A 2000 year varve-based climate record from the central Brooks Range, Alaska

Varved minerogenic sediments from glacial-fed Blue Lake, northern Alaska, are used to investigate late Holocene climate variability. Varve-thickness measurements track summer temperature recorded at Atigun Pass, located 41 km east at a similar elevation (r2 = 0.31, P = 0.08). Results indicate that climate in the Brooks Range from 10 to 730 AD (varve year) was warm with precipitation inferred to be higher than during the twentieth century. The varve-temperature relationship for this period was likely compromised and not used in our temperature reconstruction because the glacier was greatly reduced, or absent, exposing sub-glacial sediments to erosion from enhanced precipitation. Varve-inferred summer temperatures and precipitation decreased after 730 AD, averaging 0.4°C above the last millennial average (LMA = 4.2°C) from 730 to 850 AD, and 0.1°C above the LMA from 850 to 980 AD. Cooling culminated between 980 and 1030 AD with temperatures 0.7°C below the LMA. Varve-inferred summer temperatures increased between 1030 and 1620 AD to the LMA, though the period between 1260 and 1350 AD was 0.2°C below the LMA. Although there is no equivalent to the European Medieval Warm Period in the Blue Lake record, two warm intervals occurred from 1350 to 1450 AD and 1500 to 1620 AD (0.4 and 0.3°C above the LMA, respectively). During the Little Ice Age (LIA; 1620 to 1880 AD), inferred summer temperature averaged 0.2°C below the LMA. After 1880 AD, inferred summer temperature increased to 0.8°C above the LMA, glaciers retreated, but aridity persisted based on a number of regional paleoclimate records. Despite warming and glacial retreat, varve thicknesses have not achieved pre-730 AD levels. This reflects limited sediment availability and transport due to a less extensive retreat compared to the first millennium, and continued relative aridity. Overall, the Blue Lake record is similar to varve records from the eastern Canadian Arctic that document a cool LIA and twentieth century warming. However, the occurrence and timing of events, such as the LIA and Medieval Warm Period, varies considerably among records, suggesting heterogeneous climatic patterns across the North American Arctic

Steady Flow of a Cement Slurry

Understanding the rheological behavior of cement slurries is important in cement and petroleum industries. In this paper, we study the fully developed flow of a cement slurry inside a wellbore. The slurry is modeled as a non-linear fluid, where a constitutive relation for the viscous stress tensor based on a modified form of the second grade (Rivlin–Ericksen) fluid is used;we also propose a diffusion flux vector for the concentration of particles. The one-dimensional forms of the governing equations and the boundary conditions are made dimensionless and solved numerically. A parametric study is performed to present the effect of various dimensionless numbers on the velocity and the volume fraction profiles

The Role of Iron in Oxidant-Initiated Halogenation Reactions of Hydraulic Fracturing Additives

Produced water is the largest waste stream associated with hydraulic fracturing. The presence of unknown dissolved contaminants in produced water prevents its reuse. Many of these contaminants are transformation productscompounds that are generated during the fracturing process by chemical reactions between injected chemicals and reservoir components. Reactions among fracturing fluid additives, reservoir brine, and injected oxidants result in halogenation reactions that generate halogenated contaminants with high expected toxicity. Here, we investigate the role of subsurface iron in facilitating subsurface halogenation reactions. Experiments were performed using a model brine, cinnamaldehyde as a model fracturing fluid additive, two different oxidants used in hydraulic fracturing (ammonium persulfate and sodium hypochlorite), and three different iron species (iron­(II) dichloride, iron­(III) trichloride, and iron­(II) dichloride chelated with citric acid). We observed that iron­(II) dichloride increased iodination reactions in the presence of ammonium persulfate oxidant, while iron­(III) trichloride increased bromination reactions in the presence of sodium hypochlorite oxidant. Although the absence of replicate analyses in this study precludes the ability to assess the reproducibility of the data, we believe that these results can serve as inspiration for future researchers to consider the potential involvement of iron in chemical reactions of fracturing fluid additives

Integration of core sample velocity measurements into a 4D seismic survey and analysis of SEM and CT images to obtain pore scale properties

The Scurry Area Canyon Reef Operators Committee (SACROC) field, located in the Permian Basin of West Texas is an enhanced oil recovery (EOR) site into which large volumes of CO2 have been injected. We acquired core samples and 3D seismic surveys from the site in order to better characterize the movement of the CO2 injection plumes. The samples of SACROC reef limestone were used for ultrasonic velocity measurements, detailed mineralogy and Scanning Electron Microscopy (SEM) characterization, Computed Tomography (CT) scanning, thin section studies, and porosity measurements. Using a NER AutoLab 1500 at the National Energy Technology Laboratory (NETL) Core Flow Lab we have measured P and S wave velocities, porosity, and permeability at varying pressures, temperatures, and fluid saturations that simulate reservoir conditions after successive floods. Measurements were also taken with supercritical CO2 at in situ pressures and temperatures. We also modeled the expected velocities for our samples using the standard Gassmann and other rock physics. We created a tool that groups grayscale ranges into three categories, cleans boundaries between groups, and produces a polygon map of the macropores, micropores, mineral grains, and matrix. In addition, the CT and SEM pore maps were analyzed to reveal pore shape statistics. Pore volume, area, and connectivity is essential for chemistry experiments that will emulate time exposure of CO2 to limestone. Further, this analysis technique allows us to obtain pore orientation information, which is important in understanding the anisotropic conditions that may affect seismic data. This multi-scale approach can help to characterize what is occurring inside of the reservoir. Fine scale measurements of how CO2 affects pore-space dissolution can help to inform us of any changes in overall reservoir storage capacity due to changing porosity. Core-scale velocity measurements under in situ conditions will allow us to predict changes in future well log or seismic surveys. Combining microscale, mesoscale, and macroscale information should lead to a better understanding of the various processes at work when CO2 is sequestered in a limestone reservoir. © 2011 Published by Elsevier Ltd

Polymer-Cement Composites with Self-Healing Ability for Geothermal and Fossil Energy Applications

Sealing of wellbores in geothermal and tight oil/gas reservoirs by filling the annulus with cement is a well-established practice. Failure of the cement as a result of physical and/or chemical stress is a common problem with serious environmental and financial consequences. Numerous alternative cement blends have been proposed for the oil and gas industry. Most of these possess poor mechanical properties, or are not designed to work in high temperature environments. This work reports on a novel polymer-cement composite with remarkable self-healing ability that maintains the required properties of typical wellbore cements and may be stable at most geothermal temperatures. We combine for the first time experimental analysis of physical and chemical properties with density functional theory simulations to evaluate cement performance. The thermal stability and mechanical strength are attributed to the formation of a number of chemical interactions between the polymer and cement matrix including covalent bonds, hydrogen bonding, and van der Waals interactions. Self-healing was demonstrated by sealing fractures with 0.3–0.5 mm apertures, 2 orders of magnitude larger than typical wellbore fractures. This polymer-cement composite represents a major advance in wellbore cementing that could improve the environmental safety and economics of enhanced geothermal energy and tight oil/gas production