Advanced PVT and Core Analysis for Enhanced Oil Recovery Study of Unconsolidated Sandstone Reservoir
Authors: Gibrata Muhammad A , Ameish Giamal , Djanuar Yanfidra , Eldali Magdi , Huang Qingfeng , Lozano Jose , Ali Nizarudeen , Mansour Bashar 
Published: March 2023

In the matured unconsolidated sandstone reservoir of oil field, enhanced oil recovery (EOR) is important to be implemented. It is to ensure the oil production with the optimum recovery from the reservoir. It requires an integration multi disciplines rock and fluid properties evaluation. In this EOR Study with core-gas injection, it has used engineering of gas injection in advanced PVT analysis that requires a series of laboratory data to properly understand the injection solvent/reservoir fluid phase behavior and EOR displacement in core flooding.

The PVT study has been performed, initially on the gas miscibility and phase behavior that consists swelling test, minimum miscibility pressure (MMP), vapour liquid equilibrium (VLE) and multi-contact evaluation and flow assurance studies. The oil and water from the particular reservoir conditions have been used in the analysis. Then it continued with reservoir characterization, core-gas injection and water alternating gas (WAG) analysis. It has involved an in-house integrated petrophysical, geological, reservoir characterization and model in the EOR study. A 3D computed tomography (CT) image and the available RRT model have been used for core plugs selection of the EOR study.

The unconsolidated core samples have been plugged successfully by liquid nitrogen and cleaned, inject the higher salinity water until reaching a high water cut, inject the low salinity water in the same manner, and the wettability restoration a steady-state relative permeability with the selected fluids. The steady-state floods (gas-oil, water-oil and gas-water) have been designed to obtain relative permeability on plugs representing selected reservoir rock types at reservoir conditions (pressure and temperature). A digital rock analysis with steady state floods on the same rock types is validated, then digital rock analysis is used to obtain relative permeability data on all remaining rock types for fast time and effective cost. The saturation is determined by in situ saturation monitoring (ISSM) with X-Ray attenuation through the core. Injection continues until the pressure drop across the core sample and the measured saturation are stable. Gas and oil are injected into a sample initially at initial water saturation (Swi) with increasing gas/oil ratios up to maximum gas injection and the sample is at residual oil saturation. The optimum conditions for WAG and related parameters controlled by the core properties on the EOR displacement analysis are defined.

This special integrated approach of EOR study has provided the reliable technical basis and assurance for the development of unconsolidated sandstone reservoirs. The oil recovery with current reservoir conditions range has been measured. It has benefits to maximize oil recovery from current main producing reservoir with utilizing the available gas, fluid, core, logs, production and others reservoir data which is important for successful of the field development.