Evaluation of Laminated Gas Reservoirs Integrating Resistivity Anisotropy Measurements, Magnetic Resonance and Formation Micro-Conductivity Images
By
Jean-Remy Olesen1, Bill T Bryant2
(1) Schlumberger Logelco Inc, 11728 Maadi Cairo, Egypt (2) bp Egypt, Maadi Cairo,
Many deltaic reservoirs feature thinly bedded laminated sections that contain significant hydrocarbon pay and make-up a non-negligible amount of total reserves. Using conventional resistivity data, quantification of the hydrocarbon saturation of those sections is difficult, since the data is dominated by the conductivity of the laminae of shale. This situation is even further exacerbated when the hydrocarbon is gas; due to its high mobility, it is capable, over geological times, to displace capillary bound water in silts and to be produced from such poor quality reservoirs.
New developments have been made in the derivation
of resistivity data in a
plane parallel to the tool axis, which have facilitated the evaluation of such
reservoirs by removing the domination of the shale laminae. This work is focused
on the development of a resistivity anisotropy-based saturation evaluation
method that integrates information derived from consonant well logs (i.e., with
comparable vertical resolution) with NMR and micro-conductivity images. The
resistivity anisotropy model includes shale micro-anisotropy, a prevalent
condition in the Nile Delta, where this technique was validated.
The relationship linking resistivity anisotropy to a reservoir model
including shale, silt and sand is explicitly developed and the sensitivity of
the vertical resistivity derivation
to input parameters is studied. The
petrophysical evaluation results from the model are confirmed against a variety
of independent data, including surface seismic interpretation, reservoir
pressure profile and well test. The bulk volume of gas derived from this
technique is compared to results from conventional evaluation and to hydrocarbon
storage capacity estimated from NMR data.