SANDY McSURDY and CHANDRA NAUTIYAL, National Energy Technology Laboratory, US Department of Energy

Optimizing ice road networks through better understanding of water availability and environmentally sensitive areas will expedite the development of oil and gas reserves on Alaska’s North Slope.

With estimates of 100 billion bbl of total oil in place beneath the North Slope and 200 Tcf of technically recoverable gas statewide, Alaska will continue to play an important role in supplying US energy demands. But energy exploration and development in Alaska is dependent upon the ability to access remote areas under challenging conditions. Ice roads are commonly constructed to transport equipment for oil and gas development. These roads, constructed by spraying fresh water and letting it freeze into a hard surface, are designed to disappear during warm weather, minimizing impacts to the tundra and the state’s pristine habitats.

Since 1 mile of exploration ice road requires about 1 million gallons of fresh water for construction and maintenance in flat terrain, methods are needed to enable the efficient use of water resources during the ice road season while also protecting the Alaskan ecosystems that rely on freshwater lakes and ponds. To this end, the US Department of Energy’s National Energy Technology Laboratory (NETL) is collaborating with researchers at the University of Alaska at Fairbanks (UAF) and the environmental consultancy Geo-Watersheds Scientific on projects focused on improving ice road construction and water resource management practices in Alaska.

SNOW BARRIERS

Ice road builders are dependent on surface freshwater supplies, which are affected by annual recharge rates and competing uses. If sufficient water is not available from nearby lakes and supplemental water must be transported from distant sources, ice road construction can be delayed and costs can skyrocket.

The hydrological regimes of these lakes are characterized by considerable snowmelt in the spring, which provides much of the recharge, followed by drying during the summer, when evaporation generally exceeds precipitation. Some of the surface storage deficit is replenished during early fall when precipitation is at an annual maximum and evapotranspiration is rapidly diminishing. However, if the surface storage deficit is not replenished (for example, precipitation in the fall is low and/or near-surface soil is dry), lake recharge is negatively affected and water availability for the following winter is reduced.

Dr. Svetlana Stuefer of the Water and Environmental Research Center (WERC) at UAF’s Institute of Northern Engineering is studying the effects of snow management, particularly the use of snow barriers, also called snow fences, to augment water supply in Arctic lakes. Based on extensive research on snow drifting, the project has implemented practices to enhance snowdrift accumulation, which leads to decreased snow sublimation, increased meltwater production, an extended melting season and lake recharge despite surface storage deficit and/or low precipitation.

Two lakes with similar hydrological regimes were selected and monitored for two years. One is a man-made, experimental lake (a gravel pit) where a snow barrier was installed. Such barriers can be used to collect snow in ways that ensure a supply of melting snow to recharge bodies of fresh surface water, Fig. 1. Determining the optimal location of the snow barrier is considered critical to its success. The second body of water is a control lake where the natural regime has been preserved, Fig. 2. Highlights of the project to date include assessment of the snow barrier’s effect on snow distribution and sublimation, recommendations on snow barrier location and evaluation of the lakes’ responses to snowdrift melt.

Fig. 1. An experimental snow barrier and monitoring devices with accumulated snow in March 2010.

Fig. 2. The experimental lake (left) and control lake located at the Franklin Bluffs on Alaska’s North Slope in June 2009.

The research site was selected, and land-use permits authorizing installation of a snow barrier and equipment to collect snow and hydrology data were obtained from the Alaska Department of Natural Resources and the Fairbanks North Star Borough. Permission for land use was obtained from the Alyeska Pipeline Service Company (the consortium that operates the Trans-Alaska Pipeline System) and the Alaska Department of Transportation. Weather data analysis indicated that the snow accumulation season extends from September to June, the prevailing wind direction and snow drift orientation are northeast, the mean winter precipitation is 4.13 in. (105 mm). Based on the weather data, it was estimated that snow barrier height should be 10.5 ft (3.2 m) and snow barrier length should be at least 427 ft (130 m).

The automated snow accumulation data collection was initiated at three locations: the Franklin Bluffs meteorological station, a hydrological site at the gravel pit (i.e., the experimental reservoir), and a hydrological site at the control lake. Snow water equivalent (SWE) at Franklin Bluffs was measured as 6.3 in. (160 mm) on April 29, 2009. In comparison with previous years, snow depth and SWE were above average. Data from different projects in 2000–2008 were collected by WERC researchers. The SWE measured in 2009 was 33% greater than the 10-year average. In addition to a historical snow survey, snow depths were measured at the gravel pit and control pond. The barrier was installed at the end of August 2009 following the Tabler & Associates snow fence guide published by the National Research Council’s Strategic Highway Research Program. In September 2009, the barrier was reinforced and re-anchored into the permafrost.

Major water sources and sinks were measured at the experimental and control lakes. Research included a bathymetric survey, water level records and measurements of the lake outflow, rain precipitation, evaporation and water withdrawal from the gravel pit. A tower near the snow barrier was equipped with a data logger, power, a solar panel, a camera, an antenna, a radio, and relative humidity and air temperature sensors to monitor snow drift growth and melt. The radio transmited all the data and camera images from the snow barrier site to the WERC server in real time.

Snow drift elevation was measured twice in the summer of 2010 using high-precision GPS instruments. Snow drift volume was calculated in ArcGIS 3D Analyst software using drift snow density averages. The estimated drift volume on June 21, 2010, was 209,900 cu ft (5,943 cu m). SWE was estimated with the field data, and a model was developed to estimate snow drift melt based on the continuous snow depth data obtained from three sonic depth sensors. The snow drift lost about 75% of its volume during the first three weeks of melt.

Pretreatment water balance analysis for 2009 indicated that the majority of water loss was due to evaporation from the lake surface, with only half of the water loss being replaced through summer rainfall. The cumulative rainfall in 2010 was below average and equaled only half the rainfall total for 2009. However, water balance calculations indicated that there was additional inflow into the man-made lake in 2010.

Research has shown that the installation of the snow barrier reduced reservoir water loss due to snow sublimation. The resultant snow drift added an additional month of water to the lake supply that can be utilized for ice road construction. Water levels in the lake near the snow barrier were elevated during the entire 2010 open-water season. Water levels in the control lake declined during the same period. Costs for generating the additional water through snow barrier installation were one-tenth of the cost of trucking in water from other nearby sources. Data collection will continue on this project through the end of 2011 to acquire additional information on added snow amounts and cost estimates that can be used to refine recommendations for implementing similar installations.

ROUTE PLANNING AND PERMITTING

Adding to the challenge of limited or variable water availability is the need for coordination in the common use of water resources by many ice road planners. Dr. William Schnabel and his team at UAF’s Institute of Northern Engineering have developed the North Slope Decision Support System (NSDSS), a software application that can be used by both the oil and gas industry when planning ice road routes and the regulators involved in the permitting process. The decision support system is a web-based application (nsdss.net) that helps ice road planners by utilizing user input such as desired start and end points and possible sources of water to produce multiple ice road routes. The optimal road alignment algorithm finds the routes that minimize ice road length, construction time, and construction and operational cost while avoiding endangered species habitat and sensitive tundra. The system displays optional ice road routes and lists road length, construction time, cost and volume of water needed, Fig. 3.

Fig. 3. The NSDSS ice road planning tool allows users to specify the start and end points (green and red dots on the map, respectively), the lakes that may be used (dark blue) and exclusion zones where the ice road should not go. Exclusions are identified in two ways: through user specification (orange circles) and through a web service that assesses whether the intended area is suitable habitat for species such as polar bears.

Ice road planning can also be complicated due to a permitting process that can involve up to two dozen regulatory agency departments. The decision support system’s permitting assessment tool can be used by planners to view permit requirements for each regulatory agency. The tool also allows users to retrieve data from public and proprietary databases to prepare permits. An ice road plan developed using the system can be published on the Internet for easy review by stakeholders, facilitating the process of reaching consensus on the plan.

During ice road construction, the decision support system can also be used to track the amount of water that has been withdrawn as well as water quality, in order to determine the risk of insufficient water supply and the impact of water use on lake water quality.

TUNDRA TRAVEL MANAGEMENT

Most Arctic energy exploration and development activities take place in the middle of winter when the fragile tundra surface is most stable. Currently, regulatory agency personnel must visit field sites in order to measure snow and soil temperature conditions to determine when they are adequate to permit tundra travel. Geo-Watersheds is collaborating with UAF’s Geophysical Institute Permafrost Laboratory to model soil temperatures at test data stations in order to aid tundra travel managers. Using such a model to forecast conditions can help prevent delays in field verification of tundra conditions and minimize lost time during this critical window of operation for oil and gas producers. Research efforts also are continuing for snow distribution modeling, which should increase the accuracy of absolute snow measurements and wind-redistribution modeling methods. These methods are being developed primarily to aid in the forecast of short-term conditions, but can also be used by industry and regulatory agencies to predict changes in snow cover, soil temperature and water availability over time. Forecast models can save valuable time by improving the planning and logistical efforts involved in building and operating seasonal ice-road networks and maximizing the available ice road season.

An ice growth simulation tool is also being investigated for use during the ice road season. Early lake-ice formation is being characterized by a research team led by GW Scientific president and hydrologist Michael Lilly (arctic-transportation.org/atn.shtml), and end-of season aerial lake surveys are being carried out during spring snowmelt and lake recharge to provide data for the simulation effort. When changes in ice thickness can be tracked with analytical models, winter water use management can be improved to better predict ice thickness variability and to support adaptive water management permitting and management. More information is available on the ATN website.

OTHER PROJECTS

The US Department of Energy has similar research initiatives underway that focus on other Arctic energy resources. For example, DOE-sponsored projects have resulted in the drilling of the first Alaskan well targeting methane hydrates, which validated a hydrate exploration methodology developed jointly by the DOE, the US Geological Survey, BP, and other industry and academic partners. During the first quarter of 2012, the federal agency plans to implement the first field test of a novel technology for enhancing methane production from subsurface hydrates using carbon dioxide injection, with partner CononcoPhillips. Also underway are projects to develop better ways of producing light oil from frozen reservoirs and heavy oil from extensive, but as yet underdeveloped, North Slope deposits.

For more information on these projects, visit NETL’s Strategic Center for Natural Gas and Oil website (netl.doe.gov/technologies/oil-gas/index.html).