An Innovative Solution to Optimizing Production in Naturally Fractured Carbonate Reservoirs in Southern Mexico

Abstract

The results of stimulation treatments in southern Mexico's carbonate reservoirs have been significantly improved using a new fiber-assisted, self-diverting acid system. These reservoirs are thick, deep, and hot. Depths are usually greater than 15,000 feet, bottomhole temperatures reach up to 350°F, and permeabilities range from 1 to 1000 mD within the same interval. Wells are typically completed with multiple perforated intervals. In the past, high-viscosity diverting fluids have been used to improve zonal coverage during stimulation treatments. Despite repeated treatments during the life of the well, in many cases, post-treatment logs show that the treatment was not effectively diverted to lower permeability, less productive intervals. To overcome these challenges, we introduced an innovative degradable diverting acid system combining the properties of viscoelastic diverting acid (solid-free) and degradable fibers to southern Mexico. This, combined with a rigorous candidate selection process, resulted in improved zonal coverage, increased oil production, and higher ultimate reserve recovery. Maximizing oil production using this diverter system requires a detailed understanding of the petrophysical properties of the reservoir and production history. This information helps determine treatment volumes and the volume and number of diverter stages. Wells with the highest permeability contrast are often the best candidates. In many cases, producing from natural fractures depends on correctly determining the number and volume of the diverter stages. The experienced gained from treating more than 10 wells has resulted in the development of clear guidelines with respect to the treating fluid, volume, and number of diverter stages. On average, the guidelines have resulted production increases of 1,500 BOPD. By applying the treatment guidelines with an effective diverter fluid, operators can significantly increase oil and gas production in previously stimulated or new wells within naturally fractured carbonate reservoirs.

An experimental investigation on the influence of temporary plugging fibers and particles on the fracture conductivity

“…Generally, it can be used for plugging large-size fractures and prevent the proppant from flowing back. Fiber temporary plugging agents are generally used in the construction of temporary plugging and turning acid fracturing [14][15][16][17][18]. In deep formations, high-concentration cross-linked gels are often used on site, which will cause undegraded residues to pollute the formation, damage the formation and reduce the fracture conductivity [19][20][21].…”

Effect of fiber on the rheological properties of gelled acid

“…Because the natural fracture is easily connected and etched by gelled acid for creating complex fracture network, gelled acid is widely used in the acid stimulation of marine carbonate reservoirs in Sichuan Basin (Gou et al 2021a, b). To improve the performance of acid distribution and reduce acid leak-off in the acid stimulation process, degradable fiber is used to temporarily block natural fractures and acid-etching wormholes, which makes acid divert to another un-stimulated area to create new fractures and assists in controlling acid leak-off (Guo et al 2015a;Zhang et al 2020;Jauregui et al 2011;Quevedo et al 2012). Acid rheological properties have a large influence on fracture morphology, acid-rock reaction rate and the effective penetration distance of living acid, etching morphology and fracture conductivity, and acid leak-off (Gou et al 2021a(Gou et al , 2021bDong et al 2018;Rui et al 2018;Mou et al 2012).…”

“…One way of mixing is that the fiber is mixed with fracturing fluid, slick water, and the blend is injected into the formation as a diverter stage, and then followed by acid (Guo et al 2015a;Zhang et al 2020). The other way is that the fiber is directly mixed with acid (Jauregui et al 2011;Quevedo et al 2012). Either way, fiber would be contacted and mixed with acid in the wellbore sooner or later.…”