Key Drilling Fluid Technology for Well Chuanshen-1

Well Chuanshen-1 is an ultra-deep exploratory well drilled in northeast Sichuan by Sinopec. Drilling of this well was faced with several technical difficulties such as high formation temperature, complex formations penetrated, less geological data available, borehole wall instability and high mud density etc. Drilling fluid additives were selected through laboratory experiment to deal with the high-density problem. The additives selected and their concentrations were:2%SPNH, 2%SMP-3, 0.5%SMPFL (DSP-1), 3%SMT (SMS-H), 3%RHJ-3, 1%HPA, 3%nanophase SiO². A high-density polymer sulfonate drilling fluid with good rheology, strong inhibitive capacity, high temperature resistance, good settling stability and high resistance to contamination, was formulated through orthogonal experiment. This drilling fluid was successfully applied in the fourth interval of the well Chuanshen-1. Difficulties encountered in filed operations and technical measures (such as gas-liquid conversion, drilling fluid treatment for special formations, mud property maintenance in field operations and reservoir protection etc.) are discussed in this paper. The major technical measures include:1) When weighing the active mud, high density mud with low viscosity low gel strength should be used and the MBT of the mud should be reduced gradually. 2) Solids control equipment should be used to control solids content strictly under designed value. 3) Drilling fluid density can be increased when drilling into salt and gypsum formations and filter loss should be strictly controlled. pH value of the drilling fluid should be no less than 10. 4) When drilling formations with acidic fluids, pretreat the drilling fluid with high chloride content, thereby enhancing its ability to resist salt contamination. 5) High density with some additives can be used to drill broken formations, borehole instability can be resolved through coupling of mechanical and chemical measures. 6) Drilling fluid density should be strictly controlled when drilling formations at which mud losses are easy to take place. Meanwhile the flow rate should be appropriately reduced, and mud viscosity and gel strength should be increased to some extent. Temporary plugging with acid soluble lost circulation materials of different particle sizes can be used to control mud losses.