High Performance Drilling Fluid for Horizontal Drilling in the Well Jiaoye18-10HF in Fuling Shale Gas Field

The well Jiaoye18-10HF is a development well drilled in Fuling Shale Gas Field (Sinopec), with completion depth of 4 560 m and horizontal length of 1 378 m. The shales encountered in the third section of the wells in this area have high content of brittle minerals. Micro-fractures of micrometer and nanometer in size and bedding planes are so rich in the formations that oil base drilling fluids had to be used to minimize downhole troubles. Based on the study on the nature of the fractured shales encountered in the Wufeng Formation in Longmaxi block, a high performance water base drilling fluid, JHGWY-1, has recently been formulated with several major additives; PEA (amine-terminated polyether) as the core additive to inhibit the surface hydration of shales, vegetable oil oleamide as an extreme pressure lubricant to effectively reduce friction and nanometer plugging agent to strengthen borehole walls. In laboratory experiment, JHGWY-1 showed percent recovery of shale cuttings of more than 98%, coefficient of friction of 0.16 and pressure bearing capacity of the mud cake formed of more than 10 MPa. These properties satisfied the needs of drilling operation in Longmaxi area, such as drilling the micro-fracture-enriched Wufeng Formation, plugging and strengthening of formation with weak cementation, and good lubricity of the drilling fluid in horizontal drilling. This drilling fluid was first used in place of oil base drilling fluids in drilling the third interval of the well Jiaoye18-10HF which penetrated through the Wufeng Formation with designed vertical thickness of 10 m (actually 8-10 m during drilling). Tripping of drill string was smooth and the well was successfully completed. The mud had good rheology, low filtration rate and strong inhibition to shale during drilling, and the needs of drilling the third interval of the well was satisfied.