Innovative Petrophysics to Understand the Spatial Gas Distribution in a Conventional Gas Reservoir With Unexpected Unconventional Characteristics

Forsyth, David (Saudi Aramco) | Vargas-Guzmán, J.A. (Saudi Aramco)


Copyright 2013, held jointly by the Society of Petrophysicists and Well Log Analysts (SPWLA) and the submitting authors This paper was prepared for presentation at the SPWLA 54th Annual Logging Symposium held in New Orleans, Louisiana, June 22-26,2013 ABSTRACT Conventional and Unconventional Gas Resources (CGR, UGR) are a focus area for upstream studies in Saudi Aramco and its Permian clastic reservoirs in particular constitute a world class gas resource. Deposited originally in an Aeolian environment, tight rock partial-seals surround a distribution of permeable "sweet spots". Reservoir development is determined by a complex diagenetic process. The highlighted field is a typical example. During initial appraisal, a continuous gas column was interpreted from pre-production pressure data with a clear free water level. Yet, as development progressed, development wells encountered water up structure and pressure depletion showed a complex pseudo-compartmentalization, in contradiction of the initial model assumptions. As part of ongoing reservoir management, an extensive special core analysis program has been conducted on a comprehensive set of some 300 samples encompassing the range in rock quality present in the formation which ranged from highly permeable quartz rich dunes to diagenetically altered paleosols, siltstones and shales.The bulk of samples showed meso-and macro-pore structures typical of silt to clean sandstone dominated rock sequences. This is interesting because although these rock types should be filled with gas, given the expected column height of approximately 1000 ft, none of the rocks examined showed a gas sealing potential of more than a few hundred feet.

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