David A. Northrop

In-Situ Stresses: The Predominant Influence on Hydraulic Fracture Containment

In-situ experiments, which are accessible by mineback, have been conducted to determine the parameters that control hydraulic fracture containment. These experiments demonstrate that a stress contrast between the pay zone and a bounding layer is the most important factor controlling fracture height. Material property interfaces are shown to have little effect. 19 refs.

Polymorphism, compressibility and thermal expansion of thallous iodide

Abstract Thallous iodide (TlI) transforms from a layer orthorhombic (Cmcm) structure to a cubic CsCl-type structure with increasing temperature and/or pressure. We have studied the transition as a function of combined hydrostatic pressure and temperature. We also measured the compressibility (at 20°) and thermal expansion (at 1 bar) of both phases, as well as the latent heat of transformation. With increasing temperature at 1 bar, the transition temperature is 169±2°. The average transition temperature of the increasing and decreasing temperature cycles is 156±2°, and it decreases monotonically with increasing pressure with an initial slope of −53±3°/ kbar . At 25°, the transition to the cubic phase occurs at 4.70±0.10 kbar and the reverse transition at 1.15±0.10 kbar . The initial volume compressibility of the orthorhombic phase is (7.55 ± 0.20) × 10 −3 kbar −1 , and the compressibility of the cubic phase at 6 kbar is (5.10±0.20) × 10 −3 kbar −1 . The volume decreases 3.3 per cent at the transition. The lattice parameters of both phases increase linearly with temperature over the range covered. The mean linear coefficients of thermal expansion for the orthorhombic phase between 23 and 170° in units of 10 −6 o C −1 are: α a = 15-9±0.5, α b , = 48.7±0.3, and α c = 60.4±0.6. That of the cubic phase between 170 and 300° is α a = (51.0±0.3) × 10 −6 o C −1 . The measured latent heat is 293±38 cal / gm mole where 321 cal/gm mole is calculated from the Clapeyron equation. The structural and thermodynamic aspects of the transformation are discussed.

Carbon-Felt, Carbon-Matrix Composites: Dependence of Thermal and Mechanical Properties on Fiber Precursor and Matrix Structure

Properties of carbon-felt, pyrolytic carbon-matrix composites have been measured as a function of fiber precursor [rayon and polyacrylonitrile (PAN)] and matrix microstructure (smooth laminar, rough laminar, and isotropic). The primary matrix effect is caused by the graphitic nature of the heat-treated rough laminar matrix which yields a high composite thermal conductivity. The increased modulus of the PAN-based fibers results in increased composite strength and modulus and a significantly reduced thermal expansion. A heat-treated, PAN-based carbon felt, rough laminar carbon matrix composite has a superior thermal shock figure-of-merit based on these results.

Vaporization associated with surface electrical switching in semiconducting AsTeI and AsTeGe glasses

Abstract Vapor species resulting from electrically-induced threshold switching and memory filament formation on the surfaces of bulk AsTeI and AsTeGe glasses are identified. The common parent species are As 4 (most intense) and Te 2 . The results emphasize the importance of thermal mechanisms, and yield information concerning the kinetics of filament formation.

Results of the multiwell experiment in situ stresses, natural fractures, and other geological controls on reservoirs

Hundreds of millions of cubic meters of natural gas are locked up in low-permeability, natural gas reservoirs. The Multiwell Experiment (MWX) was designed to characterize such reservoirs, typical of much of the western United States, and to assess and develop a technology for the production of this unconventional resource. Flow-rate tests of the MWX reservoirs indicate a system permeability that is several orders of magnitude higher than laboratory permeability measurements made on matrix-rock sandstones. This enhanced permeability is caused by natural fractures. The single set of fractures present in the reservoirs provides a significant permeability anisotropy that is aligned with the maximum in situ horizontal stress. Hydraulic fractures therefore form parallel to the natural fractures and are consequently an inefficient mechanism for stimulation. Successful stimulation may be possible by perturbing the local stress field with a large hydraulic fracture in one well so that a second hydraulic fracture in an offset well propagates transverse to the natural fracture permeability trend.

Vaporization of arsenic telluride

Abstract The overall vaporization reaction and sublimation pressures have been determined for As2Te3. As2Te3 dissociates completely upon vaporization yielding As4(g) and Te(s). The tellurium vapor pressure is approximately a tenth of the As4(g) pressure in the 294–353°C range and thus both As4 and Te2 are present in the equilibrium vapor over Te-saturated As2Te3. The results believed closest to equilibrium yield a partial pressure for As4(g) given by: log P(atm) = (7.63 ± 0.15) – (7.59 ± 0.09) ( 1000 T ) and an enthalpy of vaporization of 34.7 ± 0.4 kcal/mole.

Current Status of the Multiwell Experiment

The Multi-Well Experiment (MWX) is a research oriented field laboratory whose objective is to develop the understanding and technology to allow economic production of the several years supply of natural gas estimated to be within the low permeability, lenticular gas sands of the Western United States. Features of MWX include: (1) three closely-spaced wells (115-215 ft, 35-66 m) for reservoir characterization, interference testing, well-to-well geophysical profiling, and placement of diagnostic instrumentation adjacent to the fracture treatment; (2) complete core taken through the formations of interest; (3) a comprehensive core analysis program; (4) an extensive logging program with conventional and experimental logs; (5) determination of in situ stresses in sands and bounding shales; (6) use of various seismic surveys and sedimentological analyses to determine lens morphology and extent; (7) use of seismic, electrical potential, and tilt diagnostic techniques for hydraulic fracture characterization; and (8) a series of stimulation experiments to address key questions. This paper presents the current MWX accomplishments resulting from the 1983 field season which featured the drilling of a third well and the first stimulation experiment.

Interpretation Of Chemical And Physical Measurements From An In Situ Coal Gasification Experiment

A second underground coal gasification experiment is being conducted at the Laramie Energy Research Centers field site near Hanna, Wyoming. The results are presented from the first phase of this Hanna II experiment in which coal seam premeability was evaluated, pneumatic linking and linking via reverse combustion were studied, and a sustained gasification process was maintained between the two linked vertical wells. Extensive in-situ and surface process instrumentation have provided considerable information on the chemical and physical mechanisms involved in underground coal gasification. Air injection alone did not increase permeability to levels that would allow sustained gasification. Reverse combustion linking was determined to be a local, relatively low-temperature process that advanced at a 5 ft/day rate and produced a high permeability carbonized path. Subsequent gasification was completed over a 38-day period. Overall, injection of 1.9 mm scf/day of air yielded 2.7 mm scf/day of gas with a heating value of 152 Btu/scf. Material balance calculations indicate that 1688 tons of coal in place were utilized. Specific discussion of reaction front configurations and interpretation of in-situ thermometry are included. (auth)

In-Situ Testing of Well-Shooting Concepts: ABSTRACT

The creation of multiple fractures from a wellbore has been demonstrated for a high-energy gas fracturing concept. In this concept, the gas pressure pulse due to the deflagration of a propellant is designed to give (1) pressure-loading rates sufficient to initiate multiple fractures, (2) peak pressures below the flow stress of the formation to avoid rock compaction, and (3) a duration of burn sufficient to allow gas penetration and extension of the fractures. Three experiments were conducted adjacent to a mine drift and the results were observed directly by mineback through the experimental areas. Tests with three different propellants to give different burning rates and, hence, different pressure loadings and pulses resulted in phenomenologically different behavior. Mine ack of the intermediate test (pressure loading rate of 20 psi (138 kPa)/msec, peak pressures of 13,800 psi (95,151 kPa), and burn time of 9.0 msec) indicated 12 separate fractures from 0.5 to 8.0 ft (0.15 to 2.4 m) long for the 20-lb (9 kg) propellant charge. Tests with a faster and slower burning propellant yielded only single fractures less than 5 ft (1.5 m) long and features normally associated with explosive and hydraulic fracturing, respectively. Multiple fracturing alleviates many of the postulated limitations of explosive and hydraulic fracturing techniques for the effective stimulation of Devonian shales. An expected test series is being conducted as part of the Eastern Gas Shales Program to examine several techniques for multiple fracturing based on this controlled-pressure-loading concept. Test results will be evaluated with respect to the application of such techniques for formation evaluation and stimulation of that resource. End_of_Article - Last_Page 1587------------