Concept: Bakken Formation
Oil and natural gas development in the Bakken shale play of North Dakota has grown substantially since 2008. This study provides a comprehensive overview and analysis of water quantity and management impacts from this development by (1) estimating water demand for hydraulic fracturing in the Bakken from 2008 to 2012; (2) compiling volume estimates for maintenance water, or brine dilution water; (3) calculating water intensities normalized by the amount of oil produced, or estimated ultimate recovery (EUR); (4) estimating domestic water demand associated with the large oil services population; (5) analyzing the change in wastewater volumes from 2005 to 2012; and (6) examining existing water sources used to meet demand. Water use for hydraulic fracturing in the North Dakota Bakken grew five-fold from 770 million gallons in 2008 to 4.3 billion gallons in 2012. First-year wastewater volumes grew in parallel, from an annual average of 1,135,000 gallons per well in 2008 to 2,905,000 gallons in 2012, exceeding the mean volume of water used in hydraulic fracturing and surpassing typical 4-year wastewater totals for the Barnett, Denver, and Marcellus basins. Surprisingly, domestic water demand from the temporary oilfield services population in the region may be comparable to the regional water demand from hydraulic fracturing activities. Existing groundwater resources are inadequate to meet the demand for hydraulic fracturing, but there appear to be adequate surface water resources, provided that access is available.
The quality and age of shallow groundwater in the Bakken Formation production area were characterized using data from 30 randomly distributed domestic wells screened in the upper Fort Union Formation. Comparison of inorganic and organic chemical concentrations to health based drinking-water standards, correlation analysis of concentrations with oil and gas well locations, and isotopic data give no indication that energy-development activities affected groundwater quality. It is important, however, to consider these results in the context of groundwater age. Most samples were recharged before the early 1950s and had (14) C ages ranging from <1000 to >30,000 years. Thus, domestic wells may not be as well suited for detecting contamination associated with recent surface spills as shallower wells screened near the water table. Old groundwater could be contaminated directly by recent subsurface leaks from imperfectly cemented oil and gas wells, but horizontal groundwater velocities calculated from (14) C ages imply that the contaminants would still be less than 0.5 km from their source. For the wells sampled in this study, the median distance to the nearest oil and gas well was 4.6 km. Because of the slow velocities, a long-term commitment to groundwater monitoring in the upper Fort Union Formation is needed to assess the effects of energy development on groundwater quality. In conjunction with that effort, monitoring could be done closer to energy-development activities to increase the likelihood of early detection of groundwater contamination if it did occur.
Ecosystems worldwide have been subject to new or intensified energy development facilitated by technologies such as horizontal drilling and hydraulic fracturing, activity that has generated concern for air, water, biotic, and social resources. Application of these technologies in the development of the Bakken oil patch has made it one of the most productive petroleum plays in North America, causing unprecedented landscape industrialization of otherwise rural, agricultural counties in western North Dakota. The region is isolated, and development impacts have not been well-studied. To identify concerns of citizens of the Bakken and determine how research and policy might support them, we conducted a two-part study: First, we held focus groups with resource management and community leaders in three major oil-producing counties. Second, we used an outline of the major concerns expressed by focus group members as a survey for landowners and farm/ranch operators. We found little relationship between survey respondents' reported categorization of energy impacts and actual land area impacted, suggesting factors such as attitude towards development, degree of compensation, and level of disturbance are relevant. Landowners agreed with focus groups on the nature of relationships between energy companies and locals and development impacts on infrastructure and communities; those reporting greater impacts tended to agree more strongly. But many specific problems described in focus groups were not widely reported in the survey, suggesting energy-community relationships can be improved through state-level public policy and respect from energy companies for locals and their way of life. Consideration of these concerns in future energy policy-both in the Bakken and worldwide-could reduce social tension, lessen environmental impact, and increase overall social, economic, and environmental efficiency in energy development.
Modern drilling techniques, notably horizontal drilling and hydraulic fracturing, have enabled unconventional oil production (UOP) from the previously inaccessible Bakken Shale Formation located throughout Montana, North Dakota (ND) and the Canadian province of Saskatchewan. The majority of UOP from the Bakken shale occurs in ND, strengthening its oil industry and businesses, job market, and its gross domestic product. However, similar to UOP from other low-permeability shales, UOP from the Bakken shale can result in environmental and human health effects. For example, UOP from the ND Bakken shale generates a voluminous amount of saline wastewater including produced and flowback water that are characterized by unusual levels of total dissolved solids (350 g/L) and elevated levels of toxic and radioactive substances. Currently, 95% of the saline wastewater is piped or trucked onsite prior to disposal into Class II injection wells. Oil and gas wastewater (OGW) spills that occur during transport to injection sites can potentially result in drinking water resource contamination. This study presents a critical review of potential water resource impacts due to deterministic (freshwater withdrawals and produced water management) and probabilistic events (spills due to leaking pipelines and truck accidents) related to UOP from the Bakken shale in ND.
A holistic risk assessment of surface water (SW) contamination due to lead-210 (Pb-210) in oil produced water (PW) from the Bakken Shale in North Dakota (ND) was conducted. Pb-210 is a relatively long-lived radionuclide and very mobile in water. Because of limited data on Pb-210, a simulation model was developed to determine its concentration based on its parent radium-226 and historical total dissolved solids levels in PW. Scenarios where PW spills could reach SW were analyzed by applying the four steps of the risk assessment process. These scenarios are: (1) storage tank overflow, (2) leakage in equipment, and (3) spills related to trucks used to transport PW. Furthermore, a survey was conducted in ND to quantify the risk perception of PW from different stakeholders. Findings from the study include a low probability of a PW spill reaching SW and simulated concentration of Pb-210 in drinking water higher than the recommended value established by the World Health Organization. Also, after including the results from the risk perception survey, the assessment indicates that the risk of contamination of the three scenarios evaluated is between medium-high to high.
The water footprint of oil production, including water used for hydraulic fracturing (HF) and flowback-produced (FP) water, is increasingly important in terms of HF water sourcing and FP water management. Here we evaluate trends in HF water use relative to supplies and FP water relative to disposal using well by well analysis in the Bakken Play. HF water use/well increased by ~6 times from 2005-2014, totaling 24.5×10(9) gallons (93×10(9) liters) for ~10,140 wells. Water supplies expanded to meet increased demand, including access of up to ~33×10(9) gal/yr (125×10(9) L/yr) from Lake Sakakawea, expanding pipeline infrastructure by 100s of miles, and allowing water transfers from irrigation. The projected inventory of ~60,000 future wells should require an additional ~11 times more HF water. Cumulative FP water has been managed by disposal into an increasing number (277 to 479) of salt water disposal wells. FP water is projected to increase by ~10 times during the play lifetime (~40 yr). Disposal of FP water into deeper geologic units should be considered because of reported overpressuring of parts of the Dakota Group. The long time series shows how policies have increased water supplies for HF and highlights potential issues related to FP water management.
Environmental impacts embodied in oilfield capital equipment have not been thoroughly studied. In this paper we present the first open-source model which computes the embodied energy and greenhouse gas (GHG) emissions associated with materials consumed in constructing oil and gas wells and associated infrastructure. The model includes well casing, wellbore cement, drilling mud, processing equipment, gas compression, and transport infrastructure. Default case results show that consumption of materials in constructing oilfield equipment consumes 0.014 MJ of primary energy per MJ of oil produced, and results in 1.3 gCO2-eq. GHG emissions per MJ (lower heating value) of crude oil produced, an increase of 15% relative to upstream emissions assessed in earlier OPGEE model versions, and an increase of 1-1.5% of full life cycle emissions. A case study of a hydraulically-fractured well in the Bakken formation of North Dakota suggests lower energy intensity (0.011 MJ/MJ) and emissions intensity (1.03 gCO2-eq./MJ) due to the high productivity of hydraulically fractured wells. Results are sensitive to per-well productivity, the complexity of wellbore casing design, and the energy and emissions intensity per kg of material consumed.