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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 67 (1983)

Issue: 3. (March)

First Page: 477

Last Page: 477

Title: Geologic and Geothermal Fluid Flow Models of Cerro Prieto Field: ABSTRACT

Author(s): Susan E. Halfman, Marcelo J. Lippmann, Ruben Zelwer

Article Type: Meeting abstract


A detailed hydrogeologic model of the liquid-dominated Cerro Prieto geothermal field in Mexico (located in Baja California about 35 km [22 mi] south of the U.S. border) has been developed to identify subsurface geothermal fluid flow paths. This was accomplished by integrating downhole temperature profiles and depth of production intervals with a geologic model derived from the interpretation of geophysical and lithologic well logs.

Two different methods were used to define the geologic model of the Cerro Prieto field. In the first, the lithology was divided into seven different formations based on correlatable groups of beds having distinct lithologic, structural, and fluid production characteristics. In the second method, the lithology was classified into three basic types of lithofacies: shales, sandy shales, and sands. Faults identified by the first method were incorporated into lithofacies sections.


Geothermal fluid flow paths were identified by integrating well temperature profiles and the depths of geothermal well production intervals with the lithofacies cross sections. Hot fluids are believed to enter the field at depths greater than 3,000 m (10,000 ft) from the east through a thick, porous sand unit, called Sand Unit Z, which dips gently to the east. This unit underlies a 450 to 600 m (1,500 to 2,000 ft) thick low porosity shale unit, named Shale Unit O, which acts as a local caprock. The fluids flow westward until they encounter a normal fault, Fault H, with downthrow to the southeast. The fluids then move up along this fault until they again encounter Sand Unit Z along the upthrown side of Fault H. Whereas most of the fluids continue to flow westward through Sand Unit Z, a small portion rise along Fault H, as evidenced by high temperatures found at shallow depths in the faulted region. The westward flow continues until it reaches a gap in the overlying Shale Unit O. There, some of the flow rises up and into the western Shale Unit O, which is sandier in this region, while the rest continues to flow westward through Sand Unit Z. Eventually, some of the geothermal fluids leak to the surface, whereas the rest mix with colder waters that surround the geothermal system. A number of cross sections detailing the subsurface movement of the geothermal fluids are shown.

This hydrogeologic model is consistent with other geologic, geophysical, geochemical, and reservoir engineering studies carried out at this field.

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Copyright 1997 American Association of Petroleum Geologists