Experimental study on plugging behavior of degradable fibers and particulates within acid-etched fracture

Abstract

As proven from field practices in North America and Northwest China, temporary plugging and diverting acid fracturing is an indispensable technology to enhance stimulation effect and hydrocarbon production of complex carbonate reservoirs. It's well-known that the key to the success of this technology lies in creating a temporary plugging within the previously created fractures. Consequently, many scholars have conducted laboratory experiments to investigate the plugging behavior of fibers and particulates. However, the current devices nearly have certain limitations in simulating temporary plugging experiments. Aiming at this problem, this paper introduced the fracture temporary plugging evaluation system with large fracture size, and high-pressure resistance, which can meet the requirement of temporary plugging experiment. In addition, 3D printing technology was used to reproduce the roughness of acid-etched fracture surface, improving the experimental accuracy. Based on the device, a series of experiments were performed to study the effect of carrier fluids type, the injection rate, the fracture width, and the fracture morphology on plugging behavior of fibers and particulates. Experimental results show that the plugging effect of HPG fracturing fluid is better than that of slick water. Moreover, the effect of temporary plugging deteriorates with the decrease of injection rate, which can be attributed to the fact that high injection rate increases the probability of bridging and plugging. When it comes to the fracture width, only fibers have favorable plugging effect under the condition of 2 mm fracture width. However, a single type of temporary plugging agent (only fibers or particulates) cannot achieve effective plugging under the condition of 4 mm fracture width. The combination of fibers and particulates can obtain favorable plugging effect. When the fracture width increases to 6 mm, it's difficult to obtain favorable plugging effect if the diameter of particulates is less than 50% of fracture width. Hence, it is recommended to add big particulates whose diameters are at least 50% of the fracture width to improve the plugging effect. Moreover, the fracture surface morphology affects the formation time of temporary plugging, but does not affect whether temporary plugging is formed or not. This study deepens the understanding the plugging behavior of fibers and particulates within acid-etched fracture and provides fundamental for field treatment design.

Prediction of the Control Effect of Fractured Leakage in Unconventional Reservoirs Using Machine Learning Method

“…In the process of actively strengthening the wellbore, the fracture tip is isolated from the wellbore pressure by the plugging material slurry, thereby preventing the expansion of the fracture. Corrective borehole strengthening is a method to effectively improve the fracture resistance of rock formations by improving the formation 2 Geofluids closure stress and increasing the hoop stress in the nearwellbore area. The most common wellbore-strengthening theories are ring compression stress enhancement (stress cage) [28,29], fracture propagation resistance (FPR) [30], and fracture closure stress (FCS) [31].…”

“…The lost circulation material is carried into the fracture by drilling fluid or a particular lost circulation slurry. The behavior of fluid and particles in this transport process can be described by equations ( 1) and (2). According to the drilling fluid loss model in a single nonsite fracture established by Li et al [33], for the non-Newtonian Heba drilling fluid, the flow velocity equation in the fracture is…”

“…In unconventional reservoir formations, leakage is one of the typical complex problems in the drilling process [1]. Faced with the problem of downhole leakage, improper treatment measures will lead to a low success rate of plugging, continuous leakage of drilling fluid, and an increase of lost working hours on-site and even further lead to wellbore scrapping (well abandonment) [2][3]. Carboniferous fractures are developed in the target layer of the Chepaizi block in Xinjiang, China, and loss of return and leakage frequently occurs during the drilling fluid process.…”

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).…”

“…During acid fracturing in carbonate reservoir, there are two types of fiber mixing ways. 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).…”