Development and Application of the Filming Protecting Agent BHJ-RF for Deep Coal-Bed Methane Reservoirs

The deep formations in the eastern margin of the Ordos basin have plenty reserves of coal-bed methane (CBM), the Shenmu-Jiaxian block in the eastern margin of the basin is an important CBM production area with huge exploration and development potential. Detailed investigation of the mineral characteristics, pore structure feature and cleat development characteristics etc. of the CMB reservoir formations in the Shenmu-Jiaxian block shows that the deep coal rocks are developed with plenty of fractures and are easy to hydrate and expand, the invasion of drilling fluid filtrates during drilling cause the coal rocks to be damaged. To deal with these problems, a filming protecting agent BHJ-RF suitable for deep CBM reservoir protection was developed, and was characterized by means of IR spectrum etc. The performance of BHJ-RF was evaluated using API filtration test etc. Experimental results show that a 4% bentonite base mud and a 2% bentonite base mud have their filtration rates significantly reduced by 25% and 35% respectively after treatment with BHJ-RF, and the accumulated 30-min filtration rate of the BHJ-RF treated base mud is 31.5 mL, 40% lower than that of the non-treated base mud. After the composition of the base mud was determined, a drilling fluid for deep CBM drilling was formulated with the filming protecting agent BHJ-RF as the core additive. Comprehensive performance evaluation of the optimized drilling fluid shows that it has good rheology and an API filter loss of 3.2 mL. The drilling fluid has good permeability recovery capacity; the average percent permeability recovery tested on cores is 87.13%. These properties of the drilling fluid satisfy the requirements of deep CBM drilling and provide a technical support for deep CBM reservoir protection in the Shenmu-Jiaxian block.