In-situ multifunctional nanosensors for fractured reservoir characterization [electronic resource]
Keywords: Energy Resources Engineering.

The goal of this research was to develop methods for acquiring reservoir temperature data within the formation and to correlate such information to fracture connectivity and geometry. Existing reservoir-characterization tools allow temperature to be measured only at the wellbore. Temperature-sensitive nanosensors will enable in-situ measurements within the reservoir. Such detailed temperature information enhances the ability to infer reservoir and fracture properties and inform reservoir engineering decisions. This thesis provides the details of the experimental work performed in the process of developing temperature nanosensors. Several potential nanosensor candidates were investigated for their temperature-sensitivity. Particle mobility through porous and fractured media was investigated. In order for temperature nanosensors to map the reservoir temperature distribution and ultimately to characterize the fracture network, they must be transported through typical porous and fractured formation rocks without significant retention within the formation pores and/or fractures. To investigate retention mechanisms, various laboratory-scaled core-flooding and micromodel transport experiments were conducted. The results showed that the size and/or size distribution, shape, and surface charge of the particles were influential parameters governing the transport of particles through porous and fractured media. There was an optimum particle size relative to the pore size distribution of the tested rock, at which the particles experience the least retention. Pore-scale observations showed that polydisperse particle size distribution affected the particle transport adversely. Experiments also indicated that elongated or nonspherical particles exhibited greater retention within the porous medium, primarily because of their shape. Compatibility of the particle surface characteristics (surface charge) with the rock material was found to be crucial for particle transport. The transport of particles, particularly silica particles, through fractured rock was investigated. Experimental results showed that the recovery of the particles was dependent on the particle size, concentration and flow rate. The controlling transport mechanisms of silica particles were also identified. Results showed that the existence of fractures facilitated the particle transport. Particles were found to flow with the fast-moving streamlines that exist within the fracture. Pore-scale experiments confirmed by visual observation that fractures are favorable conduits for particle transport. Particle tracking showed particles were flowing with velocities comparable to maximum velocity of bulk fluid assuming a parallel-plate fracture model. The concept of using particles as a fracture caliper mechanism to estimate the fracture aperture was addressed. The feasibility of estimating the fracture aperture by correlating the size of the largest recovered particles to the fracture opening was verified by injecting a wide size distribution of particles through a fracture of predetermined hydraulic aperture. Experimental results showed that the size of the largest recovered particle was similar to the estimated aperture. Visual observations using micromodels were consistent with the results of the core-scale experiments. Temperature sensing mechanisms of potential candidates were investigated. Temperature-sensitive particles investigated in this study include the irreversible thermochromic, dye-attached silica and tin-bismuth particles. A combined heat and flow test confirmed the temperature-sensitivity of the irreversible thermochromic particles by observing the color change. A detectable change in the fluorescent emission spectrum of the dye-attached silica particles upon heating was observed. A simple sensing mechanism of melting and growth in particle size of tin-bismuth particles was demonstrated. The processing and detection of silica-encapsulated DNA particles with hydrofluoric acid chemistry was tested. A protocol to release the DNA by dissolving the silica layer without completely destroying the DNA was established. The silica-encapsulated DNA particles were flowed through a porous medium at high temperature. Some dissolution of silica particles was observed, leading to a reduction in their size. This research study showed that synthesizing particles to respond to a specific reservoir property such as temperature is feasible. Using particles to measure reservoir properties is advantageous because particles can be transported to areas in the reservoir that would not be accessible by other means and therefore provide measurements deep within the formation.