Implementation of the direct demodulation method for natural gamma ray spectral logging

Spectrum analysis of natural gamma ray spectral logging （SGR） data is a critical part of surface informa- tion processing systems. Due to the low resolution, which is an inherent weakness of SGR, and the low signal-to-noise ratio problem of logging measurements, SGR is usually treated with a low confidence level. The Direct Demodulation （DD） method is an advanced technique to solve modulation equations interactively under physical constraints. It has higher sensitivity and spatial resolution than the traditional methods and can effectively suppress the logging noise. Based on standard count rate spectral data obtained from the China Offshore Oil Logging Company SGR Calibration Facility, this paper presents the application of the DD method to gamma-ray logging. The results are compared with four traditional algorithmic methods, showing that the DD method is a credible choice, with higher sensitivity and higher spatial resolution in gamma-ray log interpretation. The Point-Spread-Function of the Shengli Oil Logging Company＇s natural gamma ray spectroscopy instrument is obtained for the first time. The quantities of various radionuclides in their calibration pits are also obtained. The DD method was applied successfully to gamma-ray logging, offering a new option for SGR logging algorithm selection.

Depositional Environment,Petrophysical Evaluation and Electrical Properties of Zeit Formation,Northwestern Shore of Gulf of Suez,Egypt

The Zeit sand reservoir is one of the most prolific formations at Northwestern side of the Gulf of Suez.In this research we will try to coordinate between electrical,petrophysical properties,depositional environment and facies discrimination in order to evaluate the hydrocarbon potentiality of studied Zeit Formation.The statistical parameters for potassium(K),thorium(Th)and Th/U ratio contents have a general increase towards northwestern parts,whereas uranium(U)content has a general increase towards southeastern parts.The sandstone facies is distinguished from the other facies by its thorium content>4 ppm.U has high carbonate content(U≥1 ppm).Rocks'electrical properties vary greatly depending on a number of factors.Electrical measurements were taken at frequencies range of(5×10^(-4)Hz-100 kHz)for fully saturated samples(clayey sandstone)with NaCl(20 gm/L).As salinity,clay content,and frequency increase,consequently does the electrical properties.The continental condition are present in northwestern part(back-sea)which is distinguished by high K percent,high Th,high Th/U ratio,and low U contents.Low K,Th,and Th/U ratio contents,with high U contents,characterize the marine depositional environment that existed around the east and southeastern parts(foresea coincide with the dipping of strata).Furthermore,the studied Zeit Formation has good petrophysical properties that coincide with marine conditions.The middle and eastern parts(around ISS-94 and CSS-288)is a good reservoir(porosity 36%-39%,shale content<15%,hydrocarbon saturation 71%-92%,and net pay thickness 17-63 feet).