Breakthrough in Shallow Gas Production Technology in Coalbed Methane and Oil-gas Symbiotic Areas in China
Based on the shale gas development process, Xi'an Research Institute of China Coal Science and industry group innovated and adopted the coal measure gas development horizon optimization technology, large dip horizontal well drilling technology, extra thick reservoir stimulation and transformation technology and coal measure gas drainage and production technology, breaking through the technical bottleneck of shallow coal measure gas development in the area of coalbed methane and oil-gas symbiosis.
It is understood that limited by the preservation conditions of free natural gas, coal measure gas, as a clean gas energy with rich reserves and large-scale development, can be exploited at a favorable depth of more than 1500 meters. There has always been a bottleneck in the development technology of shallow coal measure gas.
Haishiwan coal mine of Yaojie Coal Power Group is located in a typical coalbed methane and oil-gas symbiotic mining area, and the coal measure gas is buried shallow. At the same time, there are coal and carbon dioxide outbursts in the mining area, which are prone to accidents such as oil and gas gushing, combustion and explosion. There is an urgent need to break through the technical bottleneck.
In the early work of Haishiwan coal mine, the methods of mining the upper protective layer of oil shale, bottom drainage roadway construction through layer drilling, two construction bedding drilling of working face, gas drainage in the goaf of oil shale working face, and gas drainage by trusteeship in the upper corner of working face have been tried successively, but they have not been effective.
Relying on major national science and technology projects, Xi'an Research Institute of China Coal Science and technology has developed layered pressure control and drainage technology and equipment for broken soft and low-permeability coal seams, which has solved the problem of obvious differences in physical properties of multi-source reservoirs of coal measure gas and great difficulty in CO mining.
The stratum structure of the mining area is complex. If the gas drainage in the main mining coal seam is considered only according to the traditional method and the oil shale, oil sand layer and oil a layer are ignored, it will not only effectively reduce the underground gas content, but also cause a waste of natural gas resources. At the same time, the formation dip angle is large, which brings great difficulty to horizontal well drilling.
Therefore, through theoretical analysis and field test, Xi'an Research Institute has selected coal layer 2, oil layer a and oil shale with good gas bearing, permeability, organic carbon content and gas measurement as the target horizon for coal measure gas development. In order to solve the problem of large dip angle, which is not conducive to drilling, they innovatively adopted the large angle horizontal well drilling technology, used the rotating self-guided floating shoes and floating coupling tools for the first time, solved the problem of casing running of horizontal wells in complex formations, and completed the first "L" type CBM horizontal well in Gansu Province, with a horizontal section length of 846m and a drop of 210m, At the same time, it has also created the record of the maximum drop of CBM horizontal wells in China.
Because the selected target coal layer 2, oil layer a and oil shale belong to extra thick production layers, the conventional coal seam gas fracturing method can not achieve the transformation effect. Based on the actual situation, Xi'an Research Institute creatively adopts multi-stage clustering and flow limiting perforation to improve the sand carrying capacity of liquid. They adopted a new pressure perforation technology to realize interlayer plugging and continuous fracturing, solve the problems of small spacing between oil layer a and coal layer 2, low permeability of coal layer 2 and long blowout time after fracturing, and shorten the construction cycle; The fracturing technology with large displacement, large sand volume and low sand ratio suitable for dense and extra thick production layer has been adopted to increase production. In addition, in view of the high concentration of carbon dioxide in oil layer a and coal layer 2 and the problem that carbon dioxide dissolved in water enters the pump barrel during drainage and production, it is very easy to cause gas lock and affect the pump efficiency, they innovatively adopted two technologies: reducing the pump hanging position and gravity spiral gas anchor, which greatly reduces the gas volume entering the pump barrel.
The breakthrough of these technical bottlenecks makes it possible to co mine shallow coal measure gas in coalbed methane and oil-gas symbiotic areas, and releases huge energy resources. At present, the daily gas production of a single well in Haishiwan mining area is as high as 2580 cubic meters, with a maximum cumulative gas production of 24.5 × 104 m3; The mining cost of the protective layer is saved by 267 million yuan, the excavation cost of the bottom extraction roadway is saved by 106 million yuan, and the utilization of the extracted coal system gas can create a profit of 114 million yuan.
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