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ABSTRACT: Impact of Rock Mineralogy and Use of Mud Cleaning Acid (MCA) on Oil Productivity from the Aux Vases Formation in the Illinois Basin

UDEGBUNAM, EMMANUEL O., DENNIS J. HAGGERTY, and BRYAN G. HUFF, Illinois State Geological Survey, Champaign, IL

Illinois basin operators experience S-fold or greater reduction in oil production due to mud filtrate and particle invasion. Mud cleaning acid (MCA -15% HCl with additives) has been routinely used to address this problem. In addition, operators commonly follow the MCA treatment with hydraulic fracturing or matrix acidization of the formation. Depending on its concentration and the formation temperature, HCl reacts with chlorite and some mixed-layer clay minerals and with carbonates. For this study, various Aux Vases cores selected from three oil fields in southwestern Illinois were treated with standard MCA solutions.

Experimental results showed an initial reduction in permeability after treatment with one to two pore volumes of MCA. Increases in permeability, however, were noted as acid injection continued beyond three or four pore volumes. These results are compared and related to the abundance of minerals within the cores. An acidizing simulation model is used to compare the competing effects of acid reactions with clay minerals and carbonates within each sandstone matrix. Finally, a review of various completion practices in the Aux Vases formation and the rationale behind them is presented, as compiled from interviews with a number of independent operators.


AAPG Search and Discovery Article #91013©1992 AAPG Eastern Section Meeting, Champaign, Illinois, September 20-22, 1992 (2009)