Formulating a Stable Emulsified Acid at High Temperatures: Stability and Rheology Study

Abstract

Matrix acidizing is a means to stimulate wells; in order to increase the productivity or injectivity. Amongst the wide acidizing fluids, emulsified acids are the most commonly used. Emulsified acids have a reputation to retard the reaction with formation rock, hence they cause deeper penetration. Apart from that, they need minimum additives, since acid is encapsulated by oil phase. That being said, only the oil phase is in immediate contact with the tubing. Thus, granting less corrosion issues. All of these perks of emulsified acids are based on the mere condition that they are stable during their journey in the well to reach the formation rock. Therefore, a stable emulsion (emulsified acid) is extremely critical to the acidizing job, and the degree to which it is stable dictates how successful the job will be. This work aims to experimentally study the factors which contribute to create a stable emulsion by conducting thermal stability and rheology tests. These factors include mixing means (magnetic stirrer & high-power mixer), emulsifier concentration (up to 1.5vol%), mixing speed (up to 1500 rpm), addition rate of acid phase to diesel one (separatory funnel & syringe pump). Moreover, the emulsified acid is prepared using 15wt% HCl and diesel. The volume ratio of acid-to-diesel is 70:30. And, all of the thermal stability tests are conducted at 120°C in a heating oven. Furthermore, the apparent viscosity is measured at different temperatures and supported by droplet size distribution. The results show that emulsifier concentration and mixing speed have significant effect when the emulsion is prepared using magnetic stirrer; however, this effect diminishes when the mixing means is a high-power mixer. Interestingly, the addition rate plays a key role on the stability; even a small difference as 0.5 mL/minute would result in changing the behavior of the emulsion at 120°C. Also, the results confirm that the smaller the droplet size of an emulsion, the more viscous it becomes. Furthermore, temperature increase results in emulsion degradation. This study offers a unique way to look at emulsified acids and addresses factors that have never been addressed before. The novelty of this study is the comprehensive knowledge it brings about the factors affecting the stability of HCl emulsion. It helps to better understand HCl emulsion and how it works. Hence, production engineers can design and conduct acidizing jobs seamlessly.

Investigation of change in different properties of sandstone and dolomite samples during matrix acidizing using chelating agents

“…(All values are in MMbbl/d. ) During acidizing, dolomite reservoirs are mostly soluble in acids, and acidizing in these reservoirs generates conductive pathways known as "wormholes" (Sidaoui and Sultan 2016). However, in sandstone reservoirs, only a small portion of the rock is soluble by acids and usually no wormholes are created.…”

“…Once the fractures are created, the acid then starts to react with the undamaged formation to remove the minerals (matrix acidizing) present inside the formation creating new pore spaces and channels. In order to enhance the hydrocarbon reservoir productivity, acidizing is considered one of the most effective and common techniques in the industry (Sidaoui and Sultan 2016). Acids play a key role in boosting production from hydrocarbon fields.…”

A Review on Use of Emulsified Acids for Matrix Acidizing in Carbonate Reservoirs

“…Water in oil emulsions provide better retardation due to the low diffusivity created by the oil phase around acid droplets, which allows for minimum acid volume contact with the rock–tubular surface. Thus, most research ,,− ,,,− , has adapted W/O emulsions due to their desirable retardation effect and corrosion inhibition in comparison to O/W emulsions, , as depicted in Figure .…”

“…The factor that is prominent is the droplet injection rate. As mentioned above, even a small difference can cause behavioral change; therefore, the injection rate should have consistent increment, as the emulsion volume increases when using a buret/pipet . Therefore, it is better to apply atomic dispersion as mode of injection/addition of the dispersed phase.…”

Experimental study of one-step economical retarded sandstone acid

“…The main purpose of rock matrix acidizing is to eliminate formation damage near the wellbore area during drilling, completion, workover and water injection, thereby restoring or increasing the formation permeability (Zhao et al 2020;Sidaoui et al 2016). The ideal acid system can eliminate the damage near the wellbore area and avoid the decline in oil well production caused by secondary precipitation and solid particle migration.…”