Holistic approach to estimate water breakthrough; a case study

Historically, it has been a challenge to analyze and predict water cut or water production. While predicting water production may seem less relevant as compared to oil production, produced water poses many challenges. The difficulty rises when surface facilities cannot handle the water produced and reservoir pressure declines sharply as a result of excess water production. Multiphase flowmeters (MPFMs) have in the past few decades gradually replaced the conventional approach of metering multiphase flow streams using test separators. However, MPFMs have been faced with several challenges including flow assurance problems and high bottomhole temperatures and pressures. In addition, they have a threshold below which the accuracy of the measurement of water production will be highly questionable due to design and technology limitations. As a matter of economic decisions, it is necessary to detect and estimate early and post water breakthrough trends respectively. Several models to forecast water breakthrough have been developed. Among them is the famous water cut (WC) versus cumulative production (N_p) plot. This paper presents two empirical models to address the inability of MPFM to detect early water breakthrough below a threshold and to provide an alternative technique for modeling post water breakthrough. The models developed in this work predict water breakthrough using fluid volumes, bottomhole pressure and temperature. The first technique predicts early water breakthrough when the plotted function shows a deviation from a straight-line trend. In the second model, the water cut equation is modified for post water breakthrough prediction. Previous studies of water cut (WC) have focused on the production of water above the MPFMs threshold. The models derived in this paper provide accurate water cut estimates below MPMFs threshold and reliable post water breakthrough analysis.