Historically, low-pressure, highly-fractured limestone formations have shown challenges in achieving proper acid diversion. In addition to the well deviation, this challenge becomes critical for wells close to the Water-Oil-Contact (WOC), with a latent likelihood to stimulate water zones. Consequently, a pinpoint placement technique thru Coiled Tubing (CT) plus a novel stimulation fluid is required to reduce/overcome this challenge. Common foamed acid has a short foam-stability time e.g., 10 minutes under native conditions. Hence, plain nitrified acid is pumped into the formation resulting in uneven treatment. Thus, custom foaming acids with stable foam qualities increments (e.g., 60% to 80%) are required to eliminate the risk of acid segregation to water zones. Then, wellbore fluids are over displaced by nitrogen, followed by the novel foamed acid with an initial bottom-hole foam quality of 60%, allowing the subsequent foamed stages (e.g., 65% to 80%) to divert upwards from the interval. Additionally, the CT mechanical diversion enables squeezing the treatment into the planned intervals. Carbonate reservoir stimulations in the north region of Iraq are performed using conventional hydrochloric acid (HCl) treatments. The foam acid diverting technology was implemented in challenging wells with a high risk of early water breakthrough based on water cut development in offset wells. Foamed matrix stimulation treatments were carried out through CT using a highly stable acid foam with self-diversion capability in ESP producer wells, demonstrating outstanding acid distribution over the interval of interest and sidestepping acid segregation to the water conductive zones. Despite the proximity of water zones, the use of foamed acids enhanced oil production and showcased a production gain of up to 3000 BOPD without water increase. The technology also allowed decreasing the volume of injected acid per meter of net interval by 41.7%, without jeopardizing the treatment efficacy which made it a cost-effective project. Based on the results, customized foamed acid treatments were incorporated in most of the stimulation programs. This paper discusses a novel foamed-acid system and the pinpoint placement technique used to stimulate challenging carbonate formations to get even fluid distribution, reducing the fluid segregation, thus minimizing the acid contact with the offending water zones.

This paper discusses the efficiency of design, application, and pumping schedule of organic acid treatments used for mature fields in Iraq. Due to challenging completion schematics, an enhanced fluid placement method consisting of coiled tubing (CT), nitrogen, and a fluidic oscillator tool (or combination) is presented. By the time a well completion is achieved, oil production for most wells begins to decrease because of formation damage caused by fines migration, clay swelling, scale deposition, emulsions, organic deposits, or previous unsuccessful hydrochloric acid (HCl) or HCl/hydrofluoric acid (HF) stimulation treatments. A matrix stimulation/acidization using a tool that enables pumping the treatment, either as near as possible to or reciprocating across the perforations, is necessary to help remove formation damage, enhance recovery, and increase oil production (producer wells) or water injection (injector wells). Matrix stimulation treatments were performed for both producer and injector wells for an Iraq field, demonstrating enhanced conductivity results and increasing oil production up to 2000 BOPD over the last production rate or improving the water injectivity rate by 10000 BWPD. In addition, for those wells in which an electrical submersible pump (ESP) was installed, it was necessary that the selected stimulation fluids did not adversely affect the internal components of the ESP. To reach this goal, analysis of the following parameters was performed: mineralogy, regain permeability test, temperature, fluids properties, rock properties, and formation damage. Based on the analysis, customized designs assisted by software simulations were developed to determine the most effective treatment selection. Novel/Additive Information (25-75 words suggested) This paper describes how well information and correct analysis, and design can help to develop a customized optimal intervention strategy, identify the best solution to remove the formation damage, and deliver value added to the operators.