A Thorough Investigation of PVT Data and Fluid Model for Giant Onshore Field, Hidden Lateral Trends Identified

Abstract

A best practice for PVT modeling and reliability analysis had been developed in order to characterize complex giant oil reservoir fluid model, oil in place assessment and to optimize full field development and management plan for EOR studies. This study builds on previous studies done by various parties but includes recent data and revised objectives. The primary objectives are: (1) to develop understanding of fluid properties across the reservoir and the influence of separator conditions on formation volume factor. (2) to generate PVT models for the reservoir’s units, accounting for lateral and vertical variations in properties and including the ability to predict the performance of gas injection schemes 3) to estimate the potential for asphaltene precipitation and recommend further work to improve the reliability of the reservoir simulation model. The study is divided into three phases: (1) Review of previous work and conduct Data QC of PVT data. (2) Establish lateral and areal PVT property trends and EoS fluid model. (3) Historical separator conditions issues, reserves and oil in place volumes. The undertaken review of the previous EOS modeling studies had resulted in very different fluid models, each tailored slightly to focus on the specific priorities of the different studies. In this study, the understanding of the fluid properties and their distribution within the reservoir has been achieved by: Using a thorough QC process which rejected unsuitable sample dataIdentifying C6+ mass content as the reliable indicator of the fluid compositionGenerating lateral and cross-section fluid property plots to identify regional differencesGenerating C6+ mass content versus depth plots to define compositional gradients and property trends. Besides, analysis of the later MDT samples did not appear to have been used in identifying fluid property trends in any of the previous reviews. However, after Data QC, 18 PVT samples and reports were chosen to determine the compositional trends, 16 to determine property trends and 2 were identified for development of the EoS fluid model. Therefore, vertical and lateral fluid property gradients have been identified consistent with the reservoir structural and stratigraphy model. The initial GORs in the layer-cake South/Central regions fall between Rsi= 816 scf/bbl at the top (7551 ft TVDss) down to Rsi=582 scf/bbl near the OWC (8245 ft TVDss). A similar trend is observed in the northern clinoform region, but 106.6 ft deeper. None of the earlier PVT studies had identified lateral trends within this complex reservoir. The main uncertainty in the fluid description is a lack of data below 7950 ft TVDss.