24th World Gas Conference The Global Energy Challenge: Reviewing the Strategies for Natural Gas Buenos Aires, 5 - 9 October 2009 THE GAS POTENTIAL OF THE SUB-ANDEAN BASINS; THE CURRENT EXPLORATION STATUS AND THE FUTURE PROSPECTIVITY AS AN ENERGY RESOURCE FOR THE REGIONAL MARKET Authors: Marcelo Rosso*, Patricio Malone*, Gustavo Vergani* *Geoscience Department, PLUSPETROL SA. Keywords: Sub-Andean basins; non-associated Gas, basin, Exploration Abstract This paper aims to review the Gas potential of the Sub-Andean basins in South America. Based on the exploration work carried out and the gas fields already discovered, the authors assess the remaining potential of this energy resource in the region. Due to the particular geological characteristics of the Intracratonic and the Active and Passive margin basins of South America, they are not included within the scope of this study. The sub-Andean Basins cover an area of about 2.6 million km2 extending south from Venezuela to Tierra del Fuego in the southernmost part of Argentina and Chile. These basins contain about 4% and 9 % of the total world gas and oil proven reserves respectively. This paper briefly describes the Petroleum Systems in place, the exploration maturity of the Sub- Andean Basins and the possibilities for new exploration. Finally, a succint description of the main challenges the industry is facing in the region for the gas prospection, the necessary exploration works to be carried out and the present status of the gas as an energy supply for the southern cone is given. The Gas Potential of the Sub Andean Basins 1 24th World Gas Conference, 5-9 October 2009 GEOLOGICAL SETTING: The South America basement (Pre-Cambrian) outcrops in the entire central region of the continent encompassing eastern and northern Brazil, Paraguay, Uruguay, southern Venezuela, eastern Colombia, Ecuador, Perú, Bolivia and central-southern Argentina. The deposition of the sedimentary cover started in the early Paleozoic infilling the intracratonic basins. In the pericratonic basins the deposition occurred as a sedimentary prism flanking the platform. In most of the basins the sedimentary infill extended to the Cenozoic period and many of them were subject to intensive erosion and tectonic processes. The sub-Andean basins cover a surface of about 2,580,000 km2 extending in the western part of South America for more than 8,000 km (Fig.1). The geological history of these basins is closely related to the plate tectonics. Fig.1 South America Sedimentary Basins The formation of the South Atlantic margins resulted from the breakup of the Gondwana supercontinent. (Franke et al, 2006). The South American continent separated from Africa moving to the west in a clockwise movement entering in collision with the Pacific plates. The final opening of the South Atlantic took place in Lower Cretaceous. The opening occurred diachronously rejuvenating from South to North and may be described as a successive northward unzipping of the Gondwana rift zones (Jackson et al, 2000). Several Triassic and Jurassic extensional basins were tectonically affected and evolved together with the volcanic arc in the Active Margin (Fig. 2). During the Tertiary the tectonic development of the Andean chain led to the formation of a fold and thrust belt and a segmented foreland basin that extends along the western Active Margin (Bally et al, 1980).This fold and thrust belt (”Cordillera de los Andes”) deformed and inverted the original architecture of the pre-existing rifts and marginal basins. The Gas Potential of the Sub Andean Basins 2 24th World Gas Conference, 5-9 October 2009 N IN I G G R R A A M M E E V IV I T S C S A A P Fig. 2 South America Sedimentary Basins (modified from IHS-Bally classification) Each basin has its own tecto-sedimentary complexity. Some of them have an active magmatic arc and are recognized by some authors as backarc or forearc basins depending on their position relative to the volcanic arc. Much of the length of the Andean chain has been the site of magmatism during Mesozoic and Cenozoic time and its is useful to think of the Andes as an evolving arc system controlled by the motion of South America relative to the mantle and the adjacent plates (Pindell et al,1995) In the Caribbean region (northeast Colombia, Venezuela and Trinidad & Tobago) the basins have a very complex tectonic framework due to the presence of transform dextral faults trending west- east (and where the oceanic crust is involved) forming the Caribbean folded belt (Cordillera de la Costa, Perez Mejía et al, 1980). The Austral basin in the southernmost part of South America is also deformed by tectonic movements between the South America and Scotia plates (Ghiglione et al, 2005). Since Tertiary times most of the sub-Andean basins share a common structural style forming the foreland basins with a folded and thrusted belt and an undisturbed area (platform) towards the old craton. A foredeep or trench could be recognized nearby the folded belt (associated to the subduction plate boundary of the Active Margin). The development of these trenches and the subsidence of the underlying foreland sediments have a significant impact on the hydrocarbon generation. Pre-Andean Mesozoic marine source rocks reached generative maturity for oil and gas because tectonic loading and burial by thick synorogenic clastics sequences as well the compressive deformation that defines the structural style for the trapping mechanism. The Gas Potential of the Sub Andean Basins 3 24th World Gas Conference, 5-9 October 2009 METHODOLOGY About 70 % of the total sub-Andean basins area remains in a moderately to immature exploration stage. Most of these basins have proven petroleum systems but different exploration maturity and hydrocarbon richness. Considering the different petroleum systems (Magoon et al, 1994) and for practical purposes the sub-Andean basins were divided in three major regions for their description: 1) North, 2) Central and 3) South (Fig.3). The Creaming Curve is a useful tool to analyze the reserve additions by basin by year on a cumulative basis. This graph allows perceiving the exploration maturity of the basins and the evolution of the geological concepts (play) tested in time. Each region encompasses more than one basin and may include several petroleum systems. By consolidating two or more basins in one creaming curve the methodology could mask the reality. For example, while one basin has been adding reserves over the years there has not been reserve addition in the other. In this case the consolidated creaming curve shows a reserve addition anyway. These deviations are explained in the text when appropriated. Another issue is when a basin is shared by two countries. Although the geology does not recognize political boundaries the exploration activity could be unequal in both sides (for example due to different fiscal terms or the exploration strategy followed by each country). These issues are also clarified when analyzing the exploration maturity of the basins. When making the statistics of the hydrocarbon richness, exploration drilling density and seismic density a weighted formula was used to obtain an average of all the group of basins within a specific region. Some basins have offshore extensions with little exploration activity. Nevertheless, the statistics for the basins were made considering the whole surfaces. The following is an example of the formula used to obtain the average hydrocarbon richness: EUR: Estimated Ultimate Recovery of Proven + Probable reserves (2P): ((EUR Basin A / Basin A Surface km2) + (EUR Basin B / Basin B Surface km2) + (…Basin n….)) / (Basin A+B+..n ..Surface); see Appendix “A”). It is believed that the results obtained give the perception of the exploration maturity of each region with considerable certainty. Fig.3 Su-Andean Regions Subdivision The Gas Potential of the Sub Andean Basins 4 24th World Gas Conference, 5-9 October 2009 PETROLEUM SYSTEMS AND EXPLORATION MATURITY: The South America basins contain 9% and 4.2% of the total proven world oil & gas reserves respectively (Fig. 4). The proven hydrocarbon reserves are 122 billion barrels of oil (BBO) and 264 trillion cubic feet of gas (TCF). WORLD GAS PROVEN RESERVES (TCF) WORLD OIL PROVEN RESERVES (BBO) 264 TCF 4.2 % 122 BBO 9% TOTAL 6,254 TCF TOTAL 1,342 BBO SOURCE: ; O&G JOURNAL, JAN.2009 Fig. 4 World Oil& Gas Proven Reserves - South America Percentages of the Total Reserves (Oil & Gas Journal Jan, 2009) About 90% and 95% of South America’s oil and gas reserves respectively, are in the sub-Andean basins. The remaining 10% and 5% of oil and gas reserves are located mainly in Brazil’s Atlantic margin basins and in Argentina’s intracratonic basins. The aim of this paper is to review the gas potential of these basins where so far most of the known proven gas reserves are located and to assess the gas reserves and resources able to supply the South American market. Brazil has 12.6 BBO and 12.9 TCF of proven oil and gas reserves respectively. About 90% of these reserves concentrated in three basins: Santos, Campos and Espirito Santo (Fig.5). A significant amount of contingent resources (SPE/WPC/AAPG/SPEE) of oil and gas were recently reported in the offshore Brazil. Nevertheless, the gas in Brazil has today some economic limitations. According to Cedigaz (CNR48/12/10) Brazil was flaring by February 2009 about 8.1 million cubic meters per day of natural gas from its offshore platforms. Gas in Brazil has to compete with hydroelectric plants. When they operate normally the gas-fuelled power plants have to shut down. Gas price and dropping demand due to global crisis and competition with hydroelectricity may delay the challenges of building a massive pipeline system to reach the gas fields located about 300 km away from the coast.