chapter 4 borehole environment - new mexico institute of...
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Chapter 4 Borehole Environment
Lecture notes for PET 370
Spring 2012
Prepared by: Thomas W. Engler, Ph.D., P.E.
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Borehole Environment
• Drilling mud, mudcake, mud filtrate
Rm Rmc Rmf
• Drilling fluids generally adversely affect logging tool response. Function of:
tool design
borehole size
mudcake thickness
depth of invasion
mud type:
oil, water or air
Drilling Fluids
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Borehole Environment
In gauge • borehole diameter is
equal to drilling bit size
Borehole reduction • mud cake buildup,
precursor to permeable formation
Borehole enlargement • swelling and sloughing of
shales • collapse of poorly
cemented porous rock • dissolution of salts,
evaporites Logging tools typically calibrated on 8” borehole. Corrections necessary for smaller and larger borehole sizes
Borehole Size & Shape
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Borehole Environment Borehole Size & Shape
Profile of a borehole (Bassiouni, 1994)
Bit size
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Typical caliper log, highlighted in yellow, for the Gallup formation. From Lindrith B #96, API# 303925723
Borehole Environment Borehole Size & Shape
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Borehole Environment
Applications • evaluate the borehole environment for
logging measurements • identification of mudcake deposition,
evidence of formation permeability • estimate hole volume to determine
cement volume requirements • determine competent formations to set
packers • provide position data for dipmeter
interpretation
Caliper Logging
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Borehole Environment Comparison of various caliper devices
Caliper Logging
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Borehole Environment
Comparison of various caliper devices
Caliper Logging
Skid
Arm
Short Axis
Long Axis
Borehole Center
+
+
Borehole Center
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Borehole Environment
Invasion - The pressure differential between the mud in the annulus and the formation fluid pressure, forces drilling fluid into the formation.
Invasion
Dewan, 1983
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Borehole Environment
Idealized invasion profile
Invasion
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Borehole Environment
Invasion profile – water zone
Invasion
Radial Distribution
Of Resistivities Rmf = Rw
Distance
Rxo = Rt = Ro
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Borehole Environment
Invasion profile – water zone
Invasion
Radial Distribution
Of Resistivities Rmf = Rw
Distance
Rxo = Rt = Ro
Distance
Radial Distribution
Of Resistivities Rmf >> Rw
Rxo > Rt = Ro
Rxo
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Borehole Environment Invasion
Invasion profile – oil zone
What if Rmf << Rw?
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• What if oil-based mud in a HC zone?
Rmf >> Rw
• However, it is dependent on whether oil-in-water or water-in-oil emulsion.
Borehole Environment Invasion
Rxo > Rt Rxo
Distance
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Borehole Environment
Chapter 4, Sec. 4.1-4.4, Bassiouni, Z: Theory, Measurement, and Interpretation of Well Logs, SPE Textbook Series, Vol. 4, (1994)
Fundamentals of Petroleum, 2nd Ed., (1981) UTA
Dewan, J.T.: Essentials of Modern Openhole Log Interpretation, Pennwell Publishing, Ok (1983)
Western Atlas, Introduction to Wireline Log Analysis, Houston, TX (1992), Chapter 1
Hilchie, D. Applied Openhole Log Interpretation, CSM (1978)
References