Method for transforming coal bed gas horizontal well system

Abstract

The invention discloses a method for transforming a coal bed gas horizontal well system. The method comprises the following steps that a low-rank coal bed or a construction coal bed is selected for transformation; a first horizontal well track drills through a lower bottom plate of a target coal bed, and then drilling is carried out in the horizontal direction according to the coal bed track; cement is adopted for well cementation in the first horizontal well track; windowing sidetracking is carried out on the first horizontal well track at the upper boundary portion of the target coal bed and the position with the well deviation angle being 45-75 degrees to form a second horizontal well track, and then drilling is carried out in the horizontal direction; production casing pipes are put from the horizontal section of the first horizontal well track to the well bottom and from the windowing sidetracking point of the second horizontal well track to the well bottom respectively to form a first horizontal well and a second horizontal well; directional perforation is carried out on the second horizontal well downwards, and large-scale staged fracturing or dragging fracturing is carried out; directional perforation is carried out on the first horizontal well upwards, and hydraulic jetting or small fracturing seam forming is carried out; and an oil pipe is put to the lower boundary of coal bed gas for water drainage and pressure reduction gas recovery. The development efficiency of the coal bed gas on construction coal and low-rank coal is improved.

Description

technical field [0001] The invention relates to the technical field of exploitation of underground fluid resources, in particular to a method for reforming a coalbed methane horizontal well system. Background technique [0002] Coalbed methane is usually exploited by vertical wells, directional wells and horizontal wells, and the common horizontal well technology is divided into single main branch horizontal well, two main branch multi branch horizontal well, single main branch multi branch horizontal well and multi-stage pressure well. Fractured U-shaped horizontal wells and secondary multi-stage fracturing horizontal wells, the common goal of various mining methods is to improve the efficiency of coalbed methane mining and increase the input-output ratio. [0003] Due to the diversity of coal seam geological conditions in different regions of my country, as well as the different content of high, medium and low coal ranks in each block, the mining effect is very different. ...

AI Technical Summary

Problems solved by technology

At present, structural coal and low-rank coal, which account for 80%, are still in an inefficient development state, that is, the input-output ratio is very poor

[0004] The main problems are: first, the production efficiency of vertical wells and directional wells is low

Second, the conventional horizontal well technology has poor wellbore stability in low-rank coal and tectonic coal seams, is prone to collapse, and is prone to complex accidents such as lost circulation and collapse and stuck pipe

Fifth, the trajectory of the coal seam has a great influence on the drainage; with the change of the inclination angle of the coal seam, grooves are easy to form in some well sections, and water plugs are formed when the drainage is put into production

When there is structural coal at the bottom of the coal seam and is drilled, coal ash will accumulate in the groove, causing "ash plugging" during mining, which is not conducive to high production

Sixth, low-rank coal seams have characteristics such as low permeability and coal fragmentation, resulting in low or no gas production in CBM wells

However, in the solution provided by this patent, the horizontal well is drilled in the coal seam, which still does not solve the problem of the borehole wall collapse of the low-rank coal, and with the prolongation of the mining time, the seepage channel is gradually blocked, resulting in low or no gas production in the later stage. The problem of gas production, the actual extraction efficiency is not high

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