Abstract

Colombia's Oil production is around 1.1 million barrels per day (bpd), where 57% is from Heavy Oil fields. Current oil recovery is in the 15% to 17% range; with targets to increase it up to 50% through different methods. A typical reservoir exhibits hydrocarbon viscosity variations in hundred of centipoises, with formation water salinity typically below 5000 ppm and heterogeneities driving a complex fluids distribution. Since the low amount of salt in these environments prevents low frequency conductive devices for contrasting water versus hydrocarbons, where additionally, resistivity profiles are ambiguous to assess fluids mobility in the reservoirs.

In this context, the incorporation of additional physics of measurements opens a new perspective in the reservoir evaluation in Llanos basin, by reducing uncertainties and helping in the initial reservoir characterization. The new generation of wireline measurements supporting the present job is represented by multifrequency dielectric propagation, radial magnetic resonance and dynamic testers, in addition to the conventional triple combo logs.

Since good-oil bearing rocks (high porosities and permeabilities, very clean sands, high oil saturations) do not guarantee oil production (very high water cut is likewise common), the identification of movable oil and free water volumes in low salinities is mandatory. Understanding its distribution across sands is also a critical factor in heavy oil environments.

As a resistivity and salinity-independent reservoir evaluation approach, the combination of dielectric dispersion and radial magnetic resonance, provides a valuable sensitivity for the evaluation of displaced oil, free and irreducible water, viscosity and rock quality variations. Dielectric Dispersion is the variation of relative permittivity and conductivity versus frequency, enabling pore fluids determination. With a dielectric analysis at two depths of investigation, integrated with NMR-based diffusion mesurements, a direct identification of movable oil under filtrate invasion conditions and free water presence is achieved.

The correlations encountered between the dielectric dispersion is encouraging; whereas a better understanding on the movable oil occurrence and estimation of the fluid to be moved during production is achieved. Discussions with case studies in Llanos Basin are presented in this paper.

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