The Poza Rica field is the most important and largest producing field in Mexico. It lies on the Gulf Coastal Plain approximately at 160 kms. south-southwest of Tampico and at 175 kms. northeast of Mexico City. The structure was found originally by geophysics through an almost simultaneous torsion balance and refraction shooting survey. Poza Rica No. 2 well, completed on May 2, 1930, as a gas producer, discovered a subsurface trap drilling in the gas cap in a porous Tamaba limestone at -2,047.3 meters (-6,715 feet).

Further deepening of the well brought it in as an oil producer. It was later shut in, because of high gas-oil ratio, in 1933.

Later reflection shooting revealed possible extensions and permitted development program. First exploration wells were located at distances between 600 and 1,000 meters (1,968 and 3,028 feet).

Completion of wells was first accomplished through 4 3/4-inch liner. Later wells produced through 2½-inch tubing.

There are at present 93 wells of which only 4 were dry through lack of porosity in the limestone. Seventy-eight are producing at present. The structure at Poza Rica, as revealed from both seismos and subsurface geology, is a broad anticline in a Tamabra limestone which is open, as yet, toward the west northwest. The highest well, Poza Rica No. 65, found the limestone at -1,947 meters (6,386 feet). The lowest producing well, Escolin No. 2, found the limestone still porous at -2,178 meters (-7,144 feet). Apparently the porous producing zone is due to a reef facies deposited on the highest part of a Cretaceous limestone anticline. Later regional tilting, and subsequent folding apparently displaced the porous zone toward the northeast flank, so that at present no porosity has been found o the south flank. Poza Rica No. 8 and No. 46 are the southernmost wells drilled to the limestone without finding it porous.

This field has produced 50,380,902 M³ (316,895,800 barrels) since 1930, and is considered to have a potential reserve of 143,169,000 M³ (900,533,000 barrels).

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