FLOW UNITS IDENTIFICATION AND ESTIMATION OF PERMEABILITY FROM WELL LOGS BASED ON CORE CALIBRATION AN

1
FLOW UNITS IDENTIFICATION AND ESTIMATION OF
PERMEABILITY FROM WELL LOGS BASED ON CORE
CALIBRATION AND SIMULATION OF MUD-FILTRATE
INVASION
Jesús M. Salazar The University of Texas at
Austin
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Introduction and Motivation

• This work aims at defining petrofacies and flow
  units in low-permeability gas-saturated clastic
  reservoirs.
• To study the influence of mud-filtrate invasion
  on readings of array induction logs.
• To estimate permeability based on the physics of
  mud-filtrate invasion.

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Geological Background
Bossier Formation
Data Provided by Anadarko Petroleum Corporation
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Rock Typing (I)
Porosity-Permeability
k/f parametric curves clearly define three rock
types
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Rock Typing (II)
HPMI Capillary Pressure
Rocks 1A, 2A are considered reservoir rocks. Rock
3A has very poor porosity and permeability and
sometimes can act as vertical flow barriers or
seals
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Rock Typing (III)
NMR T2 Distribution
Three T2 distribution were also observed for each
rock type
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Rock Typing (IV)
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Flow Units
Lorenz Plots to define flow units
2A
3A Shales
1A
Most Flow Units are Rock Type 2A and 1A
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Formation Evaluation (I)
Effective Porosity and Water Saturation
Dual fluid model, where the minimization of the
data misfit of formation density gives the
effective porosity as the model
Archies equation
r1 1.0 g/cm3 r2 0.8 g/cm3 m n 2
(initial guess) a 1 Rw 0.0126 Ohm-m _at_ 285 oF,
NaCl 220 kppm
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Formation Evaluation (II)
Absolute Permeability
Linear 3-variable regression based on Winlands
pore throat radius model
Klinkenberg corrected perm _at_ 2500 psi
Pore throat radius, r, is then computed from
Swirr
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Formation Evaluation (III)
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Physics of Mud-Filtrate Invasion

• Mud-filtrate invasion is a phenomenon that takes
  place in permeable porous media during the
  drilling process due to mechanical overbalance
  and mud circulation.
• The length of invasion is the radial distance
  that mud filtrate penetrates into the formation.
• The length depends on mud density, mud chemical
  composition, mud circulation pressure, and time
  of filtration. Rock properties also play an
  important role in controlling the time evolution
  of the invasion process

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Simulation Software

• INVADE-UTCHEM
• Two-dimensional chemical flow simulator which
  includes the effect of salt mixing between mud
  filtrate and connate water.
• Developed to solve the partial differential
  equations and boundary conditions for immiscible
  radial flow coupled with mudcake growth.
• Input Reservoir rock and fluid properties, mud
  properties.
• Output Cross-sections of water and hydrocarbon
  saturations and salinity as a function of radial
  distance away from the borehole, flow rate,
  mudcake growth.

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Saturation and Brine Conductivity Models
Conductivity saturation model (Archies law)
Brine conductivity salt concentration model
m, n , and a from lab measurements or other
estimation
Computations carried out in MATLABTM
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Simulation Geometry
2D Cylindrical model
Actual flow units and numerical finite-difference
grid used in the simulations of mud-filtrate
invasion
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Simulation of Mud-Filtrate Invasion (I)
Simulation in Key Well (well 1)
Flow Units 30
Bonner
Numerical Grid Nr 61 Nz 33
York
Pressure Pmud 9,400 psi Ppore 6,465
psi Salinity 32,000 ppm
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Simulation of Mud-Filtrate Invasion (II)
Sensitivity analysis to time of invasion.
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Simulation of Mud-Filtrate Invasion (III)
Sensitivity analysis to relative permeability
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Simulation of Mud-Filtrate Invasion (IV)
Resistivity Comparison in Well 1
Comparison of measured (Array Induction Tool) and
simulated shallow resistivity after 1 day of
invasion, and flow units (1A 1, 2A 2, 3A 3,
and shale 4)
New Archies parameters obtained through shallow
resistivity matching. 2A and 3A m 1.9, n
1.8 1A m 2, n 1.6
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Permeability From M-F Invasion (I)

• Initialize the simulation model and assess the
  time of invasion. All petrophysical properties
  estimated from logs (f, Sw), and extrapolated
  from core data (kri, Pc), remain unchanged.
• Perform the simulation of mud-filtrate invasion
  by keeping absolute permeability of each
  numerical layer as a variable parameter.
• Permeability is progressively adjusted until an
  acceptable match is found between the estimated
  flushed-zone resistivity and the measured shallow
  resistivity.

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Permeability From M-F Invasion (II)
Relative Wells Locations
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Permeability From M-F Invasion (III)
Simulation in Well 2
Flow Units 11
Numerical Grid Nr 61 Nz 17
Pressure Pmud 9,000 psi Ppore 6,500
psi Salinity 5000 7500 ppm
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Permeability From M-F Invasion (IV)
Mud-filtrate invasion simulation in Well 2
Low resistivity annulus
Shallow resistivitys reading zone
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Permeability From M-F Invasion (V)
Resistivity Comparison in Well 2
Comparison of measured (Array Induction Tool) and
simulated shallow resistivity after 1 day of
invasion, and flow units.
Notice the good agreement between measured and
simulated Rxo after the 1st run in INVADE.
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Permeability From M-F Invasion (VI)
Comparison of modified Winlands permeability
(initial guess) and mud-filtrate estimated
permeability
Mud-filtrate invasion permeability resulted in
the same as the initial guess.
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Permeability From M-F Invasion (VII)
Vertical Resistivity Profile in Well 3
Comparison of measured (Array Induction Tool) and
simulated shallow resistivity after 1 day of
invasion, and flow units.
Notice the mismatch between measured and
simulated Rxo after the 1st run in INVADE. In
this case the permeability is changed until a
resistivity match is accomplished.
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Permeability From M-F Invasion (VIII)
Resistivity match and comparison of initial guess
permeability and mud-filtrate estimated
permeability after 6 runs of INVADE
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Conclusions

• Traditional permeability models are not reliable
  methods to compute permeability in tight-gas
  rocks.
• The estimated permeability is consistent with the
  length of investigation and vertical resolution
  of well logs and, therefore, provides an
  upscaled version of permeability compared to
  that of rock-core samples.
• The estimated permeability could also be used in
  combination with direct measurements of
  permeability performed with formation testers to
  further calibrate other rock and fluid
  parameters.

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Backup Slides

• BACKUP

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Acknowledgements

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Rock Typing (III)
Pore Throat Radius Distribution
Three pore throat radius ranges were observed,
therefore, three rock types are identified
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Rock Typing (IV)
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Rock Typing (V)
Range of Petrophysical Properties
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Rock Typing (VII)
Litho-facies vs petro-facies
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Flow Units (II)
Stratigraphical Flow Profile
Vertical representation of defined flow units
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Formation Evaluation (II)
Absolute Permeability
Stress-dependent permeability
The level of stress dependency increases for the
lower-quality rock types
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Formation Evaluation (IV)
Absolute Permeability
Correlations between core vs estimated and NMR
permeability
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Physics of Mud-Filtrate Invasion

• Mud-filtrate invasion is a phenomenon that takes
  place in permeable porous media during the
  drilling process due to mechanical overbalance
  and mud circulation.
• The length of invasion is the radial distance
  that mud filtrate penetrates into the formation.
• The length depends on mud density, mud chemical
  composition, mud circulation pressure, and time
  of filtration. Rock properties also play an
  important role in controlling the time evolution
  of the invasion process.

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Simulation Software (I)
Simulation of Multi-Phase Fluid Flow (3-phase
4-component formulation)

• 3D Cylindrical Domain
• Material Balance Equations
• Transport Equations
• Equation of State
• Rock Compressibility
• Material Balance Equation for Salt Component

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Simulation of multi-phase fluid flow with
(3-phase 4-component formulation)
Modeling domain
Material balance equations
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Simulation of multi-phase fluid flow with
(3-phase 4-component formulation)
Transport equation
Equation of state
Rock compressibility
Material balance equation for salt component
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Simulation of Mud-Filtrate Invasion (II)
Key Well Mud Properties
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Simulation of Mud-Filtrate Invasion (VI)
Sensitivity analysis to time of invasion.
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Simulation of Mud-Filtrate Invasion (VIII)
Sensitivity analysis to relative permeability
after 1 day of invasion.
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Permeability From M-F Invasion (VII)
Simulation in Well 3
Flow Units 17
Numerical Grid Nr 61 Nz 32
Pressure Pmud 9,000 psi Ppore 6,500
psi Salinity 3000 4500 ppm
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Permeability From M-F Invasion (VIII)
Mud-filtrate invasion simulation in Well 3
Shallow resistivitys reading zone
Low resistivity annulus