Analysis of the Ballooning Effect: No Loss, Only Gain

Abstract

Abstract The purpose of this paper is to share the lessons learned from a ballooning effect that occurred in a carbonate formation in the Middle East. Typically, ballooning is recognized as a gain/loss situation, but in this instance, the loss of mud was undetected, and a slight flow was observed and after that the well was shut-in. As the well was misinterpreted as a flowing well, the remedial operations took 15 days. The mud returns on the surface were only 0.3 barrels (bbls), and the well was immediately shut-in. The shut-in drill pipe and casing pressure increased simultaneously at the same rate. The kill mud weight was 80 pounds per square foot (pcf), and the circulation was performed using the wait and weight method. At the end of the circulation, the mud weight both in and out remained at 80 pcf, and no traces of oil and gas were observed during the killing operation. The well was circulated a total of 5 times, with a final mud weight of 109 pcf. Throughout the entire killing process, the same shut-in pressure behavior was observed. When the well was opened, slight returns were confirmed for a period of 5 hours. An ultrasonic bond log was taken to the 7" liner to rule out a possible communication with a formation with higher pore pressure than the 68 pcf mud weight, the ultrasonic cement bond log gave poor results due to eccentricity because of tough logging conditions (TLC) conveyance method where the tool lays down on the low side of the wellbore. To address the potential isolation problem, a balanced cement plug was squeezed, however the cement was not injected, fluid volume pumped and returned was the same. Finally, an inflow test was performed at different equivalent mud weights (EMW), confirming that a mud weight of 68 pcf is sufficient to effectively control the well. After determining the safe mud weight, the 6 1/8" section of the well was drilled to section total depth without any influx.