Improved Well Productivity Realized By Fracturing With Frac Oil As Compared To Diesel
Authors: Shibley J.A. , Leonard R.A.F. 
Published: March 2010

Increased AOF potentials averaging 24% have been realized on tight Basal Quartz sandstone reservoirs stimulated using frac oil as the carrier fluid when compared to reservoirs similarly stimulated using diesel. This statistical study of post-stimulation results examines 36 wells in the Caroline/Carrington area of southwestern Alberta.

In consideration of the over-all economics, the improved well productivity provides earlier payout which more than offsets the slight cost premium for frac oil over diesel.

Initial laboratory core studies showed that the Basal Quartz zone was immune co damage by completion fluids, but early attempts to fracture the zone using water as the base carrier fluid resulted in very discouraging well performance. This brought about a shift to the use of hydrocarbon-based fracturing fluids. Fra oil and diesel emerged as the prime completion fluids because of their low RVP (Reid vapour pressure) which allows safe handling under high pumping pressures.

Frac oil is a refined derivative of condensate. Compared co diesel, frac oil is higher in the preferred C7 C8 and C9 constituents and lower in less desirable C11 and heavier components. In addition, it has a significantly higher percentage of solvents in the form of toluene, methylcyclohexane and xylene. Frac oil is produced by the distillation of condensate at gas plants where the condensate stream contains an appropriate mix of C5 + constituents.

Introduction

The Caroline/Garrington fields are located 120 km northwest of Calgary in the foothills of Alberta. The Basal Quartz sands in this area are typically unproductive unless stimulated by hydraulic fractures. In 1982, it was determined that wells fractured using gelled hydrocarbon carrier fluids yielded much greater productivity than those fractured using water as a carrier.

Although industry wide the majority of fracture treatments are performed using water as a base carrier fluid, water-based stimulations on the Caroline tight sandstone proved to be disappointing. Since that time Dome Petroleum has completed 72 Basal Quartz gas wells using either diesel, reformate or frac oil. This study was undertaken to evaluate the effectiveness of stimulations with gelled frac oil versus gelled diesel fuel as the carrier fluids.

Discussion

Geology

In the Caroline/Garrington area, the main reservoirs that were studied were deposited during Lower Cretaceous time within a laterally extensive tidal flat complex.

The most extensive reservoir unit in the Caroline/Garrington area, using Dome Petroleum's terminology, is the Basal Quartz ‘A’ sand (Fig. 1). This gas-prone sand occurs within the uppermost 20 m of Lower Mannville "clean sand " development.

At various stratigraphic levels within the tidal flat complex, there are two types of reservoirs:Thick tidal channel deposits.Thin but a really extensive regional sands.

A thick occurrence of the Basal Quartz ‘A’ sand (10 m to 20 m) covers a narrow arcuate strip near the western limits of the Caroline Field and consists of fine-to medium-grained quartz, rounded, moderately to well sorted with a minor amount of detrital clay matrix. Basal contacts of the thick sands are generally sharp and erosive in nature. In cores, the sands display bidirectional and trough cross laminations.