Janell D. Edman¹, Alfred J. Kaltenback¹
(1) Marathon Oil Company, Littleton, CO

Abstract: Use of geochemical data to predict oil quality: A case study from the offshore Gulf of Mexico

Oil quality impacts multiple aspects of reservoir development including exploration, production, oil value, transportation and refining. In the deep-water Gulf of Mexico, economic considerations related to oil quality can often determine whether or not a discovery is commercial. Consequently it is important to assess oil quality early in the field history, and this Gulf of Mexico case study illustrates how geochemical analyses performed on limited amounts of sample were used to successfully obtain preliminary oil quality indications.

In the well of interest, early mature, Jurassic-sourced oil in one reservoir was subcommercial due to its high viscosity. However, sidewall cores obtained in another sand suggested this interval probably contains better quality oil as demonstrated by more mature biomarkers and more light ends in the pyrolysis-flame ionization detector (PFID) analyses. These geochemical indicators of better oil quality were further corroborated by changes in color and fluorescence of the mud log shows.

Based on this information, fluid in the other sand was sampled, and analysis of this fluid confirmed the presence of oil with significantly lower viscosity and sulfur contents as well as high er API gravity. Unfortunately, the improvement in viscosity was not sufficient to make the oil commercial. Regardless, this example still illustrates the value of using geochemistry to both understand the predict oil quality, especially in deep water where sample material may be limited.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana