Some 38.6 billion cubic feet of gas are expected to be recoverable from Unocal’s Happy Valley field, the Alaska Oil and Gas Conservation Commission said in approving pool rules for the accumulation.
Happy Valley is in the northern portion of the Deep Creek unit some six miles east of the town of Ninilchik on the Kenai Peninsula.
The Happy Valley No. 1 discovery well was drilled to a total measured depth of 10,871 feet in June 2003 and tested gas from two different Lower Tyonek reservoirs. The field discovery was confirmed when the Happy Valley No. 2 well was drilled in July 2003. The No. 2 flowed gas from two other Lower Tyonek reservoirs not seen in Happy Valley No. 1.
The commission said Unocal has since drilled nine additional delineation wells and acquired some 65 line miles of 2D seismic data in an attempt to delineate the structure and reservoir distribution within the field.
The Beluga and Tyonek formations were found to be commercial in a number of the wells, and Unocal built a 15-mile natural gas transmission line to, and gas production facilities at, the Happy Valley A Pad. Gas sales began in November.
The commission said the proposed Happy Valley Beluga/Tyonek gas pool correlates with the interval between the measured depths of 2,997 feet and 10,046 feet in the Superior Happy Valley No. 31-22 exploration well.
Commingling required
The Happy Valley field produces dry gas from the Beluga and Tyonek reservoirs, with a gas composition of more than 98 percent methane. Both reservoirs have relatively low permeability.
The shallower Beluga formation reservoirs are at depths from 3,070 feet true vertical depth to 5,800 feet TVD. “Obtaining measurable gas flow from the Beluga formation has required multiple reservoirs to be open simultaneously,” the commission said.
The Tyonek formation reservoirs vary in depth from 5,800 feet TVD to 10,108 feet TVD.
Recoverable gas at Happy Valley is estimated at 38.6 billion cubic feet, with an estimated 56.3 bcf of gas in place in the Beluga formation, 23 bcf of which is expected to be recoverable, and 37.4 bcf of gas in place in the Tyonek reservoir was an estimated 15.6 bcf recoverable.
Commercial production, the commission said, requires commingled production from the Lower and Upper Tyonek and Beluga formation reservoirs. Unocal proposed a single Happy Valley Beluga/Tyonek Pool “encompassing all of the currently identified Beluga and Tyonek formation reservoirs within the field, and also any future new reservoirs of the same age that might be found within the mapped limits of the Happy Valley field.”
This maximizes resource recovery, the commission said, by “increasing the number of take points in these low permeability reservoirs.” It combines “production from multiple tight intervals;” makes resource commercial that otherwise would not likely be recovered; improves the efficiency of stimulation; and lowers “the economic threshold of field development, reducing the abandonment flow rate of wells, reducing operating expense, thereby producing longer and recovering more reservoirs.”
Unocal has told the commission that because of “the complex nature of these low permeability reservoirs … tight (well) spacing is expected necessary to maximize resource recovery.”
Poor lateral continuity
The commission said in its conclusions: “The Happy Valley Beluga/Tyonek Gas Pool reservoirs are composed of channelized fluvial and braided stream deposits that have poor lateral continuity and typically very low permeabilities. The pool is composed of numerous individual low productivity sandstone intervals.”
A large number of sands, “potentially more than 20 per well,” will need to be commingled because of “low individual sandstone productivity and poor inter-well continuity,” the commission said.
Happy Valley is in the early stages of development, with the first phase “focused upon determination of reservoir delivery and well operability.”
The field “is a series of gas accumulations with elements of both structural trapping and stratigraphic discontinuities. Future drilling may encounter off-structure stratigraphic traps and the Happy Valley Beluga/Tyonek Gas Pool area may need to be expanded,” the commission said.
A second phase of work at Happy Valley may include drilling from a second pad, “and refining pay recognition and stimulation techniques.”
