Primary oil recovery from fractured unconventional formations, such as shale or tight sands, is typically less than 10%. The development of an economically viable enhanced oil recovery (EOR) techni...

A Literature Review of CO2, Natural Gas, and Water-Based Fluids for Enhanced Oil Recovery in Unconventional Reservoirs

Modeling of multi-scale transport phenomena in shale gas production — A critical review

Significance Previously published life cycle assessments (LCAs) of greenhouse gas emissions from the production and use of shale gas have come to widely varying conclusions about both the magnitude of emissions and its comparison with conventionally produced natural gas and coal for electricity generation. We harmonize estimates from this literature to establish more consistently derived and robust summary of the current state of knowledge. Whereas median estimates for both gas types appear less than half that of coal, alternative assumptions may lead to emissions approaching best-performing coal units, with implications for climate change mitigation strategies. Recent technological advances in the recovery of unconventional natural gas, particularly shale gas, have served to dramatically increase domestic production and reserve estimates for the United States and internationally. This trend has led to lowered prices and increased scrutiny on production practices. Questions have been raised as to how greenhouse gas (GHG) emissions from the life cycle of shale gas production and use compares with that of conventionally produced natural gas or other fuel sources such as coal. Recent literature has come to different conclusions on this point, largely due to differing assumptions, comparison baselines, and system boundaries. Through a meta-analytical procedure we call harmonization, we develop robust, analytically consistent, and updated comparisons of estimates of life cycle GHG emissions for electricity produced from shale gas, conventionally produced natural gas, and coal. On a per-unit electrical output basis, harmonization reveals that median estimates of GHG emissions from shale gas-generated electricity are similar to those for conventional natural gas, with both approximately half that of the central tendency of coal. Sensitivity analysis on the harmonized estimates indicates that assumptions regarding liquids unloading and estimated ultimate recovery (EUR) of wells have the greatest influence on life cycle GHG emissions, whereby shale gas life cycle GHG emissions could approach the range of best-performing coal-fired generation under certain scenarios. Despite clarification of published estimates through harmonization, these initial assessments should be confirmed through methane emissions measurements at components and in the atmosphere and through better characterization of EUR and practices.

Harmonization of Initial Estimates of Shale Gas Life Cycle Greenhouse Gas Emissions for Electric Power Generation

Shale gas is becoming an increasingly promising alternative energy resource because of its high efficiency and environment-friendly characteristic. The amount of adsorbed gas on the shale matrix surfaces and dissolved gas in the shale matrix bulk is the dominant factor in the long-term productivity of shale reservoir. Although experimental measurements have been extensively carried out to investigate the gas adsorption and diffusion properties in the shale matrix, they cannot provide the detailed information on the microscopic transport mechanism of shale gas during the gas production process. Molecular simulation can accurately visualize the gas adsorption/desorption and diffusion processes in the shale matrix. In the present study, the recent research advances of molecular simulation on gas adsorption/desorption and diffusion in the shale matrix are reviewed. Firstly, the density functional theory (DFT) for shale gas molecule desorption/adsorption on the surface of the matrix crystal is illustrated. Then, the grand canonical Monte Carlo (GCMC) method predicting the amount of shale gas desorption/adsorption in the shale matrix crystal is introduced. Finally, molecular dynamics simulation (MD) for gas diffusion in the shale matrix is elucidated. Further developments of the molecular simulation method in shale gas production are also discussed.

Review of Molecular Simulation Method for Gas Adsorption/desorption and Diffusion in Shale Matrix

Author(s): Rosa, L; Rulli, MC; Davis, KF; D'Odorico, P | Abstract: Shale deposits are globally abundant and widespread. Extraction of shale oil and shale gas is generally performed through water-intensive hydraulic fracturing. Despite recent work on its environmental impacts, it remains unclear where and to what extent shale resource extraction could compete with other water needs. Here we consider the global distribution of known shale deposits suitable for oil and gas extraction and develop a water balance model to quantify their impacts on local water availability for other human uses and ecosystem functions. We find that 31–44% of the world's shale deposits are located in areas where water stress would either emerge or be exacerbated as a result of shale oil or gas extraction; 20% of shale deposits are in areas affected by groundwater depletion and 30% in irrigated land. In these regions shale oil and shale gas production would likely compete for local water resources with agriculture, environmental flows, and other water needs. By adopting a hydrologic perspective that considers water availability and demand together, decision makers and local communities can better understand the water and food security implications of shale resource development.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2018EF000809

The Water-Energy Nexus of Hydraulic Fracturing: A Global Hydrologic Analysis for Shale Oil and Gas Extraction

Mexico's recent energy reform (2013) has provided the foundations for increased private participation in attempts to offset or reverse the country's continued decline in fossil fuel production. This country is currently on path to becoming a net energy importer by 2020. Conversely, in 2015, and for the first time in over 20 years, the United States (US) became a net oil exporter to Mexico. One of the strategies being pursued by Mexico to prevent an impending supply–demand energy imbalance is the development of shale resources using horizontal drilling and hydraulic fracturing techniques. Hence, an evaluation of the inherent risks associated with hydraulic fracturing is crucial for Mexico's energy planning and decision-making process. This paper draws lessons from the recent ‘shale boom’ in the US, and it analyzes and summarizes the environmental, social, economic, and community impacts that Mexico should be aware of as its nascent shale industry develops. The analysis seeks to inform mainly Mexican policy makers, but also academics, nongovernmental organizations, and the public in general, about the main concerns regarding hydraulic fracturing activities, and the importance of regulatory enforcement and community engagement in advancing sustainability. We highlight that Mexico should only develop its unconventional resources after careful evaluation of all potential impacts and after the formulation of regulation intended for their mitigation. Furthermore, using the US as a case study, we argue that development of unconventional oil and gas resources in Mexico could lead to a short-term boom rather than to a dependable and sustainable long-term energy supply. Our analysis concludes with a set of recommendations for Mexico, featuring best practices that could be used to attenuate and address some of the impacts likely to emerge from shale oil and gas development.

/pdf/sustainability-lessons-from-shale-development-in-the-united-2379y6y9ql.pdf

Peter Marsters

Papers

Sustainability lessons from shale development in the United States for Mexico and other emerging unconventional oil and gas developers