The Nisku formation of the Enchant Field in southern Alberta has undergone rapid development since the first well was drilled in 1985. An extensive propped hydraulic fracturing program has been conducted while developing the less prolific sections of the field. This paper presents an evaluation of the fracturing program to quantify the stimulation process in an attempt to optimize future fracturing treatments.
Rock properties information was compiled in an effort to accurately model the fracture geometry created. Rock property logs in conjunction with laboratory rock properties testing performed on core samples were used to obtain representative values that could be used in a fracture simulator. Minifrac analyses provided insitu minimum horizontal pressures, fracture geometry and the leakoff coefficient of the fracturing fluid in the formation. Results from the pseudo three dimensional fracture simulator indicated that very large fracture heights were being created, thus making it extremely difficult to create optimum fracture lengths and conductivity.
The information obtained from the study is now being used to improve the design and execution of current fracture treatments. From the study it became evident that the lack of competent barriers was preventing desired fracture geometry under conventional fracture treatment practices. Various methods of reducing gross height are now being utilized on current treatments.
Noreen Energy Resources Limited became actively involved in producing the Nisku formation in the Enchant field of southern Alberta in 1985. The need for fracture stimulations was not as great in the first five years of operations as the wells drilled were generally of better reservoir quality. Fracture stimulation treatments have been used more frequently in the past two years as more wells have been drilled in less prolific Nisku intervals. Without stimulation treatments, production from many of the Nisku wells would not be economical.
Some of the more prolific wells in the field have only required matrix acid stimulation treatments to open the perforations and remove the drilling damage. Acid treatments have been found to be useful for these purposes but have had limited success in enlarging the effective wellbore radius. The mechanics of acidizing the Nisku formation is not well understood as of yet and will not be included in the scope of this report.
Many of the proppant fracturing treatments performed in the Nisku Formation have ended prematurely as a result t of a screen out. The fracture treatments performed initially in the Enchant field typically consisted of five to ten thousand kilograms of proppant using gelled oil or water fracturing Fluids. Less than expected post treatment production rates promoted changes to the treatment designs. Negative slope trends were experienced on the net pressure plots during many of the treatments. This negative slope indicated that unwanted height growth was occurring during the treatments. Less viscous fracturing fluids and lower injection rates were used to reduce fracture height growth during the treatments. Predicted post fracture production was consistently higher than the actual production. It was unknown whether the problem was due to using inaccurate reservoir parameters or incorrect fracture modelling.