High Plugging Capacity Drilling Fluid Technology for Deep Buried Coal-Bed Methane Drilling in Jizhong Area

Horizontal drilling of deep buried coal-bed methane in Jizhong area has been faced with several difficulties and challenges such as quite limited data for reference, many geologic uncertainties, thin coal-bed layers which are easy to collapse and have difficulties in trajectory control, as well as high risks of pipe sticking etc. Extensive studies on the characteristics of the deep buried coal-bed reservoirs have concluded that the stability of the borehole wall in the coal-bed formations is controlled both by mechanical factors and physio-chemical factors, the key points of technology in solving this problem is to improve the plugging capacity and inhibitive capacity of the drilling fluid. A drilling fluid with high plugging capacity was formulated to drill the coal-bed formations by treating a compounded salt drilling fluid with rigid micro- and nano-plugging agents and deformable plugging agents. Laboratory experiments on the drilling fluid with hot rolling test, sand-bed plugging test and ceramic filter plugging test show that this drilling fluid has inhibitive capacity and plugging capacity better than those of KCl polymer drilling fluids and compounded salt drilling fluids. This drilling fluid has been used in drilling the well Xintan-1H and proved that the plugging agents have good compatibility with other additives and no negative effect on the properties of the drilling fluid. The addition of the plugging agent into the drilling fluid greatly reduced the API filtration rate and effectively maintained the borehole wall stability. In drilling the 1,270 m long horizontal section, the coal-bed formation, after being soaked by the drilling fluid for 23 days, showed no tendency of borehole wall collapse. Cuttings out of hole have regular shapes and sizes, and from the shale shakers only mudstone sloughing was observed. Tripping into the hole and out of hole were both smoothly conducted. The use of this new drilling fluid has effectively solved the borehole wall destabilization problem encountered in deep horizontal coal-bed methane drilling and ensured the success of drilling. The application of this technology will help achieve efficient and large-scale development and breakthrough in deep buried coal-bed methane drilling and exploration.