THE AIM OF THIS PROJECT IS A BETTER DIAGRAPHIC INTERPRETATION OF HYDROCARBON RESERVOIRS BY A COMBINED USE OF SONIC AND ELECTROMAGNETIC LOGGING TOOLS THROUGH EXPERIMENTAL LAB CHECK OF THE THEORETICAL MODELS.
Petroleum geophysical methods analyse modifications to a wave propagated in the Earth. Modifications to the wave characteristics (velocity, attenuation) provide information on the nature of the media through which the wave travels. Research was carried out into the propagation of mechanical and electromagnetic waves in porous media.
With respect to the propagation of acoustic waves in natural porous media, a reliable laboratory methodology exists for sonic and ultrasonic frequency bands at pressures up to 45 MPa. For the rocks considered, terminal intrinsic attenuation in the sonic band was shown in the majority of cases to be low. This aspect is important for interpretation of sonic logs.
The study of acoustic properties was successful in terms of the dependency of velocity and attenuation on frequency. An explanation was provided for abnormally high attenuation frequently observed in the ultrasonic band both for compressional waves and for shear waves. A method for the experimental study of dispersion of velocity in rocks was developed which enabled evaluation of the limits of the application of theoretical viscoelastic models. This approach should be supplemented by a comparison with the seismic band.
With respect to the propagation of electromagnetic waves in natural porous media, the method developed provided accurate measurement of the complex dielectric permissivity of both attenuating and nonattenuating representative rock samples in the 10 Mhz to 1 Chz band.
Measurements have shown that at high frequencies (100 Mhz and greater), dielectric properties conform to the theoretical mixing laws where volume fractions are predominant, unlike acoustic properties where the microstructure is a fundamental parameter.
Acoustic anisotropy and fracture detection work concentrated in the detection of microcracking in core samples with the main aim of determining the direction of the main in situ stress. The device developed for P waves was successful in so far as velocity was concerned. Furthermore, Swave birefringence was particularly sensitive to mechanical defects in the material.
The study of permeability and surface waves provided theoretical and experimental clarification of the physics of the influence of the permeability of the propagation medium on the characteristics of acoustic waves.
AN IMPROVED EVALUATION AND KNOWLEDGE OF OIL RESERVOIRS WOULD STEM FROM A BETTER UNDERSTANDING OF THE INTERACTION MECHANISMS BETWEEN SONIC/ELECTROMAGNETIC WAVES AND THE RESERVOIR ROCKS AS A FUNCTION OF THE ROCK STRUCTURE AND OF ITS SATURATING FLUIDS. INTERPRETING THE RECORDINGS OF THE NEW (E.G. EVA) SONIC PROBES IS DIFFICULT DUE TO THE VIRTUAL LACK OF EXPERIMENTAL DATA OBTAINED TAKING INTO ACCOUNT THE EXTERNAL AND PORE PRESSURE.
A FOUR-STEP STUDY IS PROPOSED TO THIS PURPOSE:
1.- BY THE USE OF A RESONANT BAR APPARATUS AND OF IMPROVED DETECTORS,MEASUREMENTS WILL BE PERFORMED OF THE PROPAGATION VELOCITY AND ATTENUATION OF E AND S WAVES UNDER PRESSURE AT FREQUENCIES UP TO 20 KHZ AND PRESSURES UP TO 45 MPA ON SEVERAL TENS ROCK SAMPLES. ON THE MORE REPRESENTATIVES AMONG THE INFLUENCE OF THE SATURATING FLUID WILL BE EXAMINED. EXPERIMENTS IN THE ULTRASONIC RANGE WILL ALSO BE MADE.
2.- ANALOGOUS STUDIES WILL BE EXECUTED WITH ELECTROMAGNETIC WAVES < 0,8 GHZ LEADING TO INFORMATION COMPLEMENTARY TO THOSE FROM SONIC METHODS. ON ROCK SAMPLES OF KNOWN SONIC RESPONSE THE RELATIONSHIP BETWEEN POROSITY AND COMPLEX ELECTRICAL PERMITIVITY WILL BE SOUGHT USING A MODIFIED COAXIAL LINE SYSTEM. THE STUDY WILL BE PARTICULARLY FOCUSSED ON THE INFLUENCE OF THE SATURATING FLUID ON THE DIELECTRIC PARAMETERS.
3.- MEASUREMENTS OF ACOUSTIC ATTENUATION ANISOTROPY ON THE RADIAL PLANE OF ROCK CORES, POSSIBLY AXIALLY COMPRESSED, WILL BE EXECUTED AND THE RESULT ANALYSIS WILL BE PERFORMED AIMED AT CORRELATIONS WITH THE VARIOUS SOURCES OF THE MICROFRACTURES GIVING RISE TO IT.