In this paper, a calculation method of pressure loss in mist flow region has been developed and included in the wellbore flow simulator WELCARD-IV. This simulator is a modified version of WELCARD-III and applicable up to mist flow in geothermal wells. The validation of the simulator using measured data of nine wells in the Kakkonda and the Mori geothermal fields has been verified. The results are as follows: 1) When the steam quality is above 0.145, the fluid flow in the geothermal wells transforms from annular-mist flow to mist flow. In the strict sense, the mist flow in this paper is defined as the broken liquid film annular flow. 2) In the mist flow regime, the friction loss between the flowing fluid and the wall of the geothermal well is estimated accurately by the following formula. ΔPf=4τw/D(1-w)dl Where p Pf is the friction loss, τw is the shear stress, D is the well diameter and dl is the length of element. Parameter w is defined as a function of void ratio α as follows: w=0 at α<0.9 w=(10α -9)2 (21-20α) at α≥0.9 3) The average density of two-phase (steam and hot water) fluid(ρm) calculated by the following formula estimates the head loss accurately. ρm=[1+(1/χ-1)e]/[1/ρg+(1/χ-1)/ρL e]Where χ is the quality, ρ is the density and subscripts g and L show gaseous and liquid phases, respectively. Parameter e is defined as ratio of the mass of liquid phase flowing in the homogeneous mixture to the total mass of water flowing in the annular flow regime and given to be 0.9 in the mist flow regime. 4) A comparison between computational results using WELCARD-IV and the measured values of borehole temperature and pressure during production in the Kakkonda and the Mori geothermal fields was carried out, and the computational error was within 5%.
Gases of fluid inclusions in quartz and anhydrite from the Kakkonda geothermal system, , northeast Japan, were analyzed with a quadrupole mass spectrometer and a capacitance manometer. The quartz and anhydrite were collected from an outcrop and geothermal wells drilled in the shallow geothermal reservoir. Results of individual fluid inclusion analyses show that the fluid inclusions comprise mainly H2O and a small amount of CO2. The gases of N2, CH4 and Ar were not detected. Results of bulk analyses show that fluid inclusions from the outcrop and upper levels of the shallow reservoir are mainly composed of H2O(99.8 -100mol% )with very small amounts of CO2, N2 and CH4. Ar is just above the detection limit of the analytical system. The gas contents of the fluid inclusions are very low, compared with those from other geothermal systems which the authors have analyzed. CO2/N2 and CO2/CH4 ratios of fluid inclusions are relatively low, compared to those of the present-day discharge fluids of the Kakkonda geothermal system. These ratios of residual fluids increase with progressive degassing, and the difference in the CO2/N2 and CO2/CH4 ratios between the fluid inclusions and the present-day discharge fluids in the area may be ascribed to the degree of degassing. Individual inclusion analyses show that gas-rich inclusions occur at deeper levels. This suggests that fluid inclusions at deeper levels were formed from gas-rich fluids which were not undergone by dilution of meteoric water.
Alteration minerals of cores from six exploration wells are identified by X-ray diffraction, thin section and SEM observations. Five alteration zones, montmorillonite-mordenite, chlorite-laumontite, chlorite-wairakite, sericite and epidote-amphibole, were identified. Three different alteration processes were identified from the distribution pattern of such alteration zones. One is simple heating by one thermal event at present. Second is same procedure but heating event was past and now in cooling stage. Final is the overlap of past alteration and present one. Chemical analyses of major elements of whole rock samples show that the zone of hot water circulation is characterlized by big chemical change and such circulation zones moving from deep to shallow. Amphibole group which has been thought as metamorphic mineral is partly assigned as geothermal products by occurrence, chemistry and thin section and SEM observations. Mineral names for both metamorphic and geothermal amphibole are tremolite-actinolite, hornblende and edennite-ferroednite. They reflect alteration conditions and must be treated more carefully. Combination of alteration mineral and chemical study give us a good way for identifying the thermal history and present reservoir estimation.
Numerical simulations of acoustic logging were performed to infer apertures of two parallel fractures, intersecting well GF -2. The estimation is made by comparison between the results of a full waveform acoustic log and computer simulations. The simulation models are constructed based upon the results of acoustic, BHTV and other logging data. Equations of wave propagation are solved using the staggered grid finite-difference method. The best agreement between the measurements and simulated results is obtained with a model in which the fracture apertures are 1cm and a 1 cm-thick mud cake is present inside the borehole wall.
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