Hydrofractures, or hydraulic fractures, are fractures where a significantly elevated fluid pressure played a role in their formation. Natural hydrofractures are abundant in rocks and are often preserved as magmatic dykes or sills, and mineral-filled fractures or mineral veins. However, we focus on the formation and evolution of non-igneous hydrofractures. Here we review the basic theory of the role of fluid pressure in rock failure, showing that both Terzaghi’s and Biot’s theories can be reconciled if the appropriate boundary conditions are considered. We next discuss the propagation of hydrofractures after initial failure, where networks of hydrofractures may form or hydrofractures may ascend through the crust as mobile hydrofractures. As fractures can form as a result of both tectonic stresses and an elevated fluid pressure, we address the question of how to ascertain whether a fracture is a hydrofracture. We argue that extensional or dilational fractures that formed below c. 2–3 km depth are, under normal circumstances, hydrofractures, but at shallower depth they may, but must not be hydrofractures. Since veins and breccias are often the products of hydrofractures that are left in the geological record, we discuss these and critically assess which vein structures can, and which do not necessarily, indicate hydrofracturing. Hydrofracturing can suddenly and locally change the permeability in a rock by providing new fluid pathways. This can lead to highly dynamic self-organization of crustal-scale fluid flow.

While information exchange is essential in the policy process, little is known about how divergent subgroups filter actors’ technical and political information exchange, blocking learning processes. Guided by social identity, group entitativity, and self-categorisation theories, we introduce the concept and measurement of identity-based subgroups referring to informal clusters shaped by the self-referent perception of similarities among actors. The identity-based subgroup is recognised as a precursor for coalition building in a policy subsystem but received inadequate attention in the research on Advocacy Coalition Framework. We examine how divergent identity-based subgroups moderate the links between relational embeddedness and technical/political information exchanges in an adversarial fracking policy network in New York. Our quadratic assignment procedure multiple regression indicated that, despite trust, policy actors from different identity-based subgroups are less likely to share technical and political information in the network. When two actors’ identity-based subgroups are different, competition is more likely associated with lower technical information exchange in the network. These findings extend research on information exchange in adversarial policy subsystems.

Hydraulic fracturing (HF) has transformed the North American oil and gas industry, leading to increased consumer surplus and reduced carbon emissions. While HF may have similar potential for the developing world, adoption has been limited to date, plausibly because of perceptions of potential local costs and the need to develop technical proficiency. We empirically evaluate the incremental contribution of HF in the United States. We find considerable evidence of differences in application and productivity across operating firms and vertical pairings of firms, suggesting intellectual property and learning by doing may both play important roles. At the same time, secrecy regarding the chemical composition of fluids used in HF is a potential deterrent to its application for fear of local costs. Developing countries must accommodate these characteristics if adoption of HF is to help meet energy demands and achieve climate policy goals.

Using federalism as a guide, this research explores the conflicted, complementary and unique natural gas policy paths of the U.S. federal government, Wyoming and Colorado and analyzes how policies facilitate and respond to booms. Federal policymaking has consistently focused on gas ownership, leasing, interstate dispute resolution and fiscal mechanisms to stimulate and manage development. At the state level, policies are designed to enable exploration and production while protecting fuel mineral rights, minimizing waste and generating revenue. During the most recent gas boom, driven in part by technological advances like fracking, policies are being tested from local to national levels. Colorado demonstrates that states can balance economic benefits with environmental and social costs of gas booms, thus providing an example for other gas producing states. Whether states serve as stewards or laggards is a function of federalism and choice, but the direction of federal and state natural gas policy remains a long-term play.

Why people collaborate to achieve their political objectives is one enduring question in public policy. Although studies have explored this question in low-intensity policy conflicts, a few have examined collaboration in high-intensity policy conflicts. This study asks two questions: What are the rationales motivating policy actors to collaborate with each other in high-intensity policy conflicts? What policy actor attributes are associated with these rationales? This study uses questionnaire data collected in 2013 and 2014 of policy actors from New York, Colorado and Texas who are actively involved with hydraulic fracturing policy debates. The results show that professional competence is the most important rationale for collaborating, whereas shared beliefs are moderately important, and financial resources are not important. Policy actor attributes that are associated with different rationales include organisational affiliation and extreme policy positions. This article concludes with a discussion on advancing theoretical explanations of collaboration in high-intensity policy conflicts.

In conjunction with technologies such as horizontal drilling, hydraulic fracturing has transformed U.S. and world energy outlooks by adding reserves from unconventional resources. Fracturing was developed by experimentation and experience. This study empirically analyzes fracturing data for wells in the Williston Basin in North Dakota and Montana, focusing on firms' ability to improve well production over time through collaboration. Results suggest that producers gain from experience with fracturing and that proprietary additives are not generally correlated with greater production but have value for some firms. Experiential gains are stronger for operators than for contractors, but some operator-contractor pairings have productive value.

This study explores factors driving tract-level heterogeneity in the quality of leases executed by property owners who transfer their mineral rights to firms that drill for and extract natural gas. The data set consists of tract-level aggregates of lease terms, our measures of lease quality, and tract-level census data from the leases. We find that higher-quality leases are negatively correlated with higher concentration of minority households when controlling for census-tract-level characteristics. Based on the findings, we propose policies to reduce observed heterogeneity in the quality of leases and, subsequently, to reduce residents' exposure to negative effects of nearby well sites.

Hydraulic fracturing (HF) is a focal topic in discussions about domestic energy production, yet the American public is largely unfamiliar and undecided about the practice. This study sheds light on how individuals may come to understand hydraulic fracturing as this unconventional production technology becomes more prominent in the United States. For the study, a thorough search of HF photographs was performed, and a systematic evaluation of 40 images using an online experimental design involving $N=250$ participants was conducted. Key indicators of hydraulic fracturing support and beliefs were identified. Participants showed diversity in their support for the practice, with 47 percent expressing low support, 22 percent high support, and 31 percent undecided. Support for HF was positively associated with beliefs that hydraulic fracturing is primarily an economic issue and negatively associated with beliefs that it is an environmental issue. Level of support was also investigated as a perceptual filter that facilitates biased issue perceptions and affective evaluations of economic benefit and environmental cost frames presented in visual content of hydraulic fracturing. Results suggested an interactive relationship between visual framing and level of support, pointing to a substantial barrier to common understanding about the issue that strategic communicators should consider.

The lower Palaeozoic rocks of the Southern Uplands of Scotland have been interpreted as an accretionary prism of slivers of oceanic basalt and associated deep sea sediments situated on the northern margin of the lape tus Ocean. Electron microprobe analyses confirm the presence of albite, prehnite, pumpellyite, chlorite, phengite, calcite, hematite and quartz-bearing metamorphic assemblages in basalts and basic-clast greywackes in the prism. The metamorphism is prehnite-pumpellyite facies and inferred to be related to tectonic burial of the various slices of the prism as they were accreted during the closure of the lape tus Ocean.