Block Volume Research Articles

Block and graft polymerization Volume 1. Edited by R. J. Ceresa. John Wiley. 1973. pp. 371. Price: £10·00

Block and graft polymerization Volume 1. Edited by R. J. Ceresa. John Wiley. 1973. pp. 371. Price: £10·00

Determining the Elementary Matrix Block In a Fissured Reservoir Eschau Field, France

The fracturing of a reservoir is not a random phenomenon; it appears that the rock splits up into regular blocks bounded by networks of parallel fissures. A method is described for combining information parallel fissures. A method is described for combining information deduced from cores and outcrops to obtain a statistical distribution of fracture characteristics. From this we deduce the orientation, the dimensions, and the volume of the average block. Introduction In a fractured reservoir, recovery ratio and methods of calculating it are closely connected to the volume and size of the matrix blocks. The reason is that the volume and size of the block influence the way hydrocarbons escape from the rock matrix as the reservoir is depleted. This observation is valid for any depletion process, whether it be imbibition, solution gas drive, or gravity drainage. Furthermore, the orientation of blocks (which is derived from the orientation of bounding fractures) will greatly influence the flow of fluid toward the wellbore, and consequently will directly affect the location of production wells and the choice of recovery process, production wells and the choice of recovery process, both of which, in part, determine the recovery ratio. Various numerical simulation models have been designed to calculate future production, based on assumptions involving drainage mechanisms; basic to the functioning of the model are data on the characteristics of the matrix block. It would be highly desirable, then, to be able to gather data on the volume, size, and orientation of the matrix block for each well in a field. Such a goal can be achieved through production geology, because rock fracturing is not a random phenomenon, but takes place mainly under the effect phenomenon, but takes place mainly under the effect of tectonic stresses that accumulated with the rock mass during the geological history of the formation. In a study of the Laurel Gas Storage (Hocking County, Ohio), the U. S. Bureau of Mines noted that fracture orientation measured at an outcrop was similar to fracture orientation determined from oriented cores (taken at a depth of approximately 2,460 ft), and that hydraulic fracturing induced in an unfractured reservoir sample leads to a fracture orientation conditioned by the stresses that currently exist. The orientation of the induced fractures is superimposed upon that of the existing fractures. V.N.I.G.R.I. Institute of Leningrad (USSR) published similar observations based on data gathered published similar observations based on data gathered in the field from outcrops as well as on data derived from cores. From measurements of outcrops, the geologist can arrive at basic laws relating to the orientation and magnitude of fracture networks at major structural features, as both depend essentially upon tectonic stresses. The theories that now exist are general; and the laws behind them are only partly known; the theories may in some cases be used to classify into families all of the fractures encountered in cores, even if the outcrop corresponding to the subsurface structure being studied is actually missing. Subsurface observations made within a reservoir can thus be explained, and characteristics of the elementary matrix block can be determined. The aim of this study is to show, with a concrete example, the steps to take in determining the elementary, matrix block. The example is an application of a general method to a particular case. JPT P. 523

Geosynclinal Compositions and the New Global Tectonics

ABSTRACT The lithological composition of several geosynclinal sequences estimated from published measured sections in the Appalachian and Cordilleran belts shows that sedimentary rock type is not a diagnostic attribute of geosynclinal assemblages. However, though no sedimentary rock types are excluded from geosynclinal assemblages, some are generally rare (evaporite), others are particularly common in either the miogeosyncline (carbonate) or eugeosyncline (graywacke), and still others are common throughout (shale). The chemical composition of individual sequences, estimated using analyses of specific stratigraphic units and average compositions for major sedimentary and volcanic rock types reveals chemical contrasts between miogeosynclinal and eugeosynclinal assemblages, and between ancient geosynclinal assemblages and the sedimentary successions which have accumulated in the deep ocean basins and along the present-day continental margins. Miogeosynclinal and eugeosynclinal assemblages differ chemically because of the respective predominance of carbonate and volcanic rocks; both contain chemically similar, highly siliceous clastics. If miogeosynclines and eugeosynclines are the respective ancient analogues of present-day continental shelf and rise areas, their contrasting compositions may reflect long-term secular changes in the mode and locus of sedimentation as a result of organic evolution and changes in the relief, volume, and location of continental blocks, ocean basins, and plate margins during and since the Paleozoic.

Numerical Coning Applications

Abstract An analysis of water or gas coning behaviour is particularly important in determining the future performance of gas reservoirs and thick oil reservoirs of the Rainbow-Zama- Virgo types. Investigations of coning in these reservoirs have only recently become practical. This paper describes results from two numerical coning studies - one a gas-water problem, the other a three-phase problem in a Virgo reef. The implicit numerical model used is described in detail. INTRODUCTION THE CONTROL OF GAS AND WATER CONING in petroleum reservoirs is essential in optimizing recovery and minimizing operational costs. Coning is the result of high-pressure gradients around the producing well which cause the oil-water contact to rise and the gasoil contact to depress near the wellbore. Gravitational forces tend to segregate the fluids according to their densities. However, when gravitational forces are exceeded by the flowing pressure, a cone of water and/ or gas will penetrate the producing interval. Only recently has it become practical to investigate coning as a non-steady-state flow phenomenon with heterogeneous reservoir properties. These investigations are now practical utilizing numerical coning models. Coning is simulated with a 2D radial (R – Z) grid system extending out from the wellbore to some external radius (Re). To obtain proper definition of the gas and water cones, a fine grid is used near the wellbore. The pore volumes of these interior grid blocks are typically 1 to 10 barrels, At a normal producing rate and with a reasonable time-step size, the fluid throughput per time step of the inner blocks is many times the pore volume of the blocks. This high throughput causes large saturation changes per time step and, in the past, these large saturation changes have caused model instabilities. Normally, in a reservoir simulator the transmissibilities governing flow between blocks and the production rates of oil, gas and water are calculated explicitly using the saturation conditions existing at the beginning of the time step. If explicit transmissibilities and production terms are used in a coning model, a practical time-step size will cause the predicted saturations to become unstable and the GOR's and WOR's to oscillate, These instabilities can be controlled by treating the transmissibilities and production terms implicitly rather than excplicity. The computation required per time step increases with a totally implicit model, but the resulting increase in the time-step size which can be taken more than offsets the greater computation requirements. The net result is a numerical model which can be used routinely, at low cost, on practical problems. The Appendix describes in detail the mathematics of this coning model. The following section describes two coning studies. The first case is a gas pool with an underlying aquifer. The second is a single-well bioherm reef being produced under primary depletion. Initially, it is without a gas cap, but it does have a small underlying aq Uifer, Both studies used a fully compressible threephase 2D radial model.

Photoelasticity technique of analyzing heat-induced strain in concrete blocks used in hydraulic constructions

1. The effect of transverse crowding on the solution has been evaluated with the photoelasticity technique, for the two-dimensional problem of a block cooling (or heated) on a flat foundation. The error in the contact zone does not exceed 9–15%, respectively, for the elastic and perfectly rigid foundation. 2. Lateral surfaces of the heated blocks show tensile stresses of about\(0.5\tfrac{{E\alpha {\rm T}}}{{1 - \mu }}\), which may lead, in some instances, to an opening of the horizontal structural joints (sutures) or to the appearance of horizontal fractures. 3. A. correlation of stresses in a volume block with a square base with those in the corresponding block in plane deformation shows a fairly similar stress distribution in both. Strain components σx, σy, and τxy in the volume block are, respectively, 0.6–0.7, 0.5–0.6, and 0.30–0.35 of those for block in plane deformation. These figures, in conjunction with the available theoretical or experimental solutions for the plane problem, make it possible to evaluate approximately the effect of block volume on the magnitude of strain.