Abstract: A clock system is disclosed which includes a dual mode oscillator crystal having a first output having a frequency related to a temperature of the oscillator crystal and a second output having a frequency substantially stable with respect to temperature. The clock includes a temperature maintenance device. The temperature maintenance device and the oscillator crystal are disposed in a thermally insulated chamber. The clock includes a processor operatively coupled to the temperature maintenance device and the oscillator crystal. The processor is adapted to operate the temperature maintenance device so as to maintain a temperature of the chamber within a predetermined range. The processor is adapted to calculate a substantially constant frequency clock signal from the second output and a ratio of the frequency of the first output with respect to the frequency of the second output.

Abstract: An apparatus for communication with a downhole tool includes uphole and downhole equipment. The uphole equipment includes a signal source (or array) coupled to a programmable triggering system and a precision clock. Optionally, the uphole equipment may include receivers for capturing reference signals near the source and may include telemetry equipment for receiving MWD signals from the downhole equipment. The downhole equipment includes one or more receivers, signal processing equipment, memory, and a precision clock. Optionally, the downhole equipment also includes MWD telemetry equipment for transmitting data to the surface. The methods of the invention include, but are not limited to, synchronizing the recordation of signals detected downhole with the firing of the signal source and processing the recorded signals to eliminate useless information.

Abstract: There are many natural pauses during rotary drilling operations where a portion of the drill string remains stationary. Pauses include drill pipe connections, circulating time, and fishing operations. These pauses are used to obtain formation evaluation measurements that take a long time or that benefit from a quiet environment, as opposed to the naturally noisy drilling environment. Various techniques that are sensitive to the mud flow, weight-on-bit, or motion of the drill string may be used alone or in combination to identify the drilling mode and control the data acquisition sequence.

Abstract: Parametric inversion is used to advantage in a technique and apparatus for borehole logging to determine properties of anisotropic formations, and a dispersion function that varies with frequency is used in the modeling of the formations.

Abstract: A technique is disclosed for determining properties of an anisotropic elastic medium, such as earth formations. Acoustic waves are established in the medium. At several spaced locations in the medium, there are measured at least two orthogonal components of acoustic waves which have propagated through the medium. For positions corresponding to a plurality of adjacent ones of the spaced locations, there are computed model composite waves which would result from the superposition of a plurality of model acoustic waves, each having selected model parameters. The model acoustic waves include a plurality of model acoustic shear waves and the model parameters include model velocities and model polarizations for each of the model acoustic shear waves. An error value is determined, the error value depending on the differences, at each of the plurality of adjacent ones of the locations, between measured wave components and the model composite wave. The model parameters are then modified.

Abstract: Three-axis vertical seismic profile measurements are analyzed to derive values for the velocity v.sub.p and angel of incidence .PSI..sub.p of a plane compressional wave at the borehole and for the shear wave velocity v.sub.s and angle of incidence .PSI..sub.s of a plane shear wave at the borehole. In the described embodiment this is accomplished by finding values for these parameters which maximize the expression.SIGMA..sub..omega. .vertline.(a.sub.p +a.sub.s).sup.H u(.omega.).vertline..sup.2 /.parallel.a.sub.p +a.sub.5 .parallel..sup.2 +.vertline.(a.sub.p -a.sub.s).sup.H u(.omega.).vertline..sup.2 /.parallel.a.sub.p -a.sub.s .parallel..sup.2where.omega. is angular frequency;a.sub.p and a.sub.s are column vectors representing compressional and shear wave particle motions at frequency .omega. at a multiplicity of locations in the borehole;u(.omega.) represents components in a plane of waveform measurements obtained at these locations;.parallel. .parallel.