Study On Drilling Fluid Technology For Complex Formation In Offshore Oilfield

In recent years, with constant development of our country offshore oil and gas drilling technology, drilling fluid technology is facing new technological challenge. For example, anti-collapse drilling fluid system for complex shales formation of WII section, WZ12-1N Oilfield, South China Sea, and drilling fluid system for low-pressure formation of Buried-hill, Bohai Sea Oilfield and so on.Firstly, to wellbore instability problem of WII section of WZ12-1N Oilfield in South China Sea, main reasons of shale formation caving of WII section were analyzed by experimental study on fabric and physico-chemical properties in this paper. With performance evaluation of formulas for daily offshore water-based drilling fluids, fluid loss agents and sealing agents were further optimized to develop a strong sealing seawater drilling fluid formulation with good anti-collapse effect. It was proved in the experiment that this formulation had strong ability to anti-collapse and better performance of anti-pollution and reservoir protection.In order to meet the need of drilling engineering in low pressure formation of Buried-hill in Bohai sea, seawater microfoam drilling fluid system with anti-high temperature was optimal designed, which main additives were optimal selected and main influential factors were analyzed, seawater microfoam drilling fluid formula was developed eventually, with adjustal density rang of 0.6g/cm3~1.0g/cm3 and anti-temperature performace of 150℃, and which performance controll methods were achieved. It was proved by experiment that this system can meet need of offshore oilfield, with wide adjustal density range, good anti-temperture stability, strong anti-pollution ability and better performance of reservoir protection and enviorment protection. With partial shimmer microscope and infrared scanner, micro-structure and stability mechanism of new microfoam drilling fluids were studied and analyzed, relation between micro-morphology of microfoam system and stirring speed and base fluid viscosity were attained so that cognition of mechanism for microfoam drilling fluid was strengthened.