GEOTHERMAL RESERVOIR ENGINEERING

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GEOTHERMAL RESERVOIR ENGINEERING
Prof. Dr. Mahmut PARLAKTUNA MIDDLE EAST TECHNICAL
UNIVERSITY PETROLEUM AND NATURAL GAS ENGINEERING

• INTERNATIONAL SUMMER SCHOOL ON
• GEOTHERMAL GEOCHEMISRTY
• 02-15 June 2003
• Izmir - TURKEY

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RESERVOIR ENGINEERING

• Determination of well locations
• Planning and interpretation of well measurements
  (well logging, production rates, etc.)
• Determination of production mechanism
• Performance prediction studies of reservoir
  behavior

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RESERVOIR ENGINEERING ULTIMATE GOAL
Determination of optimum production conditions to
maximize the heat recovery from the reservoir
under suitable economic conditions
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QUESTIONS TO BE ANSWERED

• Most suitable development plan of the reservoir
• Number of wells with well pattern
• Production rates of the wellbores
• Heat that will be recovered
• Change in reservoir temperature with time
• Enhanced recovery techniques to increase the
  heat recovery from the reservoir

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STEPS

• Define the physical processes and develop the
  conceptual model of the reservoir
• Determine the physical and chemical properties
  of reservoir rock and fluid
• Develop the mathematical and physical models of
  the reservoir with the help of existing data.
  Define initial and boundary conditions

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SOME FACTORS SPECIFIC TO GEOTHERMAL RESERVOIRS

• Relatively high reservoir temperatures
• Volcanic origin of rocks with highly fractured
  characteristics
• Chemical precipitation of solids within the
  reservoir during production
• Boiling of water within the reservoir and/or
  wellbore

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GEOTHERMAL SYSTEMS

• Required conditions
• A heat source
• A heat carrier (except HDR)
• Reservoir rock
• Caprock

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GEOTHERMAL SYSTEMS
(Dickson and Fanelli, 1995)
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GEOTHERMAL SYSTEMS

• Vapor dominated systems
• Liquid dominated systems
• Geo-pressured reservoirs
• Hot dry rock (HDR)

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ENERGY DENSITIES OF GEOTHERMAL SYSTEMS
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ASSUMPTIONS

• A hypothetical geothermal reservoir
• Porosity 20
• Initial pressure 47 bar
• Initial temperature 260 ? C
• 7 bar pressure decline due to fluid production
• The reservoir fluid is at either saturated liquid
  or saturated vapor state

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SCENARIOS

• Scenario-1
• Originally water, remaining water
• Scenario -2
• Originally water, becoming steam
• Scenario -3
• Originally steam, remaining steam

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PHASE DIAGRAM
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PHASE DIAGRAM
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STEAM TABLES
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SCENARIOS
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Scenario-1

• Initially at 260 ? C
• hw1 1134.9 kJ/kg
• Vw1 1.2756?10-3 m3/kg
• Ew11.780 ? 105 kJ/m3

• After 30 years production
• hw2 1085.8 kJ/kg
• Vw2 1.2513 ? 10-3 m3/kg
• Ew21.7355 ? 105 kJ/m3

• Energy produced from water
• Ew4452.5 kJ/m3
• Energy produced from rock
• Er22857 kJ/m3
• Total energy
• Ea 27309.5 kJ/m3
• 83.7 from rock

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Scenario-2

• Initially at 260 ? C
• hw1 1134.9 kJ/kg
• Vw1 1.2756?10-3 m3/kg
• Ew11.780 ? 105 kJ/m3

• After 30 years production
• hs2 2800.4 kJ/kg
• Vs2 50.37 ? 10-3 m3/kg
• Es21.1193 ? 104 kJ/m3

• Energy produced from water
• Ew-s166180 kJ/m3
• Energy produced from rock
• Er22857 kJ/m3
• Total energy
• Ea 189670 kJ/m3
• 12.1 from rock

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Scenario-3

• Initially at 260 ? C
• hs1 2796.4 kJ/kg
• Vs1 42.134?10-3 m3/kg
• Es11.3274 ? 104 kJ/m3

• After 30 years production
• hs2 2800.4 kJ/kg
• Vs2 50.37 ? 10-3 m3/kg
• Es21.1193 ? 104 kJ/m3

• Energy produced from steam
• Ew2080 kJ/m3
• Energy produced from rock
• Er22857 kJ/m3
• Total energy
• Ea 24938 kJ/m3
• 91.7 from rock

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• Volume of reservoir to supply a 100 MW power
  station with steam for a period of 30 years
• Eelec 9.46 ? 1016 J
• Ethermal 5?9.46 ? 1016 J (20 efficiency)

• Scenario 1
• V 1.7319 ? 1010 m3
• Scenario 2
• V0.2494 ? 1010 m3
• Scenario 3
• V1.8967 ? 1010 m3

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Temperature measurements
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Negative Temperature Gradient
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Flowing well
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Closed well
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Temperature Profiles
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Well Completion Test

• Injection of cold wtaer into the wellbore
• The two main parameters measured
• Water loss
• Permeability

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Water Loss Test
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Example
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Pressure Profiles
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PRESSURE TRANSIENT TESTINGBUILD-UP TEST
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PRESSURE TRANSIENT TESTINGBUILD-UP TEST
Slope is proportional to PERMEABILITY
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PRESSURE TRANSIENT TESTINGDRAWDOWN TEST
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PRESSURE TRANSIENT TESTINGDRAWDOWN TEST
Slope is proportional to PERMEABILITY
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PRESSURE TRANSIENT TESTINGINTERFERENCE TEST
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TRACER TEST

• A tracer is an identifiable substance that can be
  followed through the course of a process
• Tracers
• Radioactive tracers NaI, NH4Br, I131, Br82, H3
• Chemical tracers NaCl, CaCl2,
• Organic Dyes Fluoresceine, Rhodamine-B,
  Methylene Blue
• Conventioanl tracers are identified by
  conventional analytical methods such as
  CONDUCTIMETRY, SPECTROMETRY
• Radioactive tracers are detected by the emitted
  radiation