--> Advanced Petrophysics in Mexico East Carbonates, Mendez, Javier; Bustos, Ulises D., #90100 (2009)

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Advanced Petrophysics in Mexico East Carbonates

Mendez, Javier1
 Bustos, Ulises D.2

1Development, Pemex, Poza Rica, Mexico.
2
DCS, Schlumberger,
Villahermosa, Mexico.

The exploration and development in Chicontepec area, Mexico East, has been mainly focused in Tertiary clastic targets, recently. With the extension of prospective frontiers towards deeper carbonates sequences down to the tertiary base, it was required the reservoir potential definition and the type of hydrocarbons, among others.

During the petrophysical evaluation process with different models, it was obtained better results in the water saturation estimation with variable M. This was performed with empirical methods and core calibration. Although this was a good practice, some resistivity responses were not fully understood compared with the well test results.

By incorporating the Nuclear Magnetic Resonance, it was possible to asses the porosity distribution and to estimate both the irreducible and free fluids fractions in the reservoir. Additionally, the mineralogical analysis involving clay and silica volumes (detrimental to the rock quality in these carbonates), was more robust since the incorporation of capture spectroscopy measurements. On the other hand, the fluids mobility and the fluid type were assessed with dynamic testers. The added value of those wireline measurements was enhanced with the integration into an organized workflow, enabling to evaluate the reservoir potential from both static and dynamic perspectives.

As far as water saturation computation is concerned, the porosity partitioning into micro, meso and macropores with nuclear magnetic resonance, brought the additional advantage of a variable M based on transverse relaxation times distribution (T2’s distribution) into a modified-Archie equation. In addition, the type of fluid and water cut was adjusted with downhole optical analyzers, aiming to investigate the primary hydrocarbon characteristics (viscosity, composition, gas-oil ratio).

The techniques mentioned so far were useful for matrix potential assessment. However, the presence of natural fracturing leaded to the investigation of the relationship between fractures and matrix, in order to define the type of reservoir. Since most of wells are drilled in oil base mud conditions, the natural fracturing detection and evaluation found and important component in the dispersion analysis and radial profiling with dipole sonic measurements.
A precise definition of the type of reservoir and its potential, has been of particular relevance in the decision making process for exploitation strategy in the Chicontepec carbonates.

AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil