Currently, synthetic additives are widely used in drilling fluid, but these additives have hazards, such as, toxicity, difficult to degradation, leakage and volatilization caused great influence to wellsite environment. Environmentally friendly drilling fluid has been appeared around for decade. However, because of high cost of raw materials, lack of adequate supplement and complexity of modified synthetic process, there has been no widespread industrial application in China. The majority of test wells are straight, but deviated well and highly-deviated well test is seldom reported.

A series of indoor evaluation and field applications were carried out in process of modifying low cost additives to the environmentally friendly treatment agents. HTHP aging and filtration experiment to verify temperature resistance; adding sodium chloride to verify anti-salt properties; adding bentonite and cuttings recycling experiment to verify inhibition performance of slurry and mud shale; friction resistance experiment verifies that lubrication capacity meets deviated well and highly-deviated well operations; core flow experiment to verify reservoir protection performance; heavy metal, biochemical oxygen demand, chemical oxygen demand, biological toxicity analysis experiment to verify influence of the system on environment.

Ability of temperature resist 120 °C, anti-salt ability reaches saturation and recovery of cuttings is more than 85%. Environmental performance of the drilling fluid system is ideal, EC50 value is 1.61×105, no biological toxicity, BOD5/CODcr is 0.11, easy biodegradation. Field application for morethan 30 wells, with beyond 20 deviated wells and highly-deviation angle more than 50 ° wells are 10.

The new types downhole tools for speeding-up and controlling hole size, rotary impactor and wellbore cleaner, were used to improve mechanical penetration rate (ROP) and wellbore cleaning. After employing the environment system, the drilling fluid does not need to be transshipped and processed directly in wellsite, and well fields are restored. Drilling fluid disposal process saves the cost of artificial working, transportation and environmental management. This drilling fluid system is first applied on-site in North China, which fills the blanks and provids reliable technical support and reference examples for the subsequent replacement of drilling fluid systems used now in North China.

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