South Texas Wilcox - A Situation Technology
Authors: Hill Robert A.F. , Garvin Thomas R. 
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.
This paper was prepared for the 49th Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Houston, Texas, Oct. 6–9, 1974. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussions may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Abstract
In order to realize reasonable profits from drilling and producing profits from drilling and producing the Wilcox Sands of Zapata County in Southwest Texas, special consideration was given to the operational problems encountered in this area. Modern technology with respect to drilling fluids, open hole evaluation, completion programs, cementing techniques and programs, cementing techniques and materials and stimulation procedures was brought to bear against the special geologic features of the Wilcox trend. The results of applied technology have resulted in efficient drilling and cementing operations. Some unsolved problems remain in formation evaluation problems remain in formation evaluation procedures, and stimulation efforts have procedures, and stimulation efforts have not been completely satisfactory. Technology and improved gas prices have created much interest in probing the Wilcox for new production and profitable development of the Zapata profitable development of the Zapata County reservoirs.

Introduction
Zapata County is located on the Mexico-U. S. border, east and southeast of the Texas city of Laredo. The area has a history of oil production that dates back to the twenties when shallow development created "Boom Towns" such as Mirando City. Petroleum operations caused many small cities to come to life but now there are many empty buildings standing as reminders of more prosperous times.
For many years the Wilcox formation of Zapata County (found from 5,600' to more than 12,000') remained unexplored primarily because of the high cost of primarily because of the high cost of wildcatting below the Queen City formation (Queen City base is generally found near 5,000' - 6,000'). New gas prices have helped overcome this prices have helped overcome this barrier to Wilcox development. The Queen City formation will rarely support mud weights in excess of 10 ppg while the Wilcox requires 13.5 to 14.0 ppg fox initial penetration. Protection pipe is therefore required near the midpoint of a shale section that separates the Queen City Sands from the top of the Wilcox.
The commercially attractive Wilcox of this trend includes sandstone with porosity ranging from 18 to 23% and porosity ranging from 18 to 23% and permeabilities from 5 to 35 millidarcies. permeabilities from 5 to 35 millidarcies.