During 1986 two large volume stimulation treatments were carried out on two low permeability (<0.l mD) Panther River wells. The formation treated in both wells was the Mississippian Turner Valley (mt); a thrust faulted dense dolomite reservoir rock containing sour gas (average 6% H2S) and found at about 4500 m (15 000 ft) in the Sheet III structure.
Panther River #2, a previously uncompleted well because of poor reservoir quality, was stimulated with a staged gelled pad, retarded-acid frac. Panther River #7, a suspended well with non-commercial deliverability, was stimulated with a massive propped frac using crosslinked HPG frac fluid and 40/60 sand. One of the objectives was to evaluate the response of our low permeability Panther River wells to these different stimulation techniques.
This paper reviews the selection of stimulation candidates, treatment design and execution, and the results; together with well and reservoir characteristics.
The Panther River sour gas field is situated On the eastern slopes of the Rocky Mountains about 100 km northwest from Calgary and 12 km southwest from Shell's Burnt Timber sour gas field (Fig 1). The Panther River field is located in the Bow Crow Forestry Reserve adjacent to Banff National Park. The wells are sour and located in prime protection or critical wildlife areas. Consequently well work operations are carefully regulated and controlled to safeguard the environment and minimize the impact on wildlife.
The Panther River field was discovered in 1958 with the drilling of Shell Panther River #1 (LSD 05-19-30-10 W5M). Development has been gradual due to uncertainty in drilling the deep (up to 5100 m), expensive, relatively low deliverability wells, and the unavailability of suitable processing capacity and markets for the gas. Currently Shell has ten wells drilled and cased in Panther River of which two are abandoned: Panther River #8 and #10. A brief history of individual wells is presented in Table 1.
Total gas in place is estimated to be 58 E09 m3 (2 TCF); unfortunately. the reservoir characteristically exhibits low permeability (less than 0.1mD) and low deliverability.
Two recent events sparked fresh interest in Panther River:
natural gas deregulation legislation in Canada provided new market opportunities for Panther River gas; and
decline in deliverability from the Burnt Timber wells has created capacity at nearby Burnt Timber sour gas plant.
As a result of these events, Shell is proceeding with construction of facilities to connect five Panther River wells to the Burnt Timber gas plant with production to start in 1989.
Prior to construction of the gas gathering and compression facilities. two wells were selected as stimulation candidates in an attempt to improve their deliverability and increase recoverable reserves by creation of long conductive fractures emanating from the wellbore. Massive hydraulic fracture (MHF) stimulations in similar tight gas reservoirs elsewhere had yielded promising results 1,2.
Hydrochloric (HC1) acid stimulations had been previously performed on all wells but one: Panther River #2 was only drill stem tested (DST'd).
