Abstract:
The formation rocks of the Kimmeridgian stage on the right bank of the Amu Darya River, Turkmenistan, are halite and gypsum stone. High density drilling fluids used to drill this formation have always been contaminated by calcium and magnesium from the high pressure formation water, resulting in poor mud rheology and high filtration rate. The deteriorated mud rheology and filtration performance in turn resulted in other downhole troubles. A calcium tolerant high density low clay drilling fluid, D-ULTRACAL was developed to deal with these problems. A filter loss reducer, DSP-1, was used in the drilling fluid. DSP-1 can increase the viscosity of the drilling fluid, in this way reducing the clay content, improving the calcium tolerance and minimizing the filter loss of the drilling fluid. The density of the drilling fluid was 2.0 g/cm
3, sufficient to prevent well kick and to protect the borehole wall from collapsing. The drilling fluid had salt content almost to saturation to minimize the dissolution of the salt and gypsum rocks. The properties of the drilling fluid remained stable at temperatures up to 150℃, and the filtration rate was only slightly affected by high temperature aging. On a hot rolling test, the percent recovery of shale cuttings reached 113.7%, and on a shale core swelling test, the percent reduction in the expansion of shale cores was 80.5%, indicating the strong inhibitive capacity of the drilling fluid. Calcium tolerance of the drilling fluid was 4 936 mg/L. This drilling fluid has been used to drill the well Gir-24D, which is located in the Girsan gas field, right bank of the Amu Darya River, Turkmenistan, and the thick salt and gypsum rock formations were successfully penetrated with no downhole troubles.