Abstract: An apparatus for compensated formation evaluation has an outer housing; an inner housing disposed within the outer housing; an emitter disposed within the inner housing; a first sensor disposed within the inner housing; a first window in the outer housing, positioned about the emitter, to permit signals from the emitter to pass out of the outer housing; a second window in the outer housing, positioned about the first sensor, to permit signals to reach the first sensor from out of the outer housing; a second sensor disposed within the inner housing.

Abstract: A method for analyzing data from a measurement-while-drilling (MWD) formation evaluation logging tool which compensates for rotation of the logging tool (along with the rest of the drillstring) during measurement periods. The density measurement is combined with the measurement from a borehole caliper, preferably an acoustic caliper. The acoustic caliper can continuously measure the standoff as the tool is rotating around the borehole. If the caliper is aligned with the density source and detectors, it can determine the standoff in front of the detectors at any given time. This information can be used to separate the density data into a number of bins based on the amount of standoff. After a pre-set time interval, the density measurement can then be made. The first step in this process is for short space and long space densities to be calculated from the data in each bin. Then, these density measurements can be combined in a manner that minimizes the total error in the density calculation.

Abstract: The borehole formation model is built by stacking in a spaced relationship selected glass plates to simulate the formation. Each glass plate has a circular hole in the center to simulate the oil or gas borehole. The hole can be sized in different sets to simulate various borehole diameters and for accommodating casing/cement sections for simulating cased boreholes. The glass plates are supported by plastic spacers. The spacers are sized to provide a matrix section having uniform distances between layers. The "stacked" glass/spacer matrix provides only glass for simulating the formation "pore space". The glass plates have a uniform thickness, and the porosity of the simulated formation can be changed by changing the thickness of the plastic spacers. After stacking the glass plates, a "borehole" is constructed by inserting a thin stainless steel tube through the center holes of the glass stack and sealed at the bottom.

Abstract: This invention relates to a method for analyzing data from a measurement-while-drilling (MWD) formation evaluation logging tool which compensates for rotations of the logging tool (along with the rest of the drillstring) during measurement periods. In accordance with this method, the received signal is broken down into a plurality of sections. In a preferred embodiment, the present invention calls for the breaking of the signal from the formation into four different sections: top, bottom, right, left. As the tool rotates, it will quickly pass through these four quadrants. Each time it passes a boundary, a counter is incremented, pointing to the next quadrant. This will allow for dividing the data into four spectra for each detector. Each of these four spectra will be obtained for 1/4th of the total acquisition time. The relative error is minimized by comparing the relative error in each spectrum and selecting a specific spectrum or by combining at least two spectra.

Abstract: Gamma rays from a subsurface earth formation are detected, and measurement of their respective energy levels transmitted to the surface where the resultant spectral data is stored in a plurality of narrow energy windows. Functional relationships relating photoelectric cross-section, density, and soft-to-hard ratio are developed from a formation model. These relationships are utilized with the stored spectral data in a perturbative process whereby effect of photoelectric cross-section on density is reduced and improved accuracy in density determination effected. Additionally, density is factored into photoelectric cross-section determination, compensating for effects of density on the soft-to-hard ratio. Availability of the entire spectrum permits improved resolution of the windows, monitor peaks, and detectors, and permits compensation for detector resolution in the observed spectrum.