Patent ID: 9631454
Date: 2017-04-25
CPC Classifications: E21B

Claim:
1. A wellbore pressure control system for well cementation stages, comprising: an injection pump; and a control device, configured to control the injection pump to inject a fluid or a gas through an injection pipeline to a return pipeline that communicates with an annular space in a wellbore to decrease a pressure in the return pipeline and thereby decrease the pressure in the annular space, wherein, a density of the fluid or the gas is lower than a density of a drilling fluid in the annular space; wherein the control device is further configured to execute the following operations: a) acquiring an amount of circulating flow in the annular space and a depth of the surface level of cement slurry in the annular space; b) calculating a pressure profile of the annular space according to the amount of circulating flow and the depth of the surface level of cement slurry; c) determining a discharge capacity of the injection pump, so that a pressure at any depth in the pressure profile of the annular space is between a fracture pressure of formation and a pore pressure of formation; and d) controlling the injection pump to inject the fluid or the gas according to the determined discharge capacity; and wherein a pressure at a well depth h from the pressure profile of the annular space is calculated as follows: where, where, h