The Research Of Supercharge Around The Wellbore With Repeat Formation Testing In YD Oilfield

To prevent blowout in drilling process, drilling mud is widely used to balance the formation pressure. Normally, the wellbore pressure is greater than the formation porosity pressure in drilling process, therefore mud filtrate invades into formation under the pressure difference between wellbore and the formation, which not only changes the distribution of original fluid in formation pore and the properties of formation fluid, but also lead to supercharge phenomenon in the near wellbore area in low permeability reservoirs, resulting in misinterpretation of the RFT test. Therefore, it is very important to study the characteristics of mud filtrate invasion in formation and mechanism of the supercharge effect in order to get a better understanding of the reservoir pressure system.Base on the theory of two-phase radial flow, the mud filtrate invasion is equivalent to water/oil displcement process. An oil-water two phase flow model is built which considers the influences of mud cake. The mathematical model is discretized and solved using the finite difference method. Then the supercharging effect in the process of mud invasion in F formation of YD oilfield is studied using the simulator, and the influences of formation permeability, porosity, drilling positive pressure difference, the filtrate viscosity and mud cake permeability on the supercharge are also studied. using simulator based on the actual data of the supercharge well.The research shows that: pressure increment near wellbore zone increases with the increase of drilling positive pressure difference and mud cake permeability, and decreases with the increase of formation porosity, formation permeability and filtrate viscosity.Therefore, we could use drilling fluid with smaller density to reduce positive pressure difference, and used high quality drilling mud to form low-permeability mud cake as well as the use of additives to increase the viscosity of the mud filtrate which reduces the supercharge phenomenon in the process of drilling, therefore to reduce the mud damage to reservoir, improve the production capacity of oil and gas wells. The calculation of multiple sets of data is carried out on the basis of single factor analysis by using the design method of orthogonal test, and an empirical formula is obtained that could predict the pressurization value within a certain scope through the method of multiple regression, so as to help to determine original pressure of formation. At the same time, all the influence factors are ranked according to the magnitude of influence on the pressure by comprehensive analysis of factors. The results show that the positive pressure difference has the most influence, followed by porosity and permeability of the formation, by contrast, the influence of the filtrate viscosity and filter cake permeability on supercharge is smaller.