Application of Lubricating Drilling Fluid Technology in Drilling the Fahliyan Formation of Block Y

Fahliyan Formation, the main target zone in the Block Y, is a permeable limestone formation with developed porosity, small amount of micro-fractures and high permeability. High pressure and low pressure layers are coexisting in the same formation with high pressure existing in the upper part of that formation. Pipe sticking is easy to happen under high differential pressures. To solve these problems, a drilling fluid with high lubricity and high plugging capacity was developed based on the analysis of the characteristics of the Fahliyan Formation and the mechanism of pipe sticking. The lubricity of the drilling fluid came from a high performance vegetable oil lubricant developed. Laboratory studies showed that at 25℃, 6% bentonite slurry treated with 1% vegetable oil lubricant, had its extreme pressure friction coefficient and adhesion coefficient reduced by 88.57% and 86.67%, respectively. The treatment of the bentonite slurry with a nonionic surfactant tween-80 and a Gemini surfactant C12-2-12 enhanced the high temperature stability of the bentonite slurry to 170℃. A lubricating drilling fluid was formulated with these additives and a plugging agent. This drilling fluid had mud cake friction coefficient that was less than 0.05, extreme pressure friction coefficient less than 0.2, and effectively functioned at 170℃. The application of this drilling fluid, together with a set of appropriate engineering measures in 9 wells (penetrating the Fahliyan Formation) proved successful. No pipe sticking accident occurred during drilling, ensuring the success of the drilling operation.