An Experience in Acidizing Sandstone Reservoirs: A Scientific Approach

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractSeveral sandstone fields were recently developed in Saudi Arabia. Various treatments were performed on damaged water injection wells in these fields, however, the performance of treated wells declined over a period of a few months such that these wells required re-acidizing treatments.A thorough investigation was undertaken to identify the damaging mechanism, recommend suitable acid formulae, assess the effectiveness of the treatment in the field and identify methods to minimize well damage.Laboratory and field investigations were conducted simultaneously to address formation damage and associated problems. These investigations included determining rock mineralogy, coreflood tests to screen various acid formulae, and collecting field samples to identify the damaging mechanism.Based on the results of these studies, two acid formulae were selected and applied in the field. More than forty damaged wells were treated with these acid formulae. Because of the low reservoir pressure, these treatments were conducted using a coiled tubing unit and the spent acid was lifted using nitrogen gas. Chemical analysis of acid returns (spent acid) was used to determine the type and concentration of acid additives.As a result of this study the success rate of acidizing jobs in these fields has increased to more than 85%. The target injection rate was met without drilling additional wells. No secondary precipitation was noted after the treatments. In addition, damage prevention procedures, which were implemented in the field, have resulted in a significant reduction in the frequency of performing acid jobs in these fields. This paper describes laboratory and fieldwork done to enhance the performance of damaged wells. Furthermore, it discusses the application of various damage prevention procedures in the field. would like to thank Mr. H.A. Al-Anazi for his work on the second stimulation treatment of Well G-40. SI Metric ConversionFactors ft x 3.048 E-1 = m ºF (ºF -32)/1.8 = ºC Gal x 3.785 412 E-03 = m 3 in. x 2.54 E+00 = cm md x 9.869 233 E-04 = µm 2

Iron Phosphonate Stabilized Emulsion And Formation Damage During An Adsorption Squeeze Treatment For Scale Mitigation

“…5 It has been cited by a number of authors as a potential source of damage in many chemical treatments. 6,7 In addition to the residual concentration of iron after the acid treatment, core flood studies by Company A had shown iron values of > 900 mg/L would be generated through the dissolution of the normal iron minerals as a result of the treatment chemical. There was no indication that these levels of iron would adversely affect the treatment, nor was substantial loss of permeability reported during their coreflood tests.…”

High-Viscosity-Yield Acid Systems for High-Temperature Stimulation

“…[13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] The use of a combination of organic and inorganic acids dates back to 1978. 30 More recently, Nasr-El-Din and coworkers studied the rates of reactivity by rotating disc method.…”

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

“…2 Acetic acid [3][4][5][6][7][8][9][10][11][12][13] and formic acid [6][7][8][9]12,14 have been used extensively in stimulation treatments in recent years. The application of organic acids in Saudi Arabia was first reported by Nasr-El-Din et al and Hashem et al, 8,15 where a mixture of acetic acid (5 wt%) and hydrochloric acid (5 wt%) was successfully used to stimulate water supply and injection wells in a sandstone field in central Saudi Arabia. In addition, citric and acetic acids are frequently used with hydrochloric acid as iron control agents.…”