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.