--> Abstract: Exploration Opportunities in Mexico, A Regional Perspective, by P. Cruz-Helu and J. J. Meneses-Rocha; #90937 (1998)

Datapages, Inc.Print this page

Abstract: Exploration Opportunities in Mexico, A Regional Perspective

CRUZ-HELU, PABLO, and JAVIER J. MENESES-ROCHA, Coordinacien Ejecutiva de Estrategias de Exploracien, Pemex Exploracien-Produccien

INTRODUCTION

The results of oil prospecting in Mexico, started by Pemex almost 60 years ago, have been very significant in the country's ability to fuel its industrialization and its social-economic development The panorama of ever growing requirements for fuels for domestic demand, the need to maintain its current involvement level in the world market and the comparative advantage PEMEX has to prospect in one of the three largest oil producing provinces in the world (Gulf of Mexico), have encouraged the government-owned company to develop a visionary exploration plan This plan, while respecting environmental rules and guidelines, will consider near and long term production scenarios in both the Producing Provinces and the New Areas.

PRODUCING PROVINCES

There are nine oil provinces in Mexico (Figure 1). Of these, four produce only non-associated gas (Sabinas, Burgos, Veracruz, and Macuspana), and seven produce both oil and gas (Tampico, Misantla, Cordoba, Salina del Istmo, Reforma, and Sonda de Campeche).

The major role gas is currently taking in Mexico's industrial recovery, places the gas provinces in a strategic place in PEMEX EXPLORACION Y PRODUCCION's (PEP) investment portfolio. The Sabinas, Burgos, Veracruz and Macuspana provinces hold 49% of the country's gas reserves. However, we can see significant differences regarding their individual contribution to the country's proven reserves 38% from Burgos, 10% from Macuspana, 7% from Veracruz, and 2% from Sabinas.

The Burgos Province is the geological extension of the South Texas Rio Grande embayment with producing plays of Paleocene, Eocene and Oligocene sandstones associated with rollover structures aligned along a system of down to the basin listric growth faults. Up to January 1997, 2818 wells had been drilled. Considering its proven reserves, its large area, and the number of discovered fields as well as drilled wells, the Burgos province is today the largest gas province in Mexico, This is why PEP has begun, in this area, its mature province revitalization strategy, a plan that seeks three basic objectives: 1) increase the production rates, 2) improve the operation practices, and 3) to develop new reserves.

The Sabinas Province discovered in 1974 is part of the Mexican northeastern fold belt, and it offers producing plays of sandstone from the Upper Jurassic and Lower Cretaceous. To date 102 exploration wells have been drilled in that province which have lead to the discovery of 17 fields. Our current understanding of the Sabinas province places it low in the investment projects portfolio. However, a multidisciplinary working group is being maintained, which is reevaluating its exploration possibilities.

The Veracruz Province was discovered in 1956, and represents a depocenter with a sedimentary section of about 9000 meters of conglomerate, sandstone and carbonates from the Mid Eocene-Upper Miocene. Five fields were discovered in the 1956-1968 period, four of which are located in the southwestern part of the basin. These fields produce from sandstone and conglomerates of the Middle and Lower Miocene. Since no new fields have been discovered, the production/reserve ratio has dropped to very low levels. In the early nineties a study of this province was undertaken and new exploratory concepts were introduced. These studies are yielding spectacular results such as a wildcat well that is producing 22 mcf per day from a previously untested sandstone horizon.

The Macuspana Province is located in the southeastern part of Mexico, situated in the eastern part of the state of Tabasco extending offshore to the edge of the continental platform. This province is a large basin filled with sandstone and carbonates from the Miocene-Pliocene, deposited in a marine, near shore shelfal environment In the 1940-1962 period, 14 fields were discovered 2 of which represent 70% of the proven reserves (JosC Colomo and Chilapilla), and 2 more which represent another 25% (Hormiguero and Usumacinta). The reservoirs of these fields are sandstones from the upper Miocene-Pliocene. The undiscovered potential of the area is very large and this province is high in our exploration priorities.

Opportunities and Prospecting Strategy

The exploration effort in the gas provinces is following a strategy centered on looking at deeper horizons, in identifying and delineating new prospects and in testing new horizons not tested or tested without dated technologies. All of this is being done utilizing new concepts and exploration models as well as incorporating the latest technology in seismic, interpretation, geochemistry, stratigraphic interpretation techniques, drilling and completion, as well as a stream lined work organization.

Oil and Associated Gas Provinces

The oil and associated gas provinces are the ones that have allowed Mexico to become a leading oil exporting country. These oil and associated gas producing provinces can be placed in two categories: mature and moderately explored.

Mature Provinces

The provinces listed below are, in order of discovery: Tampico-Misantla (1904), Salinas del Istmo (1905), and Cordoba (1953). Just as in other mature provinces around the world, the percentage of success and the size of the discovered fields have dropped progressively.

In the Tampico-Misantla province, Mesozoic and Tertiary plays have produced 5 billion oil equiv. barrels from the beginning of this century. There are two fractured carbonate plays; in the Ebano-Panuco region, one from the Cretaceous, and the other in oolitic carbonates of the Upper Jurassic. Both are located over horsts produced by fault inversions during the Laramide orogeny. The most productive region in those plays is located onshore with only small portion of the San Andres play extending onto the continental shelf. (Aranque field, 1968). In the Tuxpan platform there are two main plays: platform carbonates highly karstified (Golden Lane or El Abra trend) and carbonate debris breccias (Poza Rica or Tamabra trend). These plays are associated with a Middle C cons isolated platform in which the fields are a combination of stratigraphic closures and paleoreliefs with different oil-water contacts.

West of the Poza Rica tread is the Chicontepec Paleo Channel trend. The paleo channel is part of the foreland basin associated with the Laramide Sierra Madre Oriental. The channel is filled with fine-grained turbidites shed from the Sierra Madre during the mid-Paleocene to Eocene. These turbidites form tight, low productivity reservoirs with several billion barrels of oil in stratigraphic - structural traps, with a low per well productivity index.

The Cordoba Province constitutes the tectonic front of the Laramide belt of the Sierra Madre Oriental. It produces from both shelfal and slope carbonates in the upper Cretaceous. Its production comes from Middle-Upper Cretaceous plays, representing two different depositional environments: carbonate shelf and slope.

In the Salinas del Istmo province, the first giant oil fields of the Tertiary in Mexico, were discovered over irregularly shaped salt structures.

Opportunities and Prospecting Strategy

Prospecting in the three mature provinces by focusing on the traditionally productive plays will be difficult as substantial profit margins are more and more difficult to attain. A development strategy has been designed focused on two main objectives in conjunction with new concepts and application of new technologies.

The two objectives are: 1) Identify the lateral extension of producing plays in subtle traps and 2) deeper drilling under existing plays.

This strategy was applied in the Tampico-Misantla province in the early nineties. The plays in the southern part of the Ebano-Panuco area are currently being reappraised and the characterization of the Chicontepec paleochannel is also underway.

In the Salinas del Istmo province, the extension of the Tertiary plays is being pursued and new technology is being applied to appraise the sub-salt play. (See Oviedo-PCrez in this volume).

Moderately Explored Provinces

These provinces are located in the Neogene belt in the southeastern part of Mexico, which are characterized by linear structural trends that detach above the Mid Jurassic salt The Reforma province was discovered in 1972, and its offshore counterpart, the Sonda de Campeche province, in 1976. Since then both provinces have become Mexico's most important producing areas.

In the Reforma province the main plays are located in the Cretaceous and Kimeridgian Jurassic section, where dolomitization and fracturing have enhanced reservoir quality. After 10 years of exploration and development the focus of attention has moved toward the coast and the Sierra de Chiapas foreland, resulting in a range of significant discoveries of light oil, condensate and gas.

In the Sonda de Campeche province there are plays in the Kimeridgian Jurassic Cretaceous and Paleocene, related to compression and plays associated with normal faulting in the northeastern region of the province. In the mid eighties, exploration efforts moved to the northeast, southeast and northwest of the existing fields, resulting in oil discoveries in Oxfordian sandstones in the northeast part, gas and condensate along the Tabasco coastline, and oil and gas in a field located offshore in water depths greater than one hundred meters. (See Lopez-Arriaga in this volume).

Opportunities and Prospecting Strategy

A short and medium term strategy has been tailored for each of these provinces, focused on the following goals: Reforma: 1) Increase the amount of drillable prospects in the coastal region and in the foreland of the Sierra de Chiapas; 2) Outline and characterize the fields discovered in these two regions.

Sonda de Campeche: 1) Identify the lateral extension of the Oxfordian play in the northeastern region of the province; 2) increase the amount of drillable prospects along the coastline of the state of Tabasco; 3) outline and characterize the fields discovered in this last region; 4) identify and drill new prospects offshore between 100 to 200m water depth.

All of this new activity is being conducted with newly acquired 3D surveys used for both exploration and development of existing fields as well as with a program of integrated characterization field studies.

NEW AREAS

We at PEP consider the “New Areas”, those regions where no exploration has taken place, or where no commercial production of hydrocarbons has been discovered. The prospecting effort, in the short, medium and long term, will be focused in the new areas located offshore on the shelf and the slope of the Gulf of Mexico. Those areas are on trend with existing production sourced from the Late Jurassic, and reservoired in Mesozoic and Tertiary carbonates with effective traps and seal.

The Gulfs Coastal Plain

The new areas located in the Gulfs coastal plain are important because of their proximity to the country's oil producing provinces. Although the coastal plain is Mexico's most explored region, there are still areas where, with new concepts, interpretation and technology, its remaining potential can be appraised. The main areas of interest are: Papaloapan, Escarcega and Cuichapa.

The Papaloapan area is the southeast extension of the Veracruz province. In that area two exploration wells have had oil and gas shows in Miocene sandstones. Recent seismic has identified structures which detach on the shales of the lower Tertiary or Upper Cretaceous.

The Escarcega area is in the southwestern part of the Mesozoic-Tertiary carbonate bank of the Yucat^daggern. It is hence a region with low structural relief but with possible stratigraphic and/or structural traps, within its confines. Also the Oxfordian producing trend of the Sonda de Campeche could well extend towards that area.

The Cuichapa area is located in the Salinas del Istmo province, where the Tertiary plays have produced to date 1.55 BBO. Between the years 1973 and 1978, two wells were drilled in order to investigate the sub-salt potential. These wells penetrated the salt layer and encountered oil & gas shows in the Lower Miocene section. The sub-salt play in the area is being actively evaluated with new seismic.

Continental Shelf

The areas located on the continental shelf of the Gulf of Mexico bear a strategic importance because this is where large parts of Tampico-Misantla, Tuxpan, Veracruz and Salinas del Istmo are located. The most promising areas on the shelf are: Lampresa, Veracruz and Coatzacoalcos Marina. The first two will be appraised in the near term, whereas the evaluation of most of the Coatzacoalcos area will be done long term. In the Lamprea area, the extension of the Upper Jurassic Arenque play is being followed north of the Tampico-Misantla offshore area. The traps are subtle features drapfed over basement horst blocks. The use of recent 3D is helping to define this play.

The Marine Veracruz area is the offshore continuation of the Veracruz Tertiary province. Opportunities are being delineated in the Tertiary in this area, and with greater uncertainty in the Mesozoic.

The Coatzacoalcos area is divided in three regions with their own geological characteristics. The southern region is the offshore continuation of the Salinas del Istmo province with significant number of leads identified in the Tertiary. This gives the area a high priority in the overall plan. The western area lacks salt resulting in few structures and leads. Evaluation here will be short term. The northern area is on the shelf in 200-500m of water. Its structural complexity, water depth and the presence of large salt sheets will make evaluation a long-term goal.

Continental Slope

So far, PEP has only carried out preliminary work on the continental slope.

This work in conjunction with other scientific studies, has identified four areas with a combined area of 190,000 Km{2}.

These areas included for the first time in the exploration portfolio are as follows:

1) Extension of Mesozoic structures and play; in Campeche Sound in water greater than 200m.

2) Northern part of the Mexican ridges focusing on the Tertiary.

3) Mesozoic features in the Mexican portion of the Perdido fold belt.

4) Tertiary features in the southern part of the Mexican ridges.

Exploring in these frontier areas offer both technical and financial challenges. PEP is developing a strategy that will maximize operational efficiency, and in the near term allow the development of new reserves which will have a long-term effect on Mexico's energy future.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah