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The Relationship Between Depth and Temperature of Tertiary Gas Fields in the Veracruz Basin, Mexico


This work describes the relationship between temperature and subsurface depth of gas fields in the Veracruz Basin as a function of geothermal gradient, and applies the Golden Zone concept which states that 90% of oil fields and 80% of gas fields in the world's basins lie between the 60 0C and 120 0C isotherms (Nadeau, 2005 and 2011). The objective of this analysis is to define temperature limits, pressures and porosities of 51 Miocene gas fields of the Tertiary Veracruz Basin consisting of basinal sandstone reservoirs. The average geothermal gradient was determined to be 24 0C/km. The shallowest gas field is at 869 m with a temperature of 46 0C, while the deepest gas field is at 3,150 m with a temperature of 101 0C. Therefore, the known Golden Zone is 2,281 m thick, and no fields have yet been discovered in the band between 101 0C and 120 0C. Sandstone diagenesis in these Miocene fields indicates that smectite and illite formation began at about 60 0C which corresponds to the shallow depth limit of the Golden Zone, while gradual enrichment in diagenetic quartz increases exponentially at 120 0C corresponding to the deeper limit of the Golden Zone. These data confirm that the temperatures of Tertiary Veracruz Basin gas fields are in direct proportion to their depths with the temperature-depth curve indicating that the 120 0C deeper limit of the Golden Zone lies at approximately 4,000 m. Therefore, an 850 m band between 3,150 m and 4,000 m may potentially contain hydrocarbons. This could be of economic importance since the Lower Miocene and the Paleogene can be reached at these depths in the southwestern part of the basin and around Los Tuxtlas.