Paper: Gas-Liquid Contact Determination By Log Analysis In Deeply Flushed Formations

A major objective of open-hole log analysis is the determination of the fluid content of the porous formations surrounding the wellbore. However, engineers frequently encounter severe difficulty when attempting this determination in low porosity pay zones because of deep, thorough flushing of the near wellbore formation by drilling mud filtrate. This problem is compounded flow pressure gas overlies oil or water, especially when resistivity logs are not available. This difficult arises because virtually total replacement of the gas by mud filtrate will suppress the gas effect which porosity logs experience in gas-saturated zones. The technique described in this paper will help to identify gas accumulations and gas-liquid contacts in the reservoir in situations in which mud filtrate flushing has hindered such identification. Using only the dual porosity log, the compensated neutron-density log, and the definition of density-derived porosity, the log analyst can easily and accurately locate gas zones and gas-liquid contacts, thus saving the costs of additional well logging, formation testing, and/or coring.