The Evolution Of A Fracturing Technique For The Cotton Valley
Authors: Hufft H.F. 
Published: December 2007

This paper presents a review of the stimulation of the Cotton Valley formation in 13 wells of Caspiana Field, Desoto Parish Louisiana. A multiple-frac technique was initially used in the stimulation of the numerous pay sands within the Cotton Valley interval. This study resulted in the adoption of a single stage massive hydraulic fracturing treatment as the most efficient method to stimulate this formation. This paper analyzes the problems encountered with paper analyzes the problems encountered with the multiple fracturing technique and the results obtained from our first 1,000,000 pound frac job. pound frac job

Introduction

The recent increases in natural gas prices have increased the industries' prices have increased the industries' interest into areas which were previously uneconomic for exploration and development. The development of these marginal areas has facilitated improvements in stimulation treatments which in turn will result in economic investments. This paper presents Tenneco's effort to improve stimulation of the Cotton Valley formation.

The Cotton Valley formation is a series of low permeability sandstone stringers. The Cotton Valley group in the area of Caspiana Field is approximately 9000 feet deep with a gross interval that ranges from 600 to 800 feet in thickness. This gross interval contains from 100 to 250 feet of net pay. The average porosity and water saturation for the productive sands is 7% and 38% respectively. The range of productive permeabilities is from 0.01 to 0.06 millidarcies. permeabilities is from 0.01 to 0.06 millidarcies. This low range of permeability requires stimulation by means of hydraulic fracturing to establish commercial production. This paper presents Tenneco's experiences in hydraulic fracturing in Caspiana Field. The stimulation technique, analysis and examples are presented. Also presented are the results of our first massive fracturing treatment.

DRILLING AND COMPLETION

The drilling and completion technique was similar for each well in Caspiana Field. Basically the well was drilled to approximately 2000 feet and 9-5/8 inch surface casing was set. The well was then drilled to total depth and 5-1/2 inch casing was run. The well was then completed with 2-7/8 inch tubing set in a permanent packer. This sequence is shown in the packer. This sequence is shown in the typical wellbore schematic, Figure 1. The productive zones were then perforated and productive zones were then perforated and stimulated.

The stimulation technique initially used in Caspiana Field was the multiplefrac technique. The number of treatments performed on each well ranged from one to performed on each well ranged from one to five treatments. The general sequence for this multiple frac technique is shown on Figure 2. As can be seen on Figure 2, each well was perforated in the lower most productive sand body and then acidized. productive sand body and then acidized. The well in most cases was tested and a pressure buildup survey was run to evaluate pressure buildup survey was run to evaluate permeability and formation damage. The permeability and formation damage. The well was then fraced. A temperature survey and gamma-ray log were run where possible; sand bridges sometimes prevented possible; sand bridges sometimes prevented this procedure. Following this logging, the lower zone was usually tested. Upon completion of a good test, a sand plug was set across these perforations. This was accomplished by pumping sand into the tubing and allowing it to settle to the bottom.