Accurate Calculation Method Of Pressure Control For Throttle

At present, the most used pressure control method in engineering practice is standpipe pressure control method.When using standpipe pressure control method for throttling killing, Applying the casing pressure is reasonable or not depends on the applying standpipe pressure. Due to the pressure transmission delayed, the size of standpipe pressure will delay for a period of time to know, which makes the casing pressure can not be controlled timely and accurately and also increase the difficulty of pressure control. Especially in the face of complex working conditions, such as stress sensitivity of reservoir, because the security window is narrower, additional pressure is small and the casing pressure control precision needs to be very accurate, so if using standpipe pressure control method for throttling killing, there will be some problems, such as casing pressure control precision not accurate and risking the well control safety problem. So, it is needed to improve the pressure control method, changing the method of indirect pressure control into direct pressure control method-casing pressure control method.According to the basic theory of gas-liquid two phase flow, combined with two phase flow of the actual situation in annulus under the condition of throttling killing, a mathematical model for describing the annulus pressure is established. The casing pressure is obtained by numerical calculation.It is meetting with the basic principle of the throttling killing which is bottom hole pressure being slightly greater than the formation pressure and then realizes the direct pressure control-casing pressure control method through adjusting the throttle opening valve, which can reduce the difficulty of pressure control and avoid well control security risks and has an important guiding significance to improve the success rate of throttling killing under complicated working condition.In this paper, the main research contents include:(1) The analysis of pressure control methods.(2) The gas-liquid two phase flow mathematical model in annulus under the conditions of throttling killing.(3) The numerical calculation and engineering calculation software.(4) Validation test of the calculation and the dynamic simulation analysis of casing pressure under the conditions of throttling killing.The main research results of this article are obtained:(1) Engineering practice and theoretical analysis show that the standpipe pressure control method have the features of pressure transmission lag, it is needed to improve the standpipe pressure control method under the situation which have higher control accuracy requirement.(2) Simplified casing pressure control method compared with the vertical pressure control, does not exist the problem of pressure transmission delaying, but with a too much simplified calculation model, the precision is not accurate, which can only be used as a reference to well killing. (3) On the basis of the gas-liquid two phase flow in annulus, a mathematical model is established to describe the annulus pressure distribution under the conditions of throttling killing. The mathematical model in combination with the practical situation of throttling killing, which build a convenient mathematical calculation for engineering application.(4) Developing a engineering calculation software, which can run on a conventional computer, avoide to rely heavily on the computer workstation, provide a important means for accurate casing pressure control on site.(5) By contrast with the experimental measured data, the engineering calculation software simulation results are not only conforms to the measured data but also the error are far less than the simulation result of simplified casing pressure control method, which fully illustrates the engineering calculation software can provide technical support for the accurate casing pressure control under the condition of throttling killing.(6) With the aid of engineering calculation software, analyse the influence factors of the casing pressure under the condition of throttling killing, some useful results are obtained, which has important guiding significance for engineering practice.