Avista Corp. has filed a long-term resource plan with state regulators that forecasts a sufficient natural gas supply for 17 years or longer, indicating that the company won't need to acquire additional pipeline resources before 2029.

Avista filed its 2012 Natural Gas Integrated Resource Plan on Aug. 31 with regulators in Washington, Idaho, and Oregon. The plan projects an adequate long-term natural gas supply in part because of lower customer demand, but also because of increased production in the U.S.

The report also cites "the considerable drop in the long-term cost of natural gas due to the increased production from previously untapped shale gas formations throughout North America."

Access to those natural gas sources is expected to provide long-term availability and a continued lower natural gas price, which the plan notes has dropped significantly since the company last filed a natural gas resource plan in 2009.

"Robust North American supplies led by shale gas developments, coupled with lackluster demand due to the economy, has pushed prices down to levels not seen in the last decade," the plan says.

Avista says in the report that other notable changes since the 2009 filing include decreased demand driven mainly by lower customer growth and per-customer use. The plan say those reductions were lower than originally anticipated and driven mostly by the recession.

"Since our 2009 IRP, customer growth has slowed, and it is not anticipated to rebound in the near term," the report says. "We have also seen use-per-customer reductions as customers have become more household-budget conscience, changed usage behavior, and over the last few years have invested in conservation measures."

Breaking down anticipated needs by region, the company says the first natural gas resource deficits are expected to occur in Oregon in 2029, and for Washington and Idaho, in 2030. Customer accounts are expected to grow at an annual average rate of 1.6 percent in Oregon, and 1.7 percent in Washington and Idaho, over the 20-year span of the plan.

The latest plan also anticipates a 1.3 percent average annual growth in demand for natural gas in all three states over the 20-year period. However, the report says that consideration of a relatively flat forecasted demand growth has its risks.

"Implied in this outlook is existing resources will be sufficient to meet demand for most of the 20-year planning horizon," the plan says. "However, should demand growth accelerate, the steepening of the demand curve could quickly accelerate resource shortages by several years."

Other risks could include potential impacts from long-term natural gas pricing levels and availability of existing regional resources, as well as any carbon legislation.

Avista is required by state regulators to submit its 20-year resource plan every two years with a forecast of natural gas demand and potential new resources to provide natural gas service. The plan sets a course of action for resource decisions.

The company is involved in the production, transmission, and distribution of energy as well as other energy-related businesses. Avista Utilities is the operating division that currently provides electric service to 359,000 customers and natural gas to 320,000 customers. Its territory includes Eastern Washington, North Idaho and parts of southern and eastern Oregon.