The present invention relates generally to the field of electrical resistivity well logging. More particularly, the invention relates to an apparatus and a method for providing a directional resistivity tool with a slot antenna to make directional resistivity measurements of a subterranean formation.
The use of electrical measurements for gathering of downhole information, such as logging while drilling (“LWD”), measurement while drilling (“MWD”), and wireline logging system, is well known in the oil industry. Such technology has been utilized to obtain earth formation resistivity (or conductivity; the terms “resistivity” and “conductivity”, though reciprocal, are often used interchangeably in the art.) and various rock physics models (e.g. Archie's Law) can be applied to determine the petrophysical properties of a subterranean formation and the fluids therein accordingly. As known in the prior art, the resistivity is an important parameter in delineating hydrocarbon (such as crude oil or gas) and water contents in the porous formation.
With the development of modern drilling and logging technologies, “horizontal drilling,” which means drilling wells at less of an angle with respect to the geological formation, is getting popular because it can increase exposed length of the pay zone (the formation with hydrocarbons). It is preferable to keep the borehole in the pay zone as much as possible so as to maximize the recovery. Therefore, a directional resistivity tool with azimuthal sensitivity is needed to make steering decisions for subsequent drilling of the borehole. The steering decisions can be made upon measurement results of bed boundary identification, formation angle detection, and fracture characterization.
Directional resistivity measurements commonly involve transmitting and/or receiving transverse (x-mode or y-mode) or mixed mode (e.g. mixed x- and z-mode) electromagnetic waves. Various antenna configurations are well known for making such measurements, such as a transverse antenna configuration (x-mode) shown in
As described above, although the directional resistivity tools have been used commercially, a need still exists for an improved antenna configured in a directional resistivity tool.
A further need exists for an improved antenna with a simpler configuration to be easily deployed with a directional resistivity tool.
A further need exists for an improved antenna which is cost effective and easy to manufacture.
The present embodiments of the apparatus and the method meet these needs, and improve on the technology.
This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or its entire features.
In one preferred embodiment, a method for making directional resistivity measurements of a subterranean formation includes rotating a resistivity tool in a borehole, transmitting electromagnetic signals from a first slot antenna deployed on the resistivity tool, receiving the electromagnetic signals on a second slot antenna deployed on the resistivity tool, extracting a sinusoidal wave from induced voltages on the second slot antenna during a rotation round of the resistivity tool, deriving information of the orientation of a formation boundary, extracting peak-valley amplitudes of induced voltages on the second slot antenna during the rotation round of the resistivity tool and a rotation angle, and deriving information of distance and direction to the formation boundary.
In some embodiments, the first and the second slot antennas are recessed regions formed on an outer surface of the resistivity tool with a wire posited inside.
In some embodiments, the wire electrically connects an end wall of the recessed region to the center conductor of a coaxial connector at the other end of the recessed region and generates magnetic fields as a magnetic dipole.
In some embodiments, the coaxial connector links the wire in the recessed region to a circuit for signal transmission.
In another preferred embodiment, a magnetic dipole antenna deployed in a resistivity tool with a longitudinal axis and an outer surface includes an indentation formed on the outer surface of the resistivity tool, a coaxial connector deployed under the outer surface of the resistivity tool, and a wire posited in the indentation and electrically connecting an end wall of the indentation and the center conductor of the coaxial connector at the other end of the indentation. The indentation and the wire form a magnetic dipole to transmit or receive electromagnetic signals.
In some embodiments, the magnetic dipole antenna further includes a magnetically permeable material filled in the indentation.
In some embodiments, the permeable material is a magnetic material for enhancing transmission and reception of the magnetic dipole.
In some embodiments, the magnetic material is selected form the group consisting of a ferrite material, an electrically non-conductive magnetic alloy, an iron powder, and a nickel iron alloy.
In some embodiments, the magnetic dipole antenna further includes a protective material filled in the indentation.
In other embodiments, the protective material is epoxy resin.
In other embodiments, the indentation is circular shaped.
In other embodiments, the indentation is rectangular shaped.
In still other embodiments, the magnetic dipole antenna further includes multiple grooves formed on the outer surface and across the indentation on the resistivity tool to enhance transmission and reception of electromagnetic signals.
In still other embodiments, the groove is oval shaped.
In still another preferred embodiment, an apparatus for making directional resistivity measurements of a subterranean formation includes a resistivity tool with a longitudinal axis and an outer surface, multiple slots formed on the outer surface of the resistivity tool and oriented substantially parallel to the longitude axis of the resistivity tool, and multiple wires posited in the slots and electrically connecting end walls of the slots to form magnetic dipole antennas. The magnetic dipole antennas form at least one transmitter-receiver antenna group to perform transmission and reception of electromagnetic signals.
In some embodiments, the apparatus further includes a coaxial connector to connect the wires with a circuit for processing the electromagnetic signals to be transmitted or received.
In some embodiments, the apparatus further includes multiple grooves formed on the outer surface and cross the slots on the resistivity tool to enhance transmission and reception of the electromagnetic signals.
In some embodiments, the grooves are substantially transverse to the slots on the resistivity tool.
In other embodiments, the apparatus further includes a magnetically permeable material filled in the slots.
In still other embodiments, the apparatus further includes a protective material filled in the slots.
The drawings described herein are for illustrating purposes only of selected embodiments and not all possible implementation and are not intended to limit the scope of the present disclosure.
The detailed description will be better understood in conjunction with the accompanying drawings as follows:
The present embodiments are detailed below with reference to the listed Figures.
In some embodiments, the drill string 206 can further include a mud pulse telemetry system, a borehole drill motor, measurement sensors, such as a nuclear logging instrument, and an azimuth sensor, such as an accelerometer, a gyroscope, or a magnetometer, for facilitating measurements of surrounding formation. Also, the drill string 206 can be assembled with a hoisting apparatus for elevating or lowering the drill string 206.
The directional resistivity tool 212 according to the present invention can be applied not only to a logging while drilling (“LWD”) system, but also to a measurement while drilling (“MWD”) system and wireline applications. Also, the directional resistivity tool 212 can be equally suited for use with any kind of drilling environment, either onshore or offshore, and with any kind of drilling platform, including but not limited to, fixed, floating, and semi-submerge platforms.
The circuit chamber 312 can be deployed with transmitter and receiver circuits for processing electromagnetic signals to be transmitted or received.
In some embodiments, the slot antenna 302 can not only be oriented parallel with the tool axis, it can also be oriented in other directions, like perpendicular to the tool axis or located at any angle with the tool axis.
In some embodiments, a magnetically permeable material 314 can be filled in the indentation 304 to enhance transmission and reception of the slot antenna 302. The material 314 can be a magnetic material and can be deployed between the center wire and the floor of the indentation. The magnetic material can be, but is not limited to, a ferrite material, an electrically non-conductive magnetic alloy, an iron powder, and a nickel iron alloy.
In some embodiments, a protective material 316 also can be filled in the indentation 304. The protective material 316 can be for protecting the slot antenna 302 from damages caused while drilling. The protective material can be, but not limited to, epoxy resin, and can be located above the permeable material.
The present invention is in no way limited to any particular geometry and number of such slot antennas and grooves.
In some embodiments, either the transmitter antenna 500 or the receiver antenna 502 can be replaced with other types and shapes of antennas.
In operation, the transmitter antenna 500 and the receiver antenna 502 with a slot antenna configuration can act as a magnetic dipole to transmit/receive electromagnetic signals. Accordingly, the slot antenna 302 can also be called as a slot magnetic dipole antenna. During drilling, when the directional resistivity tool approaches a resistivity interface, the induced voltage on the receiver antenna 502 can reflect the presence of the interface (through the change of amplitude attenuation and phase shift), as know in prior arts. Furthermore, the sinusoidal change of the induced voltage on the receiver antenna 502 with the rotation of the directional resistivity tool 212 can indicate the direction from the resistivity interface, as the magnetic field in front of the antennas with the slot antenna configuration can be almost polarized in the azimuthal direction.
d=f(Vmax,R1,R2,∈1,∈2,μ1,μ2) (1)
At low frequency and in the non-magnetic formations, the resistivities of surrounding formations play dominant roles in determining the boundary distance. Equation (1) can be simplified as Equation (2) below.
d=f(Vmax,R1,R2) (2)
A three-dimensional look-up table, in terms of a maximum voltage and adjacent formation resistivities, can be pre-built through forward modeling in the directional resistivity tool 212 to increase the efficiency of directional measurements. The forward model provides a set of mathematical relationships for sensor responses in different environment with different electrical properties. The maximum voltage measured on the receiver antenna 502 can be the input data of the three-dimensional look-up table and then the distance from the directional resistivity tool 212 to the resistivity interface 706 can be generated with known or derived resistivities of surrounding formations, which can be pre-built in the table or measured from other devices coupled with the directional resistivity tool 212.
As illustrated above, the sinusoidally-varying induced voltage on the receiver antenna 502 can be indicative of electrical properties of surrounding subterranean formations, including, but not limited to, the distance to and direction of the resistivity interface 706. Thus, the directional resistivity tool 212 with a slot antenna configuration has azimuthal sensitivity to make steering decisions for subsequent drilling of the borehole.
In some embodiments, the first and the second slot antennas can be recessed regions formed on an outer surface of the resistivity tool with a wire posited inside.
In some embodiments, the wire can electrically connect an end wall of the recessed region with the center conductor of a coaxial connector at the other end of the recessed region and generate magnetic fields as a magnetic dipole.
In some embodiments, the coaxial connector can link the wire in the recessed region to a circuit for signal transmission, which can be deployed outside of the recessed region and under the outer surface of the resistivity tool.
The present invention is in no way limited to any particular order of steps or requires any particular step illustrated in
The present invention has been described in terms of specific embodiments incorporating details to facilitate the understanding of principles of construction and operation of the invention. Such reference herein to specific embodiments and details thereof is not intended to limit the scope of the claims appended hereto. It will be readily apparent to one skilled in the art that other various modifications may be made in the embodiment chosen for illustration without departing from the spirit and scope of the invention as defined by the claims.