Study of Hydrophobic Inhibitive Water Base Drilling Fluid System and Application in Shale Gas Well

A hydrophilically inhibitive water base drilling fluid has been developed to drill shale gas wells penetrating the Longmaxi Formation. This drilling fluid was formulated with a hydrophilically inhibitive agent CQ-SIA and a high performance lubricant CQLSA. CQ-SIA, the core additive of the formulation, is amphoteric in nature, and can render wettability reversal to the surface of rocks. It forms on the surface of rocks a hydrophilic film, thereby encapsulating and inhibiting the rocks from disintegration by water invasion. Hot rolling test results showed that 1% CQ-SIA gave percent cuttings recovery of 83.72%, remarkably higher than that obtained with KPAM, AP-1 and KCl. CQ-LSA, thanks for its special molecular groups and structure, can form lipophilic film on the hydrophilic surfaces of drilling tools, mud cakes and formation rocks, thereby greatly decreasing frictional resistance experienced in drilling. Sticking coefficient of a 5% bentonite slurry treated with 1% CQ-LSA was 0.0507, lower than the 5% bentonite slurries treated with two commonly used lubricants RH-220 and BARALUBE. The formulated drilling fluid had good rheology,high inhibitive capacity and good lubricity that were equivalent to oil base drilling fluid. Addition of 1%-3% anti-sloughing plugging agent, 1%-2% poly glycol and 0.8%-1.6% nano plugging agent rendered the formulation good plugging performance. It also had good contamination resistance. Success has been gained in the first use of this formulated drilling fluid on the well Changning H25-8. Mud properties in the horizontal fourth interval (3,079 m open hole length and 1,500 m horizontal section) were all maintained stable. No downhole problems have ever occurred. Tripping, wireline logging, casing running and well cementing were all done smoothly.