--> New Insights from the Neuquén Basin Lower Jurassic Petroleum Systems and Deep Gas Play, Mosquera, Alfonso; Villar, Héctor; Zavala, Carlso; Alarcón, Martín, #90100 (2009)

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New Insights from the Neuquén Basin Lower Jurassic Petroleum Systems and Deep Gas Play

Mosquera, Alfonso1
 Villar, Héctor3
 Zavala, Carlso2
 Alarcón, Martín1

1Exploration, Tecpetrol S.A., Buenos Aires, Argentina.
2
Grupo de Cuencas Sedimentarias.
Argentina, Bahía Blanca, Argentina.
3
Geolabsur,
Buenos Aires, Argentina.

The Neuquén Lower Jurassic-Tertiary retro-arc foreland basin accounts for a EUR of 10,000 MMBOE, generated from the Vaca Muerta, Los Molles and Agrio marine shales. Latest mass-balance data over the productive zones highlighted the low 0.2% GAE index of the Lower Jurassic Los Molles source rock, despite accounting for 35% of the total 800,000Bkg basin generated hydrocarbons. The dominant vertical fault migration pattern for these hydrocarbons in the basin center and southern margin and the very tight reservoir properties of the carriers (the Lajas and Punta Rosada deltaic and fluvial sandstones) have been invoked to explain the limited drainage efficiency of the system. Recent deep discoveries of petroleum bearing the genetic signature of Los Molles source rock along the hinge-line of the northeast margin force a review of these paradigms. The accumulations are mostly found in deep Lower Jurassic reservoirs in areas typically imprinted by Vaca Muerta sourced hydrocarbons. The integration of multidiscipline studies allows the proposal of a new lateral migration-drainage style for Los Molles sourced hydrocarbons. The migration fairway involves a system of braid-delta and shelfal lobe deposits within Los Molles Fm. developed along 150km, parallel to the basin margin, reaching up to 20km of lateral drainage until its depositional edge. This process was boosted by the unusual petrophysical properties of the carriers: average porosity and permeability values of 15% and 30mD, respectively, at depth ranges of 3,000m, resulting from the development of porosity-preserving chlorite rims at early diagenetic stages. This issue constitutes a strong evidence to support the existence of a deep gas center play associated to diagenetic traps as seen in many basins around the world, developed along de depositional edge of the braid-delta deposits over an area of 4,000km2, with direct charge from the westwards Los Molles pod. The drainage was also favored by sets of transtensive faults, enabling the vertical migration towards the Sierras Blancas, Punta Rosada and Loma Montosa shallower reservoirs. These carriers allowed further long-distance lateral migration towards the eastern margin for about 80km, as proved by the reassignment of hydrocarbons genetically linked to the Los Molles shales in the Loma Montosa reservoirs in several fields. These models may favor a new exploration phase and contribute to the understanding of the petroleum systems of this mature basin.


AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil