The Volume Fracturing Construction Of The First Coal-rock Gas Well Was Successfully Completed

Well Niu 21 is the first and deepest coal-rock gas vertical well in Qinghai Oilfield. Its main purpose is to explore the effective means of utilizing the coal-rock gas of Eboliang No. 1 and achieve a breakthrough in the field of coal-rock gas exploration in the Qaidam Basin.

For the oil test and fracturing work of this well, the technical personnel of the Oil and Gas Technology Research Institute carried out "back-to-back" design and integrated improvement with Changqing Oilfield, the Exploration Branch of the General Institute, and the Downhole Operations Institute of the Engineering Institute, and jointly carried out technical research based on a large amount of research. Through the early reservoir quality evaluation, it was found that the single-layer thickness of the coal seam in this well was small, the interlayers with sandstone and mudstone were developed, and the burial depth was deeper than the main deep coal rock in China. There were difficulties in transformation such as high construction pressure, unstable coal body structure, strong plasticity and large filtration loss. The technical personnel learned from the advanced construction practices of the main coal-rock gas transformation in China, optimized the construction scale and fracturing parameters, and combined with key information such as physical parameters, oil and gas display, cementing quality and the transformation situation of the early blocks, and put forward the "reverse composite + high displacement + combined proppant + high-intensity sand addition" volume fracturing technology idea in a targeted manner, optimized the proppant type and combination, 70/140 mesh silt sand was used to reduce filtration loss in the early stage, 40-70 mesh ceramsite was used to support the distal fractures, and 30-50 mesh ceramsite was used to fill the main fractures. Combined with the temporary plugging of secondary holes to ensure the effective transformation of each small layer and the tail chasing fiber to reduce the sand production after fracturing, the full support of the complex fracture network was achieved, the sand addition strength was improved, the conductivity was guaranteed, the fractures were finely layered vertically, and the distal ends were affected horizontally, so as to increase the complexity of the fractures and increase the transformation volume. To ensure the smooth implementation and ideal effect of fracturing construction, the technicians carefully observed the construction pressure, displacement, liquid volume, sand ratio and other data, used high-frequency pressure technology for construction monitoring, tracked the fracturing dynamics throughout the process, observed the fracturing fluid in real time, adjusted the construction parameters in time, and finally successfully completed the fracturing construction task of Well Niu 21.

The success of Well Niu 21 not only opened up a new situation for the exploration of coal-rock gas in Eboliang No. 1, but also provided important reference basis and valuable experience for the fracturing construction of coal-rock gas in the Qaidam Basin, and also laid a solid foundation for Qinghai Oilfield to achieve a breakthrough in coal-rock gas exploration.