Stimulation Techniques In the Milk River Formation, Medicine Hat
Authors: Anderson H.A. 
Published: March 2010

Recently, there has been a substantial level of activity in the shallow gas-bearing Milk River Formation of southeastern Alberta. Stimulation of the zone presents special problems, as the zone is soft, loosely consolidated, greatly affected by normal fracture fluids and low in permeability. Special materials and techniques have been developed to handle the particular problems presented by the Milk River Sand.

This paper examines these techniques, including the use of carbon dioxide, large-mesh sand, clay-control agents and foaming agents, and estimates their effectiveness. The results of some treatments are discussed.

Introduction

THE MILK RIVER ZONE consists of two sections. The upper is a fine-grained, gray sandstone with interbedding of sandy clays and gray shales; the lower section is a light gray, medium-grained, cherty sandstone with streaks of sandy shale. The zone is found primarily in the southeastern portion of the province. Together with the overlying Pawkowki zone, the Milk River is equivalent to the Lea Park Formation. Zone thickness ranges up to 350 feet for the Pawkowki zone and 300 feet for the Milk River zone. Spectroscopic analysis indicates that the major component is quartzite, with small amounts of illite, kaolinite, chlorite and montmorillonite clays. This varies from well to well, and with depth, the deeper zone containing higher quantities of water-sensitive clays. Although there are very few cores cut on the Milk River zone, it appears that porosities range around 16 per cent, permeabilities are of the order of one milidarcy and water saturations are fairly high.

Gas was first recovered from the Milk River zone in the year 1890. While exploring for coal in the Medicine Hat area, a well encountered considerable gas flows from a zone some 600 feet deep. Although little interest was shown in the Milk River section at that time, the gas discovery did spark gas well activity in the more prolific Medicine Hat Sand. However, activity was low because of the small size of local needs and because of the remoteness of any significant market. Of the few Milk River wells drilled in the early 1900's. one well, completed in 1911, continues to produce.

Interest in the shallow gas, and particularly the Milk River zone, in southeastern Alberta remained dormant until 1941. At that time, the Department of National Defence drilled three wells to supply the Canadian Forces Base at Suffield with gas. By 1965 they had drilled some thirty wells, some of which are still on production for C.F.B. and Research Station use.

Recent interest began late in 1968, with one well completed and put on production. The first frac treatment was also performed. Since that time, over two hundred fracture treatments have been conducted on the Milk River Sand with varying degrees of success.

Various authors have described techniques of fracture geometry predictions, among them: Howard and Fast(2) Kiel(a), Geertsma and de Klerk'", As pointed out by Nierode et al(z), either of the most recent formulations give similar predictions of fracture geometry.