Fine-Grind Cement Aids GOM Plug-and-Abandon Operations
Authors: Faul Ronnie , Kelm Charles , Slocum Tom , Crook Ron 
Published: October 2008

This paper presents data showing that operators have found success in using fine-grind cement (FGC) (particle size &lt; 5 mm) to plug and abandon gravel-packed wells in the Gulf of Mexico. Case evidence is presented that operators have used FGC slurry to successfully isolate high-pressure zones outside wellbores selected for permanent closure. The technique is often preferred over conventional methods because it helps protect the environment against pollution.

After well abandonment, gravel packs created in frac-pack operations1,2 often remain potential conduits for fluids and gases escaping from reservoirs to pollute the environment. Conventional-grind cement slurries have been used with marginal success to seal off reservoirs. However, many operators have found that FGC can more effectively penetrate gravel packs and obtain squeeze pressure to plug near-wellbore channels and help prevent pollutants from seeping out.

In one case, an offshore operator who had lost more than $1 million because of a blowout following squeeze and plugging problems chose FGC to help avoid additional problems and prevent similar problems in a second well. The high-pressure gas zone was successfully squeezed and plugged in one stage, and no flowback problems were noted.

The data presented in this paper show how operators have used FGC technology to improve abandonment programs. Using FGC to seal off gravel packs in abandoned wells can help safeguard health, safety, and environmental quality

Introduction

Because of widespread sand production in the Gulf of Mexico, most wells are completed with gravel packs. These gravel packs may extend only a few feet or hundreds of feet down wellbores and through producing intervals. Although they improve production and extend the lives of many wells, gravel packs seriously challenge plug-and-abandon operations.

Even after a well has been plugged with a conventional-grind cement, distillates or other unwanted fluids can migrate through the porous gravel pack, into the wellbore, and eventually, into the ocean. To reduce this pollution risk, the Mineral Management Service (MMS) requires operators to ensure that no pressure remains on wellbores following abandonment.3 Whenever hydrocarbon or other geothermal resource fluids are discovered in a well, they must be confined in their original stratum when the well is abandoned.

Proper plugging is the operator's responsibility. Cement plugs must be placed by the circulation or squeeze method through tubing or drillpipe to seal fluids out and effectively isolate any productive horizon. or stratum known to contain oil, gas, or other geothermal resource, including usable-quality water. Objectives in well abandonment include the following:protecting remaining geothermal resource reservescontrolling fluid movement within the wellbore to minimize risks of surface pollution or contamination of fresh waterlimiting fluid movement until nature can restore the static balance that existed before the well was drilled

Conventional Plug-and-Abandon Method

The conventional method of plugging a gravel-packed well involves establishing an injection rate, squeezing the perforations with conventional-grind cement, and setting cement plugs into the gravel-pack assembly. Approved plugback and abandon procedures can then be continued. Cement used in plugging and abandonment operations must be API oilwell cement, mixed according to API standards and without volume extenders.

Numerous problems are associated with this method, however, particularly in wells containing a liner or wire-wrapped screen.4,5