The assessment of stored heat in a geothermal reservoir is one of the recommended methods by the ... more The assessment of stored heat in a geothermal reservoir is one of the recommended methods by the AGRCC Geothermal Lexicon for the estimation of a geothermal reserve. Prior to development, when very little information about the reservoir properties is known, the reservoir stored heat is usually estimated using probabilistic methods to find a first guess and an uncertainty range. Once development of a geothermal reservoir has begun it is quite common to generate a numerical model and calibrate it vs. observed field data. This means that the reservoir properties needed for the calculation of stored heat are more constrained once the model is calibrated. By running a simulation through the calibration time and through a future development scenario one can calculate stored heat at each time step and thus get detailed information about the recovery factor, which is a key uncertainty in the initial stored heat estimation. A drawback in using stored heat for the estimation of a geothermal r...
Production well optimization is one of the key elements to the success of geothermal power plant ... more Production well optimization is one of the key elements to the success of geothermal power plant operation. The MCY01 production well has been in operation since 2013 to supply steam to one of the Mercury-operated geothermal plants. Since 2015, MCY01 has been experiencing an irregular cycle or coughing phenomenon in which well head pressure (WHP) and productivity vary while flow control valves (FCV) are set constant. In order to optimize its production, an evaluation has been carried out to understand the production coughing mechanism. The most likely hypothesis of MCY01 irregular performance is thought to be due to competing feed zones (FZ) and the fluid connectivity of each feedzone to neighbouring wells. Flowing PTS (pressure, temperature, and spinner) analysis from 2013 to 2015 indicates the flow rate contribution of the bottom two feed zones have changed significantly over time. In order to validate the hypothesis of the competing feed zones, the numerical model, coupled with w...
Recent Rotokawa Geothermal Field case histories illustrate the value of combined interpretation o... more Recent Rotokawa Geothermal Field case histories illustrate the value of combined interpretation of natural state temperature, MT-TDEM resistivity and hydrothermal alteration for building conceptual understanding at the development stage of a geothermal reservoir. Rotokawa Joint Venture, a partnership between Mighty River Power and Tauhara North No. 2 Trust currently operates 174 MW of generation at Rotokawa. Important conceptual elements that can be clarified in joint analysis of MT and natural state temperatures beyond what is typically feasible based on MT for exploration projects include; details of fluid upflow/outflow, influx and cross-flow paths of cooler groundwater, and permeability variations above and at the margins of the reservoir.
The Ngatamariki geothermal field is situated 17 km north east of Taupo. Mighty River Power has an... more The Ngatamariki geothermal field is situated 17 km north east of Taupo. Mighty River Power has announced plans to build an 82 MW power station on the field. As part of the consent and planning processes, an extensive programme of drilling, testing and modelling was undertaken to provide understanding of the likely response of the field to a development. Analysis of the three new deep wells drilled by Mighty River Power in 2008-9 and the four wells drilled by the New Zealand government in the 1980s, together with recent MT surveys, showed a larger field than was originally defined by the early DSIR resistivity surveys. A conceptual model was developed to encompass the new data collected from the wells and the MT surveys. Modelling of the field was undertaken with a fullfield dual-porosity numerical model together with a number of simpler process models. The challenge for the numerical modelling was to find parameter values for the model that would provide robust predictions of the fi...
An adaptive management and injection strategy has been used to ensure that the Kawerau power plan... more An adaptive management and injection strategy has been used to ensure that the Kawerau power plant has injection capacity to run at full load and balance pressure support to the field while preventing thermal breakthrough to production areas. A key part of this strategy is understanding injection well interaction. A strategy was developed with active reservoir testing and analyses used to maintain injection capacity. Injection well capacity was initially measured through standard multi-rate completion tests following drilling. Subsequent monitoring was performed by continuous monitoring of wellhead pressure and injection rate; where no positive wellhead pressure was observed, downhole pressure monitoring tubing (i.e. capillary tubing) was installed to provide a fluid level monitor injectivity increase or decline. Wellbore models were used to estimate the full injectivity curve and its change over time. Tracers and chemical signatures were used to understand injection return to produ...
In March 2013, Mighty River Power (MRP) commissioned an 82MWe binary power plant in the Ngatamari... more In March 2013, Mighty River Power (MRP) commissioned an 82MWe binary power plant in the Ngatamariki geothermal field, 17 km north east of Taupo, New Zealand. A full field numerical model and several simpler process models of the Ngatamariki system were built and tested prior to the decision to proceed with resource development (Burnell, 2011, Clearwater et al., 2011). The sensitivity of these models was tested over a limited domain by varying individual parameters of interest. Conservative forward scenario runs were simulated by a reservoir model with reduced areal extent of permeable reservoir. In the present study, the sensitivity of model results to parameter values were analyzed in detail with the inverse modeling package iTOUGH2. An optimal model was then used to propagate the uncertainties in scenario forecasting by Monte Carlo simulation. This resulted in more rigorous statistics on what parameters drive model behavior and quantitative bounds on the confidence of model predic...
The Ngatamariki geothermal field is situated 17 km north east of Taupo, New Zealand, and in 2013 ... more The Ngatamariki geothermal field is situated 17 km north east of Taupo, New Zealand, and in 2013 Mighty River Power commissioned an 82 MW power station on the field consisting of four Ormat Energy Converter units. Production is from three deep wells in the center of the field and injection is back into four deep wells split between the North and South. Four of these wells were drilled during a campaign in 2012, including three injection wells. In addition to the normal completion testing, each of the new injection wells was injected with cold river water for several weeks to determine potential for stimulation. Prior to plant start-up, proved injection capacity was less than 50% of what was required to run the plant at full generation. Data from the stimulation testing phase constrained a simple analytic model of well stimulation based on Grant et al. (2013) and this model was used to predict injectivity evolution during plant start-up. Modeling predicted the injection wells would s...
The Awibengkok (Salak) geothermal system is a liquid-dominated, fracture-controlled reservoir wit... more The Awibengkok (Salak) geothermal system is a liquid-dominated, fracture-controlled reservoir with benign chemistry and low-to-moderate non-condensable gas content. The geothermal system is hosted mainly by andesitic-to-rhyodacitic rocks, and floored by Miocene marine sedimentary rocks cut by igneous intrusions. The volcanic sequence is capped by an 8400-year-old phreatic explosion breccia, rhyolite fallout tuff (>8400 years and <40,000 years), rhyolite lavas, domes
From mid-1993 through early 1998 Unocal, under a Joint Operation Contract with Pertamina, conduct... more From mid-1993 through early 1998 Unocal, under a Joint Operation Contract with Pertamina, conducted an extensive exploration program designed to locate and evaluate commercial geothermal systems within the Sarulla Block of North Sumatra, Indonesia. The exploration ...
The Awibengkok geothermal field, also known as Salak, is the largest developed geothermal resourc... more The Awibengkok geothermal field, also known as Salak, is the largest developed geothermal resource in Indonesia, currently sustaining 377 MW of electrical generation. It is a water-dominated, naturally fractured reservoir with benign fluid chemistry. A very large ...
The Awibengkok (Salak) geothermal system is a liquid-dominated, fracture-controlled reservoir wit... more The Awibengkok (Salak) geothermal system is a liquid-dominated, fracture-controlled reservoir with benign chemistry and low-to-moderate non-condensable gas content. The geothermal system is hosted mainly by andesitic-to-rhyodacitic rocks, and floored by Miocene marine sedimentary rocks cut by igneous intrusions. The volcanic sequence is capped by an 8400-year-old phreatic explosion breccia, rhyolite fallout tuff (>8400 years and <40,000 years), rhyolite lavas, domes
The Awibengkok (Salak) geothermal system is a liquid-dominated, fracture-controlled reservoir wit... more The Awibengkok (Salak) geothermal system is a liquid-dominated, fracture-controlled reservoir with benign chemistry and low-to-moderate non-condensable gas content. The geothermal system is hosted mainly by andesitic-to-rhyodacitic rocks, and floored by Miocene marine sedimentary rocks cut by igneous intrusions. The volcanic sequence is capped by an 8400-year-old phreatic explosion breccia, rhyolite fallout tuff (>8400 years and <40,000 years), rhyolite lavas, domes and related tuffs (≥40–120 ka), and dacite-to-rhyodate lavas and domes (185–280 ka) that were erupted across the eastern part of the field from NNE-trending vents controlled by a major fault. More regionally extensive basaltic–andesite to andesite volcanic centers are mostly between 180 and 1610 ka old. Surface and subsurface fault patterns, formation image logs and tracer studies indicate strongly anisotropic permeability aligned with the dominant N to NE fracture trend, dividing the field into a number of subcom-partments that are locally connected by fractured aquifers and NW-and E-W-trending fractures. Shallow argillic alteration gives way with increasing depth and temperature to argillic–phyllic and propylitic zones, with the latter accounting for the bulk of the fluid produced from the geothermal system. The commercial Awibengkok reservoir is a moderate-to-high temperature (240–312 • C) geothermal resource with high fracture permeability, moderate porosity (mean = 10.6%) and moderate-to-low matrix permeability (geometric mean = 0.026 md). The principal deep upflow zone, with fluid temperatures in the 275–312 • C range, is located in the western part of the field. The ascending fluids move up along Nor NNE-trending structures that breach low-permeability tuff layers in the central and east-central parts of the field. Fluids in the central part of the reservoir are uniform in composition and temperature, representing the mixing of upflow and convective reflux. Fluids ascend and flow laterally to the shallow top of the reservoir in the eastern area near drilling pads Awi 1 and 13 (fluid production temperatures: 240 to 270 • C). The eastern
The assessment of stored heat in a geothermal reservoir is one of the recommended methods by the ... more The assessment of stored heat in a geothermal reservoir is one of the recommended methods by the AGRCC Geothermal Lexicon for the estimation of a geothermal reserve. Prior to development, when very little information about the reservoir properties is known, the reservoir stored heat is usually estimated using probabilistic methods to find a first guess and an uncertainty range. Once development of a geothermal reservoir has begun it is quite common to generate a numerical model and calibrate it vs. observed field data. This means that the reservoir properties needed for the calculation of stored heat are more constrained once the model is calibrated. By running a simulation through the calibration time and through a future development scenario one can calculate stored heat at each time step and thus get detailed information about the recovery factor, which is a key uncertainty in the initial stored heat estimation. A drawback in using stored heat for the estimation of a geothermal r...
Production well optimization is one of the key elements to the success of geothermal power plant ... more Production well optimization is one of the key elements to the success of geothermal power plant operation. The MCY01 production well has been in operation since 2013 to supply steam to one of the Mercury-operated geothermal plants. Since 2015, MCY01 has been experiencing an irregular cycle or coughing phenomenon in which well head pressure (WHP) and productivity vary while flow control valves (FCV) are set constant. In order to optimize its production, an evaluation has been carried out to understand the production coughing mechanism. The most likely hypothesis of MCY01 irregular performance is thought to be due to competing feed zones (FZ) and the fluid connectivity of each feedzone to neighbouring wells. Flowing PTS (pressure, temperature, and spinner) analysis from 2013 to 2015 indicates the flow rate contribution of the bottom two feed zones have changed significantly over time. In order to validate the hypothesis of the competing feed zones, the numerical model, coupled with w...
Recent Rotokawa Geothermal Field case histories illustrate the value of combined interpretation o... more Recent Rotokawa Geothermal Field case histories illustrate the value of combined interpretation of natural state temperature, MT-TDEM resistivity and hydrothermal alteration for building conceptual understanding at the development stage of a geothermal reservoir. Rotokawa Joint Venture, a partnership between Mighty River Power and Tauhara North No. 2 Trust currently operates 174 MW of generation at Rotokawa. Important conceptual elements that can be clarified in joint analysis of MT and natural state temperatures beyond what is typically feasible based on MT for exploration projects include; details of fluid upflow/outflow, influx and cross-flow paths of cooler groundwater, and permeability variations above and at the margins of the reservoir.
The Ngatamariki geothermal field is situated 17 km north east of Taupo. Mighty River Power has an... more The Ngatamariki geothermal field is situated 17 km north east of Taupo. Mighty River Power has announced plans to build an 82 MW power station on the field. As part of the consent and planning processes, an extensive programme of drilling, testing and modelling was undertaken to provide understanding of the likely response of the field to a development. Analysis of the three new deep wells drilled by Mighty River Power in 2008-9 and the four wells drilled by the New Zealand government in the 1980s, together with recent MT surveys, showed a larger field than was originally defined by the early DSIR resistivity surveys. A conceptual model was developed to encompass the new data collected from the wells and the MT surveys. Modelling of the field was undertaken with a fullfield dual-porosity numerical model together with a number of simpler process models. The challenge for the numerical modelling was to find parameter values for the model that would provide robust predictions of the fi...
An adaptive management and injection strategy has been used to ensure that the Kawerau power plan... more An adaptive management and injection strategy has been used to ensure that the Kawerau power plant has injection capacity to run at full load and balance pressure support to the field while preventing thermal breakthrough to production areas. A key part of this strategy is understanding injection well interaction. A strategy was developed with active reservoir testing and analyses used to maintain injection capacity. Injection well capacity was initially measured through standard multi-rate completion tests following drilling. Subsequent monitoring was performed by continuous monitoring of wellhead pressure and injection rate; where no positive wellhead pressure was observed, downhole pressure monitoring tubing (i.e. capillary tubing) was installed to provide a fluid level monitor injectivity increase or decline. Wellbore models were used to estimate the full injectivity curve and its change over time. Tracers and chemical signatures were used to understand injection return to produ...
In March 2013, Mighty River Power (MRP) commissioned an 82MWe binary power plant in the Ngatamari... more In March 2013, Mighty River Power (MRP) commissioned an 82MWe binary power plant in the Ngatamariki geothermal field, 17 km north east of Taupo, New Zealand. A full field numerical model and several simpler process models of the Ngatamariki system were built and tested prior to the decision to proceed with resource development (Burnell, 2011, Clearwater et al., 2011). The sensitivity of these models was tested over a limited domain by varying individual parameters of interest. Conservative forward scenario runs were simulated by a reservoir model with reduced areal extent of permeable reservoir. In the present study, the sensitivity of model results to parameter values were analyzed in detail with the inverse modeling package iTOUGH2. An optimal model was then used to propagate the uncertainties in scenario forecasting by Monte Carlo simulation. This resulted in more rigorous statistics on what parameters drive model behavior and quantitative bounds on the confidence of model predic...
The Ngatamariki geothermal field is situated 17 km north east of Taupo, New Zealand, and in 2013 ... more The Ngatamariki geothermal field is situated 17 km north east of Taupo, New Zealand, and in 2013 Mighty River Power commissioned an 82 MW power station on the field consisting of four Ormat Energy Converter units. Production is from three deep wells in the center of the field and injection is back into four deep wells split between the North and South. Four of these wells were drilled during a campaign in 2012, including three injection wells. In addition to the normal completion testing, each of the new injection wells was injected with cold river water for several weeks to determine potential for stimulation. Prior to plant start-up, proved injection capacity was less than 50% of what was required to run the plant at full generation. Data from the stimulation testing phase constrained a simple analytic model of well stimulation based on Grant et al. (2013) and this model was used to predict injectivity evolution during plant start-up. Modeling predicted the injection wells would s...
The Awibengkok (Salak) geothermal system is a liquid-dominated, fracture-controlled reservoir wit... more The Awibengkok (Salak) geothermal system is a liquid-dominated, fracture-controlled reservoir with benign chemistry and low-to-moderate non-condensable gas content. The geothermal system is hosted mainly by andesitic-to-rhyodacitic rocks, and floored by Miocene marine sedimentary rocks cut by igneous intrusions. The volcanic sequence is capped by an 8400-year-old phreatic explosion breccia, rhyolite fallout tuff (&gt;8400 years and &lt;40,000 years), rhyolite lavas, domes
From mid-1993 through early 1998 Unocal, under a Joint Operation Contract with Pertamina, conduct... more From mid-1993 through early 1998 Unocal, under a Joint Operation Contract with Pertamina, conducted an extensive exploration program designed to locate and evaluate commercial geothermal systems within the Sarulla Block of North Sumatra, Indonesia. The exploration ...
The Awibengkok geothermal field, also known as Salak, is the largest developed geothermal resourc... more The Awibengkok geothermal field, also known as Salak, is the largest developed geothermal resource in Indonesia, currently sustaining 377 MW of electrical generation. It is a water-dominated, naturally fractured reservoir with benign fluid chemistry. A very large ...
The Awibengkok (Salak) geothermal system is a liquid-dominated, fracture-controlled reservoir wit... more The Awibengkok (Salak) geothermal system is a liquid-dominated, fracture-controlled reservoir with benign chemistry and low-to-moderate non-condensable gas content. The geothermal system is hosted mainly by andesitic-to-rhyodacitic rocks, and floored by Miocene marine sedimentary rocks cut by igneous intrusions. The volcanic sequence is capped by an 8400-year-old phreatic explosion breccia, rhyolite fallout tuff (&gt;8400 years and &lt;40,000 years), rhyolite lavas, domes
The Awibengkok (Salak) geothermal system is a liquid-dominated, fracture-controlled reservoir wit... more The Awibengkok (Salak) geothermal system is a liquid-dominated, fracture-controlled reservoir with benign chemistry and low-to-moderate non-condensable gas content. The geothermal system is hosted mainly by andesitic-to-rhyodacitic rocks, and floored by Miocene marine sedimentary rocks cut by igneous intrusions. The volcanic sequence is capped by an 8400-year-old phreatic explosion breccia, rhyolite fallout tuff (>8400 years and <40,000 years), rhyolite lavas, domes and related tuffs (≥40–120 ka), and dacite-to-rhyodate lavas and domes (185–280 ka) that were erupted across the eastern part of the field from NNE-trending vents controlled by a major fault. More regionally extensive basaltic–andesite to andesite volcanic centers are mostly between 180 and 1610 ka old. Surface and subsurface fault patterns, formation image logs and tracer studies indicate strongly anisotropic permeability aligned with the dominant N to NE fracture trend, dividing the field into a number of subcom-partments that are locally connected by fractured aquifers and NW-and E-W-trending fractures. Shallow argillic alteration gives way with increasing depth and temperature to argillic–phyllic and propylitic zones, with the latter accounting for the bulk of the fluid produced from the geothermal system. The commercial Awibengkok reservoir is a moderate-to-high temperature (240–312 • C) geothermal resource with high fracture permeability, moderate porosity (mean = 10.6%) and moderate-to-low matrix permeability (geometric mean = 0.026 md). The principal deep upflow zone, with fluid temperatures in the 275–312 • C range, is located in the western part of the field. The ascending fluids move up along Nor NNE-trending structures that breach low-permeability tuff layers in the central and east-central parts of the field. Fluids in the central part of the reservoir are uniform in composition and temperature, representing the mixing of upflow and convective reflux. Fluids ascend and flow laterally to the shallow top of the reservoir in the eastern area near drilling pads Awi 1 and 13 (fluid production temperatures: 240 to 270 • C). The eastern
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