Geological and Engineering Conditions of the Ebano-Pánuco Fields, East Central México: A hundred Years of Experience in Exploitation of Heavy Oil
José G. Galicia1, Manuel Coronado1, and Hermínio J. Torres2
1 Pemex Exploración y Producción
2 Región Norte
The area began its production history in 1904, as a matter of fact, this area was the very first oil producer region of México. This heavy oil has a rank of density between 11 and 16° API. Production is from tectonic fractures in dense limestones (Chalks) of Upper Cretaceous San Felipe and Agua Nueva Formations. These formations are composed of impermeable, basically non-porous limestone with vertical extension fractures (vertical s1). Reservoir storage and flow is entirely from open fractures. There is a set of mayor faults some of which extend upwards to the surface introducing an important amount of oil seeps. In spite of the oil density, the oil ascends by spontaneous flow, essentially in the Cacalilao sector that is the structural highest part of the whole area.
The intensity of fracturing throughout the fields is a function of flexuring (controlled by basement related structural elements) and faulting. The geometry of the fracture elements is controlled by regional tectonics. Fracture orientation and apertures in cores do not exhibit a wide range of variability. Most fractures have a median aperture of 0.75 mm. Fracture porosity for the whole area, from cores, averages 0.12% but fracture permeability ranges from 1 mD to 10 Darcies. Production data reveals that the rate and style of fluid production is controlled by both the density and the absolute size of the fractures.
The energy that makes the reservoirs behaves as buoyant ones is provided by the pore pressure support of the Lower Tamaulipas Inferior formation. Areal differences in the reservoir quality of this unit due to the presence of high matrix porosity have impact on production. The wells in the west and northwest parts of the area require artificial lift due to a lack of preasure. And in the other hand, the wells in the central part (Cacalilao area) are capable to produce under natural flow for long periods of time and bears water encroachment with adequate choke control.
The way that the flow behaves is firstly a level of oil flowing toward the tubing and surface and after a time that could take few years, it comes a coning within the fractures, the water level moves upward rapidly in the area of the well bore during production. Eventually there is water breakthrough and considerable oil is by-passed.
Based on an Original Hydrocarbon in Place estimation of about 13 BBO, the global maximum recovery factor of fractured reservoirs in the fields of the Ebano-Pánuco with the current cumulative production of 1,004 MMB should fit approximately 10%.
More than 102 years have passed from the beginning of the oil exploitation of this area but these complex and rich reservoirs still have a high untouched oil potential.
AAPG Search and Discovery Article #90062©2006 AAPG Hedberg Research Conference, Veracruz, Mexico