No abstract

The occurrence, orientation, and development of fractures are key parameters in the evaluation of carbonate and volcanic reservoirs. We have used a 3D finite-element method to numerically simulate the logging responses of a newly proposed multiarray azimuthal laterolog sonde (MALS) in a fractured formation. More importantly, a physical simulation performed with a scaled-down 3D resistivity apparatus was developed to verify the numerical simulation results. Comparative analysis indicated that the laterolog resistivity curves are controlled by the fracture dip angles. High-angle fractures normally correspond to positive differences in the array laterolog curves, whereas fractures with low dip angles consistently result in a negative difference. The MALS tool also provides an azimuthal resistivity measurement that can be used to determine the fracture dipping direction. The sine-wave trend in the 2D imaging of azimuthal resistivity displays the fracture occurrence. In addition, MALS can be used to identify vertical fractures around a borehole within a certain distance. In addition, combined with laterolog data, the fracture occurrence and extension length can be evaluated.

Compressive sampling (CS) is an attractive method to implement analog-to-information conversion (AIC) for a sub-Nyquist radar, where random demodulation (RD) is the most successful AIC. However, RD only considers the sparse characteristic of one single radar pulse, and its mixing circuit still works at the Nyquist sampling rate. To exploit the strong correlation of radar echo pulses, this letter presents a pulse repetition rate compressive sampler for radar target detection. It can acquire these highly correlated pulses by setting a different sampling start time for each pulse and compresses each pulse into one single sample, which means that the low compressive sampling rate is equal to the pulse repetition rate. Compared with RD, this new system reduces the complexity of the hardware circuit and improves the signal compression ratio. Experimental results verify that the proposed radar system outperforms RD by achieving target detection from compressive samples without signal recovery.