The PT Borehole Simulator HEX-B2 Thomas Mgel Thomas Kohl GEOWATT - - PowerPoint PPT Presentation

ENGINE Workshop 4 “Drilling cost effectiveness and feasibility of high-temperature drilling” July 2-5 , 2007

03/07/07 ENGINE Reykjavik Drilling Workshop 1

The PT Borehole Simulator HEX-B2

Thomas Mégel Thomas Kohl GEOWATT AG Dohlenweg 28, CH-8050 Zürich

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Introduction

Pressure / Temperature are key parameters in reservoir characterization Borehole Measurements are expensive and require a proper data quality control P/T downhole data can be imprecise under EGS conditions

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Accuracy and Risk of Logging

Measurements in Boreholes:

• What goals should be achieved?
• How can the data be controlled?
• What happens during high flow rate experiments?
• Is accessibility in boreholes ensured?
• High Temperature
• Broken Casing
• High Mineralization

High Costs associated to data acquisition

• Logging operation
• Cleaning boreholes from cable/squeezed instruments

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New Possibility in Downhole Measurements

Requirements for data extrapolation to downhole conditions

• Require P/T information to travel from borehole head to

bottom or vice versa

• Processes related to fluid density distribution are most

critical

• Knowledge of
• Physical processes in borehole
• Geometrical layout of casing / cementing
• Rock matrix parameters

New technological developments

• Make use of use for new computer power

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Wellheads GPK2/GPK3

HEX-B2

borehole model GPK3 wellhead data

New pT- Simulator HEX-B2

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Dynamic properties and processes implemented

• Heat exchange with rock mass
• Fluid heat capacity (T, NaCl-mol)
• Fluid density (T, NaCl-mol, p)
• Buoyancy forces in the borehole
• Friction forces borehole/casing
• Fluid viscosity (T, NaCl-mol)
• Fluid volume (T,p)

Dynamic wellhead data

• 1. Wellhead pressure
• 2. Injection rate
• 3. Fluid temperatur
• 4. Fluid NaCl-molality

p(z,t) tmp(z,t)

PT (z,t)

in borehole

Resul ults ts

Injectiv tivity ty Index II (t)

+

p(z,t) tmp(z,t) Wellhead data:

• Initial pressure

Borehole data:

• Casing diameters
• Wall roughness
• MD-TVD
• Fluid losses into rock
• Initial NaCl-molality

Rock mass data:

• Thermal conductivity
• Specific heat capacity c
• Initial temperature

c (1) c (2) c (3) c (i) Flow Exit points

New pT- Simulator HEX-B2

Model parameters: Input parameters/Physical processes:

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Radial thermal diffusion (borehole completion and rock mass) Processes in borehole:

• Navier-Stokes equation
• Mass conservation
• Pipe friction
• Advection (NaCl-mol, T)
• Fluid density (NaCl-mol, T, p)
• Fluid viscosity (NaCl-mol, T)
• Fluid heat capacity (NaCl-mol, T)

Exit-/Entry points At production: Inflow of T(t) and NaCl-mol(t) Borehole model:

• Arbitrary borehole diameters
• Well completion
• Rock mass model
• Borehole trajectory

1 2 3 4 1 2 3 4 4 40% 20%

Features of HEX-B2

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Application of HEX-B2

Possible modes

• Reservoir response from measured wellhead data
• Pressure/flow rate BC at wellhead
• Calculation of injectivity/productivity indices
• Improvement of reservoir during stimulation
• Variation of downhole temperature during production
• Calculation of scenarios from reservoir parameters
• flow rate BC at wellhead; Reservoir parameters at bottom
• Pressure profile
• Production temperature
• Failure pressure at shearing events near borehole
• Optimization of production scenarios with thermosyphon effect

(Buoyancy)

• Design of well testing parameters

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Procedure for Application

Calibration of HEX-B2 Model

• Provide necessary borehole/rock parameters
• Calibrate model on existing dataset

Preparatory Phase

• Monitoring of wellhead data (pressure, temperature, molality)
• Evaluate transient effects from earlier tests

Calculation phase

• Set reference depth
• Calculate injectivity/productivity indices
• Perform sensitivity analysis

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Examples of HEX-B2: Soultz GPK3 Stimulation 2003

HEX-B2 calculation

• f injection

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Examples of HEX-B2: Soultz GPK3 Stimulation 2003

Comparison with downhole data

• pT-probe shifted from 4544 MD to 4244 MD
• good fits with measured data
• reconstruction of failed pressure data at 4544 MD

Data correction High Accuracy!

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Examples of HEX-B2: Soultz GPK3 Stimulation 2003

DEMO

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Examples of HEX-B2: Soultz GPK4 Stimulation 2004

Completion of downhole PT-data

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Examples of HEX-B2: Synthetic GPK2 Production Test

Calculation of production without additional inflows

• Tdh = 190°C
• NaCl-mol = 5

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Examples of HEX-B2: Synthetic GPK2 Production Test

Calculation of production with assumed inflows

• Tdh = 190°C
• NaCl-mol = 5
• inflows at -2200 MD
• inflows at -4500 MD

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• 50

50 100 150 Easting

• 550
• 500
• 450
• 400
• 350

Northin

• 4500
• 4550
• 4600
• 4650
• 4700
• 4750
• 4800
• 4850
• 4900
• 4950
• 5000
• 550
• 500
• 450
• 400
• 350

Northin

• 4500
• 4550
• 4600
• 4650
• 4700
• 4750
• 4800
• 4850
• 4900
• 4950
• 5000
• 400
• 300
• 200
• 100

Easting

• 100

100 200 300 Northing

• 4500
• 4600
• 4700
• 4800
• 4900
• 5000
• 100

100 200 300 Northing

• 4500
• 4600
• 4700
• 4800
• 4900
• 5000

First 24 h r < 25 m r : 25 - 50 m r > 50 m First 24 h r < 25 m r : 25 - 50 m r > 50 m GPK2 (2000): GPK3 (2003):

Examples of HEX-B2: Failure Pressure of Fractures

Near-borehole microseismicity

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• Near-borehole microseismicity
• Downhole pressure history

GPK2 (2000): GPK3 (2003):

Whole

• le open hole section activated immediately

Top-to to-down activation of open hole section

Failure pressure of all intersecting fractures immediat ediately ly exceeded Failure pressure of intersecting fractures was exceeded slowly ly

Examples of HEX-B2: Failure Pressure of Fractures

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GPK3 (2003): Depth + Time

• f near-borehole

events HEX-B2 Calculation of corresponding downhole pressures

+

• Failure pressure from 52 - 60 MPa with TVD
• Reflects depth-dependency of stress field
• Range at a given depth: fracture orientation?!
• Gradient of failure pressure: 5-10

10 MPa/400m

• 50

50 100 150 Easting

• 550
• 500
• 450
• 400
• 350

Northin

• 4500
• 4550
• 4600
• 4650
• 4700
• 4750
• 4800
• 4850
• 4900
• 4950
• 5000
• 550
• 500
• 450
• 400
• 350

Northin

• 4500
• 4550
• 4600
• 4650
• 4700
• 4750
• 4800
• 4850
• 4900
• 4950
• 5000

Examples of HEX-B2: Failure Pressure of Fractures

Fracture failure pressure for GPK3

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Examples of HEX-B2: Sensitivity Calculations

Steady-state pressure vs. Productivity Index Molality vs. productivity index

TCS [°C] PI [l/s/MPa]

150 160 170 180 190 200 1 2 3 4 5 mol = 0% mol = 10% mol = -10%

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Conclusions

HEX-B2 was used for interpretation of Soultz testing data Most useful features:

• Comparability of downhole pressure data
• Different tests during exploration phase at variable flow rates
• Extrapolation to arbitrary levels
• Comparability of data
• Calculation of injectivity/productivity indices
• Correction and reconstruction of pT-data gaps
• Sensitivity calculation
• Scenario analysis for production temperature (heat loss in well,

effect of inflow temperature,...)

• Accounting for effects of leaks in the casing (injection and

production)

Cost reduction for pT-downhole measurements