MECKEL, LAWRENCE D., and JOHN T. SMITH, Exploration Consultants, Houston, TX

ABSTRACT: The Austin Chalk: A Vast Resource in the Gulf Coast

The Austin Chalk, a low-porosity, low-permeability limestone extending from Mexico to Florida, is oil-saturated over a sizable part of its vast extent. With the advent of horizontal drilling, the probability of encountering fractures and increasing the drainage area per well have both been greatly improved, creating an attractive target in areas previously considered noncommercial. Therefore a huge fairway emerges for future oil and gas exploration, but critical geologic parameters need to be evaluated to optimize positions within the fairway.

This integrated geological, geochemical, and reservoir model study highlights those significant parameters needed to properly select future exploration and exploitation areas.

(1) One must identify an optimum thickness of clean (not marly) chalk in areas where there are no immediately subjacent wet sands (Subclarksville, Woodbine). This target zone varies from 0 to over 100 feet thick.

(2) Published geochemical data plus the distribution of production and shows support a self-charging mechanism for the downdip-mature chalk.

(3) Where dip-oriented fractures are absent, hydrocarbons have been retained in this mature belt due to the extremely low migration rate through the rock matrix.

(4) Rock-log-production data are used to define critical thickness, porosity, and saturation cutoffs for a play.

(5) A model for predicting horizontal well performance in both low and high gas/oil ratio areas is derived from the production histories of more than eighty horizontal wells in the chalk in eastern Giddings and Brookeland Fields, the areas closest to the future exploration trend.

(6) By applying this model to undrilled areas, the operator can greatly improve the probability of success and profitability.

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