Gas Well Stimulation Using Coiled Tubing and Acid with a Mutual Solvent
Authors: Taylor D.B. , Plummer R.A. 
Published: December 2007

This paper was prepared for the 47th Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in San, Antonio, Tex., Oct. 8–11, 1972 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 requested 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.

Introduction
A successful stimulation technique has been developed in several Wilcox Fields in Colorado and Lavaca Counties, Texas. The reservoirs have porosities and permeabilities of approximately 15 percent and 1 MD, respectively, with bottom-hole pressures of approximately 2,000 psi. Flow rates on a number of wells are so low that production is becoming erratic and liquids load the wells. These well conditions require stimulation to maintain constant production and meet contract requirements. Several stimulation techniques have been attempted with varying degrees of success. As a general rule, the standard acid treatments have not been as successful as anticipated and fracturing has had limited success. Often the wells have been damaged by the treatments, resulting in reduced production.
Gidley proposed a method of stimulation for gas wells using a preflush of 15 percent hydrochloric acid followed by mud percent hydrochloric acid followed by mud acid containing the mutual solvent, ethylene glycol monobutyl ether. The preflush serves as a buffer between the hydrofluoric acid and formation water and reacts with carbonates to prevent dissipating the hydrofluoric acid and prevent dissipating the hydrofluoric acid and precipitation of fluosilicates and calcium precipitation of fluosilicates and calcium fluorides. The hydrofluoric acid, in turn, removes clays and increases permeabilities by loosening and transporting fine particles away from the well bore. The limited success of other treatments may be due to fine particles migrating to the region near the well bore and eventually building up until plugging occurs. The mutual solvent makes the fines water wet and reduces the chances of their moving back to the well bore and deters formation of emulsions.

TECHNIQUE
Perforated intervals as long as 500 Perforated intervals as long as 500 feet and dual completions necessitate the use of special placement techniques. Displacing the acid through continuous coiled tubing being moved past the perforated interval has been the primary method of treatment. Other advantages of this procedure include the ability to jet out sand fill prior to the job and remove the spent acid with nitrogen after the treatment, thus returning the wells to production quickly. production quickly. Table No. 1 shows the results of the continuous coiled tubing acid - mutual solvent nitrogen treatments.