Plunger Lift Techniques Enable Sour Gas Production From Liquid-Impaired East Crossfield Wells
Authors: Troyer Jim , McCormick Lee 
Published: March 2010

Plunger lift has proven to be a viable and economical method of deliquifying 36% H2S gas wells in the East Crossfield D-I Unit. However, the sour nature of the gas presented material and environmental concerns, many of which have since been overcome. Two types of systems been installed to date. A conventional system was field tested and proved plunger-assisted production successful with little maintenance and no severe corrosion attack. Another system was devised which would allow plunger operation in wells equipped with a hydraulic nipple for a wireline retrievable subsurface safety valve (SSSV). It operates in the tubing between two bumper springs below the SSSV and offers effective liquid removal to allow sustained sour gas production with no wellhead modifications. Seven of these subsurface systems have been installed and are currently in operation at East Crossfield.

Introduction

Amoco Canada operates the East Crossfield D-l Unit which is located 40 km north of Calgary near Crossfield, Alberta (Fig. 1). There are currently 44 wells producing approximately 2000 10' m'ld of 36%, H2S gas from the Wabamum A Pool (D-1) (Fig. 2). Each 1000 m3 of sour gas produced from the East Crossfield D-l yields 0.50 tonne of sulphur which is extracted at the East Crossfield Gas Plant; residue gas can be sold, or injected into another pool during periods of low sales nomination. In recent years, the deliverability of several wells has fallen to rates insufficient to continually remove produced liquids from the tubing. In some cases, the wells have liquid loaded and died. To maintain sales deliverability and enhance sulphur revenue, methods to unload these impaired wells were investigated.

Of the alternatives evaluated to overcome the liquid loading problems, plunger lift offered the best return on investment while maintaining safe, environmentally acceptable operations. To date eight sour gas wells have had plunger lift systems installed. This paper discusses the liquid loading problem at East Cross-field and how plunger lift can be applied under corrosive conditions in environmentally sensitive areas. A plunger lift system which operates in conjunction with the subsurface safety valve will be highlighted.

East Crossfield D-1 Gas Well Performance

Sour gas is produced from the East Crossfield Wabarnum A Pool at a depth of about 2680 m (1600 m subsea). The reservoir is primarily interbedded dolomite and anhydrite and averages 30 m in thickness. Average porosity is 6%, water saturation l8%, and permeability 5 mD(l), although some wells on the edge of the pool have permeabilities less than 1 mD. In general, large volume acid fracture stimulations have been performed on all wells to enhance deliverability and improve drainage(2). Wells in the centre of the pool are still capable of producing at high rates even though the reservoir pressure has depleted from the original 25 100 kPa to as low as 5500 kPa. Wells completed in tighter portions of the reservoir had performed satisfactorily at higher pool pressures, but currently are liquid loading with lower gas rates (Fig. 3).