THE EFFECT OF STEAM INJECTION ON THE ELECTRICAL CONDUCTIVITY OF SAND AND CLAY by DAVID BUCHANAN BUTLER B. Sc., Applied Science, Queen's University, 1986 M. Sc., Geophysics, University of British Columbia, 1990 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF GEOPHYSICS AND ASTRONOMY We accept this thesis as conforming to the required standards UNIVERSITY OF BRITISH COLUMBIA November 1995 © David Buchanan Buder, 1995 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia Vancouver, Canada Date DE-6 (2/88) ABSTRACT To interpret electrical surveys used to monitor subsurface steam-injection projects, one needs to know whether steam zones are resistive or conductive relative to initial conditions. This can be determined through laboratory measurements of the effects of steam injection on the electrical conductivity of sand. Experiments presented in chapter 2 measured the combined effects of the salinity of the boiler feedwaters and the steam quality - the fraction of the injected flux that is vapour. The injection of low quality steam, boiled from a saline solution, into clean sand saturated with the same solution, resulted in a net de• crease in conductivity, and a constant equilibrium conductivity in the steam zone. The in• jection of high-quality steam, using the same solutions, resulted in conductivity dropping first to a minimum, and then increasing to an equilibrium value similar to that seen in the low quality injection. This localized conductivity minimum became progressively less conductive with time, and travelled with the steam front. The appearance of the conductivity minimum at the steam front can be attributed to the formation of a dilution bank, which temporarily decreases the local salinity. This suggests that many steam injections will create steam zones with electrically resistive fronts, which can be used to track the steam. The effects of clay on the electrical conductivity of steam zones is further investigated in chapter 3. Experimental and numerical results indicate that clay-bearing steam zones can be electrically conductive relative to initial conditions, in part due to water saturations in the steam zones that are higher than those in comparably steam-flooded clean sands. However, it is still likely that high quality steam injections will result in resistive leading edges of the steam zones. In low quality steam injections, where dilution banks do not form around the front, it is more likely that steam zones are entirely conductive relative to initial conditions, particularly in fresh water environments. ii TABLE OF CONTENTS Abstract ii List of figures V List of tables vii Acknowledgements viii Chapter 1: Introduction 1 Motivation 1 The definition of steam 2 The physical effects of steam injection 3 The electrical effects of steam injection 3 Overview of the thesis 6 Chapter 2: The effects of saline steam liquid and steam quality on the electrical conductivity of steam-flooded sands 9 Introduction 9 Parameters affecting electrical conductivity 10 Experimental apparatus 15 Procedure 17 Results 18 Discussion 21 Interpretation of the measured data 22 Numerical test of the high steam-quality interpretation 29 Summary 34 Chapter 3: The effect of clay content on the electrical conductivity of steam-flooded sands 55 Introduction 55 The electrical conductivity of clay 56 iii Experimental apparatus and procedures 59 Experimental results 62 Discussion 66 Numerical investigation of experimental data 69 Numerical extension of results to higher clay contents and higher salinities 73 Summary 80 Chapter 4: Conclusions 95 References 99 Appendix A: Details of experimental apparatus 104 Fluid system 104 Temperature measurement and control system 106 Electrical measurement system 107 iv LIST OF FIGURES 1.1 Schematic of an idealized steam flood 8 2.1 Electrical conductivity as a function of sodium chloride concentration 36 2.2 The effect of temperature on electrical conductivity 37 2.3 Laboratory steam-flood apparatus 38 2.4 Measurement locations within the conductivity cell 39 2.5 Temperature and conductivity records from experiment #1 40 2.6 Selected conductivity profiles from experiment #1 41 2.7 Surface plots of temperature and conductivity data from experiment #1 42 2.8 Temperature and conductivity records from experiment #2 43 2.9 Selected conductivity profiles from experiment #2 44 2.10 Surface plots of temperature and conductivity data from experiment #2 45 2.11 Temperature and conductivity records from experiment #3 46 2.12 Selected conductivity profiles from experiment #3 47 2.13 Surface plots of temperature and conductivity data from experiment #3 48 2.14 Interpreted physical property changes occurring in experiment #1 49 2.15 Interpreted physical property changes occurring in experiment #2 50 2.16 Interpreted physical property changes occurring in experiment #3 51 2.17 Approach used to simulate electrical conductivity response 52 2.18 Comparison of measured and modelled conductivity records 53 2.19 Comparison of measured and modelled conductivity profiles 54 3.1 Electrical conductivity of sand and clay, versus pore-fluid conductivity 81 3.2 Distribution of sand and clay inside conductivity cell 82 3.3 Effect of temperature on measured conductivity values in sand and clay 83 v 3.4 Temperature and conductivity records from steam-flood experiment 84 3.5 Selected conductivity profiles from steam-flood experiment 85 3.6 Surface plots of temperature and conductivity data from experiment 86 3.7 Calculated and observed conductivities of sand and clay, versus salinity 87 3.8 Effect of high quality steam injection on clean sand 8 8 3.9 Comparison of measured and modelled temperature records 89 3.10 Comparison of measured and modelled conductivity records in clean sand 89 3.11 Comparison of measured and modelled conductivity profiles from cell 90 3.12 Comparison of measured and modelled conductivity records in clay layer 91 3.13 Simulated conductivity responses of representative reservoirs during high quality steam injection 92 3.14 Schematic of temperature, salinity, water saturation, and conductivity changes that are observed during high quality injections 93 3.15 Simulated conductivity responses of representative reservoirs during low quality steam injection 94 A.l Schematics of thermocouple feedthroughs 109 A.2 External thermocouple multiplexer 110 A.3 External heating coil control circuit 111 A.4 Conductivity multiplexer circuit 112 vi LIST OF TABLES 2.1 Experimental parameters for three steam injections into clean sand 18 2.2 Input parameters for numerical simulation of high quality injection 33 3.1 Experimental parameters for a steam injection into sand and clay 61 3.2 Input parameters for numerical simulation of injection 71 3.3 Parameters used to simulate electrical responses of example reservoirs 74 3.4 Summary of electrical and reservoir parameters for nine simulations of high quality injections 76 3.5 Summary of electrical and reservoir parameters for six simulations of low quality injections 79 vii ACKNOWLEDGEMENTS There are many people without whom it would have been impossible to finish this thesis. The most important of these is my wife, Sandy Stewart. She has put up with my work-related absences for many years, spending many evenings, most weekends, and even some vacations on her own, so that I could puzzle my way through my work. She has been a great source of encouragement and equanimity, keeping me on a reasonably even keel throughout my time here. She has even listened to me whenever I prattle on about steam, sand, or any other work-related topic of dubious entertainment value. I am of course grateful to my supervisor, Rosemary Knight. Her insight, guidance, optimism, and boundless enthusiasm have all been very helpful. Perhaps the aspect I appreciated the most was her ability to remain calm as I broke, melted, fried, vaporized, contaminated, or otherwise destroyed numerous integral pieces of laboratory equipment. I have been lucky to have as pleasant a place to work as the Rock Physics Lab. In " particular, Paulette Tercier, Jane Rea, and Kevin Jarvis have been a invaluable for their technical expertise, and their senses of humour. Financial support was provided by an NSERC postgraduate scholarship, and a Tri- Council (NSERC, MRC, SSHRC) Eco-Research fellowship. Funding for the laboratory research was provided initially by Mobil Exploration and Production Services, and Mobil Research and Development. Additional funding was obtained from an NSERC operating grant to Rosemary Knight. Finally, I would like to thank Guiseppe Marinoni. I have benefitted greatly from his expertise. viii CHAPTER 1: INTRODUCTION Motivation Subsurface steam injection has been used for over 30 years in enhanced-oil- recovery operations (Doscher and Ghassemi, 1981). In recent years it has also proven to be a very effective technique for the removal of certain types of nonaqueous-phase-liquid contaminants from the near surface (Stewart and Udell, 1988). Despite its long history of use, however, it is not yet possible to predict how steam will travel through a rock or soil. Since the overall effectiveness of an injection depends on how much of the subsurface is treated, it is necessary to track the motion of the steam. Monitoring wells provide accurate information at isolated positions, but do not usually provide the necessary density of coverage. Thus, to ensure that all oil- or contaminant-bearing regions are treated, a reliable remote mapping technique is required.