With the rapid development of deepwater drilling operations, more and more complex technical challenges have to be faced due to the rigorous conditions encountered. One of these challenges is that the drilling fl uid used must had good rheological properties at low temperatures and high ability to inhibit hydrate formation. Synthetic drilling fl uid has been widely applied to deepwater drilling operations due to its high penetration rate, excellent rheological properties, good ability to prevent hydrate formation, and high biodegradability. A synthetic drilling fluid formulation was developed in our laboratory. The rheological properties of this drilling fluid at low temperatures (0-20 °C) were tested with a 6-speed viscometer and its ability to inhibit hydrate formation was evaluated at 20 MPa CH 4 gas and 0 °C by differential scanning calorimetry (DSC). Several factors influencing the low temperature rheological properties of this synthetic drilling fl uid were studied in this paper. These included the viscosity of the base fl uid, the amount of CEMU and organic clay, and the water volume fraction.Research on deepwater synthetic drilling fl uid and its low temperature rheological properties
The increasing application of near balanced drilling technology to low-pressure and depleted fractured reservoirs requires the use of low-density drilling fluids to avoid formation damage. Solidsfree oil-in-water (O/W) emulsion drilling fluid is one type of low-density drilling fluid suitable for depleted fractured reservoirs. In this paper, the solids-free O/W drilling fluid was developed and has been successfully used in the Bozhong 28-1 oil and gas ¿ eld, by which lost circulation, a severe problem occurred previously when drilling into fractured reservoir beds, was controlled, thereby minimizing formation damage. The O/W emulsion drilling fluid was prepared by adding 20% (by volume) No. 5 mineral oil (with high flash point, as dispersed phase) into seawater (as continuous phase). Surfactant HTO-1 (as a primary emulsi¿ er) and non-ionic surfactant HTO-2 (as a secondary emulsi¿ er) were added into the drilling À uid system to stabilize the emulsion; and YJD polymer was also added to seawater to improve the viscosity of the continuous phase (seawater). The drilling À uid was characterized by high À ash point, good thermal stability and high stability to crude oil contamination.
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