6 research outputs found
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Integrated Experimental and Modeling Study of Geochemical Reactions of Simple Fracturing Fluids with Caney Shale
Interactions between rock minerals and hydraulic fracturing fluids directly impact the geochemical and geomechanical properties of shale formations. However, the mechanisms of geochemical reactions in shale unconventional reservoirs remain poorly understood. To investigate the geochemical reactions between shale and hydraulic fracturing fluids, a series of batch reactor experiments were undertaken. Three rock samples with different mineralogical compositions and three fluid samples of different compositions [deionized water, deionized water + 2% potassium chloride (KCl), and deionized water + 0.5% choline chloride (C5H14ClNO)] were used. Experiments were undertaken at reservoir temperature and atmospheric pressure. Elemental compositions of effluents after 1, 3, 7, 14, and 28 days were analyzed using inductively coupled plasma mass spectrometry. Medical computed tomography scanning and X-ray fluorescence spectroscopy were conducted on the entire core to help upscale results obtained from rock-fluid interaction experiments. Geochemical modeling using a reactive simulator, TOUGHREACT, was undertaken to corroborate experimental results. Results show that a lower pH triggered high dissolution rates in the rock samples, especially the carbonate components. As the pH increased, the rate of dissolution declined significantly, though for most cases dissolution still continued. The observed dissolved silica concentrations were much higher than the quartz solubility, suggesting that much of the silica originated from more soluble silica polymorphs and possibly desorption from clay mineral exchange sites. The concentration of most elemental species in solution increased, but aluminum (Al) and magnesium (Mg) concentrations declined rapidly following initial entry into solution. Geochemical modeling corroborated the conclusions regarding mineral dissolution and precipitation observed from experiments, notably the dissolution of calcite and pyrite in the reacted shale samples, the likely presence of silica polymorphs such as opal, chalcedony, or amorphous silica in these samples, and the reduction of Al and Mg concentrations in solution by precipitation of secondary aluminosilicate phases. The de-flocculation of clay minerals during reaction implies fines migration after hydraulic fracturing. This is detrimental to reservoir productivity as clay fines are displaced and lodged within the micro- and nanofractures created during fracturing. The immediate consumption of Al and Mg also has implications on blockage of hydrocarbon pathways due to precipitation of new minerals in these locations
On a Unified Core Characterization Methodology to Support the Systematic Assessment of Rare Earth Elements and Critical Minerals Bearing Unconventional Carbon Ores and Sedimentary Strata
A significant gap exists in our understanding and ability to predict the spatial occurrence and extent of rare earth elements (REE) and certain critical minerals (CM) in sedimentary strata. This is largely due to a lack of existing, systematic, and well-distributed REE and CM samples and analyses in United States sedimentary basins. In addition, the type of sampling and characterization performed to date has generally lacked the resolution and approach required to constrain geologic and geographic heterogeneities typical of subsurface, mineral resources. Here, we describe a robust and systematic method for collecting core scale characterization data that can be applied to studies on the contextual and spatial attributes, the geologic history, and lithostratigraphy of sedimentary basins. The methods were developed using drilled cores from coal bearing sedimentary strata in the Powder River Basin, Wyoming (PRB). The goal of this effort is to create a unified core characterization methodology to guide systematic collection of key data to achieve a foundation of spatially and geologically constrained REEs and CMs. This guidance covers a range of measurement types and methods that are each useful either individually or in combination to support characterization and delineation of REE and CM occurrences. The methods herein, whether used in part or in full, establish a framework to guide consistent acquisition of geological, geochemical, and geospatial datasets that are key to assessing and validating REE and CM occurrences from geologic sources to support future exploration, assessment, and techno-economic related models and analyses
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Multidimensional, Experimental, and Modeling Evaluation of Permeability Evolution, The Caney Shale Field Lab, OK, USA
A key feature of unconventional shale reservoirs is low permeability. On average, only 10% of original oil in place and 25% of original gas in place is produced from these reservoirs. Understanding the mechanisms behind fracture conductivity past the first couple of years of shale production is still an ongoing research topic, as most such reservoirs report fast and massive production declines. Hydraulic fracturing is indispensable for stimulating low-permeability rocks for economical oil and gas production from unconventional reservoir rocks such as shales. In contrast, for subsurface sequestration and storage of fluids including supercritical CO2 (for carbon capture, utilization, and storage) and hydrogen gas, inadvertent creation of fractures can lead to breaching of shale caprock. The Caney Shale in southern Oklahoma is being evaluated as both a potential hydrocarbon-producing reservoir and a caprock for fluid sequestration. The Caney Shale is a Mississippian-age, organic-rich mudrock with intermittent calcareous laminae, that produces. But currently there is limited data reported regarding productivity of horizontally drilled wellbores. While many scholars have investigated fracture conductivity in shale reservoirs, the mechanisms of proppant embedment in relation to lithology are still under investigation. This study implemented a multi-scale approach towards investigating proppant embedment and fracture conductivity, from nano-scale instrumented micro/nano-indentation to millimeter (mm) scale, mono-layer propped fracture flow at reservoir temperature and pressure, and American Petroleum Institute (API)-RP19D conductivity tests using inch/cm-scale shale platens. At each scale, various material characterization tools were utilized, including Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM), Energy Dispersive Spectroscopy (EDS), Raman spectroscopy, Laser profilometry, Computed X-ray Microscopy and X-ray Diffraction (XRD). The outcomes of the micro-indentation revealed variations in mechanical properties attributed to changing mineral composition and microstructures. Outcomes from API fracture conductivity testing and flow-through testing using a monolayer of proppant demonstrated: (1) a 50% impact on proppant embedment compared to ductile samples, (2) a significant decline in fracture conductivity with increasing stress and temperatures, and (3) conductivity that was also influenced by organic and inorganic content as well as internal sample architecture. Mineralogically, ductile samples contain about 25% more clay minerals compared to brittle regions. Heterogeneity in mineral composition causes the Caney Shale to show different responses at reservoir temperature and pressure, particularly in relation to creep and proppant embedment. Geomechanical and fluid-flow modeling have been conducted at several scales to help interpret laboratory results and apply findings to field-scale operation. The outcomes from this integration should aid geological and engineering predictions for the hydrocarbon production and caprock integrity of the Caney Shale
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Using in-situ strain measurements to evaluate the accuracy of stress estimation procedures from fracture injection/shut-in tests
Fracture injection/shut-in tests are commonly used to measure the state of stress in the subsurface. Injection creates a hydraulic fracture (or in some cases, opens a preexisting fracture), and then the pressure after shut-in is monitored to identify fracture closure. Different interpretation procedures have been proposed for estimating closure, and the procedures sometimes yield significantly different results. In this study, direct, in-situ strain measurements are used to observe fracture reopening and closure. The tests were performed as part of the EGS Collab project, a mesoscale project performed at 1.25 and 1.5 km depth at the Sanford Underground Research Facility. The tests were instrumented with the SIMFIP tool, a double-packer probe with a high-resolution three-dimensional borehole displacement sensor. The measurements provide a direct observation of the fracture closure signature, enabling a high-fidelity estimate of the fracture closure stress (ie, the normal stress on the fracture). In two of the four tests, injection created an opening mode fracture, and so the closure stress can be interpreted as the minimum principal stress. In the other two tests, injection probably opened preexisting natural fractures, and so the closure stress can be interpreted as the normal stress on the fractures. The strain measurements are compared against different proposed methods for estimating closure stress from pressure transients. The shut-in transients are analyzed with two techniques that are widely used in the field of petroleum engineering – the ‘tangent’ method and the ‘compliance’ method. In three of the four tests, the tangent method significantly underestimates the closure stress. The compliance method is reasonably accurate in all four tests. Closure stress is also interpreted using two other commonly-used methods – ‘first deviation from linearity’ and the method of (Hayashi and Haimson, 1991). In comparison with the SIMFIP data, these methods tend to overestimate the closure stress, evidently because they identify closure from early-time transient effects, such as near-wellbore tortuosity. In two of the tests, microseismic imaging provides an independent estimate of the size of the fracture created by injection. When combined with a simple mass balance calculation, the SIMFIP stress measurements yield predictions of fracture size that are reasonably consistent with the estimates from microseismic. The calculations imply an apparent fracture toughness 2-3x higher than typical laboratory-derived values
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Immune plasma for the treatment of severe influenza: an open-label, multicentre, phase 2 randomised study
BackgroundInfluenza causes substantial morbidity and mortality despite available treatments. Anecdotal reports suggest that plasma with high antibody titres to influenza might be of benefit in the treatment of severe influenza.MethodsIn this randomised, open-label, multicentre, phase 2 trial, 29 academic medical centres in the USA assessed the safety and efficacy of anti-influenza plasma with haemagglutination inhibition antibody titres of 1:80 or more to the infecting strain. Hospitalised children and adults (including pregnant women) with severe influenza A or B (defined as the presence of hypoxia or tachypnoea) were randomly assigned to receive either two units (or paediatric equivalent) of anti-influenza plasma plus standard care, versus standard care alone, and were followed up for 28 days. The primary endpoint was time to normalisation of patients' respiratory status (respiratory rate of ≤20 breaths per min for adults or age-defined thresholds of 20-38 breaths per min for children) and a room air oxygen saturation of 93% or more. This study is registered with ClinicalTrials.gov, number NCT01052480.FindingsBetween Jan 13, 2011, and March 2, 2015, 113 participants were screened for eligibility and 98 were randomly assigned from 20 out of 29 participating sites. Of the participants with confirmed influenza (by PCR), 28 (67%) of 42 in the plasma plus standard care group normalised their respiratory status by day 28 compared with 24 (53%) of 45 participants on standard care alone (p=0·069). The hazard ratio (HR) comparing plasma plus standard care with standard care alone was 1·71 (95% CI 0·96-3·06). Six participants died, one (2%) from the plasma plus standard care group and five (10%) from the standard care group (HR 0·19 [95% CI 0·02-1·65], p=0·093). Participants in the plasma plus standard care group had non-significant reductions in days in hospital (median 6 days [IQR 4-16] vs 11 days [5-25], p=0·13) and days on mechanical ventilation (median 0 days [IQR 0-6] vs 3 days [0-14], p=0·14). Fewer plasma plus standard care participants had serious adverse events compared with standard care alone recipients (nine [20%] of 46 vs 20 [38%] of 52, p=0·041), the most frequent of which were acute respiratory distress syndrome (one [2%] vs two [4%] patients) and stroke (one [2%] vs two [4%] patients).InterpretationAlthough there was no significant effect of plasma treatment on the primary endpoint, the treatment seemed safe and well tolerated. A phase 3 randomised trial is now underway to further assess this intervention.FundingNational Institute of Allergy and Infectious Diseases, US National Institutes of Health