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Grain size effects have been investigated in the lubricated sliding wear of three transparent magnesium aluminate (MgAl 2 O 4 ) spinel materials with different grains sizes identified as: Nano, Fine, and Coarse. Only Fine spinel shows classical wear behavior, which is characterized by initial mild wear followed by a sharp transition to severe fracture-controlled wear. Worn surfaces of Fine spinel show extensive grain pullout, consistent with intergranular mode of fracture found in that spinel. Nano and Coarse spinels both show gradual transition from mild wear to severe wear, and both have significantly lower overall wear rates compared to Fine spinel. Worn surfaces in both Nano and Coarse spinels show transgranular fracture and material removal, which is reminiscent of lateral-crack induced chipping. The transgranular fracture mode in Nano spinel can be attributed to stronger grain boundaries in that spinel, which could be due to the Y 2 O 3 sintering additive used for grain refinement. Whilst the large scale of the grains in Coarse spinel could be responsible for the transgranular fracture observed in that spinel.

In response to a need for improving the mechanical properties of optically transparent ceramics, the nanocomposites approach is used to strengthen transparent magnesium-aluminate spinel with Si 3 N 4 nanodispersoids. The as-processed nanocomposites are found to be >70% transparent in the critical infrared wavelength range of 3–4.5 μm. Mie scattering combined with absorption by the Si 3 N 4 nanodispersoids explains quantitatively the IR transmission behavior of these nanocomposites. The nanocomposites are also found to be transparent in the visible region. Upon heat treatment (1000 °C for 4 h in air), the optical properties of the nanocomposites remain unchanged. However, the heat treatment results in a 29% increase in the average strength, accompanied by almost doubling of the Weibull modulus, and an 85% increase in the indentation toughness. The improvements in mechanical properties after the heat treatment in these nanocomposites are explained qualitatively, based on generally accepted arguments involving surface-oxidation-induced surface compression and flaw-healing. While further work is needed to fully understand and exploit these effects, this first report on transparent nanocomposites could have broad implications for the creation of mechanically robust, transparent ceramics of the future.

Here, we show that nanostructured magnesium-aluminate spinel (MgAl2O4) with a highly uniform grain-size distribution can be fabricated using Y2O3 sintering additive for infrared (IR) window/dome applications. The average grain size of this nanostructured spinel is 345 nm, and the size of the largest grain is 970 nm. As a consequence this nanostructured spinel has high room-temperature strength (470 MPa) and reliability (Weibull modulus 6.2). It also has improved erosion resistance (sand and rain) and thermal-shock resistance. Near-theoretical in-line IR transmission is observed in this nanostructured spinel at room temperature, with an optical scatter of

The U.S. Department of Energy’s National Energy Technology Laboratory (NETL) established an Extreme Drilling Lab to engineer effective and efficient drilling technologies viable at depths greater than 20,000 feet. This paper details the challenges of ultra-deep drilling, documents reports of decreased drilling rates as a result of increasing fluid pressure and temperature, and describes NETL’s Research and Development activities. NETL is invested in laboratory-scale physical simulation. Their physical simulator will have capability of circulating drilling fluids at 30,000 psi and 480 °F around a single drill cutter. This simulator will not yet be operational by the planned conference dates; therefore, the results will be limited to identification of leading hypotheses of drilling phenomena and NETL’s test plans to validate or refute such theories. Of particular interest to the Extreme Drilling Lab’s studies are the combinatorial effects of drilling fluid pressure, drilling fluid properties, rock properties, pore pressure, and drilling parameters, such as cutter rotational speed, weight on bit, and hydraulics associated with drilling fluid introduction to the rock-cutter interface. A detailed discussion of how each variable is controlled in a laboratory setting will be part of the conference paper and presentation.

New military requirements have reinvigorated the need for transparent magnesium aluminate (MgAl2O4) spinel. Surmet has developed a process that yields high quality transparent spinel at production scale. Several issues related to the extreme requirements of processing ultrafine spinel powders are described. Transmission data is presented for a significant dataset of parts made by this process. More recently, the process has been expanded to include a capability for producing domes for the Joint Common Missile program. Domes at nominal 6” and 7” diameter have been successfully fabricated. Despite early challenges related to the forming portion of the process, a repeatable capability for these domes has been demonstrated. Several challenges remain in spinel processing in order to support additional military requirements. In particular, the strength of the material needs further improvement. Also, improvements in optical quality with regard to inclusions are needed.

Abstract The U.S. Department of Energy (DOE), National Energy Technology Laboratory has been conducting research on low permeability gas reservoirs for over 30 years. Major field experiments like the multiwell experiment and the multi-site experiment at Rifle, Colorado, have provided tremendous insight into the characterization of low permeability gas sands, the associated natural fracture network, and the implications of hydraulic fracturing. Since the early 1990's, the DOE has focused its research efforts on developing technologies and methodologies to detect and characterize natural fractures in the subsurface and on demonstrating methods for enhancing production. Several successful technology advances are expected to have significant impact on the recovery of natural gas from low permeability formations. A horizontal well recently completed at 15,000 feet in the Frontier Formation in Wyoming, in conjunction with Union Pacific Resources (UPR), initially flowed 14 MMcfd and in the first 9 months recovered 2.75 Bcf of gas. UPR has two more wells underway and plans to drill additional wells based on the success of this project. Natural fracture detection techniques have been successfully demonstrated in existing fields in the Piceance and Wind River basins. An integrated 3-D seismic and geomechanical modeling approach was demonstrated in the Piceance basin and more recently in conjunction with the horizontal well drilled by UPR/DOE. The use of 3-D seismic attributes was demonstrated in the Wind River Basin. DOE initiated several new projects to begin work in October 1999 that willdemonstrate the use of natural fracture detection technologies as an exploration tool andadvance the state-of-the-art in natural fracture detection by developing new techniques to quantify fracture properties that control the flow and transport of gas. This paper will provide a detailed discussion for the projects that have recently been completed and for the new projects along with their implications for enhancing gas production from low permeability gas reservoirs. Introduction As new discoveries from conventional supplies decline, future supplies of natural gas will increasingly have to come from low permeability (tight) reservoirs. Basins containing significant resources and reserves include the Greater Green River, Piceance, Wind River, Uinta, and Anadarko. Other basins and plays also hold large resources of gas. The 1992 National Petroleum Council's (NPC) natural gas study1 concluded that 232 Tcf could be technically recoverable from low permeability sand formations. Assuming that technology improvements continued, the NPC estimated that 349 Tcf could be produced. In their most recent study2, the NPC states that "deeper wells, deeper water and nonconventional sources will be the key to future supply." Nonconventional production in the Rocky Mountain region is projected to increase by 1 Tcf per year by 2010 and as much as 1.5 Tcf per year by 2015. Significant technology hurdles must be addressed and overcome to assure a cost-competitive supply from these sources. Gas production from low permeability formations is hindered by the formations' capability to allow gas to flow to the wellbore. Hence, economic production of natural gas can only occur where the flow path to the wellbore is enhanced. Geologic processes have created natural fractures in most formations that provide channels for gas to flow. In areas where the natural fracture network is extensive and dense, economic production can be achieved without wellbore enhancements. However, most low permeability formations require hydraulic fracturing to connect the wellbore to the formation to allow commercial production. The challenges facing industry are locating the areas of dense fracture networks and determining whether horizontal wells or vertically stimulated wells are more economical.