In order to investigate the effect of cutter shape on cutting forces and cutter strength, rock cutting tests were conducted using ceramics bits with different shapes of cutters. The results of the tests are summarized as follows:(1) A cylindrical cutter (13.3mm in diameter by 5mm thick) is most preferable in rock drilling with regard to the cutting forces (horizontal and vertical forces) and the cutter strength.(2) Si3N4 has better cutter strength than Al2O3.(3) Wear resistance of Si3N4 is higher, but its cutter strength in chipping is lower when compared to that of WC-Co. From results of the previous work (Misawa et al., 1990) and the rock cutting tests mentioned above, material of ceramics, rake angle and shape of cutter suitable for rock drilling became clear. HQ size ceramics core bits were designed based on these results, and their performance was evaluated by drilling tests. The results of the tests are as follows:(1) Bits with cutters of Si3N4 can be applied to the drilling of soft rocks.(2) Fixing method of ceramics in a bit matrix used in this study can be applied to make ceramics bits. To apply ceramics bits to harder rocks, ceramic itself must be improved concerning toughness. Furthermore, the method to fix ceramics on a bit body must be investigated widely to attain firm and inexpensive fixing of ceramics.
A method to analyze interference tests for a case of multiwell with variable flow rate using the Kalman filtering is presented. The line source solution is superposed to express the pressure change at an observation well. This solution is used as a measurement equation to form the Kalman filtering. Nonlinealities in the measurement equation with respect to the parameters to be identified are linealized according to a method developed by Sen (1984). The method is applied to analyze the results of interference tests in which pressure decline caused by producing fluid with four wells was measured at one observation well (McEdwards and Benson, 1981). In this analysis, two parameters, transmissivity and storativity, are updated at every moment when the pressure data at the observation well is obtained. Reliability of the final estimates depends on the initial values of these parameters. The reliability of the parameters, however, can be improved, by iterating whole procedure of filtering by giving the final estimates as the initial values. Thus, most probable estimates can be obtained within several iteration even if discrepancies between the initial and the true values are in the order of two to three.
It is important to know the pressure drop between an injection well and a production well in the extraction of thermal energy by forced injection of water through the artificially fractured crack in the hot rock. The pressure drops of water flowing unidirectionally through a slit packed with particles were measured with varying flow rates, diameters of packed particles and void fractions. The result indicates that the measured values of the pressure drop do not agree with the calculated values by the existing equations for the packed bed such as Ergun's equation. New empirical equations for the friction factor and the permeability in the slit packed with particles are presented.
A simple mathematical model that is a wellbore model coupled with steady radial flow in a reservoir is developed for two-phase geothermal fluid with excess enthalpy. Relative Permeabilities at wellbore feed points are applied on the model. Geothermal fluid with excess enthalpy is discharged from liquid dominated reservoir owing to the effect of relative permeabilities under some paticular conditions. Discharged vapor flowrate in case of two-phase flow in a reservoir owing to reservoir flash is sometimes less than that in case of wellbore flash. The shut-in pressure of well which discharges a geothermal fluid with excess enthalpy is much higher than that of a well which discharges a fluid with non-excess enthalpy. The result of this study shows that a deeper and larger diameter well with multi feed points proves to be a high productivity and economical well to develop the geothermal energy.
In order to study the process of solidification, remelting and melting down of the subsurface heat exchange system for the direct heat extraction from molten magma, the transient behavoir of the solidified region, which is formed around a wellbore and is accompanied by a mushy region outside, is analyzed for both the closed and open heat extraction systems. The analysis utilizes the so-called enthalpy method that is a finite difference technique developed for analyzing heat conduction in a system with phase change between solid and liquid. It was revealed that the growth of solidified region due to heat extraction almost stopped in a fairly short time period in the case of the closed system. However, in the case of the open system, the solidified region is still growing even 1200 hours after heat extraction starts. The melting down analysis revealed that the heat extraction system disappeared due to melting down within a very short time period, e.g. nearly a day for a certain kind of rock, in the case of the closed system. In the case of the open system, on the other hand, the solidified region survives nearly a month at least after a complete stoppage of heat extraction.
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