Surface-induced removal of sustained casing head pressure by sealing the well's leaking cement with condensate from flowing gas

Document Type

Conference Proceeding

Publication Date

1-1-2005

Abstract

Gas migration in cemented annulus of producing wells is considered the mechanism of sustained casinghead pressure (SCP) - an irreducible annular pressure at the casing head. SCP is a hazard to well integrity, potential cause of blowouts and a source of air pollution. From the regulatory standpoint, SCP disqualifies wells for safe operation. In principle, wells with SCP cannot be produced, or plugged and abandoned (P&A) without remedial operations. At present, the SCP removal is either capital intensive, as it requires well’s workover with a rig, or less expensive but little reliable with rig-less techniques such as CARS or Bleed-and-Lube. However, gas migration in some wells may cease with little intervention when the migrating gas is wet and flow channels are small. In this paper, we present our study of a self-plugging technique based on phase behavior of wet gas flowing in the small fissures of leaking cement. A prolonged drop of pressure resulting from opening the casing head to atmospheric pressure may bring the gas in the leaking cement below dew point and set off its condensation. In the process, the condensate liquid would plug the cement fissures and stop the gas flow. In the study, we simulated the plugging process for different well conditions by considering a balance of the capillary, hydrostatic and formation pressures superimposed over the PVT gas envelope. The results show that surface-induced plugging is possible and could be analytically assessed for a SCP well before deciding to use other expensive methods. Also, shown in the paper is the self-plugging assessment procedure, example of its application, and a discussion of availability of the input data for the procedure.

Publication Source (Journal or Book title)

Canadian International Petroleum Conference 2005, CIPC 2005

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