Logging with joint ultrasound and X-ray technologies
AssigneeHalliburton Energy Services, Inc.
InventorsZhijuan Zhang, Weijun Guo, Sriram Srinivasan
Life of this patent
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Abstract
A method and system for evaluating the cement behind casing and fully inverting acoustic properties of the material, including density and the speed of sound. A density map of the cement sheath is determined using a nuclear logging technique. An acoustic impedance value of the cement sheath is provided, either by measurement using an ultrasonic logging technique or simulated using an acoustic model. The acoustic model may assume a vertical incident plane wave and flat plates for casing and the cement sheath. From the density map and the acoustic impedance value, a map of the speed of sound in the cement sheath, or a gap therein, may be determined.
Claims14
A method for evaluating a cement sheath located outside of a casing in a wellbore, comprising:
- determining a density map of said cement sheath using a nuclear logging technique;
- providing an acoustic impedance value of said cement sheath, the acoustic impedance value being provided by:
- providing an acoustic model of said cement sheath;
- calculating a simulated acoustic impedance of said cement sheath from said acoustic model;
- and
- using said simulated acoustic impedance as said acoustic impedance value;
- and
- determining a map of the speed of sound in said cement sheath using said density map and said simulated acoustic impedance.
A method for providing an inversion model to predict properties of a cement sheath located outside of a casing in a wellbore, comprising:
- providing an acoustic model of said cement sheath as a function of acoustic impedance, wherein said acoustic model approximates said casing and said cement sheath as flat plates and assumes a vertically-oriented plane wave incident signal;
- determining a density map of said cement sheath using a nuclear logging technique;
- and
- inverting said acoustic model using said density map and a simulated acoustic impedance to determine a map of the speed of sound in said cement sheath.
A system for evaluating a cement sheath located outside of a casing in a wellbore, comprising:
- a downhole logging tool arranged for determining a density map of said cement sheath using a nuclear logging technique;
- and
- a processor system arranged for determining a map of the speed of sound in said cement sheath using said density map and an acoustic impedance value of said cement, wherein:
- said processor system includes an acoustic model of said cement sheath;
- and
- said processor is operable to calculate a simulated acoustic impedance of said cement sheath from said acoustic model and use said simulated acoustic impedance as said acoustic impedance value.
Dependencies are inferred from the claim text.