Instability mechanism and countermeasures of coal bed in Daniudi gas field

When the deviated well section of horizontal wells, targeting Shanxi layer and Taiyuan layer of Daniudi gas field, come across coal bed, it is prone to wellbore collape, which affects significantly the operation safety and operation progress. To prevent the collape accidents, the collapse mechanism of coal seams analyzed from bedding architecture and fracture structure of coal seams. Both the slurry and drilling engineering technical measures are obtained to prevent coal collapse, with the study of the drilling engineering parameters and slurry parameters of the drilled horizontal wells. Fistly, within 50 m from the coal seam, the drilling fluid density should be controlled between 1.24-1.26 g/cm3, avoiding sharp fluctuations, and the filtration of drilling fluid should be less than 5 mL. Secondly, the tripping speed should be controlled not more than 10m/min, and the drilling fluid should followe the principle of large displacement and low jet when penetrating the coal bed. The study supplies some directional experience for future drilling engineering design and drilling operation of horizontal wells in Shanxi layer and Taiyuan layer, and collapse accident of drilling coal bed in other oil and gas fields.