RESUMO
Horizontal wells have significant advantages in coal bed methane exploration and development blocks. However, its application in new exploration and development blocks could be challenging. Limited geological data, uncertain geological conditions, and the emergence of micro-faults in pre-drilled target coal seams make it hard to accurately control the well trajectory. The well trajectory prior to drilling needs to be optimized to ensure that the drilling trajectory is within the target coal seam and to prevent any reduction in drilling ratio (defined here as the percentage of the drilling trajectory in the entire horizontal section of the well located in the target coal seam) caused by faults. In this study, the well trajectory optimization is achieved by implementing the following process to drill pilot hole, acquire 2D resonance, and azimuthal gamma logging while drilling. The pilot hole drilling can obtain the characteristic parameters of the target coal seam and the top and bottom rock layers in advance, which can provide judgment values for the landing site design and real-time monitoring of whether the wellbore trajectory extends along the target coal seam; 2D resonance exploration can obtain the construction of set orientation before drilling and the development of small faults and formation fluctuations in the horizontal section, which can optimize the well trajectory in advance; the azimuth gamma logging while drilling technology can monitor the layers drilled by the current drill bit in real time, and can provide timely and accurate well trajectory adjustment methods.The horizontal well-Q in the Block-W of the Qinshui Basin was taken as a case study and underwent technical mechanism research and applicability analysis. The implementation of this new innovative process resulted in a successful drilling of a 711 m horizontal section, with a target coal seam drilling rate of 80%. Compared to previous L-type wells, the drilling rate increased by about 20%, and the drilling cycle shortened by 25%. The technical experience gained from this successful case provides valuable insight for low-cost exploration and development of new coalbed methane blocks.
RESUMO
In this study, the change law of the surface subsidence coefficient under the condition of thick coal seam layered mining was investigated. The study is based on the measured subsidence data of the 1210-working face of the Mengba mine surface mobile observation station after the first- and second-layer mining. UDEC numerical simulation software was used to simulate the variation of surface subsidence coefficient after the first, second, third, fourth, fifth-, and sixth-layer mining when the thickness of slicing mining is 5 m. The maximum relative error between the simulated result and the measured result of the subsidence coefficient q is 2.7%, which further verifies the correctness of the established model. Moreover, the simulation results show that with the increase of the cumulative mining thickness, the subsidence coefficient q of the surface presents a segmented characteristic. When the cumulative mining thickness does not reach 25 m, the subsidence coefficient of the surface gradually increases with the increase of the mining thickness. On the other hand, when the cumulative mining thickness reaches 25 m, the subsidence coefficient of the surface will tend to a constant value and no longer change with the increase of the mining thickness. Finally, the calculation formula between the surface subsidence coefficient and the cumulative mining thickness of layered mining under the condition of medium hard roof is fitted, which provides a parameter basis for coal seam mining with similar geological conditions.