Laboratory Investigation of Impact of Slickwater Composition on Multiphase Permeability Evolution in Tight Sandstones

Summary Fracturing fluid filtrate that leaks off during injection is imbibed by strong capillary forces present in low-permeability sandstones and may severely reduce the effective gas permeability during cleanup and post-fracture production. This work aims to investigate the role fracturing fluid filtrate from slickwater has on rock-fluid and fluid-fluid interactions and to quantify the resulting multiphase permeability evolution during imbibition and drainage of the filtrate by means of specialized core laboratory techniques. Three suites of experiments were conducted. In the first suite of experiments, a fluid leakoff test was conducted on selected core samples to determine the extent of polymer invasion and leakoff characteristics. In the second suite, multigas relative permeability measurements were conducted on sandstone plugs saturated with fracturing fluid filtrate. A combination of controlled fluid evaporation and pulse decay permeability technique was used to measure liquid and gas effective permeabilities for both drainage and imbibition cycles. These experiments aim to capture dynamic permeability evolution during invasion and cleanup of fracturing fluid (slickwater). The final suite of experiments consists of adsorption flow tests to investigate, identify, and quantify possible mechanisms for adsorption of the polymeric molecules of friction reducers present in the fluid filtrate to the pore walls of the rock sample. Imbibition tests and observations of contact angles were conducted to validate possible wettability changes. Results from multiphase permeability flow tests show an irreversible reduction in endpoint brine permeability and relative permeability with increasing concentration of friction reducer. Our results also show that effective gas permeability during drainage/cleanup of the imbibed slickwater fluid is controlled to a large degree by trapped gas saturation than by changes in interfacial tension. Adsorption flow tests identified adsorption of polymeric molecules of the friction reducer present in the fluid to the pore walls of the rock. The adsorption friction reducer increases the wettability of the rock surface and results in the reduction of liquid relative permeability. The originality of this work is to diagnose formation damage mechanisms from laboratory experiments that adequately capture multiphase permeability evolution specific to a slickwater fluid system, during imbibition and cleanup. This will be useful in optimizing fracturing fluid selection.

Dynamic permeability evolution during fluid injection and production in ultra-deep geothermal reservoirs

<p>A geothermal well drilled into a reservoir at temperatures exceeding the critical point of pure water (>374 °C) could generate substantially greater quantities of energy than conventional geothermal wells. Although these temperatures can be found at shallow depths (<2-3 km) in high-grade geothermal resources located in volcanically active areas, similar temperatures are only found at depths >10 km beneath vast areas of continental crust with lower heat fluxes. Permeability decreases markedly with increasing depth below 2-3 km, so exploiting the tremendous heat resources of high temperature rock at such great depths will require permeability stimulation by the injection of high-pressure fluids. In this study, we use the CSMP++ platform to perform 3D simulations of transient permeability evolution around a geothermal doublet drilled to depths between 10-16 km. The simulations incorporate a well model initially devised by Peaceman (1978) to calculate well pressures and rates of fluid production/injection. The dynamic permeability model is based on Weis et al. (2012), initially developed to simulate the evolution of ore-forming magmatic-hydrothermal systems, and links a failure criterion for critically-stressed crust with depth-dependent permeability profiles characteristic for tectonically active crust as well as pressure- and temperature-dependent relationships describing hydraulic fracturing and the transition from brittle to ductile rock behavior. We investigate the permeability changes in response to high-pressure fluid injection in brittle and ductile rock, the timescales over which the zone of permeability stimulation migrates towards production wells, and dynamic permeability evolution in response to changes in injection and production parameters. These simulations aim to mitigate resource risks that could limit the ability to extract heat from geothermal resources in ductile upper crust and to help anticipate the conditions that would be required to make the exploitation of ultra-deep supercritical geothermal resources a reality. </p><p>References</p><p>Peaceman, D. W. (1978) Interpretation of Well-Block Pressures in Numerical Reservoir Simulation. SPE 6893, 183–194.</p><p>Weis, P., Driesner, T., & Heinrich, C. A. (2012). Porphyry-copper ore shells form at stable pressure-temperature fronts within dynamic fluid plumes. Science, 338(6114), 1613–1616.</p>

Dynamical magnetic behavior of anisotropic spinel-structured ferrite for GHz technologies

We have fabricated a high quality magnetic Ni0.5Zn0.5Fe2O4 ferrite powder/polymer composite sheet consisting of common and environmentally friendly elements only. The sheet was then tested for its dynamic permeability by irradiating with electromagnetic waves with frequencies up to 50 GHz. Two different originally developed methods were used for the high-frequency permeability measurements, a short-circuited microstrip line method and a microstrip line-probe method. It is challenging to measure the dynamic permeability of magnetic thin films/sheets beyond 10 GHz because of the low response signal from these materials. However, the two methods produced essentially equivalent results. In the frequency dependent permeability profile, the maximum position of the profile, $$\mu ^{\prime \prime }_{max}$$ μ max ″ , shifted towards higher frequencies upon increasing an applied (strong) static external magnetic field, $$H_{dc}$$ H dc . A linear relationship between $$\mu^ {\prime \prime }_{max}$$ μ max ″ and $$H_{dc}$$ H dc for the entire range of $$H_{dc}$$ H dc was observed even at small $$H_{dc}$$ H dc . In general, the spinel-structured Ni-based ferrites exhibit low magnetic anisotropy, but the present sample showed a uniaxial-anisotropic behavior in the parallel direction of the sheet. Our Ni0.5Zn0.5Fe2O4 powder/polymer composite sheet thus exhibits high performance at GHz frequencies, and should be applicable e.g. as an anisotropic electromagnetic wave-interference material.

Experimental Study of the Dynamic Permeability in Two-Stage Gravel Packs Considering Particle Blockage and Remigration

The two-stage gravel-packing technique has been widely adopted in the development of unconsolidated sandstone reservoirs with high sanding rates and silt contents. Compared with the traditional gravel-packing operation, the lifespan and long-term conductivity of the two-stage gravel pack improve significantly. In the present study, an experimental study was undertaken to determine the dynamic permeability change of two-stage gravel packs during sand production. Thirty-nine groups of flooding tests were carried out with various experimental settings, and the pressure drop of each section (i.e., the sanding section, gravel bed I, and gravel bed II) was monitored dynamically during flooding. The permeability characteristics of each section were used to determine the mechanisms of sanding, pore blockage, and particle remigration under different packing arrangements. Using the proposed experimental setup, a sensitivity analysis was carried out to study the parameters that may affect the permeability of the sand pack, such as the two-stage gravel size, packing length, flooding rate, and silty sand content. Based on the observed permeability recovery phenomena in gravel bed I during the experiments, a dynamic permeability prediction model considering the remigration of deposited particles was proposed. Compared with the traditional deep-bed filtration model and the experimental results, the verification showed that the new model is more suitable for predicting the dynamic permeability of two-stage gravel packs.