A Study Of Constant-Rheology Synthetic-Based Drilling Fluid System And Rheology In Deepwater

Deepwater drilling generally refers to the drilling water depth exceeds300m,water depth is greater than1500m for ultra deepwater drilling. In recent years,with the development of offshore oil industry and mining quantity increased year by year,offshore oil exploration has been gradually into deep water. However,when the temperature changes of deepwater drilling,drilling fluid rheology influenced by temperature especially the dynamic shear and low shear rate viscosity is difficult to control, the well leak equivalent circulation density(ECD)of high pressure control, a series of problems such as difficult is becoming the deepwater drilling challenges. The synthetic-based drilling fluids with its mechanical drilling velocity is high,the stability is good, has become a commonly used drilling fluid system in offshore oil and gas drilling, but the viscosity, shear stress of the drilling fluid is affected by temperature is obvious,so prone to leakage especially in the long time of drilling fluid for the stationary case more serious. In order to solve the technical problems, abroad in recent years,first developed a new kind of constant-rheology synthetic-based drilling fluid (CR-SBM), rheology especially the influence of shear force,shear and low shear rate viscosity parameters basically not affected by temperature and pressure.The synthetic-based drilling fluid with constant-rheology synthetic-based drilling fluid(CR-SBM), also known as flat-rheology synthetic-based drilling fluid (FR-SBM) is the agent processing optimization and modified to develop a suitable for deepwater drilling new drilling fluid system based on traditional synthetic base drilling fluid.In this paper, through widely consulting the domestic and foreign existing has constant-rheology synthetic-based drilling fluid literature, studies the following aspects:First, use of industrial products formulated possibility of GTL-based drilling fluid, selection can be used for a variety of industrial products processing agent for synthetic-based drilling fluid, especially the selection of the excellent performance of the organic soil, studied various performance indexes of GTL-based drilling fluid, mechanism of oil and gas treatment agent are discussed in detail, the synthetic-based drilling fluid rheology,thixotropy and filtration, and rheological changes in underground conditions, summed up the synthetic base drilling fluid performance control technology and method.Second, the synthetic drilling fluids because of their low viscosity, the rheological parameters were decreased after ageing, often found carrying cuttings and barite settlement problem, in order to solve these problems, this paper puts forward to improve temperature capability of the improver, join the flow type modifier in synthetic base drilling fluid, almost no effect on normal temperature drilling fluid viscosity, but can improve the viscosity of drilling fluid under high temperature, is conducive to resolving the synthetic base drilling fluid carrying cuttings and barite settlement.Third, effect of temperature and pressure on the rheology properties of the synthetic-based drilling fluid is very obvious, through the determination of the rheology properties of low temperature and high pressure, the temperature and pressure effect on the rheology properties of GTL based drilling fluid, and select the appropriate mathematical model to fit the, obtained can reflect the low-temperature and high-pressure flow degeneration law the equation.Fourth, the application that often appear in ordinary synthetic-based drilling fluid will cause the borehole sloughing and circulation loss and downhole complex condition, the calculation of ECD model is relatively simple, for GTL-based drilling fluids ECD were calculated. The results show that using a constant-rheology synthetic-based drilling fluid in deep water than ordinary synthetic-based drilling fluid can reduce the drilling fluid ECD, thereby reducing the possibility of causing loss circulation.