# Kilauea East Rift Geothermal Area

GEOTHERMAL ENERGYGeothermal Home
Kilauea East Rift Geothermal Area

#### Area Overview

 Geothermal Area Profile

 Location: Hawaii Exploration Region: Hawaii Geothermal Region GEA Development Phase: Operational"Operational" is not in the list of possible values (Phase I - Resource Procurement and Identification, Phase II - Resource Exploration and Confirmation, Phase III - Permitting and Initial Development, Phase IV - Resource Production and Power Plant Construction) for this property. Coordinates: 19.47836°, -154.8883°

 Resource Estimate
 Mean Reservoir Temp: 302°C575.15 K 575.6 °F 1,035.27 °R [1] Estimated Reservoir Volume: 3.4 km³3,400,000,000 m³ 0.816 mi³ 120,069,866,851.4 ft³ 4,447,032,104.6 yd³ 3,400,000,000,000 L [1] Mean Capacity: 47 MW47,000 kW 47,000,000 W 47,000,000,000 mW 0.047 GW 4.7e-5 TW [2] USGS Mean Reservoir Temp: 350°C623.15 K 662 °F 1,121.67 °R [3] USGS Estimated Reservoir Volume: 6 km³ [3] USGS Mean Capacity: 180 MW [3]
Figure 1. Geologic map showing each area of the East Rift Zone. Created with Google Earth using geologic data from the USGS.

The Kilauea East Rift Zone (KERZ) is a broad ridge located in the southwest of the big island of Hawaii. The ridge extends east from the Kilauea caldera past the easternmost point of Hawaii and into the ocean. The KERZ is divided up into three sections on land: the Upper East Rift Zone (UERZ), the Middle East Rift Zone (MERZ), and the Lower East Rift Zone (LERZ) (See Figure 1). The UERZ extends from Puhimau Crater to Mauna Uli; the MERZ encompasses Moana Uli to Heiheiahulu; and the LERZ covers from Heiheiahulu to Cape Kumukahi. To the east of Cape Kumukahi, the rift zone extends beneath the ocean for another 80 km; this segment is called Puna Ridge.[4]

The KERZ includes many volcanic features such as cinder cones, vents, and craters, including the currently active Pu’u O’o vent, which has erupted continuously since 1983.[5] Due to the uniqueness of the Kilauea volcano, much of it lies within the boundaries of Hawaii Volcanoes National Park, where geothermal development is not permitted. The entire UERZ and about half of the MERZ are within the park boundaries; however, the eastern half of the MERZ and the entire LERZ lie outside of the national park, so exploration and utilization of geothermal resources are permitted there.[4]

Figure 2. The Puna Geothermal Power Plant.

The use of the geothermal resources from the KERZ goes back hundreds of years, when the native Hawaiian people bathed in the warm geothermal waters. Soaking in hot springs is still common in Hawaii for the therapeutic benefits. Some historical records also report that King Kalākaua aspired to produce power from geothermal energy resources in the 19th century.[6]

Modern electricity production estimates of the geothermal potential from Kilauea are 750 MW for conventional geothermal production and 1,396 MW if EGS techniques are implemented.[6] One power plant called Puna Geothermal Venture is in operation in the (LERZ), near the small town of Pāhoa. The plant is situated on 25 acres of land and is about 25 km from the active Pu’u O’o vent; it has a maximum capacity of 38 MW and is owned and operated by Ormat Technologies, Inc. Puna Geothermal Venture has been in operation since 1989 and provides electricity to nearly a quarter of the population on the big island.[7] The configuration of the power plant is 10 generators, each with a capacity of 3 MW , along with an 8 MW expansion that was completed in 2011.[8]

#### History and Infrastructure

 Operating Power Plants: 1

 Developing Power Projects: 1
 Puna Geothermal Project (38 MW38,000 kW 38,000,000 W 38,000,000,000 mW 0.038 GW 3.8e-5 TW MW, ) Add a new Developing Power Project

 Power Production Profile
 Gross Production Capacity: Net Production Capacity: Owners  : Ormat Power Purchasers : Hawaiian Electric Company Other Uses:

Since the first settlements in Hawaii over 1,000 years ago, lands around Kilauea have been regarded as sacred by the native Hawaiians. The Hawaiian volcano goddess Pele was believed to live at the summit of Kilauea in the caldera. The ancient Hawaiians believed that any time there was an eruption on the island, it was caused by Pele longing for her love. Even after the Hawaiian religion was officially abolished, beliefs and worship of Pele continued. To this day, many Hawaiians hold the sacred lands around Kilauea in high regard and take offense to any kind of development that would alter or damage the pristine lands around the volcano.[9] Despite opposition from some of these groups, development in the region has still occurred.

Most eruptions of Kilauea have not been explosive. The largest threat is from lava flows, which have not resulted in fatalities, but have destroyed hundreds of homes, roads, and other structures. Although developments on an active volcano involve inherent risk, large earthquakes and volcanic eruptions in the LERZ are infrequent enough that many homes and businesses have been established there and geothermal production is considered a safe investment.[4]

Geothermal development in the KERZ as a source of electricity began in the 1970s. The first operational well, HGP-A, was drilled in 1976 and reached a depth of 1,966 m and temperatures of 358°C.[10][11] A 3-MW experimental wellhead power plant was connected to HGP-A and operated at a 95% availability factor from 1981 to 1989. During the plant’s operation, it produced about 15-19 million kWh of electricity per year. The plant was designed as a two-year demonstration project and had some interesting features. Because the plant was located in an active volcanic zone and was susceptible to lava flows, it was designed to be portable. The turbine and generator were built on skids and a crane capable of lifting the turbine and generator was available to move them out of harm’s way in the event of a lava flow. Furthermore, the well was enclosed in a concrete bunker with a set of covers that could completely enclose the wellhead, preventing potential damage should a lava flow cover the site.[7]

From 1982 to 1990, drilling operations produced three exploratory/development wells and six geothermal development wells. The wells ranged in depth from 511 m to 2,560 m, and seven of the nine wells reached temperatures and pressures suitable for commercial-grade geothermal energy production.[12]

In 1989 Ormat Technologies purchased Puna Geothermal Venture, which contained three steam-dominated production wells at the time. Ormat developed the geothermal area further by drilling several production and injection wells, and in 1993, began producing 27 MW commercially, with a maximum capacity of 30 MW.[11] The facility produces near zero emissions; 100% of its geothermal fluid and gas are re-injected back into the earth.[8]

In 2011, an 8-MW expansion of the Puna Geothermal Facility began operating; the expansion utilizes the brine component of the geothermal fluid that was originally unused. The expansion has brought the maximum production of the Puna Geothermal Facility up to 38 MW.[8]

##### Kilauea East Rift Area Timeline

1960s: Interest in geothermal energy production at Kilauea is sparked by the high cost of imported oil for power generation. Several shallow wells are drilled by private industry, but only reach low termperatures.[13]

1976: The first operational well (HGP-A) is drilled to a depth of 1,968 m, hitting temperatures of 356°C.[11]

1978: The Geothermal Resource Assessment Program is initiated in Hawaii.[7]

1981: A 3 MW experimental wellhead power plant is connected to HGP-A and successfully operated at a 95% availability factor.[7]

1987: Data from shallow wells, HGP-A, and other deep geothermal exploration wells are integrated by the USGS to form a preliminary conceptual model of the Puna hydrothermal system.[14]

1989: The Puna Geothermal Venture begins construction on a geothermal power generation project in the East Rift Zone.[7]

1989: Ormat Technologies purchases Puna Geothermal Venture with plans to further develop the resource.[11]

1990: More than 1,500 people gathered at a drill shit to protest geothermal development at Kilauea.[9]

1991: After 10 years of setbacks from environmental permitting and regulatory issues, True Geothermal Energy begins drilling their first exploration wells in the Kilauea East Rift Zone.[7]

1990-1991: The State of Hawaii sponsors the Scientific Observation Hole (SOH) program to drill and core several research holes to facilitate geologic investigations deep beneath the Kilauea East Rift Zone. SOHs 1, 2, and 4 are drilled at Kilauea Volcano, providing constraints on the structure, porosity, hydrothermal mineralization, and geothermal temperature gradient within the geothermal system.[15] [16] [17]

1991: A blowout occurred during the drilling of Puna Geothermal Venture’s KS-7 and KS-8 wells. As a result, the state of Hawaii revoked all geothermal drilling permits in the area, forcing True Geothermal Energy to abandon their exploration efforts.[6] [7]

1993: Ormat begins commercial production of 27 MW at the Puna Geothermal Venture facility.[11]

2005: Drilling resumes in the Kilauea East Rift Zone, with Dacitic magma encountered at 2,488 m depth during injection well drilling.[11]

2011: Ormat completes an 8 MW expansion of the Puna Geothermal Venture facility. The expansion brought the maximum production capacity of the facility up to 38 MW.[8]

2013: Hawaiian Electric Light Company requests proposals to add 50 MW of new geothermal power generation capacity at Kilauea.[18]

#### Regulatory and Environmental Issues

Although Kilauea has the potential to generate much more power than what is currently being produced, there has been little geothermal development. Political, environmental, and religious factors have not been generally supportive of developing geothermal resources, which has caused opposition amongst native Hawaiians on the issue of geothermal development. In 1990, over 1,500 people gathered around a drill site to protest geothermal development; 140 people were arrested during this protest. The demonstrators were outraged over rainforest destruction and the disregard for native Hawaiian rights and religious beliefs.[9]

The main religious issues revolve around the Hawaiian volcano goddess Pele. Native Hawaiians who believe in Pele argue that geothermal drilling will injure her and utilization of the steam will suck the life force out of her, which will cause her to retaliate. In addition, geothermal development interferes with their worship of Pele. These objections were taken all the way to the U.S. Supreme Court, where it was ruled that geothermal development did not interfere with religious freedoms.[7]

Many native Hawaiians also feel that their land is being disrespected because the area being developed is in the pristine Wao Kele O Puna rainforest, which is sacred ground to their ancestors. The destruction of the Wao Kele O Puna rainforest also stirs up tension amongst environmentalists, who argue that even a small amount of clearing causes significant environmental consequences. The amount of rainforest directly destroyed by bulldozing for geothermal development represents only 1% of the Wao Kele O Puna area; however the network of roads, pipelines, and power lines fragments the rainforest and hinders the natural movement of plant and animal life, thus disrupting the natural habitat and making the forest more vulnerable to invasive, non-native species. Another factor that fuels this opposition is the high percentage of the plant and animal species living in this rainforest that exist nowhere else on earth. In addition, many people believe that developing too many geothermal wells in the area might produce high levels of toxic gases, such as hydrogen sulfide, resulting in acid rain and disruption of the wildlife.[9]

The reputation of geothermal development in Hawaii was further damaged in 1991 when a blowout occurred during drilling operations of wells KS-7 and KS-8. The blowout created an uncontrolled flow of hydrogen sulfide steam and fluids at the surface, which affected nearby communities and even required evacuation of some residents. As a result of this accident, local communities have had highly negative reactions towards further geothermal development of the area.[6] After the incident a geothermal management plan was developed which enabled agencies to better regulate geothermal activities and enforce permits for operations. The facility has been accident-free since the blowout, and many residents in the area are beginning to accept geothermal production again.[7]

#### Future Plans

In February 2013, the Hawaiian Electric Light Company (HELCO) released a request for proposals to add 50 MW of geothermal energy. HELCO is pursuing bidders for the project who are committed to thoroughly addressing environmental, community, and cultural concerns.[18] A timeline for the 50-MW expansion has not been proposed as of the February 2013 news release.

#### Exploration History

 First Discovery Well
 Completion Date: 1976/04/27 Well Name: HGP-A Location: 49.944207°, 3.882614° Depth: 1968m1.968 km 1.223 mi 6,456.693 ft 2,152.224 yd [11] Initial Flow Rate: 13.8 kg/s828 kg/min 49,680 kg/hour 1,192,320 kg/day 13.8 L/s 218.734 gal/min [19] Flow Test Comment: Initial Temperature: 356°C629.15 K 672.8 °F 1,132.47 °R [11]

Figure 3. Locations of SOHs drilled in the ERZ.[20]

Interest in geothermal energy production began in the 1960s because Hawaii was so dependent on imported oil, which accounted for over 90% of the state’s energy production. Active volcanism in the KERZ was an obvious indication that geothermal energy production could be possible in the region.

In the 1960s, four private shallow geothermal exploration wells were drilled in the KERZ. These wells only reached low temperatures, and it was determined that deeper wells would be needed for electricity production.[13]

In 1976, the first deep scientific well named HGP-A was drilled. Then in 1980, developers began drilling deep commercial exploration wells. Between 1980 and 1985, three successful wells were drilled slightly north of HGP-A, and three unsuccessful wells were drilled south of HGP-A. The unsuccessful wells reached high temperatures, but permeability was not adequate for commercial production.[13]

In 1978, the Geothermal Resource Assessment Program was initiated. The first phase objective of this program was to identify 20 potential geothermal resources in Hawaii using available geologic, geochemical, and geophysical data. The second phase objective was to conduct a series of field studies to confirm and characterize geothermal resources in each area. The KERZ was considered to have a 100% possibility of geothermal energy production after the assessment.[7]

From 1989 to 1991, three Scientific Observation Holes (SOH) were drilled, referred to as SOH-1, SOH-2, and SOH-4 (Figure 3).

• SOH-1 began at 189 m above sea level and reached temperatures of 206.1°C at 1,684 m depth
• SOH-2 began at 86 m above sea level and reached temperatures of 350.5°C at 2,073 m depth
• SOH-4 began at 364 m above sea level and reached temperatures of 306.1°C at 2,000 m depth.

These holes were drilled by the Hawaii Natural Energy Institute of the University of Hawaii at Manoa. About 4,559 m of core was successfully recovered from the SOH drill holes.[20]

In 1991, two companies actively pursued geothermal exploration in the East Rift Zone. The first company, Puna Geothermal Venture, was exploring in the LERZ. The second, True Geothermal Energy Company, was conducting exploration in the MERZ. Puna Geothermal Venture was in the process of building their power plant while True Geothermal Energy was in the process of drilling their first exploratory wells. True Geothermal Energy had struggled for the previous 10 years with environmental permitting and regulatory issues, which set them back compared to Puna Geothermal Venture. When the blowout of Puna Geothermal Venture’s well occurred in 1991, the state revoked the drilling permits from both companies and True Geothermal Energy decided to abandon their exploration efforts.[7]

Puna Geothermal Venture began commercial production in 1993, and since then very little has been done in the realms of exploration and production expansion. Despite this, the KERZ is a highly unique and interesting geologic area; countless geophysical studies, not necessarily for the purposes of geothermal exploration, have been conducted there. The loss of momentum in geothermal development is due to the issues of regulation, perceived risk to the environment, and public acceptance. Also, until recently, fossil fuel prices have been so low that there has been very little economic incentive to pursue further exploration.

#### Well Field Description

 Well Field Information
 Development Area: Number of Production Wells: 3 [21] Number of Injection Wells: 4 [21] Number of Replacement Wells: Average Temperature of Geofluid: 250°C523.15 K 482 °F 941.67 °R [21] Sanyal Classification (Wellhead): High Temperature [21] Reservoir Temp (Geothermometry): Reservoir Temp (Measured): 360°C633.15 K 680 °F 1,139.67 °R [6] Sanyal Classification (Reservoir): High Temperature [6] Depth to Top of Reservoir: 1200m1.2 km 0.746 mi 3,937.008 ft 1,312.332 yd [22] Depth to Bottom of Reservoir: 2200m2.2 km 1.367 mi 7,217.848 ft 2,405.942 yd [22] Average Depth to Reservoir: 1700m1.7 km 1.056 mi 5,577.428 ft 1,859.137 yd [22]

The well field that supplies geothermal fluids for Puna Geothermal Venture has the following specifications:

• First well in area named HGP-A; drilled in 1976 [6]
• Most recent well drilled in 2005 [6]
• Number of production wells as of 2005 = 3 [21]
• Number of reinjection wells as of 2005 = 4 [21]
• Well field land area (km2) = 1-2 [21]
• Depth range of wells (m) = 500 to 2700 [6]
• Bottom hole temperature range (°C) = $\nless$ 200 – 360 [6]
• Type of reservoir = liquid/steam [21]
• Reservoir depth (m) = 2000 [21]
• Reservoir temp (°C) = 200-300 [21].

Four deep scientific holes have been drilled in ERZ: HGP-A, SOH-1, SOH-2, and SOH-4. HPG-A was the only scientific drill hole used to produce electricity. When the HGP-A well was in operation, it produced 50,000 kg/hr of 60% steam/40% liquid, had a wellhead pressure of 620 kPa, and a bottom hole temperature of 358°C.[4] Six production boreholes were drilled by Puna Geothermal Venture between 1990 and 1993. They were located near HGP-A. Logs from the wells show a temperature profile staying below 50°C until about 1,000-1,500 m depth, where there is a sharp increase in temperature; then the temperature profile follows the boiling point to depth curve, which indicates saturated steam.[6] The geothermal reservoir is classified as a high-temperature, two-phase, liquid dominated system with a variable steam fraction.[6] During the most recent injection well drilling in the ERZ in 2005, dacitic magma was encountered at 2,488 m depth.[11]

#### Research and Development Activities

A new 8-MW expansion of the Puna Geothermal Venture was completed in 2011. The expansion did not require any new wells to be drilled; it utilized the brine component of the geothermal fluid that was originally unused. No major changes were made that would affect the reservoir such that fluids are now being utilized more efficiently at the same rate of production.

Future research ideas include:[6]

• A proposal for a new revised well program with upgraded casing, cementing, and completion procedures
• Preparation of an improved program to help minimize flow interruptions and maximize data recovery

#### Technical Problems and Solutions

The pH of production fluid has been found to be about 4.5. The acidic nature of the fluid is due to CO2 and H2S at high temperatures, up to 350°C. The corrosive nature of the fluid may result in the burst or collapse of wellbore casings over time, so a new revised well program with upgraded casing, cementing, and completion procedures has been proposed.[6]

#### Geology of the Area

 Geologic Setting
 Tectonic Setting: Hot Spot [5] Controlling Structure: Fissure Swarms, Intrusion Margins and Associated Fractures [11] Topographic Features: Cinder Cone, Shield Volcano [11][4] Brophy Model: Type F: Oceanic-ridge, Basaltic Resource [11] Moeck-Beardsmore Play Type: CV-1a: Magmatic - Extrusive

 Geologic Features
 Modern Geothermal Features: Blind Geothermal System [4] Relict Geothermal Features: Volcanic Age: Recent [4] Host Rock Age: Quaternary [4] Host Rock Lithology: Tholeiitic Basalt [4] Cap Rock Age: < 1000 years old [4] Cap Rock Lithology: Overlapping a’a’ and pahoehoe flows [4]

##### Regional Setting

The Kilauea volcano is a shield volcano located over a hot spot in the middle of the Pacific Tectonic Plate. Kilauea is the most active volcano on earth today. The most recent activity has been in the MERZ, where the Pu’u’ O’o vent has been producing lava nearly continuously from January 3, 1983 to present (as of 2013). During the first three years, there were 44 eruptive episodes with lava fountains reaching up to 460 m. The spatter from these lava fountains built up a cone 255 m high. There have been many eruptive episodes since the onset of volcanism at Pu’u’ O’o, and the volcano has remained active between these events, with lava oozing from the vent and immediate surrounding areas. The most recent eruptive activity was in March 2011 when the bottom of the Pu’u’ O’o crater subsided suddenly and then collapsed. About two hours later a lava fountain burst through the surface to the west between Puʻu ʻOʻo and the Nāpau Crater. Over the course of 12 hours, a 2.3 km-long fissure opened that spewed a wall of lava 25-30 m into the air. This event was the 59th eruptive episode since 1983.[5]

Most of the terrestrial ERZ has undergone intense volcanic activity during Quaternary time.[4] The LERZ, where the Puna Geothermal Venture is located, has had two volcanic events in recent history: one in 1955 and another from 1960 to 1961. In general, volcanic activity in the UERZ has been relatively quiet in recent history.

Microseismic activity is common in the ERZ. On average, there are 6-12 events each day with magnitudes ranging from 1-2. The microseismic activity has remained stable throughout development of the geothermal area. The natural subsidence rate has been measured by the USGS beginning in 1958; it has remained relatively constant at approximately 1 cm/year.[11]

##### Structure

A large magma chamber is located beneath Kilauea Caldera at depths of about 2-7 km beneath the surface. Magma from this reservoir moves through dikes and migrates either upward toward the caldera or laterally through either the South West Rift Zone (SWRZ) or the ERZ. The ERZ contains numerous eruptive vents, spatter cones, pit craters, and normal faults. The majority of ERZ strikes N65°E to the end of the big island and continues into the ocean along the Puna Ridge. The UERZ is the only part of the ERZ that has a different orientation, which is thought to relate to the southward migration of Kilauea’s south flank and/or the northward migration of summit caldera collapses.

The ERZ consists of a series of linear fissures oriented from southwest to northeast, which are the result of spreading during the formation of the shield volcano. Also, en-echelon fault patterns are found along the ERZ associated with subsidence of the volcano. Magma generated at the summit tends to flow through these fractures forming steeply dipping dike complexes. The faults and fractures found in the ERZ run parallel to the rift, and strike to the northwest with dips to the southeast. The southeast dips are caused by the seaward slumping of Kilauea’s flank due to the land subsidence under the force of gravity. The Puna hydrothermal system where the power plant is located is in a step between two large normal faults. This area is underlain by a fracture system, which allows for adequate fluid flow. Maximum temperatures are encountered in the middle of the dike complex.[6]

The LERZ consists of active, but relatively quiet, geologic features commonly found in geothermal areas, such as cinder cones, pit craters, vents, and fractures.[11] A strong gravity high exists running parallel with the rift in the LERZ; this feature has been modeled as a complex system of high density dikes and flanking sills extending to a depth of roughly 5,000 m. This model is supported by high P-wave velocities of around 7.0 km/s interpreted from seismic refraction surveys.[23] The number of basalt dikes encountered during drilling operations has also typically been found to increase with depth.[4] Resistivity soundings in the LERZ indicate a three-layer structure with a dry, high resistivity surface layer (100s-1000s ohm-m), a saturated, more conductive central layer (1-600 ohm-m) of varying thickness, and a deep, more resistive basement layer.[23]

##### Stratigraphy

At the surface the ERZ is dominated by a’a’ and pahoehoe flows overlapping each other from each successive lava flow. Drill cores have shown that, beneath the lava flows, there are ash bed layers and numerous dikes and/or sills. Deeper in the sequence, submarine deposits are present that consist mainly of pillow basalts, as well as hyaloclastites that are intruded by mafic dikes. Drill cores have also revealed a thin layer of carbonate strata containing marine fossils that marks the boundary between submarine and aerial strata. A thick layer of limestone exists between 1,623 and 1,768 m depth beneath SOH-4. This layer contains marine fossils, sandy limestone, and conglomerate with rounded pebbles.[20]

Petrologic studies have determined that Kilauea’s composition is primarily tholeiitic basalt, which is higher in silica content than ordinary alkali basalt.[6] Three main groups of rocks have been recognized at Kilauea, and include (from oldest to youngest) the Hilina Basalt, the Pahala Ash, and the Puna Basalt. The majority of the Hilina Basalt is below the surface, and only outcrops in large fault scarps south of the Kilauea summit. The Hilina Basalt is greater than 300 m thick and consists of numerous lava flows and alternating thin ash deposits. This layer is estimated to be about 30,000-100,000 years old. The Pahala Ash lies on top of the Hilina Basalt, with an average thickness of 15 m. This ash deposit is estimated to be 10,000-24,000 years old. The top-most layers are called the Puna Basalt and cover most of the surface of Kilauea. The Puna Basalt includes lava flows younger than 10,000 years old.

90% of Kilauea and all of the LERZ are covered by Puna Basalt Group rocks with ages of $\nless$ 1,100 years. Furthermore, 75% of the LERZ is covered by Puna Basalt Group rocks with ages of $\nless$ 400 years.[4] It consists of lava flows, vent deposits, and dike intrusions. The thickness of the Puna Basalts decreases with increasing distance from the Kilauea summit. Due to magma interactions with ground water and sea water, there are at least four tuff and ash deposits within the Puna Basalts. Two major outcrops of ash and tuff exist in the LERZ; they are 340 and 200 years old, respectively. Several smaller, isolated tuff layers exist on the LERZ as well. These layers were formed from lava flows or magma intrusions interacting with seawater and/or perched groundwater resulting in violent explosions. Below the surface in the LERZ, the hydrothermal systems are hosted by flows of Hilina Basalt interbedded with hyaloclastites and pyroclastic deposits that are cut by younger dikes.[4]

#### Hydrothermal System

There are relatively few surface manifestations of the hydrothermal system in the ERZ, although several isolated steam vents, mud pools, and fumaroles do exist. The hydrothermal system around the Puna Geothermal Venture is, for the most part, a blind system with very little surface alteration.[6] Surface water runoff in the ERZ is minimal due to the high porosity of the new lava flows that blanket the region, so much of the rainfall contributes to the recharge of the groundwater system. The patterns and rates of the groundwater flow in the ERZ are controlled by topography, permeability structures, and locations of recharge. Magmatic heat sources may also influence local flow patterns. In general, the direction of water flow is from the summit of Moana Loa towards the ocean. Isotope hydrology has shown that water in the ERZ recharges at elevations of 1,300-2,800 feet (396-853m) and discharges south of the ERZ after about 10-20 years, yielding an average flow rate of just over 1 mile (1.6 km) per year.[23] Under normal conditions the water table surface loosely follows the surface topography, although complex dike patterns in the ERZ result in deviations of the water table. Dikes in the LERZ appear to form a barrier to southward groundwater flow. Water table levels in the LERZ are shown to be consistently close to sea level, although relatively closely-spaced geothermal exploration wells have encountered considerable variability in pressure and salinity between wells. This variation is an indicator of impermeable layers within the rift zone.[24]

Very young surface basalt flows dominate the ERZ; these surface basalts are mostly unaltered and have relatively large permeability values exceeding 10-10 m2. At about 1-2 km deep within the rift zone the permeability increases to $\nless$ 10-15 m2.[6] Permeability in the LERZ is about 10-9 to 10-11 m2.[24] The main mechanism for hydrothermal circulation is through faults and fractures. Permeability in the ERZ is generally controlled by near-vertical northeast-trending faults and fissures that dip to the southeast. Seismic data show that the most concentrated area of the fracture network is located south of the Puna hydrothermal system at about 1.5-2 km depth.[6] Outside of the fracture zones, convective circulation decreases to almost zero at depth. This lack of circulation indicates low permeability, which is normally associated with increased pressure and metamorphic alteration that reduce porosity. Dike intrusions at depth also interfere with permeability due to their high density and low porosity. Dikes that are low in permeability separate flow systems and define boundaries of the hydrothermal system.[6]

Beneath the ERZ, the thickness of the fresh water lens, according to the Ghyben-Herzberg formula, should be roughly 70 m. However, data from wells in the Puna area indicate that low salinities exist at depth, approximately 5% that of seawater.[6] This anomaly is currently unexplained, but there are several theories as to why the salt water concentration is so low at depth. One theory is that the Puna geothermal heat source could invert the typical fresh water lens because heated seawater becomes more buoyant than the cold fresh water. Another theory is that faults and fractures in the KERZ increase permeability to the point that freshwater recharge dominates, preventing the influx of salt water into the system. A third theory is that reaction of basaltic dikes with seawater from the south at increasing temperatures produces hydrothermal alteration minerals that rapidly seal fractures to form an impermeable boundary which prevents sea water from traveling north into the Puna hydrothermal system.[14][6]

#### Heat Source

The heat source for Kilauea is created by basaltic magma intrusions from a mantle plume beneath the volcano. Buoyant magma rises along rifts, forming pools in the shallow crust between 2 and 7 km depth. Reservoir temperatures at the center of the rift are 360°C.[6]

#### Geofluid Geochemistry

 Geochemistry
 Salinity (low): 2500 [22] Salinity (high): 35000 [22] Salinity (average): 18750 [22] Brine Constituents: Chloride, Sodium, Silica, Potassium, Calcium [25][26][27] Water Resistivity:

Chemical samples from shallow wells in the ERZ show variable water chemistry. Also, concentrations of sea water and fresh water are found to vary significantly from well to well. Water chemistry in the ERZ has the following characteristics:

• Some shallow ground water samples have higher-than-normal bicarbonate concentrations of approximately 50 mg/L while some areas have up to 100 mg/L, which might indicate anomalously high partial pressures of carbon dioxide[28]
• Silica tends to increase with temperature and chloride concentrations[28]
• Hydrothermal alteration is variable and intermittent within the ERZ due to fracture-controlled flow of fluids[6]
• When comparing chemical samples from springs vs. samples from deep wells, the results show that well fluid does not originate from the same fluid as surface springs.[28]

Geochemical studies of the deep hydrothermal system beneath the Kilauea East Rift Zone began with the sampling of fluids from well HGP-A, and includes analysis of downhole fluid samples as well as steam-condensate and liquid water samples taken at the wellhead.[25] Initial fluid sampling from well HGP-A was conducted over a 12 month period beginning in July 1976.[25][10] Values reported herein reflect the mean composition measured for the geothermal fluid across all sample sets excluding the samples collected on February 14, 1977. This sample set represents an outlier taken shortly after quenching of the well, with significantly higher downhole pH measurements falling outside of the typical range of 3 to 5 measured for the other five sample sets collected. The chloride content and salinity of the geothermal fluids was low in comparison to that of open ocean water (17,000 mg/L Cl and 33.4%), averaging 1040 mg/L Cl and 2.6 %, respectively. Silica concentrations in the geothermal fluid were abnormally high compared to normal Hawaiian ground water (<80 mg/L), showing a mean value of 440 mg/L. Minimal variations in the silica concentration of the fluid were observed with depth, however variations in silica content between sampling periods were significant. Major cation concentrations measured in HGP-A showed moderate variation with depth, with mean values of 730 mg/L Na, 123 mg/L K, 53.8 mg/L Ca, 1.0 mg/L Mg. Three samples were also collected for tritium analysis, all of which showed < 0.2 tritium units of radioactivity indicative of a mean age of the water of approximately > 30 years. Samples collected using a Weir box during steady state flow following purging of the well on January 1, 1977 returned concentrations of 780 mg/L Cl, 390 mg/L Na, 68 mg/L K, 24 mg/L Ca, 0.11 mg/L Mg, 41 mg/L SiO2 and a pH of 8.5.[25] Samples from other deep geothermal exploration wells have been found to show similar depletions in sulfate and magnesium[28]

Geochemical data suggest that geofluids analyzed from the well consist of water from several sources. At shallow depth, the well contains 5-10% ocean water, whereas well fluids from deeper levels consist of meteoric water (65%) and hydrothermal fluid (25%).[25] Waters sampled from other deep geothermal exploration wells in the East Rift Zone consist mainly of diluted seawater, and wall rocks are highly altered due to water-rock reactions at high temperature[28] Uncertainty in the mixing ratios between the three fluid types identified in HGP-A, in addition to the identification of fluid inputs from two distinct reservoirs accessed by the well has resulted in some difficulty in applying chemical geothermometers to the data. Reservoir temperatures calculated from chemical data collected during early flow testing and production of the well were 300°C (Na-K-Ca geothermometer of Fournier, 1981) and 305°C (silica geothermometer of Fournier and Potter, 1982, corrected for steam loss).[14] Reservoir temperature estimates calculated using the Na-K-Ca geothermometer were found to have declined to approximately 250°C after several years of production from the HGP-A, whereas estimates calculated using the silica geothermometer have remained fairly constant.[14] This shift in the Na-K-Ca temperatures is interpreted to have resulted from the intrusion of lower temperature sea water into the intermediate-temperature aquifer intersected by HGP-A. A similar shift is not observed in the silica temperature because of the more rapid equilibration of silica to reservoir temperatures in the intruding fluids.

#### NEPA-Related Analyses (0)

Below is a list of NEPA-related analyses that have been conducted in the area - and logged on OpenEI. To add an additional NEPA-related analysis, see the NEPA Database.

CSV No NEPA-related documents listed.

#### Exploration Activities (50)

Below is a list of Exploration that have been conducted in the area - and cataloged on OpenEI. Add a new Exploration Activity

#### References

1. Geothermal Reservoir Assessment based on slim hole drilling, Volume 2: Application in Hawaii
2. Benjamin Matek. Geo-energy [Internet]. Geothermal Energy Association. [updated 2015/04/28;cited 2015/04/28]. Available from: http://geo-energy.org/
3. U.S. Geological Survey. 2008. Assessment of Moderate- and High-Temperature Geothermal Resources of the United States. USA: U.S. Geological Survey. Report No.: Fact Sheet 2008-3082.
4. Richard B. Moore,Frank A. Trusdell. 1993. Geology of Kilauea Volcano. Geothermics. .
5. U.S. Geological Survey. Summary of Puʻu ʻOʻo - Kupaianaha Eruption, Kilauea Volcano, Hawaii [Internet]. 2012. Kīlauea's East Rift Zone (Puʻu ʻŌʻō) Eruption 1983 to present. U.S. Geological Survey. [cited 2013/06/26]. Available from: http://hvo.wr.usgs.gov/kilauea/summary/
6. Robert Kinslow,Phillip Maddi,Piyush A. Bakane,Bridget Hass. 2012. Development Overview of Geothermal Resources In Kilauea East Rift Zone. Geo-Heat Center Bulletin. 9-17.
7. Tonya L. Boyd, D. Thomas, A. T. Gill. 2002. Hawaii and Geothermal-What Has Been Happening. Geo-Heat Center Quarterly Bulletin. 23(3):11–21.
8. Mike Kaleikini,Paul Spielman,Tom Buchanan,Ormat Technologies, Inc.. 2011. Puna Geothermal Venture 8MW Expantion. GRC Transactions. 35:1313-1314.
9. Paul Faulstich. 03/02/2010. Hawaii's Rainforest Crunch: Land, People, and Geothermal Development. Cultural Survival. unknown.
10. Donald M. Thomas. 10/1987. The Geochemistry of the HGP-A Geothermal Well: A Review and an Update. Honolulu, Hawaii: Hawaii Institute of Geophysics. 5.
11. William Teplow,Bruce Marsh,Jeff Hulen,Paul Spielman,Mike Kaleikini,David Fitch,William Rickard. 2009. Dacite Melt at the Puna Geothermal Venture Wellfield, Big Island of Hawaii. GRC Transactions. .
12. Bill Rickard,B.J. Livesay,Bill Teplow,Steve Winters,Jerry Evanoff,W.T. Howard. 1995. Control of Well KS-8 in the Kilauea Lower East Rift Zone. In: World Geothermal Congress; 1995/01/01; N/A. N/A: N/A; p.
13. Gerald O. Lesperance. 1992. Status of Geothermal Development in Hawaii 1992. Geothermal Resources Council, TRANSACTIONS. 16:331-333.
14. Donald Thomas. 1987. A Geochemical Model of the Kilauea East Rift Zone. unknown: U.S. Geological Survey. Report No.: US Geological Survey Professional Paper 1350.
15. Frank A. Trusdell, Elizabeth A. Novak, Rene' S. Evans, Kelly Okano. unknown. Core Lithology From the State of Hawaii Scientific Observation Hole 1, Kilauea Volcano, Hawaii. Menlo Park, CA: U.S. Dept. of the Interior, U.S. Geological Survey. Report No.: Open-File Report 99-389.
16. Elizabeth A. Novak, Frank A. Trusdell, Renee S. Evans. 1991. Core Lithology State of Hawail Scientific Observation Hole 2 Kilauea Volcano, Hawaii. Reston, VA: Department of the Interior, U.S. Geological Survey. Report No.: Open-File Report 97-689.
17. Frank A. Trusdell, Elizabeth A. Novak, Rene' S. Evans. 1993. Core Lithology State of Hawaii Scientific Observation Hole 4 Kilauea Volcano, Hawaii. Menlo Park, CA: U.S. Dept. of the Interior, U.S. Geological Survey. Report No.: Open-File Report 92-586.
18. Jay Ignacio. 02/28/2013. Hawaii Electric Light Company News Release. unknown. unknown.
19. John W. Shupe, Paul C. Yuen. 1978. Geothermal Energy in Hawaii: Present and Future. In: Circum-Pacific Energy and Mineral Resources Conference; 1978/08/02; Honolulu, Hawaii. Honolulu, Hawaii: Hawaii Geothermal Project, University of Hawaii; p. 18
20. Keith E. Bargar,Terry EC Keith,Frank A. Trusdell. 1995. Fluid-inclusion evidence for past temperature fluctuations in the Kilauea East Rift Zone geothermal area, Hawaii. Geothermics. .
21. Ruggero Bertani. 2005. World geothermal power generation in the period 2001-2005. Geothermics. 34(6):651-690.
22. D. Bell. 1988. Puna Geothermal Venture's Plan for a 25 MW Commercial Geothermal Power Plant on Hawaii's Big Island. In: GRC Transactions. GRC Annual Meeting; 1988/06/01; unknown. Davis, CA: Geothermal Resources Council; p. 351-358
23. Murray C. Gardner,James R. McNitt,Christopher W. Klein,James B. Koenig,Dean Nakano. 1995. History and Results of Surface Exploration in the Kilauea East Rift Zone. In: World Geothermal Congress. World Geothermal Congress; 1995; Italy. (!) : International Geothermal Association; p. 1233-1238
24. The Hydrogeology of Kilauea Volcano
25. Geochemistry of a Hawaii Geothermal Well: HGP-A
26. Geothermal Fluid Analysis
27. Puna Geothermal Venture, Test Data for KS-3, KS-7, KS-8, MW-1, MW-2, and MW-3
28. Chemistry of spring and well waters on Kilauea Volcano, Hawaii, and vicinity

Some of the content on this page was part of a case study conducted by: NREL Interns

Print PDF