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Oil based drilling fluids, polysulfonate and other toxic drilling fluids have been restricted to use by strict environmental protection laws and regulations, when drilling in high temperature well in environmentally sensitive sea areas. Meanwhile, the environmental requirements of drilling fluid biological toxicity value LC50 greater than 30,000mg/L, Hg content of barite less than 1mg/L and Cd content less than 3 mg/L, which brings severe challenges for high temperature drilling fluids and offshore environmental protection. A kind of new non-toxic and high temperature polymer drilling fluid with the temperature resistance for 200°C and the biotoxicity value satisfied the discharge standard of the first class sea area has been developed in order to meet the requirements of high temperature deep well drilling operation and environmental protection. It can also drastically reduce the costs of waste disposal that is due to the drilling fluid and drilling cuttings can be discharged directly to the sea. A high temperature polymer filtrate reducer with temperature resistance for 200°Cand viscosifier with temperature resistance for 180°C both have been developed, which are used for high temperature filtration control and rheology regulation. This new system consists of these two high-temperature synthetic polymer materials, along with a special nano-plugging agent, glycol shale inhibitor, extreme pressure lubricant, and barite or formate weight materials. The formula and performance of drilling fluid are studied which suitable for drilling under different formation pressure coefficients, and the performance of drilling fluids at different bottom hole temperatures are also reviewed, so as to prove it can provide superior fluid performance for various harsh drilling conditions. The test results showed that the drilling fluid has the following main technical features: temperature resistance for 200°C, 200°C thermal stability time more than 72h, HTHP water loss 15~25mL, aquatic biological toxicity LC50 value higher than 100,000mg/L, luminescent bacteria EC50 higher than 300,000 mg/L. The test results from a high temperature deep well in Bohai offshore oil field, with depth of the bottom well 6066m, and the bottom temperature 204°C, are also presented. This drilling fluid is environmentally friendly and meets the discharge requirements of offshore, which can greatly improve the HSE operation level and eliminate the rig costs associating with drilling and waste management, especially in remote sea and deep sea drilling, that the disposal cost of waste drilling fluid accounts for more than 30% of the total drilling fluid cost.

It brings severe challenges to drilling fluids when drilling high temperature deep well in environmentally sensitive sea area and facing strict environmental protection laws and regulation requirements meanwhile, the toxic value of drilling fluid must reach up the standard requirement of 30,000 mg/L.A new, environmentally safe water-based polymer system has been developed for drilling applications with temperatures resistance to 200°C and biological toxicity value LC50 more than 100,000 mg/L. The new system consists of two basic polymeric components for high temperature rheology and filtration control, along with a special nano-plugging agent, glycol shale inhibitor, extreme pressure lubricant, and barite or formate weight material, providing superior performance for a variety of drilling environments. The system shows the base slurry is light colored and non-toxic to the marine environment, which can be discharged directly into the sea. The environmental friendly feature is a significant superiority over traditional high-temperature systems, such as sulfonated drilling fluid and oil-based drilling fluid which normally require the use of a large number of poisonous additives. Experiments show that the new system has three important characteristics. Firstly, thermal stability time is more than 72h when aging at 200°C, HTHP filtrate loss is in the range of 12 to 25mL between temperature of 150 and 200°C, and sodium chloride and calcium chloride pollution resistance reach up to 200,000ppm and 5,000ppm, respectively. Secondly, the characteristic of excellent lubricity and inhibition can be comparable to oil based drilling fluids. Thirdly, the low biological toxicity also is one the most important characteristic, 96h LC50 semi lethal concentration of artemia is more than 100,000 mg/L, and EC50 median effective concentration of luminescent bacteria is more than 300,000 mg/L, which meet the biological toxicity discharge requirements for the first level sea area. The extensive testing results of this new drilling fluid demonstrated its superiority characteristic and low biological toxicity to marine environment. Good results from field testing in Bohai offshore oil field are also presented, the deepest test well depth is 6066m, and the highest downhole temperature is 204°C.

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