Intensified exploration activity across Western Canada has resulted in increased oil and gas production from several carbonate reservoirs. Most of these new wells require hydraulic fracturing stimulation to fully maximize their potential and meet production allowables.
A residue free, "crosslinked" acid gel system using high strength hydrochloric acid has been successfully employed in treating several of these wells.
Fracture acidizing treatments have been successfully performed in the D-1 zone at Crossfield, the Pekisko limestone at Twinning, The Slave Point zone at Lubicon, and the Beaver Hill Lake zone at Judy Creek, Kaybob and Swan Hills.
This paper discusses the pretreatment formation analysis, stimulation treatment design, field application of the crosslinked acid gel system, and post-treatment well performance in these productive reservoirs.
An improved oil pricing regime has stimulated oil exploration, drilling and production across Western Canada. Combined with improved market conditions and increasing allowables, these trends are also encouraging workover activities in existing oil and gas production areas.
Technical advancements in seismic interpretation in combination with improved well logging technologies are enabling operators to maintain high success ratios for both wildcat and delineation wells.
Even with the latest in completion technology and reservoir knowledge, many of the wells completed today are of much lower quality than the early Leduc and Black Diamond discovery wells, and therefore require improved stimulation fluids and techniques to fully maximize their production potential.
To be commercially viable, poor quality reservoirs generally require conductive fractures extending out into the reservoir. Current fracturing systems, exhibiting stable fluid rheologies, are capable of uniformly distributing large amounts of proppant from the wellbore hundreds of meters deep into the reservoir. Many "sandstone" reservoirs have been successfully placed on production or had their boundaries extended as a result of successful hydraulic fracturing treatments.
Recently, a "Crosslinked" high strength acid fracturing system has been introduced to the "Western Canadian Basin" - The fluid rheology of this new Crosslinked Acid is similar to the Crosslinked Water systems used successfully in sandstone fracturing treatments. The high viscosity of the system reduces fluid loss during fracturing and greatly retards the acid reaction with the reservoir during the treatment. With this crosslinked acid system, it is now possible to successfully stimulate carbonate reservoirs by injecting live, high-strength acid, hundreds of meters out into the reservoir.
The primary reasons to fracture acidize are to create a highly conductive channel extending away from the wellbore into a low permeability formation, or to overcome formation damage that extends to a greater depth than can be effectively removed by matrix acidizing treatments.1 The successful treatment will provide a deep penetrating, differentially etched channel having a maximum fracture flow capacity after completion of the stimulation service.
The composition and properties of the acid treatment fluid utilized in fracture acidizing can significantly determine the effectiveness, of the overall stimulation service. The reaction of unaltered hydrochloric acid on carbonate formation is rapid and virtually instantaneous due to the high ratio of surface area of soluble rock to the volume of acid available, and the inherent react
