In the combination induction-electrical log used at present in the field, the induction logging tool is appropriate for the investigation of moderately invaded formations. A new induction sonde with a radius and investigation about twice as large has been developed recently for the case of deep invasion. It has very nearly the same vertical resolution as the present sonde so that thin beds are defined as accurately as before. The characteristics of the new tool are described, the corresponding interpretation charts are given and field examples are discussed.The design of the sonic logging tool has been modified to improve the calibration and the reliability. The fact that porosity can be accurately recorded by means of the sonic log has prompted new interpretation, procedures for saturation estimation, wherein the data concerning the various permeable beds in a given well are correlated.One approach consists of plotting transit time vs true resistivity, with an appropriate scale. With this approach, satu:rations can be estimated conveniently even in cases where formation water resistivity is not well known.In another approach, a comparison is made of the values of the formation waters computed from the re-SCHLUMBERGER WELL SURVEYING CORP. HOUSTON, TEX. sistivity and sonic logs. Using the concept of continuity, this procedure makes possible a quick determination of zones of saturation in shaly sands and/ or in case of appreciable variations of formation ~alinities with depth.It has been found that the comparison of porosity from the sonic log with the apparent porosity computed from a short-investigation resistivity log may reveal, in many cases, the presence of residual oil and thws detect potentially produ.ctive formations; this procedure is valuable when the true formation resistivity and the resistivity of the formation water are in doubt.
A Measurement While Drilling (MWD) system is now available to provide more downhole measurements than ever before. The measurements currently made near the bit, while drilling is in progress, include: formation radioactivityformation resistivityannular temperaturedownhole weight on bithole deviationazimuthtool face angle These geological and engineering measurements are transmitted via a continuous pressure wave through the mud inside the drill pipe. The signals are detected at the surface, where they are processed by an on-site computer. Information is plotted in real time on continuous multi-scale logs, presented digitally on video displays, printed out in hard copy, and stored on magnetic tape. This paper briefly discusses the MWD system that provides these downhole measurements in real time during drilling. Citing actual logs, the paper focuses on specific examples of how these measurements are being used to aid in formation evaluation and to improve drilling control at the well site.
bstract Formation evaluation has been grea![y improved by obtaining the data frotn drill-stem testing and a series of logs with one trip its the hole. The log is run imnaediately before and ujter the test. Both gamma ray and. resis:ivi[y curves are recorded down-hole in a seif-contained apparatus. In addition to tite basic information contained in the log itself, the combination with data obtained frotn clrill-wem testing will permit more accurate and complete jormation evaluation. Field examples are presented (O ilhcwrate results obtained with this techniqlie.
Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussions may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. Abstract A new downhole tool has been developed to indicate the presence of gas in the mud immediately above the drill bit. The new tool has many potential applications beyond the early anticipation of a kick. For instance, under favorable conditions, shallow gas bearing sands can be located without interrupting drilling operations. Consequently, drilling schedules and mud programs can be optimized for safe and programs can be optimized for safe and efficient rig operation. No electronics is used in the downhole gas detector and no modification of the drill string is necessary. operating the tool requires only a minor variation in routine drilling operations. Introduction Whenever formation gases flow into the well bore during drilling operations, a potentially hazardous condition exists. As the gas rises up the well with the drilling mud, it expands, reduces the apparent density of the well fluids and, consequently, reduces the pressure which the mud can exert pressure which the mud can exert against drilled formations. Most often, the reduction of hydrostatic pressure is small and the flow of gas into the well is quickly stopped by the buildup of a mud cake on the bore walls. However, if the initial amount of gas which enters the well as the bit cuts into the formations is high or if the mud density is abnormally low, the reduction in the well fluid hydrostatic pressure caused by the expansion-of the pressure caused by the expansion-of the gas permits more gas to enter the mud system. The additional gas causes a further reduction in the hydrostatic pressure and a corresponding additional pressure and a corresponding additional flow of gas. Unless the well is closed off, a blowout situation quickly develops. It is obviously very important to measure as accurately and as early as possible how much gas is being added to possible how much gas is being added to the mud stream near the bit in the process of drilling. If the amount is process of drilling. If the amount is small or if the flow is only temporary, the situation will correct itself and there is no reason to stop drilling operations. However, if the flow of gas is steady, it is inevitable that a dangerous condition is developing and immediate measures must be taken. Even when the gas kick is kept under control, the time required to correct the situation and the costs incurred to do so increase rapidly with the amount of gas which is permitted to enter the well bore. The laws of physics which apply to the expansion of formation gases in the well bore do not permit a simple and early detection of the kick.
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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