Research On Wellbore Pressure Control Method For Leaking And Coexisting Complex Pressure System

It is a worldwide difficult problem to drill the fractured reservoir of complex pressure system in the field of drilling technology. Because of the existence of multiple pressure coefficient, the formation pressure profile is extremely not regular. When drilling, the leakage layer and the overflow layer of different pressure gradient are unable to all packer bu using only by the casing pipe, it is often used to cause the multiple layer and multiple layers of leakage to occur simultaneously in the same bare hole and in the same time as the formation of the complex pressure system, Eventually leads to the difficulty of well control, formation contamination and complicated downhole problems. Therefore, it is significant to study the leakage and leakage of the fractured strata in the multi pressure system to prevent and control the pressure of the wellbore. This paper is aimed at the problem of the complexity of the leakage and the existence of the fractured reservoir in the drilling process and the following work has been done:Based on the theory of a single crack loss, the monolete natural loss model has been derived, and the well leakage factors has been analyzed, the results showed that: in the same other conditions, the cracks was wider the largest mud penetration depth was greater; The loss pressure was larger the largest mud penetration depth was greater; The drilling fluid dropout rate increased with the slit width becoming wider,it decreased with the leakage depth increasing, and it decreased with the dynamic shear force increasing.Based on the theory of gas flow, the formation gas invasion process and its mechanism are studied, a mathematical model of fractured formation gas invasion is established, and analyzes the influence of different parameters on the discharge. The results show that when other conditions are the same, the higher the formation permeability, the greater the amount of the reservoir is, the greater the amount of the bottom hole is, the greater the amount of the bottom hole under pressure; The intrusion rate increases with the increase of the drilling speed of the machine. The results show that the type of leakage is the decisive factor for the change of the leakage, and the width of the crack is the most significant influence on the leakage time; With the drilling fluid density increased leakage spray conversion time decreases, increases with increasing the consistency coefficient of drilling fluid and dynamic shear force and leakage spray conversion time increases rapidly.Based on the gas-liquid two-phase flow theory, the model of variable flow and gas-liquid two-phase flow is established, and the flow pattern of the wellbore is analyzed, The results show that when the other conditions are constant, the overflow can significantly reduce the dynamic pressure of the circulating pressure, thus the over balance pressure difference decreases and the leakage loss decreases obviously; Leakage will cause cyclic dynamic pressure decreases slightly, the overflow will be a slight increase. Reducing the wellbore annulus pressure is beneficial to reduce the leakage intensity, but the overflow flux will increase, and the overflow of the well is more active.The time interval of drilling fluid and the amount of suspended tank are optimized, and the H2S gas pressure is improved, the comparative analysis of the applicability of different lost circulation pressure well techniques has a good guiding role for the optimization of the wellbore pressure control method under different conditions of the same time of the drilling of multiple pressure systems.