Production logging (PLT) has been routinely applied in oil and gas industry to estimate phase production profile, determine oil/gas/water producing layers, and detect major fluid entry or exit. Through successful PLT surveys and appropriate interpretation, it may also be possible to identify thief zones and high perm channels, locate injected fluid breakthrough, monitor fluid front movements, detect crossflow and fluid migration, assist in reservoir simulation studies, etc.
Subsequent workover operation following a PLT run is frequently performed aiming at reducing water production while maintaining/increasing oil and/or gas production. Unfortunately, in practice, mixing results have been obtained through workover operations designed based on PLTs, due to poor logging procedure, unreasonable PL tool selection, poorly executed surveys, inappropriate interpretation, etc.
In the presence of multiphase flow in a well, interpretation of production logs becomes critical for achieving successful estimate of major fluid entries and thus successful workover operation. Appropriate interpretation of production logs relies heavily on the selection of a reasonable multiphase flow model to correctly estimate gas-liquid slippage and capture complex multiphase flow features.
In this paper, the major flow characteristics of multiphase flow in a wellbore will first be described. Different correlations/models to describe multiphase flow and calculate slippage will then be introduced; the pros and cons of each correlation/model will be highlighted. The impacts of multiphase flow model selection and gas-liquid slippage assessment on the interpretation results of production logs will be investigated.
Field case histories will be described to illustrate the critical roles played by reasonable gas-liquid slippage assessment in production log interpretation. PLT interpretation based on different slippage assessments will be shown and compared with actual workover results. Guidelines for appropriate gas-liquid slippage assessment for production log interpretation will be provided and key lessons learned shared.