Fingerprinting Formation Breathing and Wellbore Ballooning: Getting Mixed Signals

Abstract

The use of Managed Pressure Drilling (MPD) techniques allows the rapid differentiation of formation breathing or wellbore ballooning from a gas kick through a series of quick shut-in, build-up and flowback tests. These tests have proven to reduce uncertainty, NPT, and total drilling time by ensuring that operations do not enter secondary well control after mistaking flowback for a kick. Such tests provide definitive results when done correctly. However, when performed incorrectly, the wellbore response can appear either ambiguous or indicative of a kick. When done correctly, the ballooning test shows dissipation in both pressure build-up and flowback over time. However, when done incorrectly, both pressure and flowback can appear to gain drive. This is caused by induced losses being allowed to start equalizing with the wellbore with significant flowback volume prior to beginning the shut-in, build-up and flowback testing. As a result, ballooning testing can show classic signs of a gas kick as increasing pressure and flowback is observed or ambiguous results from the rising and then falling pressure and flowback. This can necessitate some combination of entering costly secondary well control and the need to trip back in to circulate bottoms up only to observe minimal signs of reservoir fluids. This paper presents type modelling that accounts for the observed unexpected results and reiterates rigid testing parameters for the successful implementation of diagnostic testing.