Analysis of the Inflow and Pressure Buildup Under Impending Blowout Conditions

Abstract

In this study a technique is provided for determining formation pore pressure and flow properties based upon analysis of shut-in drill pipe pressure. Both radial and spherical transient flow of slightly compressible fluid are considered. Solutions are provided in dimensionless forms. A newly developed concept of effective (equivalent) flowing rate and time is applied to replace the unknown variable flow rate which takes place prior to shutting-in the well. Two numerical examples show how to utilize the information on pit gain, approximate flow-in time and the shut-in drill pipe pressure to determine formation fluid pressure. Fluid mobility (spherical flow) and formation transmissibility (radial flow) can also be determined from knowledge of shut-in drill pipe pressure as a function of time. Application of the proposed method is simple, and therefore, useful on the rig floor.