Abstract: To discriminate optically between the various phases in a three-phase fluid, a light beam (F) of non-zero divergence is injected into a detector block (10) made of a material whose refractive index is greater than the refractive indices of all three phases of the fluid. The block (10) has a sensitive zone (18) and a total reflection zone (20) such that incident rays (Ri) parallel to the axis (12) of the block strike the sensitive zone (17) at an angle of incidence (.THETA.i) and are returned parallel to the axis (12) by the total reflection zone (20). The angle of incidence (.THETA.i) is such that a first phase gives rise to almost total reflection, a second phase gives rise to almost total transmission, and a third phase gives rise to partial transmission and partial reflection.

Abstract: An NMR pulse sequence for use in the borehole environment is provided which combines a modified fast inversion recovery (FIR) pulse sequence with a series of more than ten, and typically hundreds, of CPMG pulses according to[W.sub.i -180-.tau..sub.i -90-(t.sub.cp -180-t.sub.cp -echo).sub.j ].sub.iwhere j is the index of the CPMG echoes gathered, i is the index of the wait times in the pulse sequence, W.sub.i are the wait times, i are the recovery times before the CPMG pulses, and tcp is the Carr-Purcell spacing. Measurements are made of the signals induced in the formation as a result of the magnetic fields. Determinations of M.sub.o and/or T1 are then made from the measurements according to relationships which relate Mp.sub.o, T1 and T2 to the signal magnitude. Other relationships which provide stretched exponentials or multiple exponentials can also be used. From the M.sub.

Abstract: An acoustic method and apparatus for investigating an earth formation penetrated by a borehole are described. Acoustic transducers are mounted on a tool to accurately determine the distance between a segment of the tool and the wall of the borehole. The acoustic transducers are positioned in such manner that the stand-off distance between individual resistivity measuring electrodes in an array, which is also mounted on the tool segment, and the borehole wall can be measured. The stand-off measurement is recorded and may be used to correct the electrode resistivity measurements. In one embodiment a calibration of acoustic transducers as a function of depth is obtained by employing acoustic calibrating transducers to compensate for borehole environment effects on the performance of the acoustic transducers as well as determine the acoustic velocity of the borehole fluid, such as mud. Several embodiments are described.