Low resistivity zones at contacts of igneous intrusions emplaced in organic‐rich formations and their implications on fluid flow and petroleum systems: A case study in the northern Neuquén Basin, Argentina

D´ODORICO, ALEJANDRO; SENGER, KIM; LEANZA, HECTOR ARMANDO; PALMA, OCTAVIO; RUIZ, REMIGIO; SPACAPAN, JUAN BAUTISTA; GALLAND, OLIVIER; MANCEDA, RENE

BASIN RESEARCH

WILEY-BLACKWELL PUBLISHING, INC

Año: 2019 vol. 32 p. 3 - 24

0950-091X

Igneous sills and laccoliths emplaced in sedimentary basins may significantly impactpetroleum systems, both positively and negatively. Igneous intrusions provide heat tomaturate regionally immature organic‐rich host rocks, act as fractured reservoirshosting commercial accumulations of hydrocarbons, and form structures affectingfluid flow and trapping at different scales. Nevertheless, the petrophysical implications of igneous intrusions on their host rock are poorly known. In this study, we analyse 200 wells in the Río Grande Valley oil field, Neuquén basin, Argentina, wherethe main reservoirs are in fractured igneous sills. This dataset represents a globallyunique possibility to characterize the igneous?host rock interaction using both wireline logs and core material. We identify a systematic Contact Low Resistivity Zone(CLRsZ) at both the upper and lower contacts of the sills emplaced in the organic‐rich Vaca Muerta and Agrio Formations. We characterize the nature of these CLRsZand their petrophysical properties by integrating resistivity and gamma ray well logs,petrographic analyses, petrophysical tests and geochemical analyses. The low resistivity signal of the CLRsZ is dominantly carried by massive‐sulphide deposits,mainly pyrite, observed both in the host rock and the chilled margin of the sills. Welllog images and porosity‐permeability analysis on core plugs show that both the sillsand their associated CLRsZ can act as carrier for fluid flow and reservoir for hydrocarbons storage. The thickness of the upper and lower CLRsZ correlates linearly withthe thickness of the sill, and the volume of both the upper and lower CLRsZ represents ca. 40% with respect to the volume of their associated sill. The thickness of theCLRsZ represents ca. 13% of the thickness of contact aureole induced by the sills. Inthe CLRsZ, a great proportion of kerogen was transformed to hydrocarbon, so thatCLRsZ were restricted to the innermost contact aureole of the sills. Our results showthat the CLRsZ can have major implications on fluid flow and should be consideredin reservoir models in volcanic basins hosting sills emplaced in organic‐richformations.