The Design of Refrac Treatments for Restimulation of Subsurface Formations
Authors: Coulter G.R. , Menzie D.E. 
Published: December 2007

This paper was prepared for the Rocky Mountain Regional Meeting of the Society of Petroleum Engineers of AIME, to be held in Casper, Wyoming, May 15–16, 1973. 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 OF PETROLEUM TECHNOLOGY or the SOCIETY OF publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon requested to the Editor PETROLEUM ENGINEERS JOURNAL is usually granted upon requested to the Editor of the appropriate journal, 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
Since the introduction of the hydraulic fracturing process, there have been in excess of 500,000 treatments conducted. Approximately 35 percent of these treatments have been retreatments. Very little information has been published concerning refrac design procedures. published concerning refrac design procedures. Considerations for refrac treatments have been proposed by Howard and Fast and by Johnson. proposed by Howard and Fast and by Johnson. A discussion is given concerning considerations prior to conducting a refrac treatment. These prior to conducting a refrac treatment. These considerations are related to determining if a refrac treatment might be beneficial. The primary considerations would be remaining reservoir energy and recoverable reserves.
Laboratory tests were conducted to determine a method of removing or replacing the old proppant system in the fracture. This would be necessary if the old proppant system did not have sufficient flow capacity for the reservoir. Based upon these tests and published fracture width, fracture area and proppant transport equations, the results of the previous treatment may be evaluated and the technique for replacement of the old proppant system calculated. With this information the requirements for placement of a new proppant system may be calculated.
Two techniques are discussed for removal or replacement of the old proppant system. Examples are given showing results of calculations and the economic advantages for each of these techniques.

Introduction
The hydraulic fracturing process was introduced to the petroleum industry on a commercial basis in 1949. This process is normally used to stimulate the production or injection rate of a subsurface formation. Basically, the process utilizes hydraulic pressure to take the formation to failure, whereby a pressure to take the formation to failure, whereby a crack or fracture is created. This fracture increases the effective wellbore radius giving greater production or injection rates. In most hydraulic fracturing treatments, a propping agent is required to keep the fracture open after the applied hydraulic pressure is removed. pressure is removed. Since 1949, in excess of 500,000 hydraulic fracturing treatments have been conducted. Approximately 35 percent of these treatments have been refrac treatments on wells previously fractured.