Lessons Learned from Acid Pickle Treatments of Deep/Sour Gas Wells

Abstract

Pickle treatments are commonly conducted to remove various contaminants from the wellbore prior to performing chemical treatments in various wells. Introduction of these contaminants into the formation during the treatment can cause loss of well performance, especially in tight formations. These treatments should be designed to remove various contaminants from well tubulars in an efficient and cost effective way.A pickle treatment was designed to clean well tubulars in several wells prior to performing acid fracturing in the carbonate formation. The pickle treatment consisted of several fluids such that each fluid removed one type of contaminants. This paper examines the effects of fluid composition, volume, and placement (bullheading versus coiled tubing) on the efficiency of pickling treatments. More than twenty pickle treatments performed on deep, sour, hot gas wells were examined.To assess pickle treatments in the field, spent acid was analyzed and the concentrations of key ions were measured. Sufficient measurements were made to obtain concentration profiles of chemical species in the spent pickle acid. These profiles were numerically integrated and the data were used to assess the outcome of each pickle treatment. In addition, particulate solids present in the spent acid were separated and analyzed using XRD and XRF techniques.Pickle treatments were conducted on more than twenty gas wells. Some of these wells were perforated, while others were not perforated. Un-perforated wells were pickled using 1.75" high-pressure coiled tubing. On the other hand, perforated wells were pickled using bullheading. The pickle treatments consisted of slugs of surfactants, organic solvents, hydrochloric acid and gelled fluids. Samples of all pumped fluids were collected and analyzed. In addition, well flow back samples were collected every two minutes and were also analyzed to determine their composition.Analysis of spent acids indicated that the major tubular contaminants are mill scale and pipe dope. Spent acid samples collected from deep sour gas wells contained up to nearly 105,500 mg/L of total iron. The efficiency of removing pipe dope was followed by tracing the concentration of zinc, the main acid-soluble constituent in the pipe dope, in the spent acid. The concentrations of acid and iron were used to determine acid reaction with the corrosion products present in the tubing. The concentration of the chloride ions was used to determine the dispersion and mixing behaviour of the acid slug.This paper presents the results obtained from analyzing more than 2000 samples obtained from twenty treatments. The results of this work have been used to enhance the efficiency of the pickle treatments and to significantly reduce the treatment cost. 4 Another main source of wellbore contaminants is iron scale. New low-carbon steel pipes (J-55, C-95 and L-80) are always covered with mill scale (magnetite, Fe 3 O 4 ). 7-10 Iron oxides dissolve in HCl and release ferric and ferrous ions into the acid. Ferric ions will precipitate once th...

Development and Field Application of a New Measurement Technique for Organic Acid Additives in Stimulation Fluids

“…Details of the pickle treatment itself are described by Nasr-El-Din et al 31 Details of the acid stimulation treatments are reported separately by Nasr-El-Din et al 32 Pickle treatment results from Well C show that the concentration of formic acid in the flowback samples was more than 85% of the concentration in the injected acid (Fig. 7).…”

“…The samples were collected at short time intervals that varied from 0.5 to 5 minutes. Details of the tubing pickle treatments were reported by Nasr-El-Din et al, 31 while the acid stimulation treatment details were reported by Nasr El-Din et al 32 Each sample from these treatments was mixed thoroughly, then accurately diluted with deionized water before determining formic and acetic acid concentrations.…”

Long-Term Comparative Evaluation of HCl/Formic Acid System Used To Stimulate Carbonate Formations at Severe Conditions in Saudi Arabia

“…The main objective of pickling super Cr-13 tubulars is to remove pipe dope and other greasy material from the wellbore, before the fracturing treatment. The pickling procedure was similar to that used in low-carbon steel tubulars, 27 however, in the case of super Cr-13, there was no acid used.…”

Modeling of Tubing Pickling in Conjunction with Acidizing Treatments

“…Acid additives included a corrosion inhibitor and a water-wetting agent. More details on the acid formulation were given by Nasr-El-Din et al 2 It is important to note that the gases produced contained hydrogen sulfide. Therefore, a hydrogen sulfide scavenger was added to the acid.…”