In-Situ Multifunction Nanosensors for Fractured Reservoir Characterization

Abstract

Acquiring specific data about the reservoir pressure and temperature, near the wellbore and far out in the formation, and correlating such information to fracture connectivity and geometry are key for the optimum energy extraction from geothermal resources. Existing fracture characterization tools and analysis approaches allow for pressure and temperature to be measured only at the wellbore. The development of temperature- and/or pressure-sensitive nanoparticles would provide the capability of in-situ measurements within the reservoir, through the concept of nanosensing. This paper provides details of experimental work performed toward the ultimate goal of making temperature and pressure nanosensors, in order to develop a new method to predict reservoir parameters and characterize fracture networks in geothermal reservoirs. The paper addresses the feasibility of using nanomaterials as tracers to determine the in-situ reservoir properties. Preliminary testing with the injection of various nanofluid suspensions was carried out to investigate the viability of transporting nanomaterials through a porous rock. This is a critical step toward the development of functional nanosensors. Berea sandstone and slim tubes packed with sand and glass beads were used. The nanoparticles injected into Berea sandstone cores were shown to pass through the rock, and hence provided a proof of concept in the use of nanoparticles as tracers. Spherical SiO2 nanoparticles were transported through the pore space of the rock and were detected in the effluent. These nanoparticles were also recovered after transport through a 10 meter long sand-packed slim tube. Following the successful injection of spherically shaped nanoparticles, an investigation was initiated to assess the practicability of transporting rod-like nanoparticles (silver nanowires and iron oxide nanorice) through the pores of Berea sandstone. These nanowires and nanorice are precursors for the injection of functional nanosensors such as pressure- and temperature-sensitive nanotracers. It was found that the silver nanowires and hematite nanorice of the sizes used were unable to pass through the pore spaces of the core sample. The hematite nanorice was also injected into a slim tube packed with glass beads, to investigate their mobility in the absence of rock material (such as clays). Scanning electron microscopy micrographs of effluents from that injection showed traces of the hematite nanorice.