Development of the Upper Cretaceous reservoirs in southeastern Alberta has witnessed continuing modifications to completion procedures and techniques. Of particular interest are the changes in fracturing procedures that have occurred over the past several months. It is the purpose of this paper to present a discussion of the three major fracturing techniques currently utilized by operators in southeastern Alberta and the theoretical advantages and disadvantages of each general type of stimulation. A method of evaluating the effectiveness or the various techniques, based on pressure build-up data, is reviewed. Field results of analyses conducted for several wells completed utilizing the various stimulation programs are presented. Based on these analyses it is concluded that operators would benefit by reviewing in detail various completion procedures on the initial wells in a specific project. It is also concluded that the newly developed "Combo-Frac" procedure can provide significant stimulation benefits for Upper Cretaceous reservoirs.
The two Upper Cretaceous reservoirs with which this paper is most applicable are the Milk River and the Medicine Hat Sands. The Milk River formation (1) has an upper and a lower member. The upper section is fine-grained, grey sandstone with some interbedding of sandy clays and grey shale's. The lower member is light grey, medium grained, cherty sandstone with some streaks of sandy shale. The gross thickness of this formation can be up to 300 feet. The Medicine Hat Sand(1) is fine to medium-grained sandstone; interbedded with shale, up to 45 feet in gross thickness.
It has been the authors' r experience that the assumption the two formations will produce similarly, because they were deposited in a blanket like manner, from north to south and east to west across the Medicine Hat, Jenner, Princess and miscellaneous other southeastern Alberta fields is invalid. Review of various projects has indicated that depositional differences occur from area to area. It is imperative that operators experimentally evaluate the efficiency of various completion methods which could be utilized on a proposed project prior to completing all project wells following a non-varying program.
In general, the very low permeability of both these reservoirs results in production rates which are uneconomic unless stimulated by hydraulic fracturing (Kowalchuk and Coles(2)). Various authors have described the types of stimulations performed on the Upper Cretaceous Sands. The types of fracturing currently used to stimulate these reservoirs, and a method for evaluating the effectiveness of the treatments utilizing pressure build-up data, will be discussed in the text of this paper.
Anderson(3) discussed the use of liquefied carbon dioxide and the use of large mesh sand in conducting Milk River formation stimulation programs. This type of fracturing treatment, which is the most commonly used to date, has been labeled as the "Conventional CO2 – Water Frac".
There are many variations in the manner in which this kind of treatment is performed. The size of the jobs are usually in the order of 300 to 400 barrels of water, and 30,000 to 60,000 pounds of sand.