Rock magnetic properties of drill cutting from a hydrocarbon exploratory well and their relationship to hydrocarbon presence and petrophysical properties

Abstract

AbstractThe Golfo San Jorge Basin is one of the most important hydrocarbon-producing basins in Argentina. A study of magnetic properties performed on drill cutting from an oil well drilled in this basin was carried out. The cutting samples, taken from an interval of about 400 m thickness, correspond to the upper units of the Pozo D-129 Formation, the main source rock of the basin. Magnetic susceptibility measurements were made and rock-magnetism studies were conducted. Concentration indices of the different magnetic species determined were calculated based on isothermal remanent magnetization acquisition curves. A correlation analysis among magnetic properties, hydrocarbon content and well logs (sonic, neutron, density, induction, resistivity and photoelectric factor) was performed. Several kinds of significant correlations were found: a positive correlation between susceptibility and relative hydrocarbon content; a positive correlation between magnetic properties and porosities (especially good with the neutron log porosity); and a negative correlation between the concentration indices of some magnetic species (magnetite and pyrrhotite) and resistivity. Pyrrhotite could be directly related to the presence or migration of hydrocarbons through the porous units.The qualitative correlations between magnetic data and key petrophysical parameters such as porosity, along with the association of magnetic mineralogy to hydrocarbon presence or migration, suggest the potential usefulness of these techniques for subsurface exploration.