The analysis is based on data from thousands of fracking operations in the USA and natural rock fractures in Europe and Africa.
It is believed to be the first analysis of its type and could be used across the world as a starting point for setting a minimum distance between the depth of fracking and shallower aquifers used for drinking water.
The new study, published in the journal Marine and Petroleum Geology, shows the probabilities of 'rogue' fractures, induced in fracking operations for shale gas extraction, extending beyond 0.6 kilometres from the injection source is exceptionally low. The probability of fractures extending beyond 350 metres was found to be one per cent.
During fracking operations, fractures are created by drilling and injecting fluid into the rock strata underground to increase oil and gas production from fine-grained, low permeability rocks such as shale. These stimulated fractures can significantly increase the rate of production of oil and gas from such rocks.
Fracking operations in the USA are growing in number and many countries across the world are looking at shale gas as a potential energy resource. The process of fracking has come under increasing scrutiny. A recent test well in the UK near Blackpool, Lancashire, was stopped after some minor earthquakes were felt at the surface. The UK government is allowing the test fracking to resume but critics have also warned of other possible side-effects including the contamination of groundwater.
Researchers from Durham University, Cardiff University and the University of Tromsø looked at thousands of natural and induced fractures from the US, Europe and Africa. Of the thousands artificially induced, none were found to exceed 600 metres, with the vast majority being much less than 250 metres in vertical extent.
Fracture heights are important as fractures have been cited as possible underground pathways for deep sources of methane to contaminate drinking water. But the likelihood of contamination of drinking water in aquifers due to fractures when there is a separation of more than a kilometre is negligible, the scientists say.
Professor Richard Davies, Director of Durham Energy Institute, Durham University, said: "Based on our observations, we believe that it may be prudent to adopt a minimum vertical separation distance for stimulated fracturing in shale reservoirs. Such a distance should be set by regulators; our study shows that for new exploration areas where there is no existing data, it should be significantly in excess of 0.6 km.
"Shale gas exploration is increasing across the world and sediments of different ages are now potential drilling targets. Constraining the maximum vertical extent of hydraulic fractures is important for the safe exploitation of unconventional hydrocarbons such as shale gas and oil, and the data from the USA helps us to understand how fracturing works in practice.
"Minimum vertical separation distances for fracturing operations would help prevent unintentional penetration of shallow rock strata."
Professor Davies' team looked at published and unpublished datasets for both natural and stimulated fracture systems in sediment of various ages, from eight different locations in the USA, Europe and Africa.
Professor Richard Davies said: "Sediments of different types and ages are potential future drilling targets and minimum separation depths are an important step towards safer fracturing operations worldwide and tapping into what could be a valuable energy resource.
"We need to keep collecting new data to monitor how far fractures grow in different geological settings."
The team accepts that predicting the height and behaviour of fractures is difficult. They now hope that the oil and gas industry will continue to provide data from new sites across the globe as it becomes available to further refine the probability analysis.
Analysis of new sites should allow a safe separation distance between fracking operations and sensitive rock layers to be further refined, the scientists say. In the meantime, the researchers hope that governments and shale gas drilling companies will use the analysis when planning new operations.
Carl Stiansen | EurekAlert!
Mineral discoveries in the Galapagos Islands pose a puzzle as to their formation and origin
19.10.2018 | Johannes Gutenberg-Universität Mainz
Massive organism is crashing on our watch
18.10.2018 | S.J. & Jessie E. Quinney College of Natural Resources, Utah State University
Scientists at the Max Planck Institute for Polymer Research (MPI-P) in Mainz (Germany) together with scientists from Dresden, Leipzig, Sofia (Bulgaria) and Madrid (Spain) have now developed and characterized a novel, metal-organic material which displays electrical properties mimicking those of highly crystalline silicon. The material which can easily be fabricated at room temperature could serve as a replacement for expensive conventional inorganic materials used in optoelectronics.
Silicon, a so called semiconductor, is currently widely employed for the development of components such as solar cells, LEDs or computer chips. High purity...
Augsburg chemists present a new technology for compressing, storing and transporting highly volatile gases in porous frameworks/New prospects for gas-powered vehicles
Storage of highly volatile gases has always been a major technological challenge, not least for use in the automotive sector, for, for example, methane or...
When we put water in a freezer, water molecules crystallize and form ice. This change from one phase of matter to another is called a phase transition. While this transition, and countless others that occur in nature, typically takes place at the same fixed conditions, such as the freezing point, one can ask how it can be influenced in a controlled way.
We are all familiar with such control of the freezing transition, as it is an essential ingredient in the art of making a sorbet or a slushy. To make a cold...
Thin organic layers provide machines and equipment with new functions. They enable, for example, tiny energy recuperators. In future, these will be installed...
Das Zusammenspiel aus Struktur und Dynamik bestimmt die Funktion von Proteinen, den molekularen Werkzeugen der Zelle. Durch Fortschritte in der...
17.10.2018 | Event News
16.10.2018 | Event News
02.10.2018 | Event News
19.10.2018 | Earth Sciences
19.10.2018 | Life Sciences
19.10.2018 | Health and Medicine