Genesis and characterization methods of non-horizontal fluid contacts in reservoirs of the unstable shelf in Arabia

The Mesozoic unstable shelf of Arabia is a world-class oil field enrichment zone. Reservoir traps are predominantly long-axis anticlines featuring large-scale reservoirs. Non-horizontal fluid contacts are widespread within these reservoirs, exerting a significant influence on reserve assessment and development strategy selection. The characteristics of non-horizontal fluid contact morphology are influenced by multiple factors including tectonic activities, reservoir properties and fluids types. However, a systematic characterization method is currently lacking. This paper employs methods of comparative reservoir case studies, fluid potential analysis, and simulation modeling to summarize four genetic types. Furthermore, a characterization methodology based on reservoir dynamic data, such as core analysis and pressure testing, is established: (1) Utilize pressure test data to construct composite maps of reservoir structure overlaid with equipotential water lines. Generate separate fluid pressure gradient plots per well and per fluid type. Calculate the free water level position at each test well. (2) Determine the genetic type of the reservoir’s non-horizontal fluid contact based on composite maps and other relevant plots. (3) Define the 3D trend surface of the reservoir’s free water level according to the identified genetic type. (4) Calibrate the trend surface using the FWL positions at well points and assess the associated uncertainty.