A great quantity of groundwater flows out of the Abo tunnel which passes through the high mountain areas between Gifu and Nagano Prefectures. A plan which utilizes the groundwater to melt snow on a connecting road to the tunnel is under consideration. Efficiency of the snow-melting system for road is affected by many factors such as air tempera ture, wind velocity, weather, velocity of snowfall, temperature of the groundwater, depth of the embedded pipe, diameter of the pipe, interval of the pipes, thermal properties of the pipe, flow rate of the groundwater and thermal properties of the road bed, etc. ... To obtain an optimum snow-melting system utilizing groundwater, the effects of the above factors are discussed separately and synthetically. Using the theoretical studies, a short experimental road, 22m in length and 4.5m in width, was constructed. It included the parallel-pipes system and the hairpin bend pipes system. On and around the road, many sensors were set up to measure the thermal factors for each experimental condition. Some of the important results are as follows: 1) Optimum interval was 20cm for pipe of 2.5cm in diameter embedded by 7cm in depth. 2) Flow rate of groundwater, 12°C at inlet, necessary to melt the snow is 0.45m3 hr-1 per pipe. 3) Temperature of the groundwater flowing through the pipe falls exponentially. 4) Temperature of the groundwater flowing through the embedded pipe should be maintained above 2°C at outlet to melt the snow on the road.
It is well recognized that casing cementing is the most important operation for long life geothermal production wells. However, it has been a very difficult operation to get the cement slurry to return to the surface, especially when formations have many lost circulation zones. Various methods have been developed to fill cement slurry from bottom to top of the casing strings. But still no guarantee of success can be planned prior to the operation. What often happens is the formation fractures and cement slurry is lost into open thief zones during cementing operations. Finally the top of the cement is found a few hundred meters from the surface within the annulus between the surface and inter mediate casing strings. It is not only very difficult to maintain but also dangerous to produce such a well. But if cement slurry is poured into the annulus from the surface, water will be trapped between two cement plugs and when steam production starts, water in the annulus heats up and finally collapses the casing. So some conventional top casing cementing methods have been devised. However, these methods have major disadvantages. The basic concept of this newly developed method is to remove the mud from the annulus, so that the annulus can be filled with cement without leaving water pockets. Then there will be no collapse of the casing when steam production starts. Therefore this new concept has been applied for one production well in which the primary cementing failed. The cement top depth was about 300m in the 18 5/8 in. and 13 3/8 in. casing annulus. To remove the annulus fluids, steam was circulated in the well to heat and dry the annulus. After the annulus was dried, water was circulated in the well to cool the annulus. Then cement slurry, with the specific gravity of 1.90, was pumped through the small diameter pipes and placed the annulus to the surface. This top-job operation was successfully conducted and no casing expansion nor casing collapse has occurred during extended well production. This new procedure has the following advantages compared to the conventional ones: (1). no possibility of water pockets, therefore no collapse casing, (2). even if the cement top is 300m or deeper this method is applicable, and (3). it is possible to fill the annulus with high density cement slurry which strengthens both yield strength of the cement sheath and bonding strength between the cement sheath and casing. A patent has been applied for relating to this method.
Distributed Temperature Sensor features measurement and recording of multipoint temperature with a single line of optical fiber. This sytem is applied to measure surface temperature on the snow melting road by flowing water through the underground embedded pipes. Surface temperature over the embedded pipes decreases with the temperature decrease of water in the pipe. However, the surface temperature of the road is affected by the distribution of the embedded pipes, the direction of water flow through pipes and the structure of the road. The surface temperature tends to decrease at the edge of the road, therefore, the temperature values show periodic variation with 9m period which is the double of road width.
The pressure drop through model fractures with cylindrical contact areas has been studied experimentally. The model fractures are made of two parallel acrylic plates whose dimensions are 2m (length)×0.44m (width), and the created aperture has a dimension of 2mm, which is common to all model fractures. In the mid portion of the opening space (0.8m in length), the cylindrical obstacles, whose diameters are 120mm, 40mm and 20mm, are glued between the acrylic plates. The water is pumped up from the reservoir and led to one end of the model fracture. The pressure drops along the flow direction are monitored. The nature of water flow in the model fracture, for example laminar or turbulent, is also determined by using the streakline visualization technique and the laser Doppler velocity meter. Experimental results show that the line of friction coefficient A plotted vs. Re, is parallel to 96/Re for Re<100, but deviates from this line for Re>600. This means that the shear stress of the parallel plate walls governs the phenomena at low velocities. In other word Darcy's law is a good approxima tion model for predicting the pressure drop of model fractures at low velocities if the aperture depth is replaced by a hydraulic mean depth. In contrast at high velocities, the drag force of cylinders becomes strong, and the pressure drop is controlled mainly by the force. The pressure drop predicted by the presented model which is expressed by the combination of the shear stress and the drag force, agrees well with the experimental data over all Re region.