Showing papers in "The Log Analyst in 1978"

Use Of V.h.f Dielectric Measurements For Borehole Formation Analysis

Abstract: A study of the dielectric properties of sedimentary rocks at a sufficiently high frequency may provide useful data for the evaluation of borehole wall formations in exploration and production wells. An experimental program carried out between 1960 and 1967 on sandstone and limestone samples lent further support to these expectations. At frequencies above 20 Mc/s both real and imaginary parts of the complex epsilon* = epsilon' - j epsilon'' were measurable. Moreover, at higher frequencies, epsilon' proved to be independent of the salinity of the water filling the pores, and insensitive to the way in which the oil and the water are actually distributed. The value of epsilon'', on the other hand, turned out to be indicative of the prevailing salinity. By combining other logging data (for instance from an electric or porosity log) with a series of such v.h.f. measurements of epsilon' and epsilon'', the oil or water saturation, the effective formation porosity, the pore-filling fluid salinity, and the rock matrix formation factor might be deduced, if the depth of investigation can be made large enough to overcome the invasion effects.

Stratigraphic Interpretation Of Seismic Data

Abstract: For a number of years now interpreters have endeavored to derive stratigraphic information from seismic cross sections instead of limiting themselves to the more classical interpretation of structural features. Up until recently, one approach to stratigraphic problems was based upon the relationship, on a macroscopic scale, between lithology and seismic propagation velocity in layers outlined by good quality reflections. Seismic velocity analysis procedures, based on reflection curvatures which had originally been designed for the processing of multiple coverage profiles, were soon put to use for the estimation of interval velocities. However, such estimates could be made with acceptable accuracy only over large interval, in the best of cases in the order of 100 meters. But the accuracy and detail of the information obtained from wells, as well as of the correlations sought for by geologists between this information and seismic results, are of an entirely different order of magnitude. A more detailed analysis of seismic sections was sometimes attempted by taking into account the character of the seismic traces themselves and associating the modifications of the shape of the signal with the stratigraphic evolution as recognized in neighboring wells, by correlating the seismic traces with the synthetic traces derived frommore » Sonic logs. However, such interpretations, based upon analogies between the shapes of complex signals, are lacking in resolution power and could be used only for qualitative interpretations.« less

Estimation of aquifer permeabilities from electric well logs

Abstract: Evidence from core data and log studies shows that permeability is related to formation resistivity factor. Empirical correlation relating the two rock parameters is determined using core data. Knowing the formation resistivity factor from electric logs, it is possible to calculate the permeability of a given formation interval. Field examples show that the proposed method is applicable in both water bearing and hydrocarbon bearing zones. The ability to predict the permeability of water bearing zones from electric well logs is of great importance in the assessment of aquifers geopressure energy resource.

Origin Of Abnormal Formation Pressures In Central North Sea Lower Tertiary Clastics

Abstract: The existence of definite seals bounding an abnormally pressured formation in Central North Sea Lower Tertiary argillaceous sediments is questioned. The hypothesis submitted favors a self-sealing mechanism, provided by four major factors: high clay content, dominance of swelling clays, discontinuous limestone stringers, and gas.

Seismic Applications Of Sonic Logs

Abstract: The continuous sonic log was developed to provide a detailed record of velocity for seismologists and even today the majority of sonic logs are run for this purpose, particularly in intermediate and surface runs An examination of the principle of sonic tools currently used indicates some often overlook limitations, which can cause severe errors from the seismic point of view (ironically, particularly in surface and intermediate logging runs) even when the logs are routinely calibrated by a well-shoot velocity survey Improved techniques for log calibration by well-shoot velocity surveys now compensate for limitations of present tools, and new tools which are far less limited are being developed These will need careful evaluation by the industry Although current developments may possibly reduce the seismic importance of sonic logs, improved tools will benefit the log analyst

Physical and Chemical Signals Around Oil and Gas Traps

Abstract: Oil and gas reservoirs in the earth are nonequilibrium dynamic systems which are never at rest over geologic time. From the early time of precipitation of organic vegetable and animal decay products within the mud and ooze of sediments, migration of organic matter occurred in a water borne transportation process as a result of sedimentary compaction and other diagenetic processes. Entrapment of organic matter in transit is visualized as occurring within upward-converging semipermeable rock strata, the hydrocarbons being retained in one or more subhorizontal spaces therein. A hydrochemical plume is formed in the vertical escape path of the transporting waters. Those ascending waters can produce such effects as mineral alteration by leaching, changes in the redox properties of the rocks, temperature anomalies, residual traces of hydrocarbons, differential compaction, vertical electrotelluric currents, near-surface electrical potential sinks, and magneto-electrotelluric effects. The latter are of special interest, as they are the basis of a versatile oil and gas exploration system bordering on direct oil finding. End_of_Record - Last_Page 9---------

Density-neutron Crossplot Analysis For Shaly Gas Sands Using Hand-carried Calculators

Abstract: A program for hand-carried calculators has been developed for shaly gas sand crossplot analysis. This program processes data obtained from a log suite consisting of FDC-CNL-GR and a deep-investigation resistivity log, and prints out values for effective porosity, shale content, and water saturation. The program uses an analytical method that describes the shaly-sand crossplot technique. This technique is capable of handling cases where the density porosity at the clay point is either positive or negative. The program executes the crossplot analysis accurately and quickly, taking less than 30 seconds for each data point.

The Dual Guard/forxo Logging Device

Abstract: A Dual Guard Electrode Logging System was initially suggested in the literature on resistivity well logging, but no details as to how the combination should be accomplished were given. With the introduction of the Dual Laterolog, the dual electrode-type device was labeled difficult to implement. This paper discusses the successful implementation of a dual guard electrode logging system. This system measures simultaneously two focused logs of formation resistivity, with different depths of investigation, and has excellent thin resistive bed definition. The complex problem of coupling interference between electrode systems has been solved with an innovative electrode configuration and driving circuitry. Sample logs from several locations are shown, and charts for the interpretation of the logs are given.

Fluid Contact Monitoring In Some Western Canadian Reefs

Abstract: Thirty years have passed since oil was first discovered in reefal reservoirs in the Western Canadian Sedimentary Basin. The early giants such as Redwater, Leduc, and the large Swan Hill pools have been followed in subsequent years by the development of reef pools of declining size, culminating with the discovery of the Keg River reefs of the Rainbow Zama area some 10 years ago. Unfortunately the majority of reef pools are reaching a mature stage in their productive cycle. With this maturity comes an increasing need for the log analyst to diversify his role from merely recognizing hydrocarbons during the discovery process, to the analysis of remaining hydrocarbon distribution within the depleting reservoir. The monitoring of fluid movement has become an integral part of reservoir description. Geologist, log analyst, reservoir and production engineer must work as a coordinated team to explain the often anomalous fluid distributions that occur in the well bore. Oil recovery from the Devonian Leduc age reef at Golden Spike, Alberta has been, until recently, by displacement with a miscible solvent bank. The monitoring of gas--fluid interfaces has been accomplished by the use of pulsed neutron logs in cased holes and the combination of SNP-Density and SNP-Acousticmore » data in open hole situations. At Judy Creek premature advances of formation water and inefficient reservoir depletion resulted from a highly stratified reefal reservoir. Pulsed neutron logs, used after the recognition of the production problems, have helped define oil-water distributions in the reservoir and led to an improvement in recovery efficiency. Rainbow Devonian Keg River reefs are subjected to gas, miscible and water injection recovery schemes. A pool that has been converted from a primary gas expansion drive to water drive by injection has used the pulsed neutron log to monitor the effectiveness of this change.« less

Can In-situ Reservoir Hydrocarbon Composition Be Predicted From Hydrocarbon Analysis Of The Mud Stream?

Abstract: Mud logging is a geological well-setting service which provides, among others, a measurement of the hydrocarbon content of the circulated drilling mud stream. Many attempts have been made to quantify the data, that is to provide some insight into the hydrocarbon composition and productive capacity of the reservoir from the analysis of the hydrocarbons in the mud system. Unfortunately, the great number of variables involved between the downhole cutting of the formation and the gas aeration in a surface trap seem to limit such quantitative utilization of mud logging data. This paper presents one attempt to compare the relationship between the hydrocarbon gases and hydrocarbons as observed in the drilling mud at the surface to their subsurface environment and to evaluate the reliability of mud stream hydrocarbon analysis for the prediction of reservoir hydrocarbon content and production potential.