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Birds Nest aquifer
 

Aquifer Saline Injection in Utah's Uintah Basin

The briny water that is a normal byproduct of oil and gas drilling is a major management consideration in the energy production industry. Eastern Uintah Basin gas producers dispose of the produced water by injecting it into the already saline Birds Nest aquifer. However, proposed new petroleum wells would produce huge volumes of saline water, and no one knows for sure how that volume will affect the aquifer and surrounding water resources. UWRL researchers are exploring those scenarios to ensure the sustainable, safe development of Utah's water and energy resources.

 
Bird Nest aquifer
The deep saline Birds Nest aquifer is so named because of voids in the rocky outcrop of the aquifer that appear similar to a swallow's nest.

Study Area:

Uinta Basin, UT
(Uintah, Duchesne, Carbon, Grand, Emery, and Wasatch Counties, and the cities of Vernal and Duchesne)

Principal Investigators:

Richard Peralta
(richard.peralta@usu.edu)

Co-Researchers

Michael D. Vanden Berg
(Utah Geological Survey)

Rick Lyons(PhD student)

outline map of Utah with star on Uintah Basin

Project Description

All of the significant oil shale deposits in Utah are located in the Uinta Basin, a petroleum-rich basin that is home to significant conventional oil and gas production activities. In the last few years, the basin has seen a large increase in unconventional gas production activity. In these operations, natural gas is produced from reservoirs of very low inherent permeability. One of the significant technical and environmental issues in these operations is the disposal of the salin water that is a natural byproduct of these mining processes. One method of disposing this water is to inject it into aquifers of sufficient capacity. Eastern Uinta Basin gas producers dispose of produced water in the Birds Nest aquifer located in the Parachute Creek Member of the Green River Formation because of its suitability for large volume disposal. Utah's oil shale deposits are also located within the Parachute Creek Member. The Birds Nest aquifer is typically several hundred feet above the richest oil shale interval, the Mahogany zone. 

Agencies are concerned about possible impacts of dramatic Uintah Basin petroleum production increases. Oil and gas production also produce saline water. From 2001 to 2011, natural gas, crude oil, and saline water production increased 208%, 160%, and 86%, respectively. In the future, the 25,000 proposed new petroleum wells would produce a huge volume of saline water requiring disposal. For environmental reasons, the preferred Uintah basin disposal method is subsurface injection. Gas producers plan to increase saline water injection into the Birds Nest Aquifer (BNA), which exists within the oil shale horizon. This aquifer has veins of solid hydrocarbon Gilsonite that can affect groundwater flow, and its effect on horizontal or vertical groundwater flow are not well known. The northwestern part of the BNA is eligible for saline water injection because its salt concentration already exceeds 10,000 mg/L total dissolved solids (TDS). Southeastern aquifer water which has less than 10,000 mg/L TDS is protected from injection.

The Utah Geological Survey (UGS) and US Bureau of Land Management (BLM) have identified possible negative injection consequences. Horizontally flowing injectate could harm existing groundwater supply wells, increase fresh water spring discharge, and cause saline springs that might contaminate surface waters. Injection could also economically harm Gilsonite mining. Water could also flow downward through Gilsonite veins into fractures in fracked oil-shale strata and flood future petroleum-harvesting activities. Clearly, the physical setting is complex, and guidance is needed.

Unfortunately, no good groundwater flow and contaminant transport models exist of the impacted area. To address the range of concerns agencies have expressed about the effects of saline water injection on the aquifer and the fractures resulting from lower stratum fracking, UWRL researchers are developing two appropriately discretized calibrated flow models.

  • First, a calibrated transport flow model is needed to predict salinity concentrations at target locations in the BNA and associated higher and lower strata.
  • Second, a porous media flow simulation is needed to represent fracture-flow through BNA vertical fractures caused by hydro-fracking.
These models will help the Utah Division of Oil, Gas, and Mining (UDOGM), of the Utah Geological Survey (UGS), to establish safe optimal saline injection strategies in order to develop viable management scenarios. Strategies require a spatial/temporal distribution of injected saline water.  The strategies are obtained using a simulation-optimization (BNA S-O) model, i.e. a model that couples the BNA simulation model with mathematical optimization algorithms.

Results

  • Geographic and other information needed for the BNA S-O model was gathered from the UGS, UDOGM, Utah Department of Natural Resources (UDNR), and the Utah Division of Water Rights (DWR).  Using data from a modeling report by Glover in 1996, a preliminary steady-state MODFLOW groundwater flow model was formulated for the Uinta/Duchesne layer of the Uintah Basin. The model computes flow directions and heads similar to those of Glover. At many observation wells, the head levels are much closer to observed values than those calculated by Glover.
  • A 1 layer, 22 row, and 50 column grid groundwater flow simulation model was used to represent the top stratum of the Uintah Basin subsurface. Previous models assumed uniform thickness and elevation. Well water elevations and aquifer thickness for the model were primarily derived from well logs and records of well construction. The model was populated with estimated hydraulic parameters and some boundary conditions (hydraulic head, deep percolation from precipitation, and recharge into and discharge out of the various rivers that traverse the Uintah basin).
  • Instead of assuming a flat aquifer of uniform thickness, the use of ground surface and stratum elevation data allows for the creation of a more representative model. However, this approach also creates the need for more specific system parameter values, many of which are not readily available. These values can be estimated from related information such as soil type, rock type, visible fractures, rock outcrops, etc.

study site location

bird nest aquifer study area

Benefits to Utah

The project will provide critically needed guidance for Utah energy-development decisions that have significant economic, environmental, social, and political ramifications. Results of the simulation will also help project the economic consequences and impacts of management scenarios. For example, a sample scenario would optimize saline injection at candidate wells over a 20-year period, without causing excessive fresh water spring discharges, saline discharge at springs feeding surface waters, the southward movement of 10,000 TDS fresh-saline water interface, or harmful domestic well impacts. 

Collaboration between agencies and industry will help assure practical utility of the project results and will aid the sustainable safe development of and energy resources in the Uintah Basin, with applicability worldwide.