PUEX, ANTHONY N., Shell Development Company, Houston, TX

ABSTRACT: Routine Quantification of Oil Expulsion from Source Rock Data: An Example from the Utica Formation (Ordovician) of the Michigan Basin

Methodology for the quantitative interpretation of source rock quality from routine data--TOC, pyrolysis yields, maturity, and visual kerogen analysis--is described. The methodology involves an estimation of the oil content from pyrolysis data, current and original quality of oil-prone kerogen, oil generation, oil ultimately to be generation, and oil expelled. Two independent methods of estimating the quantity of oil expelled are presented. One of the methods, although very straight forward, is new to the literature and easily applicable to routine source rock analyses. The proposed new method is based on the variation of oil and kerogen contents in a set of rocks, identical except for varying richness. The second method is based on the difference between the oil generated to the curr nt maturity and that estimated to be in the rock. A new method for estimating the in situ oil content from a pyrolysis analysis is described. This allows such calculations to be made from routine source rock data. This methodology is designed to be insensitive to variable volatile loss from rock samples during storage and is thus applicable even to ditch samples stored for years in hot warehouses.

Quantitative source rock evaluation parameters are proposed to replace, or at least supplement, the qualitative assessments such as "fair," "good," "excellent," etc. as follows (all parameters are in units of millions of barrels of oil per square mile per foot, or other suitable field units):

OPI = Oil Performance Index - Oil generated from VR 0.4 to the present maturity;

OGI = Oil Generative Index - Oil ultimately to be generated from VR 0.4 to 5.0;

OE = Oil Expelled - Oil expelled from a source rock;

OR = Oil Retained - Oil retained in a source rock (with volatiles lost on sampling and storage restored).

The proposed source rock evaluation methodology is demonstrated by an example drawn from a lean (0.5 to 1.6% TOC), mature (VR 1.0) source rock core of the Ordovician Utica Shale in Northern Michigan. The core is a 60 ft conventional core sampled at one foot intervals throughout. It has the rather unusual and valuable distinction of being in the oil window with richnesses spanning the non-expelling/expelling boundary. In fact one of the oil expulsion methodologies discussed was discovered in examining data from this core.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.