{"id":637,"date":"2026-04-08T21:34:28","date_gmt":"2026-04-08T20:34:28","guid":{"rendered":"https:\/\/pnnplus.com\/?page_id=637"},"modified":"2026-04-21T15:03:18","modified_gmt":"2026-04-21T14:03:18","slug":"pulsed-neutron-neutron-pnn-tool-for-porosity-measurement-in-cased-wells","status":"publish","type":"page","link":"https:\/\/pnnplus.com\/index.php\/pulsed-neutron-neutron-pnn-tool-for-porosity-measurement-in-cased-wells\/","title":{"rendered":"Pulsed Neutron Neutron (PNN) Tool for Porosity Measurement in Cased Wells"},"content":{"rendered":"\n
<\/div>\n\n\n\n

Pulsed Neutron Neutron (PNN) Tool for Porosity Measurement in Cased Wells<\/strong><\/h1>\n\n\n\n
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<\/div>\n\n\n\n
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Introduction<\/h2>\n\n\n\n

Well logging has been used since the 1920s to evaluate reservoir properties such as porosity, saturation, and permeability. Among these, porosity is one of the most critical parameters<\/strong>, as it directly influences reservoir evaluation and production potential.<\/p>\n\n\n\n

While many porosity measurement methods exist for openhole conditions<\/strong>, options are limited in cased wells<\/strong>. This is especially relevant for older fields where historical porosity data is often missing.<\/p>\n\n\n\n

The Pulsed Neutron Neutron (PNN) tool<\/strong>, primarily designed for reservoir monitoring and saturation evaluation<\/strong>, can also provide valuable porosity information<\/strong> when properly modeled and calibrated.<\/p>\n\n\n\n

PNN Tool and Measurement Principle<\/h2>\n\n\n\n

The PNN tool operates as a neutron\u2013neutron logging system<\/strong> equipped with:<\/p>\n\n\n\n

    \n
  • an electrical neutron generator<\/strong><\/li>\n\n\n\n
  • two neutron detectors<\/strong><\/li>\n<\/ul>\n\n\n\n

    Neutrons emitted into the formation interact with surrounding materials and lose energy through collisions. The rate of energy loss depends mainly on hydrogen content<\/strong>, making neutron tools sensitive to the Hydrogen Index (HI)<\/strong>.<\/p>\n\n\n\n

    \ud83d\udc49 Since hydrogen is mainly present in formation fluids (water, oil)<\/strong>, the measurement indirectly reflects formation porosity<\/strong>.<\/p>\n\n\n\n

    Neutron Porosity Measurement Theory<\/h2>\n\n\n\n

    Neutron logging is based on the principle that:<\/p>\n\n\n\n

      \n
    • Neutrons slow down most effectively when colliding with hydrogen nuclei<\/strong><\/li>\n\n\n\n
    • The thermalization process<\/strong> (slowing to thermal energy) depends on hydrogen concentration<\/li>\n<\/ul>\n\n\n\n

      In clean formations:<\/p>\n\n\n\n

        \n
      • Hydrogen \u2192 fluid-filled pores \u2192 porosity indicator<\/strong><\/li>\n<\/ul>\n\n\n\n

        However, corrections are needed for:<\/p>\n\n\n\n

          \n
        • shale content (bound water, OH groups)<\/li>\n\n\n\n
        • mineral effects<\/li>\n<\/ul>\n\n\n\n

          Specific Advantages of the PNN Tool<\/h2>\n\n\n\n

          The PNN tool introduces key improvements compared to conventional neutron tools:<\/p>\n\n\n\n

          1. Time-Channel Measurement<\/h3>\n\n\n\n
            \n
          • Measures thermal neutrons in 60 time channels (36 \u00b5s each)<\/strong><\/li>\n\n\n\n
          • Allows detailed analysis of neutron decay behavior<\/li>\n<\/ul>\n\n\n\n

            2. Ratio Imaging Technique<\/h3>\n\n\n\n
              \n
            • Generates ratio images<\/strong> from time-channel data<\/li>\n\n\n\n
            • Enables extraction of optimized curves for interpretation<\/li>\n<\/ul>\n\n\n\n

              3. Optimal Porosity Zone Detection<\/h3>\n\n\n\n
                \n
              • Best porosity results are obtained from channels 5\u20139<\/strong><\/li>\n\n\n\n
              • These correspond to the thermalization zone<\/strong>, closest to:\n
                  \n
                • true porosity response<\/li>\n\n\n\n
                • epithermal neutron behavior<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/div>\n\n\n\n
                  <\/div>\n\n\n\n
                  \n

                  Porosity Evaluation Using PNN<\/h2>\n\n\n\n

                  Although not originally designed for porosity, the PNN tool becomes highly effective when:<\/p>\n\n\n\n

                    \n
                  • calibrated with openhole neutron porosity data<\/strong><\/li>\n\n\n\n
                  • used to build correlation models<\/strong><\/li>\n<\/ul>\n\n\n\n

                    Workflow:<\/h2>\n\n\n\n

                    Extract ratio curves (e.g., channels 7\u20139) Correlate with openhole neutron logs Build porosity model Apply model to wells without porosity data<\/p>\n\n\n\n

                    Field Applications<\/h2>\n\n\n\n

                    The PNN-based porosity approach is especially useful for:<\/p>\n\n\n\n

                      \n
                    • Old wells<\/strong> without reliable porosity logs<\/li>\n\n\n\n
                    • Cased hole environments<\/strong> where openhole tools cannot be used<\/li>\n\n\n\n
                    • High salinity or complex formations<\/strong><\/li>\n\n\n\n
                    • Reservoir monitoring and re-evaluation of existing fields<\/strong><\/li>\n<\/ul>\n\n\n\n

                      Key Benefits<\/h2>\n\n\n\n

                      Provides porosity estimation in cased wells<\/strong> Reduces influence of:<\/p>\n\n\n\n

                        \n
                      • high neutron capture cross-section fluids<\/li>\n\n\n\n
                      • formation minerals<\/li>\n<\/ul>\n\n\n\n

                        Improves:<\/p>\n\n\n\n

                          \n
                        • reservoir characterization<\/li>\n\n\n\n
                        • saturation analysis<\/li>\n\n\n\n
                        • field development decisions<\/li>\n<\/ul>\n\n\n\n

                          Conclusion<\/h2>\n\n\n\n

                          The Pulsed Neutron Neutron (PNN) tool<\/strong> extends beyond its primary role in saturation logging by offering a reliable alternative for porosity evaluation<\/strong>, particularly in challenging environments.<\/p>\n\n\n\n

                          By focusing on measurements near the thermalization zone<\/strong> and using ratio-based processing<\/strong>, the PNN method minimizes environmental effects and delivers accurate results.<\/p>\n\n\n\n

                          \ud83d\udc49 This makes the PNN tool a powerful solution for:<\/p>\n\n\n\n

                            \n
                          • legacy fields<\/strong><\/li>\n\n\n\n
                          • cased hole analysis<\/strong><\/li>\n\n\n\n
                          • advanced reservoir evaluation<\/strong><\/li>\n<\/ul>\n\n\n\n
                            \"PNN
                            Detailed PNN Plus well logging analysis including porosity measurements, lithology interpretation, and gas separation indicators. Advanced visualization for accurate reservoir evaluation and subsurface analysis.<\/figcaption><\/figure>\n<\/div>\n\n\n\n
                            <\/div>\n<\/div>\n\n\n\n
                            <\/div>\n","protected":false},"excerpt":{"rendered":"

                            Pulsed Neutron Neutron (PNN) Tool for Porosity Measurement in Cased Wells Introduction Well logging has been used since the 1920s to evaluate reservoir properties such as porosity, saturation, and permeability. Among these, porosity is one of the most critical parameters, as it directly influences reservoir evaluation and production potential. While many porosity measurement methods exist […]<\/p>\n","protected":false},"author":2,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-637","page","type-page","status-publish","hentry"],"jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/pnnplus.com\/index.php\/wp-json\/wp\/v2\/pages\/637","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pnnplus.com\/index.php\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/pnnplus.com\/index.php\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/pnnplus.com\/index.php\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/pnnplus.com\/index.php\/wp-json\/wp\/v2\/comments?post=637"}],"version-history":[{"count":15,"href":"https:\/\/pnnplus.com\/index.php\/wp-json\/wp\/v2\/pages\/637\/revisions"}],"predecessor-version":[{"id":1121,"href":"https:\/\/pnnplus.com\/index.php\/wp-json\/wp\/v2\/pages\/637\/revisions\/1121"}],"wp:attachment":[{"href":"https:\/\/pnnplus.com\/index.php\/wp-json\/wp\/v2\/media?parent=637"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}