New Technology in Gas Migration Control

Abstract

ABSTRACT Recent research investigating causes and control of annular gas flow has resulted in new concepts pertaining to gas migration. Previous investigations have identified that the combined effects of fluid loss volume reductions and static gel strength development control the actual pressure loss – and ultimately gas flow – in a cement column. The recently developed concept describes delayed development of cement gel strength as a means of preventing gas flow. Delaying gel strength development allows the cement column to transmit essentially full hydrostatic pressure, and thus prevent gas entry into the cement column, for an extended time period. Test results are presented showing that fluid loss rate decreases with time so that most volume losses due to fluid loss occur during the delayed gel strength period. Thus, stringent slurry fluid loss requirements for probable gas flow situations may be relaxed. The conclusion of the delayed gel strength phase is followed by rapid progression to the set state thus helping prevent gas entry into a cement column. Another feature of delayed gel strength development, shutdown safety factor, is also presented. Pumping of delayed gel strength cements can be restarted without excessive horsepower or pressure requirements in the event of a shutdown during placement. Subject paper presents laboratory test results and field case histories documenting use of delayed gel strength cement for prevention of gas migration.