Experimental Study On Drilling Fluids For Low Temperature

In recent years, shortage of energy becoming increasingly serious, the exploration and development of new resources should be without delay. With exploration and development of the new resources and new energy, Plateau permafrost and gas hydrate exploration are an important component parts. Plateau permafrost is prolific in mineral and oil resources, worthy for exploration and development. In exploration, the work must be carried out at low temperature because of special geographical positions and gas hydrate occurrence conditions. In order to meet the needs of the exploration and development work, the drilling fluids for low temperature should be developed as soon as possible.One of the critical problems of Plateau permafrost and gas hydrate exploration is low temperature resistance of the drilling fluids. Choosing glycol as antifreeze agent meets the requests of drilling work. Property parameters of drilling fluid systems are studied at room temperature through orthogonal test method. These property parameters contain the liquidity, water-loss property, preventing collapse property and lubricating property. After optimization to the drilling fluids formulation, experiment should be done under low temperature to test Anti-low temperature property and the property of each reagent of drilling fluids. Drilling fluid formulations are further optimized, and drilling fluid formulations for the low-temperature are got.Through large number of test, four formulations used -20℃are identified:⑴PVA(2%)+PHPA(0.03%)+glycol(25%)+Na-CMC(0.075%)+NaCl(7.5%);⑵PVA(2%)+PAM(0.0625%)+glycol(25%)+Na-CMC(0.0375%)+NaCl(7.5%);⑶PVA(1.875%)+PAC-141(0.075%)+glycol(30%)+Na-CMC(0.0625%)+NaCl(7.5%);⑷PVA(2%)+KPA(.125%)+glycol(27.5%)+Na-CMC(0.05%)+NaCl(7.5%).With strong low temperature resistance, well liquidity and preventing collapse capability, the determined drilling fluid systems are non-polluting drilling fluid systems. The formulations of drilling fluids are got when anti-low temperature property is-20℃, however the exploration temperature is always above -20℃in Plateau permafrost and gas hydrate exploration. The drilling fluid formulations can be adjusted with temperature conditions. It can be known from the test that anti-low temperature property of drilling fluids can reach -5℃, -9℃and -16℃, when the glycol concentration reach 7.5%, 12.5% and 17.5% in the drilling fluids. Anti-low temperature property of drilling fluids can be adjusted according to actual work conditions.With good economy, the cost of drilling fluids is between 1500 yuan/m3 to 3000 yuan/m3 according to different requirements of low-temperature. The chief factor determined the cost of drilling fluids is the concentration of glycol in drilling fluids.According to the test at room temperature, some conclusions are got as follows: With the increase of PVA concentration, viscosity and preventing collapse property of drilling fluid increase, however the amount of water-loss decrease accordingly. With the increase of PHPA,PAM,PAC-141 and KPA concentration, viscosity of drilling fluids increase, however the amount of water-loss and density scarcely variation. Conclusion can be got that the preventing collapse property of PAC-141 is the best of all, with the one of KPA and PHPA wealer and the one of PAM worst. The viscosity of drilling fluids used KHm is less than Na-CMC, and the result shows that Na-CMC has a more contribution on improving viscosity than KHm.. The water-loss amount of drilling fluids used KHm is lower in evidence than Na-CMC, and it shows that KHm has a more contribution on the water-loss effect than Na-CMC. The amount of NaCl has great effect on preventing collapse property, and the viscosity increase with the amount of NaCl increase, also. With the amount of glycol increase, viscosity, density preventing and collapse property of drilling fluids increase, while the amount of water loss scarcely variation.According to test at low temperature, some conclusions are got as follows: Glycol and polymers have good compatibility, and inorganic salt and organic processing agent can greatly reduce freezing point of drilling fluids. Test finds that when the concentration of glycol reaches to 20% to 30%, the drilling fluids keep well liquidity at-20℃. At low temperature, the viscosity of formulation used KHm is bigger than Na-CMC, and the result shows that KHm is more sensitive to temperature than Na-CMC. Therefore, anti-low temperature drilling fluids select Na-CMC as water-loss agent. Contrasting property of formulation used PHP,PAM,PAC-141 and K-PAM, with the temperature decreasing, the viscosity change of PAC-141 is the least, Conclusion can be got that the temperature sensitivity of PAC-141 is the least, with the one of KPA and PHPA biggerr and the one of PAM biggest. For the same drilling fluids, the viscosity and the density increase with the temperature decreasing, while the amount of water loss reduce with the temperature decreasing. Conclusion can be got that drilling fluids have well preventing collapse property at low temperature. When the temperature is above freezing point, drilling fluids is Newton liquid, while non- Newton liquid property of drilling fluids strengthen with the temperature decreasing.