An Investigation of Annular Gas Flow Following Cementing Operations
Authors: Garcia J.A. , Clark C.R. 
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.
This paper was prepared for the Society of Petroleum Engineers of AIME Symposium on Formation Damage Control, to be held in Houston, Tx., Jan 29–30, 1976. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal, provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Abstract
A severe problem that has occurred following cementing operations on multizone wells is the influx of gas during early cement setting time. This problem occurs more frequently where open zone pressures differ greatly and where the lower pressured formations are permeable and exist above higher pressured zones. Occurrences of flow following cementing operations have long been recorded and several theories and studies have been proposed and made through the years to explain the phenomenon. Barring man-made causes, the most popular theory on annular gas flow has been that of head loss in the lower portion of the hole resulting from cement first setting at or near the cement top.
Starting in 1968, Exxon initiated studies to obtain a more clear definition of the causes for the phenomenon in hopes of obtaining potential solutions to its occurrence. The initial feasibility work and the later highly sophisticated lab simulation of well types exhibiting the phenomenon took place over a three-year period. Field work done to trace the problem as it occurs in the hole has also been done since and is presented here. The results of these investigations indicate that annular gas influx can occur if cement fluid loss or uneven slurry setting occurs high in the hole such that hydrostatic head communication no longer exists between the bottom of the hole and the mud column above the set cement point. While high cement setting itself does not cause loss of head to occur below it, any additional loss of fluid below the set spot "bleeds off" trapped head allowing capable high pressured gas bearing formations to feed in and cause a well pressured gas bearing formations to feed in and cause a well control problem under difficult conditions for control.
This paper presents the findings of the study, outlines conditions under which the problem occurs, and recommends preventative actions and practices to minimize flow occurrences. preventative actions and practices to minimize flow occurrences

Introduction
Much work has been done in recent years to define and arrest the causes for annular gas flow in wells following primary cementing operations. Some of the earliest work done by the industry specifically aimed at studying pressure behavior of a cement column was done by Exxon and Dowell in 1968.
P. P.