Drilling Fluid Technology for Drilling Nanpu Buried Hill Oil Reservoir

The Nanpu buried hill oil reservoir(Jidong Oilfield) is characteristic of deep burial at 4, 000-5, 600 m, high formation temperature(4.22℃/100 m, and 223℃ atbottom hole), low formation pressure(pressure coefficient 0.96), and developed fractures.The produced oil has high gas/oil ratios.A high temperature low density low solids content drilling fluid and a high temperature gel plug have been developed for use in reservoir drilling in Nanpu.The high temperature drilling fluid retains its good performance at 220℃, and the gel plug functions at 170℃.In formulating the high temperature low density low solids drilling fluid, two tetra-polymers were chosen as the high temperature viscosifiers and high temperature filter loss reducer, respectively.SMP, SPNH and a high temperature sealing agent, FT3000, were also used to improve the properties of the drilling fluid.A high temperature oil-in-water drilling fluid was formulated with two emulsifiers, HWZR and HWFR, (both are high temperature stable and salt resistant) a viscosifier HVF-H and two high temperature filter loss reducers, HWFL-H and HVS-H.The two drilling fluids have good performance after aging at 220℃ for48 h, and densities ranging between 0.98 g/cm³ and 1.08 g/cm³.Using the gel plug, oil and gas zones are isolated and protected during pipe tripping and casing tieback.The high temperature low density low solids drilling fluid has been used in 8 wells, the oil-in-water drilling fluid used in 13 wells, and the gel plug used in 2 wells, all proved successful in reservoir protection.