ELECTROMAGNETIC PROPAGATION LOGGING: PROPAGATION LOGGING: ADVANCES IN TECHNIQUE AND INTERPRETATION Abstract The Electromagnetic propagation Tool (EPT*) is a downhole microwave instrumentation device which channels 1.1 GHz energy into the formation and measures the travel time and attenuation of the microwave signal as it propagates through the invaded zone. The relevant electromagnetic field theory, the basic measurement technique, and the tool block diagram are reviewed. The present interpretation techniques are then discussed, followed by several log examples which show the utility of the EPT. Specifically, the EPT-derived porosity, when compared with neutron/density porosity, porosity, when compared with neutron/density porosity, allows one to distinguish between hydrocarbon-bearing and water-bearing zones in formations having varying lithologies and water salinities.

The compensated dual resistivity (CDRSM) tool is an electromagnetic propagation tool for measurement while drilling. The CDR tool provides two resistivity measurements with several novel features that are verified with theoretical modeling, test-tank experiments, and log examples. IntroductionThe CDR tool 1 is a 2 ~ 106-cycles/sec electromagnetic propagation tool 2 . 3 built into a drill collar. This drill collar is fully selfcontained and has rugged sensors and electronics. The CDR tool is borehole-compensated, requiring two transmitters and two receivers. The transmitters alternately broadcast electromagnetic waves, and the phase shifts and attenuations are measured between the receivers and averaged. Phase shift is transformed into a shallow measurement, R ps ' and attenuation is transformed into a deep measurement, Rad' The CDR tool has several new and important features. I. Rad and Rps provide two depths of investigation and are used to detect invasion while drilling. For example, in a I-a· m formation, the investigation diameters (50% response) are 30 in. for Rps and 50 in. for Rad' 2. ROil and Rps detect beds as thin as 6 in.; however, these measurements are affected differently by shoulder-bed resistivities and both require corrections in thin resistive beds. Rps has a better vertical response than Rad' Rad and Rps cross over at the horizontal bed boundaries; this crossover can be used to measure bed thickness.3. Both Rad and Rps are insensitive to hole size and mud resistivity in smooth boreholes. Borehole corrections are very small even for contrasts of 100: I between formation and mud resistivities. Rugose holes and salty muds together, however, can cause larger errors than indicated by the borehole-correction charts. In these conditions, borehole compensation is essential for an accurate measurement.An extensive research program was conducted to verif'y these features and to ensure that the CDR tool provides a high-quality log. To achieve wireline quality, the CDR tool's physics was studied thoroughly, and its environmental effects were modeled and experimentaly measured. Two theoretical models are used for the CDR tool. The first model treats the tool geometry in detail but assumes a homogeneous medium outside the tool. This model is verified by test-tank experiments and by air measurements. The second model assumes a simplified tool geometry but treats boreholes, caves, beds, and invasion in detail. This model is used to study environmental effects and to prepare correction charts. Experiments with artificial boreholes, caves, step-profile invasion, and horizontal bed boundaries verif'y the predictions of the second model. Finally, CDR logs are compared to wireline logs to demonstrate the new features.

A new version of the Nuclear Magnetism Logging tool (NML) has been developed and will be available for limited commercial use in the near future. The tool measures the earth's field proton free induction decay of formation fluids. Since this tool operates exclusively with the CSU well-site computer system, it is capable of real-time computation and presentation of the free fluid index (FFI) and the spin-lattice relaxation time (T1). Other new features include a centralized coil sonde and improved electronics for higher signal-to-noise ratio and greater reliability. Engineering prototypes have been extensively field tested and have proven to be dependable in a logging environment. Logs correlate well with other porosity measurements from core data and sonic, nuclear, and electromagnetic propagation well logging tools. Data from NML logs can be applied to the determination of irreducible water saturation, porosity in unusual lithologies, residual oil saturation, and porosity in unusual lithologies, residual oil saturation, and to the estimation of permeability.

The basic theory upon which the microwave Electromagnetic Propagation Tool (EPT) has been founded is reviewed, and the measurement technique is discussed in terms of a functional block diagram. Two methods of interpreting the propagating wave's measured phase and attenuation are reviewed. Specific log examples which distinguish between hydrocarbon and water-bearing zones in several lithologies are presented..

Measurement of formation porosity and lithology in azimuthal quadrants around the borehole is now available. This new information is provided by a nuclear tool that makes azimuthal density, photoelectric factor and neutron porosity measurements while drilling. In addition, an ultrasonic sensor provides a tool standoff measurement in each quadrant. While rotating, the quadrants are defined by a magnetometer and oriented with the gravity vector, so that bottom, left, right and top quadrants are identitled.The tool Cim be run with several different stabilizer sizes or without a stabilizer, giving the driller more latitude in configuring the bottomhole assembly. The azimuthal capability allows the measurement of porosity with an unstabilized or "slick" tool without degradation of the measurement. This is accomplished by computing the porosity from the bottom quadrant where there is little tool st,mdoff in deviated or horizontal wells. Utilizing bottom quadrant porosities also results in improved measurement accuracy in cases where borehole conditions are poor due to enlargement or washouts. When the tool is stabilized, the quadrant porosity and lithology measurements result in improved geosteering as well as providing a quantitative measure of formation heterogeneity. At bed boundaries, comparison of top and bottom logs in real time results in better bed boundary detection and confirmation of the tool location within the pay zone. When the tool is between boundaries. an beterogeneity indicator can be computed from the quadnmt density, lithology and neutron porosity logs to better evaluate complex formations.The measurement of tool standoff per quadrant provides information on borehole size, shape and rugosity. The data can be used to indicate borehole stability on subsequent bit trips.The paper describes the method of the measurement. h,u'd- 137ware implementation and log examples illustrating the tool features.