摘要:
A standoff compensation system is disclosed for use in an LWD system implementing gamma density and/or neutron porosity measurements. An acoustic transducer is provided to measure the standoff distance between the logging tool and the borehole wall. The present invention includes a downhole processor for determining a weighting factor for the density and/or porosity measurements based upon the measured standoff distance. The weighting factor can either be calculated by the downhole processor according to a predetermined weighting function, or can be retrieved from a pre-calculated look-up table in ROM. The processor then multiplies the weighting factor by the count data from the sensor to determine a weighted count value. The weighted count values are accumulated during an averaging period and normalized, so that a single normalized count value can be generated and either stored in downhole memory, used immediately, or transmitted by telemetry to the surface.
摘要:
Statistical variations in nuclear borehole logs are reduced using digital moving average data processing while maintaining responsiveness to formation changes, by transitioning through a combination of long and short filtered data as a function of the statistical variation of the differences of the long and short derived averages.
摘要:
A method of logging earth formations to ascertain relative elemental abundancies of potassium (K), uranium (U) and thorium (T) is disclosed. A natural gamma ray spectrum of an unknown borehole is compared with individual standard gamma ray spectra of potassium, uranium and thorium in at least four energy ranges or bands. Decay peaks of the three elements are encompassed by three of the energy bands and at least one other energy band is used to monitor the changes in shape of the unknown spectrum caused by borehole conditions differing from that of the standard or calibration boreholes. A function derived from the gamma ray count rates in the four bands is used to compensate the elemental abundancies of the three elements to be detected in the unknown spectrum for the effects of differing borehole conditions in the unknown borehole from the standard borehole conditions.
摘要:
In the preferred and illustrated embodiment taught herein, method steps for monitoring of raw materials to be used in drilling mud are disclosed. The materials are monitored for radioactivity. Procedures for taking such measurements are disclosed, and the extent of gamma radioactivity in the raw materials used in drilling mud is determined. This is correlated to the increased radiation attributable to mud made from these materials and the effect the mud would have on gamma ray measuring logs. An alternate procedure for testing drilling mud, typically at the well site, is also disclosed. The method detects mud radioactivity from any additives including barite, potassium chloride, well cuttings or others. Excessive background levels due to mud gamma radioactivity in a well may very well mask the data obtained by various logging procedures dependent on gamma radiation. Procedures are also described for either rejecting mud which is too radioactive or correcting the log measurements for mud effects.
摘要:
A method is disclosed for simultaneous determination of borehole and formation thermal neutron decay time components. The methods employ pulsed high energy neutron sources and time gated dual spaced detectors. Exponential decay curves are assumed for each of the components and iterative least squares fitting employing rapid convergence techniques are utilized.
摘要:
An improved pulsed neutron porosity logging system is provided in the present invention. A logging tool provided with a 14 MEV pulsed neutron source, an epithermal neutron detector and an inelastic scattering gamma ray detector is moved through a borehole. The detection of inelastic gamma rays provides a measure of the fast neutron population in the vicinity of the detector. Repetitive bursts of neutrons irradiate the earth formation and, during the bursts, inelastic gamma rays representative of the fast neutron population is sampled. During the interval between bursts the epithermal neutron population is sampled along with background gamma radiation due to lingering thermal neutrons. The fast and epithermal neutron population measurements are combined to provide a measurement of formation porosity.
摘要:
Earth formations surrounding a well borehole are bombarded with high energy neutrons which react with chemical elements in the formation components, giving rise to gamma radiation. The gamma radiation is detected by two separate, spaced detectors from which well logs are obtained indicating a ratio of the relative presence of silicon to oxygen in the formations.
摘要:
An improved pulsed neutron porosity logging system is provided in the present invention. A logging tool provided with a 14 MEV pulsed neutron source, an epithermal neutron detector, and a fast neutron detector is moved through a borehole. Repetitive bursts of neutrons irradiate the earth formations and, during the bursts, the fast neutron population is sampled. During the interval between bursts the epithermal neutron population is sampled along with background gamma radiation due to lingering thermal neutrons. The fast and epithermal neutron population measurements are combined to provide a measurement of formation porosity.
摘要:
An illustrative embodiment of the invention includes methods for linearizing the gain of borehole gamma ray energy measurement apparatus. A known energy peak (or peaks) which is prominent in the gamma ray energy spectra of borehole measurements is monitored and any drift in its apparent location in the energy spectrum is used to generate an error voltage. The error voltage is applied in an inverse feedback manner to control the gain of system amplifiers to cancel the drift.
摘要:
Compensation of photoelectric absorption measurements for borehole effects during nuclear logging of downhole earth formations is accomplished by detecting low energy gamma radiations entering two detectors in the logging tool along paths having substantially constant formation components but varying borehole components.