Laboratory determinations Of the permeabilities, porosities, and residual water saturation of rocks of oil-and gas-bearing areas are usually based on data obtained under atmospheric conditions.Investigations [1][2][3][4] have shown that the reservoir properties of deeply buried rocks differ markedly from those of the same rocks under atmospheric conditions. These differences are due to the physical conditions under which the values are determined. Owing to the natural differences between the rocks which act as reservoirs, we cannot use the experimental data obtained for individual specimens to assess the same characteristics of rocks from other oil-and gas-bearing areas. The great variety displayed by reservoir rocks is governed by the depth of occurrence, the chemical composition of the minerals, their grading, roundness, grain-size composition, the amount and quality of the cementing substance, the ratio of plastic and elastic minerals, the packing of the mineral grains, etc.The filtration characteristics of rocks depend on their depth of occurrence (on pressure and temperature, which cause deformation of the porous medium). To study the effects of pressure and temperature on the filtration characteristics of rocks, the Laboratory of Seam Physics of SNIIGGiMS designed an apparatus [5] enabling us to simulate a whole group of physical conditions, the specimen being tested under the natural conditions of occurrence.Before tests on liquid permeability were performed, the pore volume of the specimen was determined under given pressure and temperature conditions. This was effected as follows. The specimen was dried at 105-110~ saturated with distilled water to constant weight under vacuum, and then placed in a core holder [5], in which its lateral surface was subjected to a hydraulic pressure of up to 1.5-2 atm by means of a thin-walled rubber jacket and oil, fed through a connecting pipe. An impermeable steel cylinder was pressed against the upper face of the specimen by a ram, and a steel cylinder with an orifice and trap with ducts for obtaining an intraporous hydrostatic pressure was pressed against the lower face. The cylinder and trap were pressed against the lower face of the specimen by a nut and a movable punch. The specimen was heated to the given temperature, at which it was maintained automatically. During this process the water expands and collects on the bottom of the trap. The volume of water due to thermal expansion is determined from the formula = (P0 -do Vo) / a0, where W 0 is the volume of water obtained from the specimen due to thermal expansion and reduced to 20~ P0 is the weight of water completely saturating the specimen at 20~ v 0 is the pore volume of the specimen at 20~ 0 is the temperature in degrees, d o is the specific gravity of distilled water at 0, and d o is the specific gravity of water at 20~ Thermal expansion of the grains was neglected (to the best of my knowledge, no investigations are being performed on the temperature dependence of rock porosity in absence of external pressur...
The coefficients of compressibility of the pore spaces of reservoir rocks are important in calculations of the optimum modes of working deposits of mineral fuels.They are usually measured under static loads and estimated by means of the quantity of liquid displaced by compression from water-saturated specimens [i]. It is also well-known that the compressibilities of porous media can be determined by means of the elastic wave propagation velocityHitherto, laboratory measurements of the compressibility coefficient have been made separately in different laboratories, and it has not been possible to study the true relation between the velocity and compressibility and to change to the simpler longitudinal wave velocity measurements instead of compressibility measurements.The relation between the longitudinal wave velocity and the compressibility gives a physical basis for estimating the compressibilities of seams in situ by means of data from acoustic measurements from boreholes. It is therefore of interest to make combined measurements of the velocities and the static compressibility coefficients.The main difficulty in making combined measurements lies in the creation of ultrason%c transducers which can transmit axial thrust to the testspecimen. One of the transducers must also have an outlet for liquid extruded from the specimen by the pressure.Another difficulty in designing the transducers is that they must satisfy requirements of sealing and smallness (the diameter of a rock specimen for testing in a high-pressure chamber is 28 ram). Transducers for this purpose have been constructed by theauthors. This article describes them and gives some test results.The transducers were tested in a core holder which permitted uniform or heteroaxial compression [4]. Figure 1 shows the design of the proposed transducer, which has a piezoelement I in the form of a disk of TsTS-19 piezoceramic (disk diameter 22 ~ml, thickness 2'n~n, working frequency of order 500 kHz).The piezoelement is placed in a steel housing 3, closed by a lid 6, which is held to the housing by two bolts 5. Steel tube Ii (internal diameter i mm) is the outlet for extruded liquid and is soldered through the base of housing 3. In circular disk i is drilled a hole so that it can be positioned on the polished surface of the bottom of the housing.For insulation purposes, a PVC sleeve 12 is slipped onto tube ii. On the top of the piezoelement is laid a brass disk 2 with a hole for tube II. To disk 2 is soldered one end of insulated lead 4, with screen 8 soldered to the lid 6. The screened lead has external PVC insulation i0. The piezoelement disk and the brass disk are pressed together by an insulating cover of textolite (resin-impregnated cloth) 14. Spring 13 improves the contact between piezoelement i and the bottom of housing 3 and improves the useful transfer of elastic energy from the specimen.To the end of steel tube i is joined a glass measuring capillary to measure the volume of water extruded from the specimen by nonuniform or uniform pressure.For sealing...
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