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DECC Consultation on Shale Gas-Induced Seismicity

DECC have launched an invitation for comments on induced seismicity resulting from shale gas fracturing. You can read the details of this here:

Submitted 29 May 2012

1. This submission has been produced jointly by the Geological Society of London and the Petroleum Exploration Society of Great Britain:

i. The Geological Society of London (GSL) is the national learned and professional body for geoscience, with over 10,000 Fellows (members) worldwide. The Fellowship encompasses those working in industry, academia and government, with a wide range of perspectives and views on policy-relevant geoscience, and the Society is a leading communicator of this science to government bodies and other non-technical audiences.

ii. The Petroleum Exploration Society of Great Britain (PESGB) represents the national community of Earth scientists working in the oil and gas industry, with over 5,000 members worldwide. The objective of the Society is to promote, for the public benefit, education in the scientific and technical aspects of petroleum exploration. To achieve this objective the PESGB makes regular charitable disbursements, holds monthly lecture meetings in London and Aberdeen and both organises and sponsors other conferences, seminars, workshops, field trips and publications.

2. We understand that the scope of the present report is limited, and concerns only induced seismicity mitigation (with the exception of Appendix B). If shale gas exploration and production is to be safely carried out and appropriately regulated, and policy in this area developed so as to engender public confidence and industry engagement, it is vital that all aspects of safety and perceived risk are considered in the round. We note the ongoing Royal Society (RS) / Royal Academy of Engineering (RAEng) inquiry into shale gas, to which our organisations also made a joint submission. We understand that the RS/RAEng inquiry is also limited in scope (though broader than the present report), in that it seeks to examine all aspects of safety and local environmental impact of shale gas exploration and production, but not the global environmental effects of the subsequent use of the gas produced (i.e. its impact on carbon emissions). For the avoidance of doubt, the comments we offer here do not necessarily indicate our approval of shale gas exploration and production in other respects than induced seismicity, nor of its unbridled use without carbon capture and storage (CCS).

3. Regulation of shale gas exploration and production should be scientifically well-founded, with the basis for thresholds and detection limits transparently justified. It should address not only induced seismicity but all aspects of safety and perceived risk in respect of:

• the siting, planning and drilling of wells
• hydraulic fracturing and associated processes including water management (access and disposal)
• subsequent gas production
• baseline data gathering and characterisation before operation, and monitoring during stimulation and subsequent production

Such regulation should be effectively applied by appropriately skilled and resourced regulators. Responsible hydrocarbons companies (which share government’s interest in building public confidence in their operations) welcome such regulation – a point emphasised by Melvyn Giles (Global Theme Lead for Unconventional Gas, Shell) at a recent public lecture at the Geological Society (see

4. It is not for independent scientific experts to determine policy objectives. They can and should advise on uncertainty, risks and the expected outcomes of decisions. But it is in both their own and policy-makers’ interests that their independence be maintained, and be seen to be maintained, as far as is reasonably possible. They need to be careful not to make explicit or implicit value judgments which should properly be made by policy-makers, and policy-makers should not ask them to do so. The interaction of scientific and other factors in policy-making and regulation can be complex and may not be explicitly apparent, and should be made as transparent as possible in order to engender public confidence.

5. An important role for scientific experts is to provide peer review of the scientific basis for the regulatory framework and its implementation. We would be pleased to help identify experts in seismology and other relevant geoscience specialisms (such as structural geology and geomechanics – see comments at paragraph 10 regarding interaction between seismic activity and host geology, for instance), to assist in this process. We have not identified individuals here, but would be pleased to do so, to advise on their areas of expertise, and to help ensure that relevant areas of science are adequately covered in any scientific advisory or review structures.

6. Some of our members (not only those from industry) have raised concerns with us about the 0.5M threshold recommended in the report for triggering the proposed traffic light system. This is not motivated by a wish to see exploration and production more lightly regulated. Rather, there is concern that the threshold may be perceived to be arbitrary, rather than based on a sound geophysical model and reasoning. We do not question the quality of the work done to support this element of the report, but there is insufficient detail presented to understand how the threshold of 0.5M was arrived at and is justified. Other geoscientists have suggested other thresholds. For instance, we understand that Richard Davies and Gillian Foulger (Durham University) are submitting a response to the report, in which they recommend 0.75M which they describe as a ‘more justifiable’ threshold. And Cuadrilla’s consultants, in the work assessed by the authors of the current report, recommended 1.7M. (As magnitude is measured using a logarithmic scale, the differences between these proposed thresholds are very significant.)

7. The models used to determine thresholds in each case appear to be quite different. In preparing this submission, we have not been able to get independent experts to review the various models and advise on their suitability (though we recommend that this be done, and would be pleased to advise on that process). But it is also clear that the objective of the threshold of 0.5M identified by the authors of the report is quite different to that in Cuadrilla’s earlier report. On page 12, they write that they ‘consider the threshold value of 1.7M suggested by the consultants is unnecessarily high’ and that a lower threshold would ‘reduce the likelihood of events perceptible to local residents’. A threshold set on the basis of minimising the chance of perceptible events will be considerably lower than one set on the basis of minimising the chance of damage to property, or to public safety. All of these bases correspond to perfectly sensible policy objectives – as the report points out, public acceptance of shale gas extraction is likely to be enhanced if there are no perceptible induced seismic events. But these are not judgments which can or should be made by independent expert scientists alone. For the avoidance of doubt, we are not endorsing one or other of the proposed thresholds referred to in paragraph 6. Rather, we advocate that the objective of the threshold be clearly established, that the scientific basis for its determination then be identified, and that this basis and its application then be subject to peer review. In the absence of such a process, it would be premature to set a threshold at this stage.

8. We also note that the Lancashire dataset is necessarily relatively small. Any policy decision should take into account the implications of much more extensive datasets, including those from the US (see, for example, Warpinski, N.R. et al (2012), Measurements of Hydraulic-Fracture Induced Seismicity in Gas Shales. (Paper SPE 151597 presented at the SPE Hydraulic Fracture Technology Conference, The Woodlands, Texas. 6-8 February 2012)). An example of a comprehensive analysis of hydraulic fracture extent is Davies, R.J. et al (2012), Hydraulic Fractures, how far can they go? (Marine and Petroleum Geology), and we would welcome a similar approach to induced seismicity to inform appropriate regulation.

9. In setting thresholds for induced seismicity in the context of shale gas exploration and production, it would be wise to bear in mind that this is likely to set a precedent for other uses of the subsurface, both with regard to hydrocarbons (for extraction and storage) and in other contexts (geothermal, engineered subsurface structures, etc). If thresholds are set at a lower level than they need to be to avoid actual damage, this may have significant broader implications for (and may in future limit) our use of the subsurface. If thresholds are initially set at a low level for the purpose of engendering public confidence, these might subsequently be raised in the light of experience and growing public confidence. In any case, any such thresholds should be periodically reviewed. Continuing exploration under such conditions, suitably monitored, would also generate further valuable data to inform future decision-making.

10. We support much in the report. Among the key points raised in the report, we agree that:

• Induced seismicity is normal whenever significant volumes of fluid are injected into rock, for example in CCS and geothermal energy operations. Indeed, small earthquakes occur naturally in the UK in a variety of settings. It is important that thresholds are set and subsequent monitoring carried out in the context of knowledge of natural background levels of seismicity, data on which are available from the British Geological Survey (BGS). One eminent seismologist consulted in preparing this submission is of the view that the seismic events under investigation in this report would have occurred naturally with time – in other words, it may just be their timing which was affected by shale gas operations.

• Simple models of seismic activity, its propagation and its relation to ground motions are likely to be inadequate – factors such as stress anisotropy, the variety of source mechanisms and radiation patterns for seismic events, site conditions and potential ground acceleration will have a significant effect. The latter can be established and incorporated in a hazard analysis (with a suitable baseline survey). There may be lessons to learn from other sectors, regarding the perception of motion by humans and impacts on buildings and infrastructure. (See, for example, Bommer, J.J. et al (2006), Control of hazard due to seismicity induced by a hot fractured rock geothermal project, Engineering Geology 83 287-306.)

• It is important to have a detailed understanding of the local structural geology and geomechanical characteristics of the subsurface (both overburden and potential shale gas reservoir), to improve identification and characterisation of faults, and modeling and mitigation of induced seismicity (as well as other possible impacts). The report concludes that the seismic events under investigation were caused by fault reactivation but the precise location of the fault(s) is not clear. More data and studies are needed, as these features may be anomalous, both within the basin or compared with other basins in which shale gas is found.

• Drilling in or near fault zones should be avoided.

• Smaller volumes of fracking fluid should be injected initially – though we note that the detail of this recommendation is vague (monitoring for a ‘reasonable length of time’
would need clarification, for example, as part of the wider regulatory regime).

• Extensive baseline data and monitoring before, during and after operations are required. We note that real time event detection and calibration is not straightforward. Good surface and/or borehole arrays are needed, and further study on the design of site surveys and monitoring arrays may be required. While the automated detection of larger events is done routinely, detecting low magnitude events is not yet routine. It is also important to note that interpreting and assessing microseismic data carries with it uncertainty, and such data may be open to differing interpretations by different scientists – they represent a valuable tool, but will not always provide clear-cut unequivocal answers. The licensing regime should require public deposit of such data after a reasonable period (as is done for North Sea hydrocarbon seismic survey and well data – downhole geophysical logs, cuttings, core, etc), so that they can be inspected by the wider scientific community.

11. We believe that a strong regulatory framework should be established, on the basis of clearly identified scientific models and reasoning, to address all aspects of UK shale gas exploration and production, with the close involvement of a pool of independent experts from a range of appropriate disciplines. This framework should inform both policy decision-making, and subsequent implementation. In so doing, it is vital to take a holistic view. As noted above, the interaction of seismic activity and local-scale structural geology is complex. It is important to consider issues such as the potential effect of seismic activity on gas migration, well integrity and the contamination of groundwater. In particular, it is premature to set a threshold for the seismic traffic light system, in isolation from other factors and in the absence of a clear policy decision on the objective of this threshold (albeit a decision which itself should be informed by expert advice from geoscientists and others).

12. We note that the report refers only to the Bowland Basin. Conclusions made for this particular setting may not represent a universal ‘recipe’ for rolling out shale gas exploration and production to other areas. It is important that a consistent regulatory framework be established which is applicable universally, and also that variation of specific details appropriate to areas with different geology be carefully thought through and made explicit. We also note that other countries in Europe are likely to pay close attention to policy-decisions and the basis for regulation in the UK, heightening the need for careful peer review and expert engagement.

13. We would be pleased to discuss further any of the points raised in this submission, to provide more detailed information, or to suggest specialist contacts. We would value the opportunity for a more detailed engagement with DECC, particularly as the consultation period for this report was relatively short,. We would also be pleased to discuss what geoscience expertise would be useful and how it might be deployed appropriately, as and when this process moves ahead.