Plugging-Removable Drilling Fluid System for Reservoir Protection in Deep Fractured Gas Reservoir

As the deep fractured gas reservoirs are characterized by narrow safety density window and drilling fluid intrudes deep into the formation along fractures, causing serious reservoir damage, plugging-removable drilling fluid that combines enhanced bearing pressure ability and reservoir protection was studied. The acid soluble polylactic acid fiber plugging agent was developed with the maximum bearing pressure ability of 8MPa and the acid solubility of 90%, which could block fractures with width of 0.5–3 mm by bridging and stacking. The acid soluble Mn3O4 weighting agent was invented with the density of 4.7 g/cm3, the particle size of 0.2–7 μm and the acid solubility of 95%, which could reduce the flowback pressure because of regular spherical and excellent suspension ability. A plugging-removable drilling fluid system for reservoir protection in deep fractured gas reservoir has been formulated which has temperature tolerance of 180 ℃, bearing pressure ability of 10 MPa and core permeability recovery value of 91.5%. The plugging-removable drilling fluid system was applied in 20 wells in GM block, that increased test gas production by 43–181%, indicating that the drilling fluid has broad application prospects in deep fractured gas reservoir.