Method and apparatus for acoustically investigating a casing and cement bond in a borehole

Patent · Tue Mar 10 04:00:00 EST 1981

OSTI ID:6313105

Havira, R

Methods and apparatuses for acoustically investigating a casing in a borehole to derive the quality of a cement bond behind the casing and casing thickness are described. The techniques employ an acoustic pulse source having a frequency spectrum selected to stimulate a selected radial segment of the casing into a thickness resonance. The selected frequency spectrum enhances the reverberations between the inner and outer walls of the casing which traps the thickness reverberations with significant amplitudes for a duration depending upon the amount of acoustic energy leaked into adjacent media. The acoustic pulse causes acoustic returns which are formed by the reflections from interfaces between media of different acoustic impedances and acoustic energy leaked into the bore of the casing from the acoustic thickness reverberations stimulated within the casing walls. The acoustic returns are detected to generate a reflection signal which is processed to determine casing thickness or to evaluate the cement bond. The acoustic pulse has a frequency spectrum which is particularly effective in discriminating different cement bond conditions caused by small cement separations known as micro-annuli, around the casing. Several signal processing techniques and tools are described to provide accurate and high resolution cement bond evaluation and casing thickness determination by processing a portion of the reflection signal representative of the thickness reverberations.

• Assignee: Schlumberger Technology Corp
• Patent Number(s): US 4255798
• OSTI ID: 6313105
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020300* -- Petroleum-- Drilling & Production
03 NATURAL GAS
030300 -- Natural Gas-- Drilling
Production
& Processing
BOREHOLES
BUILDING MATERIALS
CAVITIES
CEMENTS
DIMENSIONS
EQUIPMENT
FREQUENCY SELECTION
MATERIALS
NATURAL GAS WELLS
OIL WELLS
PULSES
REFLECTION
SONIC LOGGING
THICKNESS
WELL CASINGS
WELL LOGGING
WELL LOGGING EQUIPMENT
WELLS