Several fields in Colombia are in the maturity phase. While the efforts are mainly focused on workflows and technology incorporation for either increasing hydrocarbon production and/or minimizing water cut, the combination of variable salinities due to production/waterflood with complex mineralogies and shales distributions, is detrimental to a proper saturation assessment with archie methods. The content of clay, thin laminations and small pore sizes add to the rock an important conductivity component that translates into low resistivity responses when measuring with low frequency conductivity devices (either based on induction or laterolog principles) and low contrast between sand and shales. Such formation evaluation issues are detrimental to achieve representative hydrocarbon saturation computations in many interest zones in this case study.

In this context, we propose a formation evaluation solution based on wireline dielectric dispersion measurements. Using a 1-inch vertical resolution wireline-conveyed device, we polarize the reservoirs with a multi-frequency electromagnetic field and evaluate the formation response to the application of this field. At higher frequencies, the electronic polarization phenomena enable to displace cloud of atoms in the formation where information on low dielectric constant materials (hydrocarbons, matrix) is assessed. At intermediate frequencies, the molecular polarization occurs by rotating-reorienting the dipoles (water molecules) creating a strong attenuation and phase shift of the electromagnetic field; consequently, allowing to measure salinity and resistivity-independent water volume. Lastly, at lower frequencies the predominance of Maxwell-Wagner effects which are related to the electrical charge redistribution at interfaces due to electromagnetic field application, enable to obtain information on rock textural information (tortuosity and cation exchange capacity). By building a petrophysical model with dielectric dispersion and nuclear logs, we then obtain a high-resolution resistivity and salinity-independent formation evaluation that solves for porosity and water vs oil saturation with a single and fast wireline logging run.

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