Mathematical programs to simulate two-phase flow in wellbores have been developed for water and/or water-carbon dioxide mixtures. “Bubble rise velocities” in the slug flow regime are estimated using three methods: Orkiszewski (1967), Nicklin et al. (1962) and a modified Nicklin method. The modified Nicklin method uses ∧= 0.1 instead of ∧= 0.2 as in the Nicklin method. A package has been developed to estimate the phase behaviors of the water-carbon dioxide system. The three methods are evaluated by comparing calculated results with measured data from a Japanese geothermal field. Good results are obtained at moderate to large production rates, however there are some differences between the predicted and actual data at low rates. The average absolute deviation of percentage errors between predicted pressure losses and the field data is 6.21, with standard deviation of 5.72, excluding the low rate cases. The simulation program can estimate the following variables: pressure, temperature, specific enthalpy, flashing point, flow regime, carbon dioxide solubility in water, and can give phase diagrams of the water-carbon dioxide system, which includes the carbon dioxide content of the water and gas phases, and the quality of the gas phase.
Hosokura Ag-Pb-Zn ore deposits consisting of fissure-filling veins of epithermal type, occur in andesitic lava and pyroclastics of the Miocene Hosokura Formation in northeastern Japan. The hydrothermal alteration is observed along the veins. Based on the mineral assemblages, the alteration around the veins is classified roughly into two zones, the potassic zone (SD, SS) and the argillic zone (M), from the vein side outwards. Characteristic minerals are K-feldspar and quartz in the former, montmorillonite and mixed layer minerals in the latter. The alteration zones are developed in brecciated zones; one along the ore vein which was originally fault breccia, while the other along the top of andesitic lava which was flow-top breccia. Width of the alteration zones is generally larger in the upper horizons wherever the permeable zones exist. It is considered that the neutral deep hot waters rise along the fracture zones (veins and fault breccia zones) and flow laterally into near-surface aquifer (flow-top breccia zones). These permeable zones changed to impermeable zones by alteration. The cap rocks are divided into the primary type and the secondary one, called the “alteration cap rock”. Based on the studies of the hydrothermal alteration in the Hosokura deposits, the alteration cap rock is interpreted as impermeable zone of near-surface aquifer sealed by alteration minerals which are precipitated by mixing of upflow of deep hot waters, and cold groundwater.
A hydraulic fracture was made in the laboratory parallel to the rift plane in a block of Inada granite. Cylindrical specimens containing a part of the fracture were then taken from the block by boring the block perpendicular to the fracture surfaces. Two kinds of the specimens were prepared, separated specimens called fracture specimen and non-separated specimens called process zone specimen, and both flow conductance and closure of the fracture were measured simultaneously under normal stress up to 25 MPa.Main results obtained in this study are summarized as follows: (1) Both the fracture closure and the flow conductance of the fracture specimen were much greater than those of the process zone specimen. (2) The fracture was dozed non-uniformly. The fracture closure of the fracture specimen increased with normal stress obeying to Goodman's empirical relation except for high levels of normal stress. (3) The flow conductance of the fracture specimen decreased with the fracture closure according to the so-called cubic law for normal stress up to 5∼7 MPa. For the process zone specimen, the cubic law did not hold for the whole range of this study. The flow conductance of the process zone specimen did not decrease appreciably when normal stress was greater than 8∼9 MPa. (4) The hydraulic initial aperture, calculated from the cubic law, of the fracture specimen increased both with the fractal dimension of the surface roughness and with the mean mechanical initial aperture. However, the hydraulic initial aperture was much smaller than the mechanical initial aperture. (5) Normal stiffness of the hydraulic fracture was not a simple function of the rms of the surface roughness. The flow conductance of both the fracture specimen and the process zone specimen increased with the slope B in the log (normal stress)-fracture closure diagram.
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