Case Study on the Effectiveness of Nitrogen Foams and Water Zone Diverting Agents in Multistage Matrix Acid Treatments

Abstract

Summary Chevron has successfully stimulated several oil wells producing water usingmultistages of mud acid, nitrogen foam and producing water using multistages ofmud acid, nitrogen foam and water zone diverting agents. This procedure hassignificantly improved well performance while having little or no effect onpost treatment water production. The diverters' effectiveness was analyzedusing radioactive tracers, gamma spectroscopy logs, and surface pressureequipment. The results of these analyses indicate that both water zonediverters and nitrogen foam are effective diverters when used in matrix acidstimulations. Case histories and associated data are included in the paper. Introduction Chevron has successfully used nitrogen foam and water zone diverting agentsin multistage matrix acid treatments to achieve stimulation of gravel packedintervals and to effectively divert the acid. This procedure, which consistedof injecting a water zone diverter before multiple stages of acid separated byfoam pills, has played an important role in reducing or eliminating formationdamage in wells producing both oil and water. To date, this method has beenused in two fields (totaling five wells) and has improved performance andincreased ultimate recovery. In fact, by reducing performance and increasedultimate recovery. In fact, by reducing the drawdown across these completions, production has been increased on the average of 700 BOPD/well or 307%. Onlyminor water cut increases were observed in the subject wells after acidizing. In contrast, wells in these fields cutting water that were stimulated withoutthese diverting procedures had drastic water production increases. Based onthese results, it appears that production increases. Based on these results, itappears that the combined use of water zone diverters and foam has a positiveimpact on post treatment water production. Radioactive tracers, production logging techniques and surface pressureequipment were used to determine the effectiveness of these diverters. Radioactive tagging was used in three of the five wells treated to determinethe specific placement of the fluids within the perforated intervals.