Effects of Rocks Heterogeneity on Thermal Propagation: An Integrated Measurement and Analysis Approach

Abstract

Abstract The objective of this study is to reduce uncertainties and optimize thermal applications. Thermal methods are the most effective to mobilize and produce heavy oil. The process can use different heating sources, e.g., steam, resistive heating, microwave, or radiofrequency. Optimization and prediction algorithms used in several studies assumed the reservoir to be homogeneous; however, lab characterization shows that heat propagation within the formation depends on the variations in several different parameters, including composition, thermal and physical properties, structural and grain morphology and contact. Heterogeneity affects the rate and the patterns of heat propagation into the formation, which ultimately determine the impact of thermal production and recovery operation. This work combines different advanced characterization and visualization techniques to map heat propagation in the formation rocks. The results provide the means to characterize heterogeneity, design more effective thermal recovery methods, and improve forecasting for optimal production and recovery. The study used four heating sources: resistive heating, radiofrequency, microwave, and steam injection. The first three are considered advanced methods, while the last is commonly used in the heavy oil fields. This study will focus on heat propagation within the rocks regardless of the type of heating source and the focus on rock characterizations. Analyses were performed before and after exposure to these thermal sources; it comprised core description, surface profile, high-speed infrared/resolution (IR) thermography, differential thermal analysis (DTA), scanning electron microscope (SEM), X-ray diffraction (XRD), computerized axial tomography (CT scan), and Autoscan, which provides hardness, composition, velocity, and spectral absorption. Pre- and post-thermal samples are thoroughly analyzed using different methods. These are integrated to characterize heat propagation in the formation as a function of the formation variables and its heterogeneity. Thin sections are used to analyze mineralogy, cementation, grains and other geological features. IR thermography captured heat propagation and the evolution of thermal gradients. DTA is used to characterize the thermal behavior of the rock such as melting, collapsing, and dissociation of minerals. SEM is used to characterize microstructures, microfractures, minerals morphology, cementations and clays identifications. XRD is used for clay characterizations. AutoScan provides rock physical properties such as permeability, velocity, and hardness. The results show that, for example, clays with illite/smectite (I/S) mixed layer collapsed at 375 °C temperature, while Kaolinite collapsed at higher temperature of 550 °C, and feldspar minerals expanded 0.3% of their original size at 200 °C, while quartz expanded 0.14%, the expansion and collapsing of these minerals affect the heat propagation as these absorb heat. The expansion of these minerals caused microcracks, which dissipated heat and disrupted heat transfer. This study provides in-depth heterogeneity characterization utilizing an integrated approach. The data collected from rock properties, mineralogy, structural, and thermal sources are integrated to characterize heterogeneity in the rock sample.