--> A Comparison of Najmah Kerogen Adsorption and Desorption Gas Characteristics With North American Source Rocks

AAPG ACE 2018

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A Comparison of Najmah Kerogen Adsorption and Desorption Gas Characteristics With North American Source Rocks

Abstract

Core-based desorption and adsorption characteristics of gas-bearing source-rock formations are an important analytical tool used in the evaluation of production potential. Evaluation of gas-in-place (GIP), including desorption and adsorption characteristics, is critical to predict this potential.

A study of 26 wells is underway to evaluate the economic potential for gas production in the Najmah Kerogen in Kuwait. As a part of this study, Kuwait Oil Company has conducted multiple wellsite desorption analyses in an effort to determine the total adsorbed gas as a function of organic content. The desorbed gas content is classified as 1) the amount of gas lost during core retrieval 2) the amount of measured matrix gas desorbed at the surface and 3) the amount of gas released following the crushing of the surface samples. Subsequent analysis determined the adsorption isotherm characteristics using a multi-component gas mixture at multiple pressures.

We compare the desorption and adsorption characteristics of the Najmah Kerogen with a variety of North American source rocks (Duvernay, Eagle Ford, Haynesville, Marcellus, Montney and the Utica) in order to interpret the volumes of gas from desorption analysis and the relationship between declining reservoir pressure and the contribution of adsorbed gas to the overall production of gas (adsorption isotherm analysis).

The results indicate that the Najmah Kerogen averages desorbed gas volumes of 42 scf/ton, very close to the mean for North America shales. Adsorption isotherm analysis of the Najmah Kerogen yields an average methane isotherm at 4000 psi of 133 scf/ton, with an average TOC volume of 10.6%. The Lower Marcellus exhibits similar over-all geochemical characteristics yielding a methane isotherm at 4000 psi of 105 scf/ton, with an average TOC volume of 6.6%. Our experience indicates that the adsorbed component is only one factor in the computed reserve estimate and may be low due to a variety of factors. While the adsorbed gas content may be low, the total gas in the system may be significant. The Najmah Kerogen fits this category, being a dominantly free-gas play similar to the Haynesville Shale.