Stimulating the Triassic Carbonates In the Foothills Gas Trend of Northeast British Columbia
Authors: Wade R.P. , Aziz K. 
Published: March 2010

BP Exploration Canada Limited operates eight sour gas wells in the Foothills Gas Trend of northeast British Columbia. The eight wells penetrate five low-porosity (3–4%) and low-permeability (&lt;10 mD) Triassic reservoirs.

Six of the eight wells were stimulated with multiple-acid-fracture (MAF) treatments, which cost between $300,000 and $450,000 per stimulation. The results of the MAF treatments were mixed, and are discussed in this paper. Two of the eight wells did not require MAF treatments to attain high deliverabilities. Examination of the eight wells and their stimulations suggests that natural flow capacity, as probably mainly influenced by the existence and extent of the natural-fracture system in each well, determines if a well requites a MAF treatment to attain high deliverability.

Also, use of a hydrochloric (HCl)/acetic (HAc) acid blend during the MAF stimulations is not recommended. In its place, 28% Hel acid is recommended, which would reduce the cost of the stimulations 25 per cent, or $100,000 to $200,000 per treatment. On the most recent BP-operated well (which is not discussed in this paper), BP et al. Bullmoose a-43-E, high deliverability was attained after a MAF treatment using 28% HC1 acid. The cost of the treatment was reduced $150,000 by using 28% HCI instead of the HCI/HAc-acid blend.

INTRODUCTION

In October 1964, an exploration well was spudded in the Rocky Mountain Foothills of northeast British Columbia (Fig. 1). This well, Triad BP Sukunka a-43-B, 93-P-5, tested sour gas at 476 103m3/d from several Triassic carbonate zones, in particular from the Pardonet and Baldonnel formations. After stimulating with 22.7 m3 of 15% HC1 acid, a wellhead AOF rate of1,280.103m3/d was calculated. Immediately following this discovery, three wells were drilled which were off-structure and abandoned. Due to low gas prices and high drilling costs, there was no further drilling in the area until 1974.

Since 1974, seven gas and five dry wells have been drilled by BP Exploration Canada Limited and partners in search of natural gas in the Triassic carbonates of northeast British Columbia. Two of the seven successful wells further delineated the Sukunka structure discovered by the initial well, Sukunka a-43-B; two were drilled into the Bullmoose structure, and the other three successful wells penetrated the East Sukunka, West Sukunka and Murray River structures (Fig. 1). In addition to the eight gas wells mentioned above, another well in the Bullmoose structure has recently been completed (BP et al. Bullmoose a-43-E, Fig. 2), but will not be discussed in detail in this paper.

(Figure in full paper)

When the initial two wells drilled in 1974 /75, BP et al. Bullmoose d-77-E, 93-P-3 and BP East Sukunka d-37-A, 93-P-5 (Fig. 2), did not respond to modest stimulations similar to the Sukunka a-43-B treatment in 1965, laboratory tests were conducted on core samples to determine an effective stimulation treatment. Based on the laboratory results, multiple-acid-fracture (MAP) treatments were designed for the wells in the Sukunka/ Bullmoose/ Murray-River reservoirs.

In general, MAF treatments are designed for carbonate-productive wells which have a number of productive zones over a thick gross interval.