EXPERIMENTAL RESERVOIR ENGINEERING LABORATORY WORK BOOK O. Torsæter M. Abtahi Department of Petroleum engineering and Applied Geophysics Norwegian University of Science and Technology August, 2000 i PREFACE This book is intended primarily as a text in the course SIG4015 Reservoir Property Determination by Core Analysis and Well Testing at the Norwegian University of Science and Technology. Part of this course introduces the basic laboratory equipment and procedures used in core analysis and the theoretical aspects of the parameters. The book also includes detailed description of laboratory exercises suitable for student work. Chapter twelve of the book concludes a “Problem Based Learning (PBL)” project for the students. Appreciation is expressed to the Dr.ing. students Medad Tweheyo Twimukye and Hoang Minh Hai for their contributions to this work. Ole Torsæter Manoochehr Abtahi ii CONTENTS Preface………………………………………………………………………….. ii 1. Introduction……………………………………………………………………. 1 2. Cleaning and saturation determination……………………………….……... 3 2.1. Definitions 3 2.2. Measurement methods 3 2.2.1. Direct injection of solvent 3 2.2.2. Centrifuge flushing 4 2.2.3. Gas-driven solvent extraction 4 2.2.4. Soxhlet extraction 4 2.2.5. Dean-Stark distillation extraction 4 2.2.6. Vacuum distillation 5 2.2.7. Summary 6 2.3. Experiments 7 2.3.1. Saturation determination, Dean-Stark distillation method (Exp.1) 7 3. Liquid density..………………………………………………………………… 9 3.1. Definitions 9 3.2. Measurement of density 9 3.3. Experiments 10 3.3.1. Fluid density using the pycnometer (Exp.2) 10 4. Viscosity……...………………………………………………………….……... 12 4.1. Definitions 12 4.2. Effect of pressure and temperature on viscosity 13 4.3. Method for measuring viscosity 13 4.3.1. Capillary type viscometer 13 4.3.2. Falling ball viscometer 14 4.3.3. Rotational viscometer 15 4.4. Experiments 17 4.4.1. Liquid viscosity measurement using capillary type 17 viscometer (Exp. 3) 5. Porosity……...………………………………………………………….……… 20 5.1. Definitions 20 5.2. Effect of compaction on porosity 21 5.3. Porosity measurements on core plugs 21 5.3.1. Bulk volume measurement 22 5.3.2. Pore volume measurement 22 5.3.3. Grain volume measurement 24 5.4. Experiments 24 5.4.1. Effective porosity determination by helium porosimeter 24 method (Exp. 4) 5.4.2. Porosity determination by liquid saturation method (Exp. 5) 25 iii 6. Resistivity…...………………………………………………………….………. 27 6.1. Definitions 27 6.2. Effect of conductive solids 29 6.3. Effect of overburden pressure on resistivity 31 6.4. Resistivity of partially water-saturated rocks 31 6.5. Experiments 32 6.5.1. Resistivity measurements of fluid-saturated rocks (Exp. 6) 32 7. Surface and interfacial tension..……………………………………….……... 34 7.1. Definition 34 7.2. Methods of interfacial tension measurements 35 7.2.1. Capillary rise method 35 7.2.2. Wilhelmy plate method 36 7.2.3. Ring method 36 7.2.4. Drop weight method 37 7.2.5. Pendant drop method 38 7.2.6. Spinning drop method 40 7.3. Experiments 40 7.3.1. Interfacial tension (IFT) measurement, 40 pendant drop method (Exp. 7) 7.3.2. Measurement of IFT with the ring tensiometer (Exp. 8) 42 8. Contact angle and wettability....……………………………………….……... 44 8.1. Definitions 44 8.2. Measurement of wettability 46 8.2.1. Measurements on core samples 46 8.2.1.1. The Amott method 47 8.2.1.2. The centrifuge method 48 8.2.2. Contact angle measurements 50 8.2.2.1 The contact angle/imaging method 50 8.3. Experiments 51 8.3.1. Contact angle measurement using imaging method (Exp. 9) 51 9. Capillary pressure……………...……………………………………….……... 54 9.1. Definitions 54 9.2. Capillary pressure measurement methods 56 9.2.1. Porous plate method (restored state) 56 9.2.2. Centrifuge method 57 9.2.3. Mercury injection (Purcell method) 60 9.2.4. Dynamic method 61 9.2.5. Comparison of methods 62 9.3. Converting laboratory data 62 9.4. Experiments 63 9.4.1. Capillary pressure measurement using porous plate (Exp. 10) 63 7.4.2. Capillary pressure measurement using centrifuge (Exp. 11) 65 10. Permeability…….……………...……………………………………….……... 67 10.1. Definition 67 10.1.1. Darcy’s law 67 10.1.2. Kozeny-Carman model 67 iv 10.1.3. Klinkenberg Effect 69 10.1.4. Ideal gas law 70 10.1.5. High velocity flow 71 10.2. Measurement of permeability 72 10.2.1. Constant head permeameter 72 10.3. Experiments 74 10.3.1. Measurement of air permeability (Exp. 12) 74 10.3.2. Absolute permeability measurement of water (Exp. 13) 75 11. Relative permeability…….…...……………………………………….………. 77 11.1. Definitions 77 11.2. Flow of immiscible fluids in porous media 78 11.3. Buckley-Leverett solution 80 11.4. Welge’s extended solution 82 11.5. Relative permeability measurement methods 84 11.5.1. Steady state method 84 11.5.2. Unsteady state method 84 11.6. Experiments 86 11.6.1. Gas/oil relative permeability measurement, 86 unsteady state method (Exp. 14) 11.6.2. Oil/water relative permeability measuring, 89 unsteady state method (Exp. 15) References 92 v 1. INTRODUCTION Knowledge of petrophysical and hydrodynamic properties of reservoir rocks are of fundamental importance to the petroleum engineer. These data are obtained from two major sources: core analysis and well logging. In this book we present some details about the analysis of cores and review the nature and quality of the information that can be deduced from cores. Cores are obtained during the drilling of a well by replacing the drill bit with a diamond core bit and a core barrel. The core barrel is basically a hollow pipe receiving the continuous rock cylinder, and the rock is inside the core barrel when brought to surface. Continuous mechanical coring is a costly procedure due to: - The drill string must be pulled out of the hole to replace the normal bit by core bit and core barrel. - The coring operation itself is slow. - The recovery of rocks drilled is not complete. - A single core is usually not more than 9 m long, so extra trips out of hole are required. Coring should therefore be detailed programmed, specially in production wells. In an exploration well the coring can not always be accurately planned due to lack of knowledge about the rock. Now and then there is a need for sample in an already drilled interval, and then sidewall coring can be applied. In sidewall coring a wireline-conveyed core gun is used, where a hollow cylindrical “bullet” is fired in to the wall of the hole. These plugs are small and usually not very valuable for reservoir engineers. During drilling, the core becomes contaminated with drilling mud filtrate and the reduction of pressure and temperature while bringing the core to surface results in gas dissolution and further expansion of fluids. The fluid content of the core observed on the surface can not be used as a quantitative measure of saturation of oil, gas and water in the reservoir. However, if water based mud is used the presence of oil in the core indicates that the rock information is oil bearing. When the core arrives in the laboratory plugs are usually drilled 20-30 cm apart throughout the reservoir interval. All these plugs are analyzed with respect to porosity, permeability, saturation and lithology. This analysis is usually called routine core analysis. The results from routine core analysis are used in interpretation and evaluation of the reservoir. Examples are prediction of gas, oil and water production, definition of fluid contacts and volume in place, definition of completion intervals etc. Data from routine core analysis and from supplementary tests and the application of these data area summarized in Table 1.1. 1 Table 1.1: Routine core analysis and supplementary measurements. Data Application Routine core analysis Porosity Storage capacity Permeability Flow capacity Saturations Define the mobile hydrocarbons (productive zones and contacts), type of hydrocarbons Lithology Rock type and characteristics (fractures, layering etc.) Supplementary measurement Vertical permeability Effect of coning, gravity drainage etc. Core-gamma surface log Identify lost core sections, correlate cores and logs Matrix density Calibrate the density log Oil and water analysis Densities, viscosities, interfacial tension, composition etc. Special core analysis includes several measurements with the objective of obtaining detailed information about multiphase flow behavior. Special core analysis gives information about the distribution of oil, gas, and water in the reservoir (capillary pressure data), residual oil saturation and multiphase flow characteristics (relative permeabilities). Measurements of electrical and acoustic properties are occasionally included in special core analysis. This information is mainly used in the interpretation of well logs. The effect of pressure and temperature on rock and fluid properties is in some reservoir formations significant, and laboratory measurements should therefore be made at, or corrected to, reservoir conditions wherever possible. Included in special core analysis is in some cases detailed petrographical analysis of rocks (grain size distribution, clay identification, diagenesis etc.). Wettability analysis and special tests for enhanced oil recovery (EOR) are also often part of special core analysis. Table 1.2 is a list of the various special core analysis tests. Table 1.2: Special core analysis. Tests/Studies Data/Properties Static tests Compressibility studies Permeability and porosity vs. pressure Petrographical studies Mineral identification, diagenesis, clay identification, grain size distribution, pore geometry etc. Wettability Contact angle and wettability index Capillarity Capillary pressure vs. saturation Acoustic tests Electric tests Dynamic tests Flow studies Relative permeability and end point saturations EOR-Flow tests Injectivity and residual saturation 2 2. CLEANING AND SATURATION DETERMINATION 2.1 Definitions Before measuring porosity and permeability, the core samples must be cleaned of residual fluids and thoroughly dried.