Pulse neutron tools

Pulse neutron tools are mainly used for cased-hole application. Possibilities for applications of the PNN system are really huge. Most widely exploited application of all pulse neutron measurements, and PNN also, is the determination of water saturation in hydrocarbon reservoirs. Now with the PNN system, and their processing and interpretation techniques, salinity problem that first existed with standard pulse neutron tools is not any more a so big problem. When Initial hydrocarbons bearing zones have been evaluated with open-hole logs, PNN analysis results can then be used to monitor the depletion profile behind casing at any time during the producing life of the well.
This information gives:

  • remaining (possibly residual) hydrocarbon reserves
  • location of oil-water, gas –water and gas-oil contacts;
  • Warning of impending gas or water breakthrough at producing zones.
  • Coal detection

  • So-called time lapse technique eliminates the need of accurate mineral and shale interpretation. By using of this technique a base-log must be measured after the well is been completed, when saturation distribution is well known (some weeks after well completion). Later PNN measurement runs, done for monitoring purposes during the life of the reservoir, can easily be calibrated.
    Residual oil saturation can be estimated in cased-hole or observation wells. Various special techniques such as “Log-Inject-Log” are available to enhance the accuracy of the Residual Oil Saturation determination.

    As it was mentioned before formation fluid contacts can be evaluated not only by sigma interpretation but also by using dual spacing count-rate data. This can be very successfully used for monitoring of underground gas storage behavior.

    With the PNN system the evaluation of old wells is available for possible recompilation. PNN log provides information on:

  • porosity
  • shale or clay fraction,
  • hydrocarbon saturation and type
  • In an old well, where perhaps only an early electrical survey has been run, an evaluation can be made of shalliness, porosity and initial hydrocarbon reserves using PNN interpretation results. Gas zones can be identified, and present hydrocarbon saturation can be estimated.

    Where bad hole conditions prevent and influences the acquisition of a comprehensive open hole logging suite, PNN log can be run through drill pipe, or after completion to supplement logging data (Lithology, porosity, and hydrocarbons. Although rarely run in openhole, PNN can be used with openhole tools to give better definition of the lithology, particularly the clay fraction.

    PNN can also be run in cased hole to solve some of production logging problems as

  • holdup of fluids inside borehole
  • Possible behind casing flow.
  • PNN also can be run to solve some of environmental problems. It can be run in garbage disposals, water supply zones...etc.