THE IMPORTANCE OF SPECIAL CORE ANALYSIS IN MODELLING REMAINING OIL SATURATION IN CARBONATE FIELDS

摘要

An integrated study has been carried out to understand the field performance and remaining oil distribution of a number of heterogeneous and oil-wet carbonate reservoirs under waterflooding. Demonstrating the impact of basic rock characterization and special core analysis (SCAL) laboratory data on waterflood performance of a Cretaceous carbonate reservoir is the main focus of this paper. The rock characterization programme includes measuring detailed permeability distribution along reservoir intervals and integration with geological facies modeling. The SCAL programme consists of drainage and imbibition capillary pressure and relative permeability measurements for the predominant rock types using rock and fluid samples under representative reservoir conditions of pressure, temperature and wettability. To ensure data quality and repeatability, a combination of steady state with end-point bump floods and centrifuge techniques have been used for measuring the relative permeability curves extended to waterflood residual oil saturation. Numerical simulation was used to reconcile the various SCAL datasets and derive a consistent set of saturation functions. The SCAL measurements took into consideration the importance of core sampling, cleaning and the proper procedures for obtaining reliable drainage capillary pressure data. We show that both imbibition capillary pressure and relative permeability have major impact on the waterflood sweep efficiency and cross-flow between adjacent oil-wet layers and hence on the distribution of remaining oil saturation. An incorrect understanding of the distribution of remaining oil saturation may lead to ineffective well and reservoir management and IOR/EOR decisions.