Laboratory-based Rates Research Articles

Application of laboratory-based rate of penetration model for polycrystalline diamond compact bit to geothermal well drilling

The modeling of the rate of penetration (ROP) considering the degradation of drilling performance owing to bit wear is essential for planning efficient and economical drilling. In the present study, a laboratory-based ROP model for a polycrystalline diamond compact (PDC) bit is reviewed and the applicability of the model to the field data obtained in the four drilling tests performed by drilling structural boring wells in geothermal regions is investigated. It is validated that, on the whole, a parameter representing bit performance exponentially decreased with drilled length, suggesting that the decrease in ROP owing to bit wear is appropriately considered by the model, except when inherent performance of a PDC bit is not sufficiently exerted for some reason, e.g., inefficient transport of cuttings. The findings of the present study are expected to contribute to the optimization of drilling plans, including appropriate bit selection and bit life estimation.

A microphysical interpretation of rate‐ and state‐dependent friction for fault gouge

The evolution of fault strength during the seismic cycle plays a key role in the mode of fault slip, nature of earthquake stress drop, and earthquake nucleation. Laboratory-based rate- and state-dependent friction (RSF) laws can describe changes in fault strength during slip, but the connections between fault strength and the mechanisms that dictate the mode of failure, from aseismic creep to earthquake rupture, remain poorly understood. The empirical nature of RSF laws remains a drawback to their application in nature. Here we analyze an extensive data set of friction constitutive parameters with the goal of illuminating the microphysical processes controlling RSF. We document robust relationships between: (1) the initial value of sliding (or kinetic) friction, (2) RSF parameters, and (3) the time rates of frictional strengthening (aging). We derive a microphysical model based on asperity contact mechanics and show that these relationships are dictated by: (1) an activation energy that controls the rate of asperity growth by plastic creep, and (2) an inverse relationship between material hardness and the activation volume of plastic deformation. Collectively, our results illuminate the physics expressed by the RSF parameters, and which describe the absolute value of frictional strength and its dependence on time and slip rate. Moreover, we demonstrate that seismogenic fault behavior may be dictated by the interplay between grain properties and ambient conditions controlling the local shear strength of grain-scale asperity contacts.

Rates of low-pH biological Fe(II) oxidation in the Appalachian Bituminous Coal Basin and the Iberian Pyrite Belt

Low-pH Fe(II) oxidation can be exploited for the treatment of acid mine drainage (AMD). However, natural or engineered terraced iron formations (TIFs) are underutilized for AMD treatment because of uncertainties with respect to treatment performance. To address this problem we measured the rates of Fe(II) oxidation multiple times at eight sites in the Appalachian Bituminous Coal Basin and at three sites in the Iberian Pyrite Belt (IPB). Longitudinal geochemical transects were measured downstream of emergent anoxic AMD sources. Water velocities were measured at each sampling location and used to transform concentration versus distance profiles into concentration versus travel time for kinetic analysis of field data. Zero-order Fe(II) oxidation rates ranged from 8.60 to 81.3×10−7molL−1s−1 at the Appalachian sites and 13.1 to 67.9×10−7molL−1s−1 at the IPB sites. First-order Fe(II) oxidation rate constants ranged from 0.035 to 0.399min−1 at the Appalachian sites and 0.003 to 0.010min−1 at the IPB sites. Faster rates of Fe(II) oxidation were measured at two sites (one in Appalachia and one in IPB) where the emergent pH values were the lowest and little to no oxidative precipitation of Fe(III) occurred. Laboratory-based rates of Fe(II) oxidation were measured with TIF sediments and emergent AMD collected from seven Appalachian sites. First-order laboratory rate constants normalized to sediment biomass concentrations (measured by phospholipid fatty acids; PLFA) were positively correlated to first-order field rate constants. Biomass composition was relatively similar between all sites, and predominately comprised of proteobacteria and general PLFAs. A zero-order lab-based removal rate for dissolved Fe(T) was used to calculate area-based design criteria of 2.6–8.7gFeday−1m−2 (GDM) for both natural and engineered TIFs.

Temperature limits for preservation of primary calcite clumped isotope paleotemperatures

Solid-state reordering of C–O bonds in the calcite lattice can alter the clumped isotope composition of paleotemperature archives such as fossil brachiopod shells without inducing significant changes in shell microstructure and trace element concentrations, metrics commonly used to gauge preservation quality. To correctly interpret the paleoenvironmental significance of clumped isotope-derived paleotemperatures, it is necessary to understand the temperature–time domain in which solid-state C–O bond reordering is important. We address this question using a combination of laboratory and natural geological experiments on Paleozoic brachiopod shells. The laboratory experiments involve heating fossil brachiopod calcite at different temperatures and times to directly observe rates of 13C–18O bond reordering. The resulting Arrhenius parameters are indistinguishable from values previously determined for an optical calcite with similar trace element compositions. We develop an alternative kinetic model for reordering that accounts for non-first-order reaction progress observed during the initial several hundred minutes of laboratory heating experiments, and show that the simplified first-order approximation model (Passey and Henkes, 2012) predicts reaction progress equally well for temperatures and timescales relevant to sedimentary basins. We evaluate our laboratory-based rate predictions by studying brachiopod calcite from several sedimentary basins with independently constrained burial temperature histories. Specifically, we use the laboratory-derived Arrhenius parameters to predict the evolution of brachiopod calcite clumped isotope compositions during successive one million-year time steps reflecting the burial and exhumation temperature paths of each basin. While this exercise is limited by the relatively large uncertainties in the temperature histories of these basins, we find general correspondence, within error, between predicted and observed clumped isotope values. We present simplified temperature–time diagrams for calcite showing domains where primary clumped isotope compositions will be preserved, partially reordered, and fully reordered. In conclusion, calcite samples dwelling at ∼100°C or lower for 106–108 year timescales should not be affected by solid-state C–O bond reordering.

Linking nm-scale measurements of the anisotropy of silicate surface reactivity to macroscopic dissolution rate laws: New insights based on diopside

The interfacial zone between a bulk fluid and a mineral surface is where all exchange of matter and energy occurs during chemical weathering. However, our knowledge is still limited with respect to understanding where and how the rate-determining dissolution reactions take place. A complicating factor is the commonplace formation of amorphous Si-rich surface layers (ASSLs), which may hinder contact between the fluid and the mineral surface. To address the role of ASSL, we investigated the dissolution of a common silicate (diopside), and related the bulk dissolution rate with the nanoscale dissolution rate and surface chemistry of its individual prevalent faces. While ASSL were evidenced on all of the investigated faces, only those formed on (110) and (11¯0) were passivating, thereby controlling the reactivity of the underlying faces. The (110) and (11¯0) faces intersect the highest density of Mg–O–Si and Fe–O–Si bonds, and this specificity may explain the passivating behavior of the corresponding ASSL. Moreover, we evidenced an inverse relation between aqueous silica concentration and the bulk dissolution rate of crushed diopside grains, which suggest that the (110) and (11¯0) faces are predominant in a powder. By considering ASSL as a separate phase that can control silicate dissolution rates, extrapolated laboratory-based rates at conditions relevant to the field can be lowered by up to several orders of magnitude, thereby decreasing the large gap between laboratory and natural rates. This has important implications for more accurately modeling chemical weathering reactions, so important today for the C cycle and CO2 sequestration.

Conversion of grassland to coniferous woodland has limited effects on soil nitrogen cycle processes

In the last century, conversion of native North American grasslands to Juniperus virginiana forests or woodlands has dramatically altered ecosystem structure and significantly increased ecosystem carbon (C) stocks. We compared soils under recently established J. virginiana forests and adjacent native C 4-dominated grassland to assess changes in potential soil nitrogen (N) transformations and plant available N. Over a 2-year period, concentrations of extractable inorganic N were measured in soils from forest and grassland sites. Potential gross N ammonification, nitrification, and consumption rates were determined using 15N isotope-dilution under laboratory conditions, controlling for soil temperature and moisture content. Potential nitrification rates ( V max) and microbial biomass, as well as soil physical and chemical properties were also assessed. Extractable NH 4 + concentrations were significantly greater in grassland soils across the study period ( P ≤ 0.01), but analysis by date indicated that differences in extractable inorganic N occurred more frequently in fall and winter, when grasses were senescent but J. virginiana was still active. Laboratory-based rates of gross N mineralization (ammonification) and nitrification were greater in grassland soils ( P ≤ 0.05), but only on one of four dates. Potential nitrification rates ( V max) were an order of magnitude greater than gross nitrification rates in both ecosystems, suggesting that nitrification is highly constrained by NH 4 + availability. Differences in plant uptake of N, C inputs, and soil microclimate as forests replace grasslands may influence plant available N in the field, as evidenced by seasonal differences in soil extractable NH 4 +, and total soil C and N accumulation. However, we found few differences in potential soil N transformations under laboratory conditions, suggesting that this grassland-to-forest conversion caused little change in mineralizable organic N pools or potential microbial activity.

Changes in sediment characteristics following drawdown of Big Muskego Lake, Wisconsin

Changes in surficial sediment physical and chemical composition and internal P loadings due to lake drawdown and refill to promote macrophyte growth in shallow Big Muskego Lake, Wisconsin were examined. Thirteen percent of the sediment area was exposed for ∼1 year, while over 80% of the sediment area was exposed for a period of 6 months. Mean sediment (upper 10 cm) moisture content and organic matter content decreased (92 % to 86 % and 45 % to 39 %, respectively), while sediment density increased from a mean of 0.078 g/mL to 0.149 g/mL due to lake drawdown, suggesting consolidation of sediment and some oxidation of organic matter in the sediment. Porewater ammonium-nitrogen and soluble reactive phosphorus, and laboratory-based rates of phosphorus release from sediment, increased substantially shortly after lake refill, but then declined 1 year later. Total phosphorus and extractable phosphorus forms of the surficial sediment declined in both concentration and mass after drawdown, which may be attributed to uptake by biota. These positive (i.e., sediment consolidation) and negative (i.e., sediment nutrient release) impacts of drawdown on sediment dynamics need to be considered in shallow lake rehabilitation programs.

DISTRIBUTION OF SEDIMENT PHOSPHORUS POOLS AND FLUXES IN RELATION TO ALUM TREATMENT

ABSTRACT: The distribution of sediment physical characteristics, sediment phosphorus (P) pools, and laboratory-based rates of P release from the sediments were used to identify regions and dosage for alum treatment in Wind Lake, Wisconsin. Using variations in sediment moisture content, we identified an erosional zone at depths < 1.4 m and an accumulation zone at depths > 2.6 m. Mean concentrations of porewater P, loosely-bound P, iron- and aluminum-bound P, and mean rates of P release from sediments under anoxic conditions were high in the accumulation zone compared to sediment P characteristics in the erosional zone, indicating focusing of readily mobilized sediment P pools from shallow regions and accumulation to deep regions. We determined that a future alum treatment for control of internal P loading would be most effective at depths > 2.6 in the accumulation zone. The mean rate of anoxic P release from sediments encountered in the accumulation zone (8.3 mg m-2 d-1) was used in conjunction with a summer anoxic period of 122 d, and a treatment area of 1.6 km2 to estimate an internal P load of 1,600 kg to be controlled. Our results suggest that an understanding of the distribution of sediment P pools and P fluxes in lakes provides a strategy for estimating alum dosage and application areas.