This paper presents a new method for accessing thin, gas-bearing sands in previously completed shallow wells in western Canada. Of the thousands of shallow gas wells completed in this large field, many contain gas zones that were never completed. Many of these zones were believed to be uneconomical or too thin to be completed with conventional limited-entry fracturing technology. As gas prices have increased, these previously bypassed gas zones have become more attractive to operators in the area. Now, an improved recompletion technique integrates conventional fracturing, coiled tubing, and retrievable downhole tool technology to access the previously bypassed gas zones.
The challenge for gas producers is to find a more economical method of completing bypassed zones in a shallow-gas region of western Canada. These thin, cretaceous-age sandstones are reported to contain as much as 14% of the total hydrocarbon reserves of western Canada. The oldest of these gas pools occurs within the Medicine Hat Sandstone, discovered in 1890 as a result of the search for coal reserves in the area.
Previously, to access the bypassed zones properly, operators had to use a servicing rig, jointed pipe, and isolation packers to selectively stimulate the bypassed zones when perforations above were open. Bypassed zones that have open perforations below them can be accessed with limited-entry fracturing techniques. However, some operators and service companies believe that limited-entry fracturing techniques may not provide the most effective method of stimulating these particularly thin, multizone sandstone reservoirs.
One solution to this challenge uses a combination of technologies for selectively fracture-stimulating bypassed zones in shallow-producing gas wells. This specialized service integrates coiled tubing (CT) technology, conventional fracturing equipment, and a new retrievable CT fracturing (RCTF) packer.
The benefits of CT fracturing have rapidly increased the demand for this new technology in western Canada. CT fracturing has the following benefits:
Thin gas zones can be selectively stimulated.
A well can be completed and cleaned up more quickly.
Early production results are improved.
The method is typically more economical than traditional service-rig-assisted methods of accessing bypassed gas zones.
The geology of the region and the condition of the completed wellbores have directed the development of CT fracturing job design and equipment. Fig. 1(Page 4) shows the shallow gas area, covering parts of southeastern Alberta and southwestern Saskatchewan. Currently, there arc more than 21,000 producing wells in this region with a combined annular gas production of more than 0.3Bcf/yr.
This gas field, which contains a substantial quantity of western Canada's gas, is vast (about 3.9 million acres), and covers an area approximately 120 mileslong in an cast-west direction and 70 miles wide in a north-south direction. Typically, the targeted bypassed zones are thin, individually contain marginal quantities of gas, and may have lower permeabilities than the accessed zones.