Understanding Diversion with a Novel Fiber-Laden Acid System for Matrix Acidizing of Carbonate Formations

Abstract

Recently, a new fiber-laden, self-diverting, and viscoelastic acid has been successfully used for matrix acidizing of highly heterogeneous carbonate formations The fibers have been designed to be inert under surface and pumping conditions, and their geometry allows them to form strong and stable fiber networks that can effectively bridge across natural fractures, wormholes, and perforation tunnels. Eventually, the fibers degrade into a water-soluble organic liquid that is produced back to the surface during flowback.In the case of perforated wells, experiments suggest that diversion with fibers operates in three phases. First, as the early volumes of fiber-laden acid reach the perforations, the acid penetrates the reservoir as if no fibers were present. Second, as the fibers bridge, they accumulate inside the perforations and form a fiber cake. Third, the fibers plug the perforation, and the injectivity decreases locally, promoting diversion into other perforations. The pressure drop through a plugged perforation was analyzed by performing 340 separate fine-scale 3D simulations. The original work was based on theoretical and laboratory-based experiments, considering typical perforation schemes and for various permeability ratios between the generated fiber cake and the formation's original permeability. The results were compiled, and a correlation was made to model the resulting skin. The model was implemented into an acid placement simulator and was extensively tested and validated in the field.In this paper, we present the model that describes the effect of fiber accumulation within perforations and explain how some of the model parameters such as formation-permeability contrast, fiber-cake permeability, and total permeability thickness (kh) may affect diversion efficiency. Case studies from field testing of the model illustrate methods of pressure history matching, job design, and treatment history evaluation.

An Innovative Methodology for Real-Time Control and Optimization of Dual Injection Increases Efficiency of Carbonate Stimulation in Horizontal Openhole Water Injectors

“…Due to the presence of long openhole sections that were very likely to feature several washouts and thus a variable hole diameter, the use of inflatable packers was rapidly ruled out. It also became evident that using self-diverting acids alone might not be as effective; although they perform well in presence of limited permeability contrasts, the existence of significant thief zones and potentially large fractures was known to limit their impact (Cohen et al 2010). The main challenge was to make sure that the stimulation fluid pumped at the toe would remain there and effectively treat that section of the well, without traveling back to shallower thief zones.…”

“…Although several fluid placement simulators are today readily available (e.g., Jones and Davies 1998;Glasbergen and Buijse 2006;Tardy et al 2007;Cohen et al 2010), most of the difficulty to determine an appropriate design stems from the proper evaluation of key input parameters, such as rock characteristics or permeability distribution, which are often not well known. This poor characterization unfortunately leads to situations in which one would not know what to expect once pumping starts, nor even which fluid to use and/or which workflow to implement to efficiently control fluid placement.…”

Advanced Understanding of Matrix Stimulation Treatments Through In-Job and Post-Job Evaluation of Real-Time Downhole Measurements with Coiled Tubing: A Case Study

“…Execution of matrix stimulation treatments can be obtained via bullheading, or using CT for fluid placement at depth, or even by dual injection using both at the same time (Cohen et al 2010;Kalfayan and Martin 2009). Both techniques can utilize mechanical (e.g., bridge plugs, packers) and chemical (e.g., particulate diverters, self-diverting acids, and foams) means for diversion of the treatment fluids.…”

Using Fiber-Optic-Enabled Coiled Tubing to Quantify Fluid Placement and Optimize Stimulation Effectiveness During Matrix Stimulation Treatments in Carbonate Reservoirs

“…Although this notion is debatable depending on the well and formation types, as well as on the long-term vision for the well and field, fluid placement simulators are today readily available to investigate how the formation would react to specific job schedules and operational constraints. Those models are based on various parameters, such as the types of fluid used, their rheology, the formation mineralogy, reservoir properties, and the damage characteristics (e.g., Cohen et al 2010;Glasbergen and Buijse 2006;Jones and Davies 1998;Tardy et al 2007). Unfortunately, as afore-mentioned, many of those parameters are rarely known with accuracy, thus prompting engineers to sensitizing their designs and selecting the one that is most robust to unknown and/or uncertain variables.…”

“…Placement techniques may involve the use of bullheading, or coiled tubing, or a combination of both. Kalfayan and Martin (2009) and Cohen et al (2010) give extensive reviews of placement and diversion methods for matrix acidizing treatments, with their advantages and disadvantages. In most of those techniques, it is usually implied that one already knows where fluids need to be pumped along the wellbore, before starting the job.…”