ABSTRACT

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 pressure gradients and fluid contacts are analyzed and detectable when well logs are examined. Material-balance analysis independently corroborates the influence of overpressure as well. Overpressure is most likely derived from a combination of rapid burial and a compressional tectonic setting.

Well performance can be either (1) short lived, rapid decline, and early water breakthrough or (2) long lived, low decline, low water production. Rapid-decline well performance is associated with lower upper Miocene submarine-channel and fan sandstones, whereas low-decline performance is associated with lower Miocene submarine-channel and fan conglomerates. Material-balance evaluation does not indicate pressure maintenance from water influx in rapid-decline performance wells. Rather, water production is interpreted to be due to 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.