349A

resulting integrals are presented in terms of special functions. Solutions for the location of the phreatic surface and spring point are presented in parametric form. Numerical results have been evaluated for various slope angles and are plotted in dimensionless coordinate space.

916145 Adaptive error analysis in seepage problems Burkley, V J; Bruch, J C lnt J Num Meth Engng V31, N7, May 1991, P1333-1356

The application of a computationally simple error estimator (Zienkiewicz-Zhu) to an existing finite element code is demon- strated. The estimator used allows both local and total errors to be estimated. From the local estimates, mesh refinements are calculated to reach a prescribed error tolerance. These refinements are used by a mesh refiner to produce a modified mesh which lowers the overall error whilst keeping the mesh as crude as possible. Free surface flow through an earth dam with a toe drain is analysed to illustrate the benefits of this approach.

916146 Inverse approach to the construction of fracture hydrology models conditioned by geophysical data Long, J C S; Karasaki, K; Davey, A; Peterson, J; Landsfeld, M; Kemeny, J; Martel, S lnt J Rock Mech Min Sci V28, N2/3, May 1991, P121-142

Attempts to construct statistically identical models of fracture networks for fracture flow analysis are extremely difficult, as only a small percentage of visible fractures are hydrologically active and at any scale only a few fractures dominate beha- viour. An alternative approach uses a model strongly condi- tioned by geology and geophysics. Large features are identified tomographically and their hydraulic behaviour estimated using an inverse approach known as simulated annealing. It is illustrated using data for inflow into a set of boreholes in the Stripa Mine granite.

916147 Numerical simulation of solute transport in rough fractures Thompson, M E J Geophys Res V96, NB3, March 1991, P4157-4166

Two dimensional numerical simulation of flow and solute migration in a fracture with fractal surfaces is presented. Mac- roscopic transport properties of the fracture were developed from comparisons with results of numerical modelling of one dimensional advection-dispersion. Effective solute velocities and dispersivities are then developed for the fractal surfaces. Adsorption, travel distance, and channelling effects are taken into account. Results indicate that, because of effects of trans- verse and longitudinal dispersivity and diffusion, effective velocity of solute is less than that of the average fluid particle.

916148 Discrete-kernel method for simulating pumping tests in large- diameter wells Barker, J A J Hydrol N124, N1/2, April 1991, P177-183

The discrete-kernel method is a simple and popular numerical procedure for simulating pumping tests in large diameter wells. It has, however, been previously implemented using a Theis well function, which is inappropriate as this function only applies to wells of infinitesimal rather than finite diame- ter. A suitable correction using a well function for a large diameter well without storage is presented.

916149 Devonian shale gas production: mechanisms and simple models Carlson, E S; Mercer, J C J Pet Teehnol V43, N4, April 1991, P470-482

Large accumulations of gas are found in the Devonian shales of the eastern USA. The rocks are very tight and much of the gas is stored in the sorbed state. These gas reservoirs are exam- ples of the classic dual porosity, fractured reservoir models, of matrix elements and fractures. The special properties of the rock result in relatively high gas flow rates into the fracture system at low fracture pressure and vice versa. A dual porosity equation formulation of the Devonian shale reservoirs is developed. When modelling the reservoir, failing to take into account the special properties of the rock results in underesti- mation of production in the long term.

916150 Permeability estimation: the various sources and their interrelationships Ahmed, U; Crary, S F; Coates, G R J Pet Technoi V43, N5, May 1991, P578-587

Rock mass permeability may be estimated from well log analy- sis, measurements on cores, or well testing. Many comparisons have been made between permeabilities determined using these techniques. In situ environment, fluid saturation, direction of flow, and scale of measurement can all have important effects on the value of permeability obtained. Taking this into account, interrelations between permeabilities measured using the variety of commercially applied methods are reviewed. Calibration using field data is essential.

916151 Modelling water and solute transport in macroporous soil. I. Model description and sensitivity analysis Jarvis, N J; Jansson, P E; Dik, P E; Messing, I d Soil S¢i V42, N1, March 1991, P59-70

A detailed mechanistic model is presented of movement of water and transport of a nonreactive solute in a macroporous soil. It may be run in one or two domains (mobile and immo- bile water) of flow using the same hydraulic characteristics. Water and solute movement in the micropores is computed using the Richards and convection-dispersion equations, and is coupled to fluxes of water and solute in the macropores by empirical interaction terms, which are redundant in the one domain model. Numerical simulations are presented.

916152 Modelling water and solute transport in macroporous soil. II. Chloride breakthrough under non-steady flow Jarvis, N J; Bergstrom, L; Dik, P E J Soil Sci 1/42, N1, March 1991, P71-81

A model for water and solute transport through a macro- porous soil (Jarvis al, 1991) has been evaluated using column breakthrough experiments under field conditions. Macropores are seen to account for about 80% of total water flow. Diffu- sive exchange of the chloride between the two flow domains is the major factor in variability of leaching.

916153 Tidal response on the reservoir pressure at the Gullfaks oil field Furnes, G K; Kvamme, O B; Nygaard, O Pure Appl Geophys V135, N3, March 1991, P421-446

Detailed analysis of a bottom hole pressure record from the Gullfaks field in the North Sea is presented. A variability is superimposed on the large scale reservoir pressure, which can lead to misinterpretation of gradients coupled with short term

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