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Production and Pressure Characteristics of Gas Reservoirs, Veracruz Basin, Mexico

By

HOLTZ, MARK H., GARCIA, JAVIER, SAKURAI, SHINICHI, WAWRZYNIEC, TIMOTHY F., and JENNETTE, DAVID C.

Bureau of Economic Geology, John A. and Katherine G. Jackson School of Geosciences, The University of Texas at Austin, Austin, TX,

BOLAÑOS, JUAN JOSÉ

PEMEX, Veracruz, Mexico

 

The Veracruz Basin, located in southeastern Mexico, has produced from 17 gas reservoirs since the 1960’s. Cumulative production is currently 150 Bcf from 22 wells. Data from these wells and reservoirs were analyzed to determine their production and pressure characteristics in order to predict the performance of future exploration wells and aid in the delineation of geologic plays. Decline-curve analysis, material balance, and various pressure analyses were integrated with sequence stratigraphy and log analysis.

Investigations determined that gas reservoirs in the Veracruz Basin are initially overpressured. This overpressure is measurable when analyzing pressure gradients and fluid contacts and also detectable from well log analysis. Material balance analysis independently corroborates the influence of overpressure. Overpressure is most likely derived from a combination of rapid burial and a compressional tectonic setting.

Well performance falls into two categories: (1) short-lived, rapid decline, early water breakthrough and (2) long-lived, low decline, lack of water production. The rapid-decline well performance is associated with early upper Miocene submarine channel and fan sandstones, whereas the low-decline performance is associated with lower Miocene channelized conglomerates. Material-balance evaluation does not indicate pressure maintenance from water influx in the rapid-decline performance wells. Rather, water production is interpreted to be due to the sandstones not residing at irreducible water saturation within the reservoir. This saturation state is likely to occur where breached reservoir seals have caused the rock to undergo an imbibition phase of water migration.