Acoustics – Geophysical or subsurface exploration – Well logging
Reexamination Certificate
1998-09-25
2001-04-10
Dang, Khanh (Department: 2837)
Acoustics
Geophysical or subsurface exploration
Well logging
C181S108000
Reexamination Certificate
active
06213250
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to a method and apparatus utilized in hydrocarbon exploration. More specifically, the invention relates to the utilization of acoustic sources and receivers to determine acoustic properties of geologic formations as a logging tool traverses them, be it a wireline logging tool or a logging while drilling tool. More particularly, the present invention is directed to methods of and apparatus for converting between acoustic energy and electrical signals.
BACKGROUND OF THE INVENTION
Geologists and geophysicists are interested in the characteristics of the formations encountered by a drill bit as it is drilling a well for the production of hydrocarbons from the earth. Such information is useful in determining the correctness of the geophysical data used to choose the drilling location and in choosing subsequent drilling locations. In horizontal drilling, such information can be useful in determining the location of the drill bit and the direction that drilling should follow.
Such information can be derived in a number of ways. For example, cuttings from the mud returned from the drill bit location can be analyzed or a core can be bored along the entire length of the borehole. Alternatively, the drill bit can be withdrawn from the borehole and a “wireline logging tool” can be lowered into the borehole to take measurements. In still another approach, called “measurement while drilling” (“MWD”) or “logging while drilling” (“LWD”) tools make measurements in the borehole while the drill bit is working. There are a wide variety of logging tools, including resistivity tools, density tools, sonic or acoustic tools, and imaging tools.
An acoustic logging tool collects acoustic data regarding underground formations. The purpose of such a tool is to measure the “interval transit time” or the amount of time required for acoustic energy to travel a unit distance in a formation. In simple terms, this is accomplished by transmitting acoustic energy into the formation at one location and measuring the time that it takes for the acoustic energy to travel to a second location or past several locations. The measurement is complicated by the fact that the tool is roughly in the middle of a borehole of unknown diameter and is surrounded by mud. Further, the formation along the borehole may have been disturbed by the action of the drill bit and may no longer have the same acoustic characteristics as the undisturbed formation.
SUMMARY OF THE INVENTION
In general, in one aspect the invention features an acoustic logging apparatus comprising a tool body and a housing. A transducer operating in the bending mode is mounted in the housing. The transducer operates such that it is excited by or emits acoustic energy in only one of the two directions substantially perpendicular to the face of the transducer.
Implementations of the invention may include one or more of the following. The transducer may be a unimorph. The transducer may be a bimorph. The transducer may be utilized as an acoustic transmitter. The transducer may be utilized as an acoustic receiver.
In general, in another aspect, the invention features an acoustic logging apparatus comprising a tool body, a housing, a transducer operating in the bending mode mounted in the housing. The housing is mounted substantially removed from the axis of the body.
In general, in another aspect, the invention features an acoustic transmitter comprising a piezoelectric crystal for use in an acoustic logging tool configured to generate acoustic energy in response to an electric signal, the acoustic energy generated in a preferred direction being at least 3 dB larger than the acoustic energy generated in a direction substantially perpendicular to the preferred direction.
In general, in another aspect, the invention features an acoustic receiver comprising a piezoelectric crystal for use in an acoustic logging tool configured to generate an electrical signal in response to acoustic energy, the signal for acoustic energy of a magnitude received from a preferred direction being at least 3 dB larger than signals for acoustic energy of the magnitude received from a direction substantially perpendicular to the preferred direction.
In general, in another aspect, the invention features an acoustic transponder comprising an outer sleeve and an inner assembly coupled to the outer sleeve, the inner assembly being substantially acoustically isolated from the outer sleeve.
In general, in another aspect, the invention features an acoustic logging tool comprising an acoustic transmitter and an acoustic receiver. The acoustic receiver has a different electrical ground from the acoustic transmitter.
In general, in another aspect, the invention features an acoustic receiver for converting acoustic energy to an electronic signal comprising a hat, a piezoelectric crystal mounted within the hat, and a first compliant element separating the crystal from the hat.
Implementations of the invention may include one or more of the following. The hat may comprise a thermoplastic. The thermoplastic may comprise polyetheretherketone. The hat may comprise a metal. The acoustic receiver may include an excluder separated from the crystal by a second compliant element. The excluder may comprise a thermoplastic. The excluder may comprise a metal. The acoustic receiver may include a connector, a wire coupled to the connector and to the piezoelectric crystal, a portion of the wire being supported by the excluder.
In general, in another aspect, the invention features an acoustic receiver comprising an outer sleeve having a flange, a hat being slidably mounted within the outer sleeve.
Implementations of the invention may include one or more of the following. The hat may have a flange. The flange of the hat may move toward the flange of the outer sleeve as the hat slides into the outer sleeve. A first compliant element may be placed between the flange of the hat and the flange of the outer sleeve. The acoustic receiver may further comprise a piston, and a second compliant element between the piston and the hat. The acoustic receiver may further comprise a securing element configured to secure the piston relative to the outer sleeve. The securing element may comprise a snap ring. The acoustic receiver may comprise a lower housing coupled to the outer sleeve, a port through the lower housing for communicating with a chamber formed by the outer sleeve, the hat and the lower housing, pressure compensating fluid for filling the chamber, and a seal for preventing the pressure compensating fluid from escaping the chamber. The pressure compensating fluid may comprise oil. The seal may comprise one or more o-rings. The seal may separate the lower housing from the outer sleeve, and the hat from the outer sleeve. The compensation fluid, the hat, and the lower housing may compensate for pressure and temperature variations. A piezoelectric crystal may be secured within the assembly comprising the hat and the lower housing. The hat and crystal assembly may be configured to move relative to the lower housing. The movement may compensate for pressure and temperature variations.
In general, in another aspect, the invention features an acoustic transmitter comprising a main housing, and a hat slidably supported within the main housing.
Implementations of the invention may include one or more of the following. A compliant element may separate the hat from the main housing. A support element may rigidly separate the transducer housing from the compliant element. The support element may comprise metal. The support element may comprise a thermoplastic. The thermoplastic may comprise polyetheretherketone. The hat may comprise thermoplastic. The hat may comprise a metal.
The acoustic transmitter may comprise a piston engaging the main housing and a first compliant element separating the upper side of the hat from the piston. The acoustic transmitter may comprise a second compliant element configured to bias the hat against the first compliant element. The acoustic transmitter
Arian Abbas
Varsamis Georgios L.
Wisniewski Laurence T.
Dang Khanh
Dresser Industries Inc.
Speight Howard L.
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