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Advances in Oil and Gas Exploration & Production Daniel Cabrera S. Fernando Samaniego V. Experimental Mechanics of Fractured Porous Rocks Advances in Oil and Gas Exploration & Production Series Editor Rudy Swennen, Department of Earth and Environmental Sciences, K.U. Leuven, Heverlee, Belgium The book series Advances in Oil and Gas Exploration & Production pub- lishes scientific monographs on a broad range of topics concerning geo- physical and geological research on conventional and unconventional oil and gas systems, and approaching those topics from both an exploration and a production standpoint. The series is intended to form a diverse library of reference works by describing the current state of research on selected themes, such as certain techniques used in the petroleum geoscience business or regional aspects. All books in the series are written and edited by leading experts actively engaged in the respective field. The Advances in Oil and Gas Exploration & Production series includes both single and multi-authored books, as well as edited volumes. The Series Editor, Dr. Rudy Swennen (KU Leuven, Belgium), is currently accepting proposals and a proposal form can be obtained from our representative at Springer, Dr. Alexis Vizcaino ([email protected]). Daniel Cabrera S. . Fernando Samaniego V. Experimental Mechanics of Fractured Porous Rocks 123 Daniel Cabrera S. Fernando Samaniego V. Fractured Rocks Laboratory Petroleum Engineering Department School of Engineering School of Engineering UNAM UNAM Mexico City, Mexico Mexico City, Mexico ISSN 2509-372X ISSN 2509-3738 (electronic) Advances in Oil andGasExploration & Production ISBN978-3-031-17737-8 ISBN978-3-031-17738-5 (eBook) https://doi.org/10.1007/978-3-031-17738-5 ©TheEditor(s)(ifapplicable)andTheAuthor(s),underexclusivelicensetoSpringer NatureSwitzerlandAG2022 Thisworkissubjecttocopyright.AllrightsaresolelyandexclusivelylicensedbythePublisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting,reuseofillustrations,recitation,broadcasting,reproductiononmicrofilmsorinany otherphysicalway,andtransmissionorinformationstorageandretrieval,electronicadaptation, computersoftware,orbysimilarordissimilarmethodologynowknownorhereafterdeveloped. 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ThisSpringerimprintispublishedbytheregisteredcompanySpringerNatureSwitzerlandAG Theregisteredcompanyaddressis:Gewerbestrasse11,6330Cham,Switzerland Preface This book presents a practical approach for petrophysical laboratory tests in which whole core samples of naturally fractured reservoirs, with two porous media, the secondary porosity with vugs and fractures, and a pseudo-matrix of low permeability, present at effective stresses higher than 3000 psi conditions of an equivalent single porosity médium. An important percentage of worldwide hydrocarbon reserves are stored in the formations of these systems, especially carbonates. The advantage of whole cores (with typical dimensions of 4.5'' diameter and 6–7'' length) is that it at least partially includes the secondary porosity, which can be studied through the procedures described in this book. In the petroleum industry, petrophysics is considered on a laboratory scale as a set of standard experiments to be carried out on natural or artificial homogeneous rocks; such tests are applied as routine or advanced procedures. Scaling is the translation from a larger scale to a smaller one or vice versa; the petrophysical properties of the system are fundamental to scaling the experiments, under conditions in which the geomechanical behavior of the rock (fluid and rock dynamics) is physically similar to the reservoir at field conditions. This work presents petrophysical methods for obtaining and characterizing the physical properties of fractured carbonate and sandstone rocks. The experimental design of models for laboratory-scale representation of naturally fractured reservoirs predicts the properties and flow behavior of fluids at the reservoir scale in a short laboratory testing time, which develops in an oil field over several years. This book deals with physical models which allow visualizing the effects of the different factors that influence the production of hydrocarbons. This knowledge usually contributes to the improvement in the computational programs (simulators) used to adjust and predict reservoir behavior. Some- times the laboratory experiments (whole core, plugs) of the reservoir performance permit the identification (inference) of some effects that govern the production of hydrocarbons. Such physical effects can be modeled and implemented to improve reservoir simulation software. The challenge for the realization of experiments at the laboratory scale consists of studying and simulating the behavior of the prototype (reservoir scale) in a reasonable period in the laboratory scale with field conditions (high pressure, temperature, field reservoir fluids (oil and water), effective stress), in a reduced size model (a core). v vi Preface The whole core sample analysis is important for the understanding of the complex physical behavior derived from the double porosity of naturally fractured reservoirs at the field scale. Measurements in these types of rocks are essential to study the basic and special petrophysical properties, such as directional permeability, porosity, relative permeability, capillary pressures, compressibility, wettability, fluid saturation in secondary porosity (vugs and fractures), and pseudo-matrix region. The complex properties of whole cores, like double compressibility and ductility under high pressure and temperature, permit the realization of an advanced experimental test. The analysis of representative fractured rocks allows us to interpret the behavior of the naturally fractured reservoir under study, due to its characteristics of heterogeneity and anisotropy, distinctive of the secondary porosity (vuggy-fracture region). The experimental time increases exponentially depending on the volume of the sample rock. The long experimentation time should be considered an investment of time and resources, to obtain a deep and representative characterization of the rock, and valuable information for predicting reservoir performance with potential economic benefits. Further- more, a combination of theoretical, numerical, and experimental análysis must be applied in the interpretation of the data to establish new laboratory methodologies and procedures. Experimental results and field data are key to this process and to vali- dating computational simulations (interaction between reservoir and laboratory scale). A classification of rocks is discussed, for developing conventional and special petrophysics experimental studies. The presented classification can be extended to a reservoir classification, which coincides with other classifica- tions in the literature. The reported values of the compressibility range are hard data for numerical reservoir simulation and rock mechanics studies. This classification is based on the petrophysical properties of porosity, permeability, compressibility, and experimental effective stress applied to obtain representative results at reservoir conditions for whole core samples (diameter = 4 in) (high pressure and temperature). Field experience regarding reservoir engineering studies (i.e., material balance and numerical simulation) has indicated that professionals in the industry tend to use smaller values for the formation compressibility (bias by the homogeneous porous médium assumption), increasing implicitly other reservoir production mechanism active in the reservoir, thus resulting in poor performance predictions. Whole core samples are useful in naturally fractured reservoir evaluation due to their larger volume compared to conventional plug-type samples, and they contain a complex vuggy-fracture system and the matrix system. Therefore, they are more closely physically representative samples of a naturally fractured reservoir. The experimental determination of the permeability tensor developed allows the identification of the directional permeability of the rock analyzed and its dependence on the effective confining stress. With the principal permeability directions determined, the mayor permeable direction is defined for developing representative immiscible displacement (water-oil) under reservoir conditions. The experimental utility Preface vii of the permeability tensor contributes to discretizing the values of the properties of the fractures and the matrix system, a key aspect for estimating the residual oil saturation in the double porosity system (matrix—fractures), since the morphology of the rock depends on the confining pressure. The experimental data provide a basis for improving reservoir simulation models, in order to obtain realistic predictions of reservoir behavior. The design of an immiscible displacement test (gas-oil, water-oil) is presented to determine the residual oil saturation in porous fractured rocks. It is possible to determine the residual oil saturation in the fracture and matrix system of the rock, depending on the effective stress applied to the rock. The values of residual oil saturation to water Sorw, and to gas Sorg, are the most important data for the design and implementation of an enhanced oil recovery process, so reliable estimations are imperative. The experimental design procedure exposed in this work allows for obtaining this essential information. The way forward: The developments presented in this book may have been visualized a few years back as difficult, but an investigative industry- based effort has made it posible to advance the previous methodologies. Thus, the future of the petrophysical studies to meet the challenges identified in the daily field operations is open. Mexico City, Mexico Daniel Cabrera S. Fernando Samaniego V. AcknowledgmentsTheexperimentsweredevelopedwithinthefacilitiesoftheFractured RocksLaboratory“EdgarR.RangelGerman”oftheNationalAutonomousUniversityof MexicoinMexicoCity. Contents 1 Petrophysics or Geomechanics: A Branch of Mechanics . .... 1 1.1 Experimental Design in Reservoir Engineering . ..... .... 1 1.1.1 Physical Models .. .... .... .... .... ..... .... 1 1.1.2 Mathematical Models .. .... .... .... ..... .... 1 1.2 Experimental Analysis of Fractured Porous Rocks ... .... 2 1.3 Advantages of Whole Core Fractured Rocks Samples .... 3 1.4 Book Overview..... .... .... .... .... .... ..... .... 6 1.5 Industrial Applications ... .... .... .... .... ..... .... 6 References. .... .... ..... .... .... .... .... .... ..... .... 7 2 Petrophysical Classification of Rocks .... .... .... ..... .... 9 2.1 Rock Type l: Limestone Rock with Very Low Porosity and Permeability .... .... .... .... .... .... ..... .... 9 2.2 Rock Type ll: Compact Rock, with Low Porosity and Permeability .... .... .... .... .... .... ..... .... 10 2.3 Rock Type lll: Sandstone Rock of Intermediate Consolidation . ..... .... .... .... .... .... ..... .... 11 2.4 Rock Type IV: Sandstone Rock of Intermediate Consolidation . ..... .... .... .... .... .... ..... .... 12 2.5 Rock Type V: Fractured Rock with Low Porosity and Permeability Matrix .. .... .... .... .... ..... .... 12 2.6 Rock Type Vl: Fractured Rock with High Porosity and Permeability Matrix .. .... .... .... .... ..... .... 13 2.7 Rock Type Vll: Rock with Triple Porosity (Matrix, Vugs, and Fractures) .. .... .... .... ..... .... 15 2.8 Rock Type Vlll: Salt Rock .... .... .... .... ..... .... 16 2.9 Rock Type lX: Artificial Porous Media .. .... ..... .... 17 2.9.1 Compressibility of Rocks ... .... .... ..... .... 19 References. .... .... ..... .... .... .... .... .... ..... .... 20 3 Experimental Permeability Tensor for Fractured Porous Rocks .. .... ..... .... .... .... .... .... ..... .... 21 3.1 Introduction .. ..... .... .... .... .... .... ..... .... 21 3.2 Literature Review ... .... .... .... .... .... ..... .... 21 3.3 General Methodology .... .... .... .... .... ..... .... 23 3.4 Experimental Methodology .... .... .... .... ..... .... 24 3.5 Experimental Analysis Results . .... .... .... ..... .... 26 3.6 Linear Compaction Tendency .. .... .... .... ..... .... 27 ix x Contents 3.7 Vertical Permeability. .... .... .... .... .... ..... .... 29 3.8 Transverse Directional Permeabilities .... .... ..... .... 29 3.9 Permeability Linear Functions.. .... .... .... ..... .... 33 3.10 Permeability Tensors for Fracture and Matrix Permeability .. ..... .... .... .... .... .... ..... .... 33 3.11 Conclusions .. ..... .... .... .... .... .... ..... .... 34 References. .... .... ..... .... .... .... .... .... ..... .... 34 4 Scaling Experimental Immiscible Flow and Geomechanics in Fractured Porous Rock. .... .... .... .... .... ..... .... 37 4.1 Introduction .. ..... .... .... .... .... .... ..... .... 37 4.2 Dimensional Analysis and Inspectional Analysis .... .... 37 4.3 Background... ..... .... .... .... .... .... ..... .... 39 4.4 Experimental Design. .... .... .... .... .... ..... .... 41 4.4.1 Sample Cutting and Trimming ... .... ..... .... 42 4.4.2 Core Cleaning and Drying... .... .... ..... .... 42 4.4.3 Bulk Porosity, Effective Porosity, Compressibility, and Permeability Data. ..... .... 43 4.4.4 Wettability... .... .... .... .... .... ..... .... 44 4.4.5 Fluids Saturation .. .... .... .... .... ..... .... 45 4.4.6 Scaling and Geomechanical Dimensionless Time .. ..... .... .... .... .... .... ..... .... 46 4.5 First Displacement (Residual Oil Saturation in Vugy-Fracture-Matrix System) . .... .... .... ..... .... 50 4.6 Second Displacement (Residual Oil Saturation in the Pseudo-matrix System) ... .... .... .... .... ..... .... 52 4.7 Discretization of Residual Oil Saturation in the Pseudo-matrix and Vuggy-Fracture System.... ..... .... 53 4.8 Physical Similitude Between Model and Prototype ... .... 54 4.9 Conclusions .. ..... .... .... .... .... .... ..... .... 54 References. .... .... ..... .... .... .... .... .... ..... .... 55 5 General Conclusions ..... .... .... .... .... .... ..... .... 57