Zubairy, Raheel (2014-05). Gas Kick Mechanistic Model. Master's Thesis.
Gas kicks occur during drilling when the formation pressure is greater than the wellbore pressure causing influx of gas into the wellbore. Uncontrolled gas kicks could result in blowout of the rig causing major financial loss and possible injury or loss of lives.
The influx of gas into the wellbore and the subsequent migration of gas towards surface affect different parameters related to the control of the wellbore such as wellbore's annulus pressure profile, mud density, pit-gain and temperature profile in the annulus. This research focuses on these changes in these parameters to be able to detect the occurrence of gas kick and the circulation of the gas kick out from the well. In this thesis, we have developed a model that incorporates a mechanistic approach to determine the transition of the flow as the gas migrates to surface. The model is implemented in a simulation program to present the behavior of these parameters.
The simulator initially creates a profile of the mud-circulation in the well-bore using user specified geometry of the well, drilling mud's characteristics and temperature properties of the formation and the drilling mud. The simulator then uses user-specified estimation of the formation pressure and other formation properties at a user-specified depth to calculate the gas-inflow into the wellbore. From this gas flow into the wellbore, the simulation shows changes in the annulus pressure and pit gain at surface as function of time, in addition to the changes in temperature profile and mud properties as gas migrates to surface.