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Review of Assessment Procedures for Shale Gas Well Casing Installation

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Review of Assessment Procedures for Shale Gas Well Casing Installation Review of assessment procedures for shale gas well casing installation The Environment Agency is the leading public body protecting and improving the environment in England and Wales. It’s our job to make sure that air, land and water are looked after by everyone in today’s society, so that tomorrow’s generations inherit a cleaner, healthier world. Our work includes tackling flooding and pollution incidents, reducing industry’s impacts on the environment, cleaning up rivers, coastal waters and contaminated land, and improving wildlife habitats. This report is the result of research commissioned and funded by the Environment Agency. Published by: Author(s): Environment Agency, Horizon House, Ben Fretwell Deanery Road, Bristol, BS1 5AH Tim Haines www.environment-agency.gov.uk Judith Glazier Tony Marsland ISBN: 978-1-84911-289-5 © Environment Agency – October 2012 Dissemination Status: Publicly available All rights reserved. This document may be reproduced with prior permission of the Environment Agency. Keywords: Well casing, hydraulic fracturing, unconventional gas The views and statements expressed in this report are those of the author alone. The views or statements Research Contractor: expressed in this publication do not necessarily AMEC Environment and Infrastructure Limited represent the views of the Environment Agency and the Canon Court Environment Agency cannot accept any responsibility for Abbey Foregate such views or statements. Shrewsbury SY2 5DE Further copies of this report are available from our 01743 342000 publications catalogue: http://publications.environment- agency.gov.uk or our National Customer Contact Environment Agency’s Project Manager: Centre: T: 08708 506506 Ian Davey, Environment and Business Directorate E: [email protected]. Product code: LIT 7311 ii Review of assessment procedures for oil and gas well casing installation Evidence at the Environment Agency Evidence underpins the work of the Environment Agency. It provides an up-to-date understanding of the world about us, helps us to develop tools and techniques to monitor and manage our environment as efficiently and effectively as possible. It also helps us to understand how the environment is changing and to identify what the future pressures may be. The work of the Environment Agency’s Evidence Directorate is a key ingredient in the partnership between research, guidance and operations that enables the Environment Agency to protect and restore our environment. The Research & Innovation programme focuses on four main areas of activity: • Setting the agenda, by providing the evidence for decisions; • Maintaining scientific credibility, by ensuring that our programmes and projects are fit for purpose and executed according to international standards; • Carrying out research, either by contracting it out to research organisations and consultancies or by doing it ourselves; • Delivering information, advice, tools and techniques, by making appropriate products available. Miranda Kavanagh Director of Evidence Review of assessment procedures for oil and gas well casing installation iii Executive Summary This report presents information on the assessment procedures for well casing installations used in the exploration and development particularly in regard to shale gas. This information was obtained by reviewing practices for protecting groundwater when installing, developing, maintaining and decommissioning onshore shale gas exploration and production wells. The aim of the project was to inform Environment Agency staff of current practices in this field. The shale gas industry is most developed in the USA with currently more limited exploration in Europe. In the UK, exploration to date has focused on the Sabden and Bowland shales of NW England, which lie 1600–2800 metres below ground. Other types of unconventional resources include coal bed methane and underground coal gasification. The exploration and production of unconventional gases is based on techniques developed by the conventional oil and gas industry. Drilling of deep onshore wells for oil and gas is not new to the UK but there are differences in the way that the techniques are applied. The main differences are that unconventional gas exploitation requires a larger number of closely spaced wells, which are normally extended by horizontal or directional drilling. More use is also made of hydraulic fracturing The gas-bearing shale formation is hydraulically fractured by injection of fluid under pressure to break it up and release gas via the well. A proppant, typically sand, is added to the fluid to hold the fractures open. Chemicals may be added to the fluid to help the hydraulic fracturing process. The well is cased using steel pipe cemented into the borehole as it is drilled. This: • permits control of pressure; • prevents the formation from caving into the well; • prevents flow between formations and isolates them; • provides a means of preventing the entry of formation fluids into the well; • provides a means to install downhole equipment; • provides protection to any groundwater that the well passes through. Wells are plugged and abandoned when they no longer provide beneficial use. The exploration and development of onshore unconventional gases requires a Petroleum Exploration and Development licence (PEDL) from the Department of Energy and Climate Change (DECC) and further consents to drill exploration boreholes and to develop a field. Drilling and production are also regulated by the Health and Safety Executive (HSE) under The Offshore Installations and Wells (Design and Construction, etc.) Regulations 1996 and The Borehole Sites and Operations Regulations 1995, to minimise risks to workers and others. Planning consent is required from the Minerals Planning Authority (MPA). Risks to groundwater The geological formations in which hydrocarbons are present are generally very deep and at some distance vertically below formations containing good quality groundwater, frequently used to provide water supplies. The vertical separation between unconventional gas host rocks and aquifers, combined with appropriate borehole construction, should mean that risks to this groundwater are low. However, boreholes iv Review of assessment procedures for oil and gas well casing installation drilled through aquifers may provide a pathway for movement of pollutants and therefore need to be constructed to a high standard. There is the potential to pollute groundwater with drilling muds, cements, hydraulic fracture fluid, hydrocarbons and deeper formation water as a result of: • spills and leaks of liquids stored at the surface; • leakage into aquifers of fracturing fluids and drilling muds from exploration and production boreholes; • leakage into aquifers via natural discontinuities (joints and fractures) as a result of the introduction of fluids under high pressure; • leakage into aquifers via induced discontinuities as a result of the high- pressure injection of fracturing fluids; • well failure due to poor construction or loss of well control, with the potential for the damaging release of fluids; • borehole or well damage as a result of induced seismicity from the high pressure fracturing operations; • interference between closely spaced wells or abandoned water wells, mine shafts and so on. Good practice This review has found that the following is considered currently to be good practice: • The well should be designed to protect groundwater, particularly through the design and placement of casing. • Good use should be made of modelling to aid the well design and the design of hydraulic fracturing. • The well should be drilled carefully to ensure that drilling fluids do not invade the formations, to avoid flow into the well during drilling and to create a wellbore of known dimensions. • The wellbore should be conditioned (that is, cleaned to remove contaminants by circulating fresh drilling fluid) before casing installation. • Casing must be installed in stages, with casing strings of decreasing diameter installed inside each other as the well is drilled to greater depths. • Casing should be cemented in place. Cement should fill the annulus of surface casing and must prevent movement of fluids and gases from permeable formations at all depths. • The quality of cementing should be demonstrated by pressure testing and supplemented, where necessary by geophysical methods. • Real-time monitoring should be undertaken during drilling, cementing and hydraulic fracturing to allow response to adverse effects. • The well should be pressure tested before hydraulic fracturing and periodically to demonstrate well integrity. • Well abandonment (that is, the activities involved in decommissioning) should be undertaken to ensure that all hydrocarbon bearing formations are separated from the surface by at least two permanent plugs; and Review of assessment procedures for oil and gas well casing installation v • Flowing horizons should be isolated from other permeable and porous formations to prevent cross flow between them after abandonment. vi Review of assessment procedures for oil and gas well casing installation Contents 1 Introduction 1 1.1 Background 1 1.2 Objectives 2 1.3 Structure of the report 2 1.4 Sources and applicability of data 3 1.5 Glossary of terms 3 2 Drilling operations overview 4 2.1 Unconventional gases 4 2.2 Stages and programme 4 3 Risks to groundwater 15 3.1 Overview 15 3.2 Groundwater protection 16 3.3 Hazards to groundwater 18 3.4 Pathways 26 4 Licensing and regulation
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