We offer a solution to the problem of efficiently translating algorithms between different types of discrete statistical model. We investigate the expressive power of three classes of model-those with binary variables, with pairwise factors, and with planar topology-as well as their four intersections. We formalize a notion of "simple reduction" for the problem of inferring marginal probabilities and consider whether it is possible to "simply reduce" marginal inference from general discrete factor graphs to factor graphs in each of these seven subclasses. We characterize the reducibility of each class, showing in particular that the class of binary pairwise factor graphs is able to simply reduce only positive models. We also exhibit a continuous "spectral reduction" based on polynomial interpolation, which overcomes this limitation. Experiments assess the performance of standard approximate inference algorithms on the outputs of our reductions.
A new telemetry system enables remote point recording of electrical well logs. Simultaneously with logging operations on offshore Louisiana wells, film records are being produced in a New Orleans ofice more than 100 miles away. The system, using microwave as a data link, was installed to reduce costly shut-down time caused by delays in transporting logs to the ofice, and to extend well coverage by key personnel.At the well site, simultaneously with the recording o f an optical log, a portable quantizer converts log data to digital signals suitable for transmission over microwave and/ or telephone facilities. A t the receiving end the transmitted data are decoded into analog signals and recorded on film in a standard optical recorder. The film recording at the receiver is synchronized with the offshore logging operation and the log is available at the ofice as soon as at the well.A n alternate procedure is to record the digital output on magnetic tape for subsequent transmission. This procedure is used when microwave facilities are not immediately available on the well platform. The tape may then be taken to the nearest microwave station or telephone for transmission.The system is applicable to the transmission o f most types of electrical well logs. Induction-electrical surveys and Sonic logs have been successfully transmitted.
New logs and greater flexibility in electrical well logging applications are now provided by truck-mounted computer systems. These special computers digitize and record on tape the data from well surveys. Simultaneously with the recording of a subsequent log, the computers merge taped data and perform continuous log analysis computation. The optical recordings of these computations provide a rapid means of formation evaluation in the field. Two computer systems have been developed. In one the data are recorded digitally on punched paper tape. The second system records the data digitally on magnetic tape using a format compatible with most digital computers. A major application of the truck-mounted computers systems has been the merging of data from an induction-electrical survey with that from either a sonic or a formation density log. The resulting formation analysis log consists of continuous curves of Rwa, Fr/Fs (or Fr/Fd), and apparent porosity. The location of potential pay zones is more easily and quickly accomplished by scanning these computed logs than by manually performing the many computations required for a similar study. Since computations are automatically performed on all zones, it is unlikely that productive zones will be overlooked. Other combinations of log data are also possible. Introduction Several years ago a method was proposed by Tixier, et al., in which simple computations of data from resistivity and sonic logs provide more reliable "quick look" interpretations. These techniques, which involve the manual computation of an apparent water resistivity Rwa and of an Fr/Fs ratio, have been widely used by the industry. The methods use the sonic data to normalize formation resistivities for variations in porosity and shaliness. In the application of the techniques, Rwa and Fr/Fs values are computed and tabulated for many levels. Computations are made not only for zones of apparent interest on the resistivity curves, but also for obvious water-saturated intervals and shaly sections. The tabulated results or, even better, semi-continuous plots, as shown in Fig. 1, focus attention on the zones of interest. Oil- or gas-bearing intervals are indicated by Rwa and Fr/Fs values significantly higher than obtained for water-saturated zones. The log analyst may then concentrate his attention on the formations that offer production possibilities. He can selectively use his more complete and more precise methods of interpretation and, thus, perform the necessary evaluations in the shortest time. These quick look methods are particularly beneficial at the wellsite. JPT P. 22ˆ
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