Study and Application of Environmentally Friendly High Performance Water Base Drilling Fluid

In the field application of high performance water based drilling fluids, several technical problems have been encountered, such as complex composition, properties difficult to adjust and control, as well as excessive biotoxicity and heavy metals. To solve these problems, an environmentally friendly filter loss reducer EFR-1 was developed with a natural high molecular weight polymer and an inorganic nanocomposite through hydrophobic association and grafting modification. Laboratory evaluation of the EFR-1 filter loss reducer showed that EFR-1 is able to function normally at high temperatures up to 170 ℃. Saturated saltwater drilling fluids treated with EFR-1 have filtration rate of only 14.8 mL, EC₅₀ (biological toxicity) of 96 500 mg/L and BOD₅/COD_Cr (biodegradability) of 18.56%. The use of EFR-1 helped solve the mutually restraining problems such as temperature resistance, salt resistance and environmental friendliness. A high performance water based drilling fluid HPHB was developed with EFR-1. HPHB, a drilling fluid of simple composition, has stable rheology and filtration property in field operations, its HTHP filter loss is only 7.8 mL and EC₅₀ of 56 800 mg/L. HPHB has been successfully used on 20 wells drilled in Shengli Oilfield and Zhunzhong block in Xinjiang. Hole sections drilled with this HPHB drilling fluid have percent hole enlargement of less than 5%. The HPHB drilling fluid is not only technically feasible, but also environmentally friendly, it has provided a technical support to the “green” development of complex oil and gas reservoirs buried in deep/ultra-deep formations and in deep waters, as well as the “green” development of unconventional oil and gas reservoirs.