EI Research report. The use of nitrate treatment in oilfield systems to control reservoir souring: A review of current status

Transcription

1 EI Research report The use of nitrate treatment in oilfield systems to control reservoir souring: A review of current status

2 RESEARCH REPORT THE USE OF NITRATE TREATMENT IN OILFIELD SYSTEMS TO CONTROL RESERVOIR SOURING: Second edition September 2017 Published by Energy Institute, London The Energy Institute is a professional membership body incorporated by Royal Charter 2003 Registered charity number

3 The Energy Institute (EI) is the chartered professional membership body for the energy industry, supporting over individuals working in or studying energy and 250 energy companies worldwide. The EI provides learning and networking opportunities to support professional development, as well as professional recognition and technical and scientific knowledge resources on energy in all its forms and applications. The EI s purpose is to develop and disseminate knowledge, skills and good practice towards a safe, secure and sustainable energy system. In fulfilling this mission, the EI addresses the depth and breadth of the energy sector, from fuels and fuels distribution to health and safety, sustainability and the environment. It also informs policy by providing a platform for debate and scientifically-sound information on energy issues. The EI is licensed by: the Engineering Council to award Chartered, Incorporated and Engineering Technician status; the Science Council to award Chartered Scientist status, and the Society for the Environment to award Chartered Environmentalist status. It also offers its own Chartered Energy Engineer, Chartered Petroleum Engineer and Chartered Energy Manager titles. A registered charity, the EI serves society with independence, professionalism and a wealth of expertise in all energy matters. This publication has been produced as a result of work carried out within the Technical Team of the EI, funded by the EI s Technical Partners. The EI s Technical Work Programme provides industry with cost-effective, value-adding knowledge on key current and future issues affecting those operating in the energy sector, both in the UK and internationally. For further information, please visit The EI gratefully acknowledges the financial contributions towards the scientific and technical programme from the following companies Apache North Sea Repsol Sinopec BP Exploration Operating Co Ltd RWE npower BP Oil UK Ltd Saudi Aramco Centrica Scottish Power Chevron North Sea Ltd SGS Chevron Products Company Shell UK Oil Products Limited CLH Shell U.K. Exploration and Production Ltd ConocoPhillips Ltd SSE DCC Energy Statkraft DONG Energy Statoil EDF Energy Tesoro ENGIE Taqa Bratani ENI Total E&P UK Limited E. ON UK Total UK Limited ExxonMobil International Ltd Tullow Oil Innogy Uniper Kuwait Petroleum International Ltd Valero Maersk Oil North Sea UK Limited Vattenfall Nexen CNOOC Vitol Energy Phillips 66 Woodside Qatar Petroleum World Fuel Services However, it should be noted that the above organisations have not all been directly involved in the development of this publication, nor do they necessarily endorse its content. Copyright 2017 by the Energy Institute, London. The Energy Institute is a professional membership body incorporated by Royal Charter Registered charity number , England All rights reserved No part of this book may be reproduced by any means, or transmitted or translated into a machine language without the written permission of the publisher. ISBN Published by the Energy Institute The information contained in this publication is provided for general information purposes only. Whilst the Energy Institute and the contributors have applied reasonable care in developing this publication, no representations or warranties, express or implied, are made by the Energy Institute or any of the contributors concerning the applicability, suitability, accuracy or completeness of the information contained herein and the Energy Institute and the contributors accept no responsibility whatsoever for the use of this information. Neither the Energy Institute nor any of the contributors shall be liable in any way for any liability, loss, cost or damage incurred as a result of the receipt or use of the information contained herein. Hard copy and electronic access to EI and IP publications is available via our website, Documents can be purchased online as downloadable pdfs or on an annual subscription for single users and companies. For more information, contact the EI Publications Team. e: pubs@energyinst.org

4 CONTENTS Page Foreword Acknowledgements Introduction Introduction Microbiological metabolism The biological nitrogen cycle Nitrate-reducing bacteria (NRB) Introduction Denitrification Dissimilatory nitrate reduction to ammonium (DNRA) Nitrate assimilation Anammox Nitrate treatment Introduction Effect of nitrate addition Mechanisms of action Impact on microbiological diversity Treatment strategy Introduction Nitrate stoichiometry Inhibitory nitrate concentration Environmental limits for successful application Dosing Current dosing practice Concentration Nitrate salts and alternative products Injection point Compatibility with organic biocide treatment Associated risks Case studies Summary Monitoring and analytical techniques Introduction Chemical analysis Bacterial analysis SRP (sessile and planktonic): NRB (sessile and planktonic): NRSOB (sessile and planktonic): General heterotrophic bacteria (GHB) (sessile and planktonic): Species identification Molecular microbiological methods (MMM)

5 Contents continued Page DNA fingerprinting NGS and metagenomics Monitoring equipment Nitrate application for microbiologically enhanced oil recovery (MEOR) Introduction Current status MEOR processes Surfactant production Biomass production MEOR case study...37 Annexes Annex A Acronyms/abbreviations...38 Annex B References and further reading

6 Figures LIST OF FIGURES AND TABLES Page Figure 1 Illustration demonstrating a change in cell morphology in a biofilm prior to nitrate treatment (top) and four days after addition of NO 3 (bottom) Adapted from Dunsmore et al. (2006) Tables Table 1 Inhibitory NO 3 concentrations Table 2 NFPA hazard rating for health and instability...22 Table 3 Chemical parameters for monitoring

7 FOREWORD Over the past 15 years, a method that has emerged to considerably reduce the level of biogenic hydrogen sulfide (H 2 S) production in oilfield systems is the treatment of injection water with nitrate (NO 3 ). Nitrate treatment technology is increasingly used for the control of sulfate (SO 4 2 )-reducing microorganisms, and hence the prevention and mitigation of biogenic H 2 S by oil production and oilfield service companies. However, its success and the effect of NO 3 on corrosion processes vary considerably and appear to be specific to operating conditions. For instance, the use of nitrate treatment in seawater injection has not been observed to increase corrosion rates and there is indication that it may even reduce corrosion. However, there is evidence that the application of NO 3 in a produced water reinjection (PWRI) system can lead to an increase in both general and localised corrosion. With that in mind, this review supersedes the first edition, The stimulation of nitrate-reducing bacteria (NRB) in oilfield systems to control sulfate-reducing bacteria (SRB), microbiologically influenced corrosion (MIC) and reservoir souring: An introductory review, 2003, Energy Institute (EI). Currently, nitrate treatment is used on a number of installations in a variety of environmental conditions. Based on the current literature, reports and presentations, as well as the experimental and trial data, this review aims to enhance this publication with information now available, relating to experimental investigation and industry experience. 6

8 ACKNOWLEDGEMENTS This project was commissioned by the EI's Microbiology Committee. The work was carried out by Andy Price, William Palmer-Brown and Benjamin Folwell, Oil Plus Ltd. and steered by members of the Microbiology Committee, who during the project included: Fred Passman Simon Christopher Jan Kuever Joan Kelley Geert van de Kraan Graham Hill Gareth Williams Clara Di Iorio Beate Hildenbrand Kerry Sinclair Alex Few Brian Crook Andrew Ryan Jim Stott Neil Whitehead Carol Devine Richard Johnson Bob Eden Leanne Walker Bart Lomans Elaine McFarlane (Chair) Torben Lund Skovhus Biodeterioration Control Association BP Bremen Institute for Materials Testing Conidia Bioscience Ltd Dow ECHA Microbiology ECHA Microbiology ENI Energy Institute Energy Institute ExxonMobil HSL Intertek Intertek Production and Integrity Assurance Minton, Treharne & Davies (MTD) North East Corrosion Engineers Ltd (NECE) Oil Plus Ltd. Rawwater Rawwater Shell Shell VIA University College The EI wishes to record its appreciation of the work carried out by the authors and also its gratitude for the valuable contributions made by the Microbiology Committee during the course of the project. In addition, the EI would like to thank the following people who made significant comments during the stakeholder review: Sandra Dixon and Jan Hilmers (Yara), Alaxander Galushko (Agrophysical Research Institute) and Casey Hubert (University of Calgary). 7

9 1 INTRODUCTION 1.1 INTRODUCTION Water injection is a recognised and frequently used procedure for pressure maintenance and the improvement of oil recovery in many oilfields around the world. However, an unwanted side effect of water injection can be reservoir souring, which refers to the increase in concentration of hydrogen sulfide (H 2 S) in production fluids. This is typically due to the introduction of sulfate (SO 4 2 ) from the injected seawater into the formation water, leading to the proliferation of SO 4 2 reducing microorganisms and the formation of sulfide (S 2 ). Whilst several biotic and abiotic mechanisms have been proposed as contributors towards reservoir souring (Khatib and Salanitro, 1997), the reduction of SO 4 2 by sulfate-reducing bacteria (SRB) and sulfate-reducing archaea (SRA) is thought to be a significant source of souring in water-injected reservoirs. These two groups of microorganisms, SRB and SRA, are collectively referred to as sulfate-reducing prokaryotes (SRP) and it is thought that their growth is promoted due to the combination of abundant electron donors such as selected oil components and carboxylic acids in the formation water and electron acceptors (SO 4 2 ) in the seawater, river, lake or aquifer water. Reservoir souring is of major concern to the oil industry, as H 2 S is toxic and corrosive, increases the safety risk to personnel, affects crude oil sales value and requires substantial capital expenditure/operating expenditure for remedial operations. Therefore, considerable attention has been focused on reducing H 2 S concentration in produced fluids. To prevent H 2 S production, biocides are often added to the injection water. However, the treatment can be expensive and is often ineffective due to inhibition of the biocide by high temperatures or reaction with biofilm and minerals. Recalcitrant biocides also lead to environmental problems and moreover, certain biocides decompose during the process, potentially serving as additional growth substrates for SRB (Myhr et al, 2002). However, an alternative method known to reduce the level of produced H 2 S is nitrate treatment. This is achieved by controlling the microbiological production of H 2 S as well as reducing H 2 S already present in a petroleum reservoir by adding nitrate (NO 3 ) to the injection water and pumping it to the oil-bearing formation. As such, many oil production and oilfield service companies recognise the addition of NO 3 as a method for decreasing the net production of H 2 S. 1.2 MICROBIOLOGICAL METABOLISM In order to better understand the role and impact of microorganisms involved in the processes of reservoir souring and nitrate treatment, it is first helpful to have a basic knowledge of microbiological metabolism and the terms used to describe such processes. Metabolic reactions characteristically proceed in a systematic and highly regulated manner that maximises the use of the available nutrients and energy. In order to carry out metabolic processes, microorganisms require a constant input and expenditure of usable energy. Microorganisms often obtain their energy by mediating chemical reactions which typically involve the use of an electron donor (a reducing agent that donates electrons to another compound) and an electron acceptor (an oxidising agent that accepts electrons transferred to it from another compound), referred to as reduction-oxidation (redox) reactions. There are a number of different electron donors and acceptors, both organic and inorganic that can be utilised by microorganisms; however, it should be noted that organic molecules are the most common electron donors in an oilfield environment. 8

10 Microorganisms can either be: organotrophs organisms that, during electron transfer, can use organic molecules (i.e. petroleum hydrocarbons) as an electron donor, or lithotrophs organisms that are capable of obtaining their energy from inorganic compounds (i.e. sulfide). In a simple example, consider bacteria growing on an organic carbon source in the presence of oxygen (O 2 ): Carbon source + O 2 carbon dioxide (CO 2 ) + water (H 2 O) + Energy In this example the carbon source has been oxidised, donating electrons in the presence of O 2, or aerobically, resulting in the reduction of O 2. This is because organic carbon tends to be oxidised preferentially by the electron acceptor that supplies most energy to the microorganisms, namely O 2. Consider also, a bacterium growing on a carbon source in the absence of O 2 with only a carbon source available to act as both the electron donor and acceptor, resulting in fermentation: Carbon source Alcohol + CO 2 + Energy However, this process is not energy efficient and so bacteria often utilise alternative electron acceptors such as NO 3 and SO 4 2 in the absence of O 2. Therefore, when conditions become anoxic, reduction of other electron acceptors becomes energetically favourable. For instance, once O 2 is depleted, certain facultative anaerobes bacteria that are capable of proliferating with or without O 2 can use NO 3 as an electron acceptor. As O 2 levels decrease even further, obligate anaerobes bacteria that survive and grow only in the absence of O 2 begin to use the remainder of the available electron acceptors. Consequently, redox conditions begin to rapidly change, usually from oxidising to reducing conditions. 1.3 THE BIOLOGICAL NITROGEN CYCLE The global biogeochemical nitrogen cycle (N-cycle) consists of varied processes that interconvert the different nitrogenous compounds in the biosphere, in which prokaryotic microorganisms (organisms that lack a membrane bound nucleus, i.e. bacteria and archaea) play a principal role. Inorganic nitrogen is found in several oxidation states, ranging from ammonium (NH 4+ ) (3), its most reduced form, to its most oxidised, NO 3 (+5). The N-cycle includes both oxidative and reductive reactions catalysed by enzymes with different redox cofactors (Schmidt and Schaechter, 2011), for assimilatory, dissimilatory or respiratory purposes. These processes perform key roles in a given ecosystem and will be discussed in further detail in section 2. 9