Toshihiro Uchida

Genesis of the plutonic-hydrothermal system around quaternary granite in the kakkonda geothermal system, Japan

The Kakkonda plutonic-hydrothermal system has as its heat source the Quaternary Kakkonda granite. The Kakkonda granite has a thick (∼1.3 km) contact-metamorphic zone, known mainly from the geothermal survey well WD-1a (total depth: 3729 m) drilled by the New Energy and Industrial Technology Development Organization (NEDO). The Kakkonda granite is a stock several tens of square kilometers in area with an upper contact about 1.5–3 km deep. It is a composite pluton varying from tonalite to granite. The early-stage granitic rocks are slightly metamorphosed to biotite grade by late-stage granitic rocks. K-Ar ages of separated minerals from the granitic rocks in both stages show the same cooling ages of 0.24–0.11 Ma for hornblende, 0.21–0.02 Ma for biotite, and 0.14–0.01 Ma for potassium feldspar. These are the youngest ages for granite in the world. The K-Ar ages become almost zero at ∼580°C for biotite and potassium feldspar, and at ∼350°C for illite. The Kakkonda granite intruded into a regional stress field in which the minimum principal stress was ENE–WSW and nearly horizontal. The regional stress field coincides with that of a previously recognized F2 fracture system before ∼0.4–0.3 Ma. Both stages of the Kakkonda granite and the contact aureole are fractured by recent tectonism, resulting in a zone of hydrothermal convection from about 2.5–3.1 km depth up to the surface. The boundary between the zone of hydrothermal convection and the underlying zone of heat conduction occurs ∼250–550 m below the upper contact of the Kakkonda granite, and has a temperature of ∼380–400°C.

Deep geothermal resources survey program: igneous, metamorphic and hydrothermal processes in a well encountering 500°C at 3729 m depth, kakkonda, japan

Abstract The exploration well WD-1a was drilled to a depth of 3729 m in the Kakkonda geothermal field, northeast Japan, using efficient borehole cooling techniques. The well penetrated an entire shallow hydrothermal convection zone, an entire contact metamorphic aureole and part of a neo-granitic pluton. The recovered temperature of the well indicates a boiling point-controlled profile up to 380°C to a depth of 3100 m, and a conduction-controlled profile with a very high gradient from 3100 m to the bottom of the hole, where the temperature is 500°C. WD-1a may be the first geothermal well that encountered 500°C, which exceeds the conventional hydrostatic boiling-point curve. An inflection point of the temperature–depth profile at 3100 m and about 380°C reflects the brittle–plastic boundary. The brittle–plastic boundary constrains the maximum depth of fracture formation, and the fracture distribution constrains the maximum depth of hydrothermal convection.

High-temperature measurements in well WD-1A and the thermal structure of the kakkonda geothermal system, Japan

Abstract The New Energy and Industrial Technology Development Organization (NEDO) drilled well WD-1a between 1994 and 1995 in the Kakkonda geothermal field as part of their Deep Seated Geothermal Resources Survey project. High-temperature measurements were carried out in WD-1a. Logging temperatures above 414°C were confirmed at 3600 m and 3690 m depth after 82 h standing time. Simple Horner extrapolations based on observed temperatures up to 82 h after shut-in suggested a temperature of about 500°C at 3500 m depth. Temperatures between 500°C and 510°C were also confirmed at 3720 m depth after 129–159 h standing time, using calibrated melting .tablets. These are the highest temperatures measured in a geothermal well. These results suggest a thermal structure consisting of three layers. Layer one is a shallow permeable zone of the reservoir, at less than 1500 m depth, at 230°C to 260°C. The second layer is a deep zone of the reservoir, which is less permeable and has a temperature of 350°C to 360°C from 1500 m to about 3100 m depth. The third layer is a zone of heat conduction. The transition between the hydrothermal-convection zone and the deeper heat-conduction zone is at 3100 m depth in well WD-1a.

Drilling procedures, techniques and test results for a 3.7 km deep, 500°C exploration well, kakkonda, japan

Abstract The Japanese government-funded geothermal exploration well WD-1A reached a depth of 3729 m in a Quaternary granite, where the bottom-hole static temperature is more than 500°C. This is the highest-temperature formation ever drilled at this depth in the world. A newly developed method was used to cool the sophisticated drilling tools while running them into the hole. A detailed borehole dynamic temperature experiment produced data useful for practical drilling operations. Drill-bit seal conditions were also inspected after use. A total of 14 cores, as well as a fluid sample from the bottom of the well, were taken for scientific investigations.

The origin of hypersaline liquid in the Quaternary Kakkonda granite, sampled from well WD-1A, Kakkonda geothermal system, Japan

Abstract Hypersaline metal-rich liquid (ca. 40 wt% total chloride species) was obtained from a depth of 3708 m in the Kakkonda geothermal system. Sampling of well WD-1a was conducted by reverse circulation after a standing time of about 196 hours (with temperature recovering to >500°C). Tritium content and the relationship between δD and δ18O showed that the river water that was circulated in the well had mixed with an isotopically heavy fluid during the standing time. Phase separation occurred during temperature recovery, concentrating the hypersaline liquid in the bottom of the well. This original hypersaline liquid has a salinity of about 55 wt% NaCl eq., consisting of Na–Fe–K–Mn–Ca chloride, rich in Zn and Pb but poor in Cu, Au and Ag. The fluid originates from the Kakkonda granite and mixed with circulating water from the well in a zone of fine fractures induced by thermal stress during drilling.

Fracture systematics in and around well WD-1, Kakkonda geothermal field, Japan

Abstract Interpretation of FMI (Schlumbergers Fullbore Formation MicroImager) logs from well WD-1 and observation of spot cores from well WD-1 in the Kakkonda geothermal field have provided important clues about the nature and configuration of the fracture networks controlling circulation of high-temperature hydrothermal fluid. The fractures comprise four groups: (1) fractures striking NW, (2) high-angle fractures striking NE to E, (3) low-angle fractures striking N, and (4) low-angle fractures striking E. Most permeable fractures in the shallow (

Seismic reflection and VSP in the Kakkonda geothermal field, Japan : Fractured reservoir characterization

A seismic reflection survey and a VSP (vertical seismic profiling) survey were conducted to obtain insight into the detailed characteristics of the fractured reservoir in the Kakkonda geothermal field, Japan. The geothermal reservoirs in this field are located in fractured Tertiary formations and a pre-Tertiary formation in contact with a younger Quaternary pluton. The seismic survey technique with a very long off-set distance proved to be effective at clearly imaging deeper reflective events that correlate with the top of the deep pre-Tertiary basement. Attenuation of the seismic signal (a very weakly reflective or dim zone) has been found to be much greater in areas where major geothermal reservoirs have been identified. The weakly reflective zone also corresponds to the concentration of microearthquake hypocenters. We suggest that such weakly reflective zones on the seismic reflection section may be favorable drilling targets. By combining the results of microeathquake monitoring (rate of occurrence, magnitude) with further case studies of seismic reflection data of different fractured reservoirs, such a hypothesis can be tested. The comprehensive seismic technique promises valuable insights into deep structures and fractured reservoirs for geothermal exploration.

Synthetic fluid inclusion logging to measure temperatures and sample fluids in the Kakkonda geothermal field, Japan

Synthetic fluid inclusion logging is a new tool to measure temperatures and sample fluids in high-temperature geothermal wells. Fluid in the microcracks of a crystal can be trapped in inclusions through healing. Fluid inclusions in quartz, for example, can be synthesized easily in geothermal boreholes and can be used as long as the host crystal is stable (e.g. α-quartz is stable up to 573°C). This technique can be applied to high-temperature geothermal wells where conventional temperature measurement methods are not feasible. Cracked crystals of quartz, soaked in silica-saturated solutions in gold or platinum capsules mounted on containers, are placed in a geothermal borehole. Geothermal fluid enters the microcracks in the crystals at the selected sampling depths, and inclusions containing ambient fluid are formed through crack healing. Trapping temperatures of fluid inclusions in quartz are determined by microthermometry using a heating stage with pressure corrections. Other cracked crystals mounted in containers with rupture disks are used for fluid sampling. The first borehole experiment was conducted at WD-1, a deep research hole drilled in the Kakkonda geothermal field, northeast Japan, from September to October 1994 (24 days). Results from the experiment confirmed that temperatures measured from fluid inclusions are consistent with borehole temperatures measured by conventional logging tools.

Frontier Geothermal Drilling Operations Succeed at 500 C BHST

The Japanese government funded geothermal exploration well WD-1A reached 3,729 m at TD, where the BHST is more than 500 °C. A trajectory correction run was carried out with a PDM and MWD tool where the formation temperature is greater than 350 °C. A TDS was used to cool the BHA while running each drill pipe stand in the hole. A borehole dynamic temperature experiment and drill bit tests were carried out in this well.

Deep geothermal resources survey project in the Kakkonda geothermal field

Abstract The New Energy and Industrial Technology Development Organization (NEDO) has been conducting a research project named “Deep-Seated Geothermal Resources Survey” since 1992 in order to establish a desirable direction for development of deep geothermal resources that exist beneath the already developed shallow reservoirs. A deep drill hole, WD-1, reached a depth of 3,729u2009m in July 1995 by applying the latest drilling techniques, such as a top-drive drilling system, enabling the collection of highly valuable information for understanding the characteristics of deep geothermal systems. Side-track drilling of WD-1 was started from a depth of 2,200u2009m in September 1996, targeting productive fractures expected near the boundary of the granite in a depth range from 2,800 to 3,000u2009m. We successfully encountered large lost circulation at some depths, and the side-track drilling was terminated at a depth of 2,963u2009m in January 1997.