Optimal and fast drilling technology for coalbed methane horizontal wells in Liupanshui Coalfield

The Liupanshui Coalfield features significant terrain fluctuations and complex lithology. When implementing drilling for coalbed methane horizontal wells within the mining area, experiences from other provinces are generally referenced. However, there hasn't been a systematic study and analysis on the compressive strength, hardness, drillability, internal friction angle, and other rock mechanical properties of the coalfield strata, in addition, corresponding profiles of rock mechanical parameters are also unavailable. Therefore, there exists challenges in horizontal well placement, improper wellsite layout, poor compatibility between drill bits and drill stems, oversized bottom hole assembly (BHA), and unreasonable engineering parameter design during coalbed methane horizontal well drilling. To effectively address these issues, a novel "well factory + matrix layout + diamond target setting + 124" intensive land use step-by-step drilling mode and an optimized mechanical specific energy model were adopted. And the variability of drillability along the vertical stratigraphic sequence within the coalfield was thoroughly analyzed, leading to the establishment of a drillability prediction table for the coalfield strata. Additionally, optimization was conducted on parameters such as the number of PDC bit blades, the size and shape of cutting teeth, tooth arrangement, drill stems and BHA, engineering parameters, and high-performance drilling fluid systems, all aimed at enhancing energy utilization efficiency, properly improving the mechanical specific energy model correction coefficients, and delaying the onset of instability. The research results show that by employing the new step-by-step drilling mode and optimized tools, materials, BHA, engineering parameters, drilling fluid systems, etc., the cost of a single well on site was by 12.00% compared with the before, and the average rate of penetration for each spud was increased by more than 18%, which realized the speed-up, cost-reduction and efficiency-enhancement drilling of coalbed methane horizontal wells.