WILLIAMS-ROJAS, CARLOS T., Colorado School of Mines, Department of Geology and Geological Engineering, Golden, CO

ABSTRACT: Geological Controls on Reservoir Performance in Two Gas Fields, Southeast Mexico

Fields M and C are important producing fields in northwest Chiapas State, Mexico. They produce from Cretaceous fractured carbonates. The objective of this integrated study was to define the stratigraphic and structural controls that caused early water production in those fields.

Open-hole log correlation of 45 wells served to define 8 reservoir zones, based on petrophysical characteristics. Petrophysical properties were mapped using a volumetric parameter to analyze the anisotropy of the gas storage capacity in the fields. Dipmeter and borehole image jogs were interpreted in 14 wells using cumulative dip and vector plot techniques to define unconformities, flooding surfaces, and faults. Borehole images were extremely useful to detect evidence of sedimentological and structural features. Fracture density depends on petrophysical properties of the reservoir rocks. In situ stress directions were determined in 18 wells using borehole breakouts to define the predominant NW-SE orientation of the open fractures.

Two dominant fracture sets determined from seismic attributes and borehole images are parallel to seismically determined faults.

According to this study, early water production is caused by coning through fractures, faults, and karstic zones. Some water-producing intervals depend on the location of perforations, especially when these are located within highly fractured rocks and close to the gas-water contact. To minimize early water production the operator must avoid wells in fault zones, on the flanks close to the gas-water contact and deviated wells drilled perpendicular to the direction of open fractures.

AAPG Search and Discovery Article #90909©2000 AAPG Foundation Grants-in-Aid