section of this patent method is constructed in the coal seam, and there is also the problem of only solving the extraction of a single coal seam, and it is only suitable for the hard coal seam with relatively good coal structure, not suitable for the broken soft coal seam, because in the broken soft coal seam Drilling is prone to technical problems such as collapse and buried drilling, difficulty in well completion, failure to drill horizontal well sections, and difficulty in running casing

Therefore, the above two patents are not suitable for the CBM extraction of thin coal seam groups with large spacing

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