David K. Potter

Detection of magnetic nanoparticles against proppant and shale reservoir rocks

With the expansion in the production of shale oil and gas, there is a desire to obtain detailed information of the downhole environment resulting from hydraulic fracturing (fracking). Nanomagnetite (nMag) has been proposed as a suitable contrast agent for magnetic imaging. In order to determine its suitability, 15 nm oleic acid-stabilised magnetite nanoparticles were synthesised and the magnetic susceptibility was measured and compared against two types of proppant. Although frac sand is diamagnetic (−0.20 × 10−5 SI), ceramic proppant is paramagnetic (25.7 × 10−5 SI) due to the presence of Fe2O3. The quantity of the nanoparticles that would be required for differentiation against the background levels in the proppant pack was calculated to be 0.269 g/L for sand and 1.01 g/L for ceramic, which correlates to a minimum of 15,000 kg and 56,000 kg per well, respectively. In order to determine the contrast with the reservoir rock itself, the magnetic susceptibility was mapped for cores from two typical shale gas reservoirs (Harrison and Rackley, Arkansas), which show a general low level of paramagnetism (ca. 45 × 10−5 SI). However, regions are observed with higher susceptibility (>200 × 10−5 SI) necessitating the use of 242,000 kg nMag per well in order to provide contrast with the reservoir.

PMTec: A new MATLAB toolbox for absolute plate motion reconstructions from paleomagnetism

Abstract Established on Euler rotations (rotation poles and angles), quantitative representation of plate motion history has been one of the focus fields in geoscience since the beginning of the age of plate tectonics. Here we present a new MATLAB based toolbox PMTec primarily developed for (1) construction of apparent polar wander paths (APWP, in the form of running means and spherical splines) from paleomagnetic data and (2) absolute plate motion calculations through APWP geometric parameterizations. We choose to build the graphical users interface of PMTec using MATLAB considering its powerful mapping toolbox for geospatial data visualization and its rising popularity in the geoscience community. Theoretical background, functioning modules, and data and file management in PMTec are formulated in this paper. The computational and graphical capabilities of PMTec are demonstrated using published data to provide an overview about its operation procedure and potential applications. The PMTec package and associated tutorials are available for download from the website: http://www.ualberta.ca/~vadim/software.htm . PMTec is a freeware for plate tectonic research and education purposes and allowed to be redistributed among users.

Geophysical Signal Parameterization and Filtering Using the fractional Fourier Transform

The fractional Fourier transform (FrFT) domain operations offer an alternative to the conventional Fourier Transform (FT) in signal processing, especially for seismic data. It is shown that subsurface reflection events in a two-dimensional (time-spatial) seismic data behave like linear chirps for each frequency in the frequency-spatial domain. Since the FrFT kernel is a set of linear chirps, frequency-spatial domain seismic data processing is better suited using the FrFT than the FT. An analytical relationship between linear seismic events and FrFT parameters is derived and illustrated with an example. Seismic data from a field survey is used to show that the FrFT filtering performs better in coherent noise attenuation than the FT.

Quantifying the Transport of Superparamagnetic Nanoparticles in Porous Media Using an Acrylic Flow Cell and Integrated Magnetic Susceptibility Sensor Technique

Nanoparticle technology is starting to be explored by several groups worldwide in the petroleum industry, with potential applications of magnetic nanoparticle injection ranging from monitoring the progress of hydraulic fracturing jobs to enhancing oil recovery. However, there is currently a little published information regarding the optimum conditions for the transport of dispersed magnetic nanoparticles through reservoir material. Magnetic nanoparticles have a tendency to aggregate together, potentially blocking pore connections and degrading reservoir quality. We report results of initial experiments designed to determine the ideal conditions to transport superparamagnetic nanoparticle suspensions through simulated unconsolidated core material. We used a non-metallic flow cell and integrated magnetic susceptibility sensor technique to quantify the transport of the nanoparticle suspensions. The flow cell was made of an acrylic material and allowed simultaneous magnetic susceptibility monitoring at various positions along the cell whilst the flow experiments were taking place. Such “in-line” quantitative magnetic susceptibility monitoring of the nanoparticle suspensions during a fluid flow experiment represents a significant step forward in characterization techniques. Simultaneous magnetic susceptibility monitoring is not possible using traditional stainless steel flow cells. The new flow cell is also transparent, allowing visual observation of the progress of the nanoparticle suspensions. We describe the effect of different dispersants, sonications, injection rates, permeability of the porous media and nanoparticle types on the transport of the nanoparticle suspensions. The flow cell and magnetic monitoring system have several other potential applications, including simultaneous monitoring of fines migration along the length of a core plug during various fluid flow experiments.

A Review of Hybrid Fiber-Optic Distributed Simultaneous Vibration and Temperature Sensing Technology and Its Geophysical Applications

Distributed sensing systems can transform an optical fiber cable into an array of sensors, allowing users to detect and monitor multiple physical parameters such as temperature, vibration and strain with fine spatial and temporal resolution over a long distance. Fiber-optic distributed acoustic sensing (DAS) and distributed temperature sensing (DTS) systems have been developed for various applications with varied spatial resolution, and spectral and sensing range. Rayleigh scattering-based phase optical time domain reflectometry (OTDR) for vibration and Raman/Brillouin scattering-based OTDR for temperature and strain measurements have been developed over the past two decades. The key challenge has been to find a methodology that would enable the physical parameters to be determined at any point along the sensing fiber with high sensitivity and spatial resolution, yet within acceptable frequency range for dynamic vibration, and temperature detection. There are many applications, especially in geophysical and mining engineering where simultaneous measurements of vibration and temperature are essential. In this article, recent developments of different hybrid systems for simultaneous vibration, temperature and strain measurements are analyzed based on their operation principles and performance. Then, challenges and limitations of the systems are highlighted for geophysical applications.

Absolute reconstruction of the closing of the Mongol‐Okhotsk Ocean in the Mesozoic elucidates the genesis of the slab geometry underneath Eurasia

Understanding the present-day fast seismic velocity anomalies in the mantle requires an accurate kinematic reconstruction of past convergent tectonics. Using the paleomagnetism-based absolute reconstruction method from Wu and Kravchinsky [2014], we present here the restoration of the closing of the Mongol-Okhotsk Ocean (MOO) that existed between Siberia and North China-Amuria (NCA) during the Mesozoic. Three stages, i.e., 250-200 Ma, 200-150 Ma and 150-120 Ma, are identified from the time-varying convergence rates of Siberia and NCA. The spherical distance between the suture margins was reduced by ca. 66.7% at an average convergence rate of 8.8±0.6 cm/yr during the first stage at 250-200 Ma, when ca. 62.5-76.1% of the slabs associated with the MOO lithosphere were formed primarily through intra-oceanic convergence. In the second stage at 200-150 Ma, the spherical distance was reduced by another 21.1% with a convergence rate of 3.6±0.3 cm/yr. During this stage, ca. 14.2-30.9% of the MOO slabs were formed and continental-oceanic convergence outpaced intra-oceanic subduction. In the last stage at 150-120 Ma, the convergence rate dropped to ca. 0.4-0.6 cm/yr with the formation of ca. 4.6-9.8% slabs associated with the MOO lithosphere. The final closure of the MOO remnant basin could have been accomplished by 130-120 Ma, which explains the origin of the fast-velocity anomalies inside the restored continents at 120 Ma near the suture margins.

Temperature dependence on the mass susceptibility and mass magnetization of superparamagnetic Mn–Zn–ferrite nanoparticles as contrast agents for magnetic imaging of oil and gas reservoirs

ABSTRACT The mass susceptibility (χmass) and mass magnetization (Mmass) were determined for a series of ternary manganese and zinc ferrite nanoparticles (Mn–Zn ferrite NPs, MnxZn1−xFe2O4) with different Mn:Zn ratios (0.08 ≤ x ≤ 4.67), prepared by the thermal decomposition reaction of the appropriate metal acetylacetonate complexes, and for the binary homologs (MxFe3−xO4, where M = Mn or Zn). Alteration of the Mn:Zn ratio in Mn–Zn ferrite NPs does not significantly affect the particle size. At room temperature and low applied field strength the mass susceptibility increases sharply as the Mn:Zn ratio increases, but above a ratio of 0.4 further increase in the amount of manganese results in the mass susceptibility decreasing slightly, reaching a plateau above Mn:Zn ≈ 2. The compositional dependence of the mass magnetization shows less of a variation at room temperature and high applied fields. The temperature dependence of the mass magnetization of Mn–Zn ferrite NPs is significantly less for Mn-rich compositions making them more suitable for downhole imaging at higher temperatures (>100 °C). For non-shale reservoirs, replacement of nMag by Mn-rich Mn–Zn ferrites will allow for significant signal-to-noise enhancement of 6.5× over NP magnetite.