INTRODUCTION TO GEOTHERMAL ENERGY
Presented in: Geothermal Short Course by Geothermal Department IAGI
STTNAS Yogyakarta September 15th, 2016
Presented by :
Alfiady Geologist and Geochemist
Supreme Energy
Outline Overview of geothermal resource
Stages in geothermal project
Geothermal system vs. Petroleum system
Geology in geothermal exploration
Geology in geothermal development
Geology in resource management
Presentation take-away
Geothermal utilization
Underground resource model (Model showing the origin of geothermal energy) Source: Geothermal Energy, Serial No. 87 (July 1999
Encyclopedia Britannica, Inc., 2011
Thermal energy generated and stored in the earth
Heat ‘mining’ from the earth Heat transfer through circulating fluids
(convective), either naturally or engineered
Used either directly (low enthalpy) or indirectly (high enthalpy)
The presentation will be focused on ‘conventional magmatic high-terrain geothermal system’ for electric generation
Geology setting is a key success factor of Geothermal development
Top green fields in Indonesia
Focus in Java and Sumatera
Geothermal Fields in Indonesia
Supreme Energy
Produksi / wells
Rajabasa
Rantau Dadap
Muaralabuh
Sibayak
Gn Salak Darajat
Wayang Windu
Lahendong
Kamojang
Sarulla
Hululais
Lumut Balai
Geothermal in Indonesia (tectonic setting)
Most of the producing
geothermal field are located in
West Java
Dieng (60
MWe)
Sumatra Quaternary volcanism
along strike-slip SFZ
Lahendong and Tompaso
Geothermal resources in remote area with low
electricity demand
Geothermal in Indonesia (current condition)
Resource potential
29.4 GW Badan Geologi, March 2015
Geothermal concession
69 WKP 19 Existing WKP 50 New WKP
Current capacity
1438.5 MW From 11 power plant
Obstacles • Low power price • Forestry and land
overlapping • Permitting • Social issues
• Resource risk
The highest risk phase
Pre-feasibility Exploration Feasibility
Exploration drilling (resource identification)
Development drilling (resource delineation & quantification)
Feasibility study of power plant, etc
Discharge testing Reservoir assessment Environmental impact
assessment
Environmental report Bid document preparation Contract award (plant &
civil) Pipeline routing &
design Final design
Construction & plan installation
Contract management, supervision of construction, inspection
Field management
Construction Design Commissioning & production
Geology Geochemistry Geophysics
Geotechnical Preliminary
engineering design
How to Develop Geothermal Energy from A to Z
Operation and Maintenance
Stages in geothermal project
Cum. Cost
Good geothermal exploration practice will drive good decision making
Geothermal Development (stages)
Stage by stage activities in developing geothermal field is intended to gradually reduce the risks
The highest risk is related to subsurface activity (upstream), i.e. pre-feasibility and exploration stage
The highest cost is related to surface facility construction
The risk is significantly reduced after exploration drilling
Gehringer and Loksha, 2012.
3G Exploration
Resource Risk : Temperature (Enthalpy) Reservoir Depth Permeability Fluid Chemistry Reservoir Extend and
Sustainability
Economic Risk Power Price Demand Gov. Policies (Regulation and
Subsidies) Social Issue
Geothermal Development Risk
Decreasing The Risk By: Application of best practice 3G
technique Development of appropriate
conceptual models Proper planning and execution of
Test Drilling/Exploration Drilling Proper “Reserve” Assessment
and feasibility study
Geothermal system
• Heat source • Reservoir and fluid pathway • Cap rock (clay cap) • Circulating fluid
Heat flow Porosity and permeability Controlling factor Temperature and chemistry
Cumming, 2009
Geothermal vs. Petroleum system
Geothermal Component Petroleum
Heat source is cooling intrusion or batholith not too old (Quaternary) to provide sufficient heat
Source Source rock is organic rich strata mature enough to generate hydrocarbon
Commonly within volcanic environment Reservoir Commonly sedimentary environment
Commonly clay alteration zone (smectite layer) Protecting hot system from surrounding cold water
Cap Impermeable strata (shale, salt, etc.) Trapping hydrocarbon and prevent further migration
Circulating hydrothermal fluid Fluid Accumulated hydrocarbon (oil or gas)
Commonly under pressured Pressure Commonly over pressured
Geothermal vs. Petroleum system
Geothermal Component Petroleum
Covers local geological/volcanic setting Spatial Regional/basin-wide setting
Quaternary volcanoes overly the older formation
Volcano-stratigraphy Temporal
Wider time frame Basin evolution over various tectonic events Lithostratigraphy, tectono-stratigraphy, sequence-stratigraphy, etc.
Geothermal exploration (key questions)
Boseley, et al., 2010
How to prove it through lowest cost exploration drilling Pad location Well targeting
If yes, then How big is it? Area Reservoir thickness Recovery factor
Is it there? Reservoir temperature Fluid chemistry Permeability
Geothermal Exploration Geological and Surface Studies
Geochemical Survey
Geophysical Survey
Surface geology mapping (Volcanic Product Thickness + Heat Source)
Thermal features chemical analysis, and physical features
Magnetotellurics and other resistivity survey as subsurface indicator of system extension
Locating and mapping active geothermal surface features (Possible CM and system extension)
Geothermometry and fluid chemistry analysis (water and gasses) as reservoir temperature indicator, brine chemistry, and flow pattern
Gravity and magnetic as subsurface structure indicators
Structural geological interpretation (Possible permeable structure)
Soil sampling , gas flux reservoir as indicator permeability
Heat flow and temperature gradient as indicator of resource size and extension
Passive seismic as indicator of permeable structures
Provide a framework for Conceptual Model(CM)
Provide a hard data for reservoir temp, type , origin , possible flow pattern for developing CM
Provide a description of subsurface structure which related to reservoir geometry and size
Geothermal exploration (Geology) Regional tectonic setting, fault maps,
and stratigraphy provide general framework for conceptual model of geothermal system
Volcano-stratigraphy, alteration zones and detail structural mapping
Identify possible heat source & major structure permeability
Volcano-stratigraphy or migration of eruption-center sometimes related to timing of formation of various geothermal systems
Volcanic facies model can be guidance to estimates matrix primary porosity distribution
Geothermal exploration (Geochemistry) • Geochemistry
represents reservoir fluid conditions such as temperature, fluid phase, acidity, scaling potential, fluid origin, etc.
• Geochemistry also represents convective hydrothermal flow/hydrologic model (upflow and outflow)
Geothermal exploration (Geophysics)
Combination of various methods instead of one single solution (like reflective seismic for oil/gas industry)
Deep resistivity imaging through EM method (i.e., Magnetotelluric/ MT)
Imaging the base of cap instead of reservoir strata
Combined with • Gravity (basement setting,
intrusion) • Geomagnetic (alteration,
demagnetized body) • Micro-EQ (permeability, fluid flow)
Survey design data acquisition and QA/QC data processing modeling interpretation
Geothermal exploration (data integration) Integrating geological setting,
geochemistry information, geophysical model and thermodynamic principles Geologist leads the process Integrated conceptual model guides
further assessments and decisions (resource estimation, exploration drilling strategy, uncertainty management) Alternative models to capture the
range of uncertainty
Exploration drilling strategy (testing the models)
Exploration wells for proving/disapproving various conceptual model, instead of targeting the ‘unexplained’ anomalies
Using conceptual model elements
• Isotherms to define bulk pattern of permeability
• Thermal manifestation chemistry to constrain isotherms and system geometry
• Resistivity to image low permeability alteration boundary
• Structures to illustrate boundaries and permeable paths
• Geology, geophysics etc to provide context
Well objectives as the drilling program driver: Temperature gradient hole Confirmation well/ Exploration well Production well Make up well Step up well
Well prognosis as a representation of well objectives and covers: Location Well objectives Design well track: KOP, AZI, INC Expected geology characteristic ,
pressure, temperature, and chemistry PCS(Size will affect well derivability) Target depth
Drilling team is responsible to the well construction and drilling operation
Exploration Drilling
rig and steam kick on geothermal well
Exploration drilling
ML-A1 ML-B1
Drilling rig
Cutting
Geologic well data
Core samples
Integration between well data and geophysics
To prove the preliminary interpretation based on 3G survey
Wellbore geology (lithology, alteration, structures)
Fluid chemistry (liquid, gas, condensate) Pressure and temperature profile Permeability (connectivity to the
reservoir)
Key Features Well objective Conceptual Model:
To set well location base on temperature target, target depth, and interpreted reservoir extension Top of reservoir:
Can be predicted from MT data (BOC) for production casing set (PCS)
Expected permeability: Fault target and targeted permeable interval
Conceptual model of Silakitang field , Sarula Source : Gunderson et al., 2000
Pre-Drilling CM to drive well emplacement
Updating conceptual model Post-drilling
conceptual model is constrained by P/T profiles, permeability, reservoir connectivity, chemistry, etc. acquired from wells
Either bigger or (commonly) smaller than early prediction
Numerical simulation and reserve confirmation
Updated conceptual model
Geologic modeling
Numerical model
Model matching
Forecasting
Working process Conceptual Model Numerical Model
Predictive Runs of Development Alternatives
Recommended Development Strategy
Size of Development Production Location
Injection Location Amount of production and injectate
in each location
Geology
Geochemistry
Geophysics
Reservoir
Development drilling and power plant construction
Power plant
Pipe-line
Separator
Yard
Turbine
Cooling tower
Control room Pipe-line Separator GRS
Producing geothermal field
After exploration and field development, Geoscientist’s should involves in reservoir management and monitoring Reservoir management is
important to maintain resource sustainability (balance between extracted and injected fluid) Monitoring effort is mandatory to
detect any significant changes in reservoir dynamic process
Reservoir monitoring
Problems during production phase • Reservoir drying out • Excessive pressure decline • Scaling on wells and surface facilities • Corrosion on wells and surface
facilities • Marginal recharge and cold water
influx • Injection breakthrough • Subsidence • Induced seismicity • Landslides and other geo-technical
issues • Others…
Reservoir monitoring
Reservoir engineering, chemistry, and geophysics provide the data
Geology provides the story
Presentation take-away Geothermal in Indonesia (with low power price and
expensive development cost) needs resource risk reduction to improves its economic
Geologist’s as main player in early stages (where the risk is high) should lead
Good geothermal exploration practice will drive good decision making
The Conceptual model should be the driver of exploration drilling program
Good well planning and execution is require for the success of the project
Thank You
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