Application and improvement directions of rodless drainage technology in coalbed methane wells: A case study from east margin of Ordos Basin

The eastern margin of Ordos Basin has a huge amount of coalbed methane resources, and has become one of the main coalbed methane producing areas in China. Since the development of the block, hydraulic rodless pump, hydraulic jet pump, electric submersible pump and diaphragm pump drainage and production process tests have been carried out for highly deviated wells and horizontal wells in medium shallow coal seam. During production, it is found that the above four types of rodless drainage and production processes have the advantages of effectively avoiding eccentric wear of pipes and rods in highly deviated wells and horizontal wells, however, they have general ability to prevent pulverized coal and sand, corrosion and scale and some disadvantages such as the risk of high-pressure puncture and leakage, the limited depth of lowering the pump, and the poor reliability of ground equipment. By analyzing the test results of rodless drainage technology of medium shallow coalbed methane wells in the early stage of the block, the advantages and disadvantages of various rodless drainage technologies are summarized, and the improvement direction of rodless drainage technology of medium shallow coalbed methane wells is pointed out. At present, as the exploration and development field of coalbed methane has gradually shifted from medium shallow coal seam to deep coal seam, the original rodless drainage and production process of medium shallow coalbed methane wells has been unable to meet the drainage and gas production demand of deep coalbed methane wells. In view of the geological characteristics of deep coalbed methane, such as “development of primary structure coal, high formation pressure, high gas content, high saturation, coexistence of free gas and adsorbed gas” and the production characteristics of “early gas breakthrough and high gas-liquid ratio”, it is considered that the rodless drainage process of deep coalbed methane wells needs to jump out of the rodless drainage process of medium shallow coalbed methane wells. We can learn from the gas production process experience of pilot test wells of tight gas and sea land transitional phase shale gas in the block, and carry out the tests of “concentric pipe gas lift”, “small tubing + bubble drainage” and “coiled tubing + plunger + gas lift” on the production site, which can effectively avoid the shortcomings of the traditional rodless drainage process and realize the efficient development of deep coalbed methane.