Methods and apparatus to calculate a distance from a borehole to a boundary of an anisotropic subterranean rock layer

#This disclosure relates generally to oil production and, more particularly, to methods and apparatus to calculate a distance from a borehole to a boundary of an anisotropic subterranean rock layer.

#Oil and gas producers typically image subterranean rock layers to determine the location and shape of the subterranean rock layers. Such imaging may also be used to identify a boundary between the subterranean rock layer and an adjacent subterranean rock layer. The imaging is often performed using an imaging tool disposed within a borehole drilled into the subterranean rock layer to be imaged.

#Identifying a boundary of a subterranean rock layer is an important aspect of oil or gas well production. For example, identifying such a boundary of a rock layer enables oil or gas producers to plan well locations to efficiently and optimally extract oil or gas. Additionally, knowing the boundary of a rock layer may prevent oil and gas producers from drilling into undesired rock layers.

#FIGS. 1A-1D show typical seismic-while-drilling tools with one or more transmitters located at the surface.

#FIG. 2 shows a graph representing the effect of anisotropy within a subterranean rock layer.

#FIG. 3 shows an example wellsite system including a transmitter and receivers to implement the example methods and apparatus described herein.

#Certain examples are shown in the above-identified figures and described in detail below. In describing these examples, like or identical reference numbers are used to identify common or similar elements. The figures are not necessarily to scale and certain features and certain views of the figures may be shown exaggerated in scale or in schematic for clarity and/or conciseness. Although the following discloses example systems including, among other components, software or firmware executed on hardware, it should be noted that such systems are merely illustrative and should not be considered as limiting. For example, it is contemplated that any form of logic may be used to implement the systems or subsystems disclosed herein. Logic may include, for example, implementations that are made exclusively in dedicated hardware (e.g., circuits, transistors, logic gates, hard-coded processors, programmable array logic (PAL), application-specific integrated circuits (ASICs), etc.) exclusively in software, exclusively in firmware, or some combination of hardware, firmware, and/or software. Accordingly, while the following describes example systems, persons of ordinary skill in the art will readily appreciate that the examples are not the only way to implement such systems. Further, the examples may be implemented by acoustic signals that may include seismic signals, sonic signals, ultrasonic signals and/or any other shear and/or compression signals.

#Currently, oil and/or gas producers use time-indexed waveforms of a signal to image a boundary of a subterranean rock layer adjacent to a wellbore or a borehole. The frequency, amplitude, and/or energy of the signal are specified so that the signal can propagate through the rock layer being logged but reflect off a boundary of the rock layer. For example, a signal having a frequency of 8000 Hertz (Hz) may be specified to enable the signal to propagate through a first rock layer. However, a signal at this frequency may reflect off a boundary of the rock layer. The boundary may include a change in rock type from the subterranean rock layer being logged to a second type of rock in a second subterranean rock layer, a change in a lithology of the subterranean rock layer, a change in a fault of the subterranean rock layer, or a change in an unconformity within the subterranean rock layer.

#The boundary is imaged by transmitting one or more acoustic signals from a transmitter and recording when the signals are received by one or more receivers. Each receiver may include one or more sensors circumferentially located around the receiver so that each sensor may detect the transmitted signal from a specified direction. The sensors may include any type of transducer to convert a detected acoustic (e.g., seismic, sonic, ultrasonic, etc.) signal into an electrical signal and/or impulse decipherable by a microcontroller, a transistor, and/or a processor. By aligning the sensors in specified directions, oil and/or gas producers can determine the direction from which a signal was reflected. Typically, one or more transmitter(s) are located at the surface in proximity of a well site while receivers are included within a tool that is placed within a wellbore or borehole of a rock layer bring logged.