Abstract
Abstract Large-scale staged hydraulic fracturing stimulation technology is an effective method to increase shale oil and gas recovery. However, cracks will appear along with the cementing interface and expand under the drive of fluid while hydraulic fracturing, failing wellbore sealing. To solve this problem, the synchronous propagation model of hydraulic fractures and cementing interfacial cracks in hydraulic fracturing is established. The Newton iteration method and displacement discontinuity method are used to solve the propagation length of each fracture, and the effects of cement sheath parameters and fracture parameters on the interface failure range are studied. The results show that when multiple hydraulic fractures expand, the interfacial cracks are also affected by “stress shadow,” offering an asymmetric expansion, and the cementing interfacial cracks in the area between hydraulic fractures are easier to expand. The failure range of interface between the hydraulic fractures expands rapidly if the cement elastic modulus increases from 5 GPa to 10 GPa; while the cement elastic modulus is higher than 10 GPa, the failure area is mainly affected by the number of hydraulic fractures; the failure range is not affected by the number of hydraulic fractures if the hydraulic fracture spacing is less than 10 m or more than 30 m; while the crack spacing is between 10 m and 30 m, the more the number of hydraulic fractures, the easier it is to cause the interface failure range to increase and connect. The research results can provide a theoretical basis for the optimization of cement slurry systems and fracturing parameters.
Highlights
In recent years, the “unconventional oil and gas revolution” in the United States has realized the rapid growth of shale oil and gas production and promoted unconventional oil and gas development into a new stage
The interface failure of the annulus sealing system can be divided into the following three processes: (a) After the cement sheath near the perforation is damaged by perforation, the initial fracture appears at the interface, and the fracturing fluid enters the hydraulic fracture and interfaces failure area. (b) Hydraulic fractures expand during fracturing fluid injection. (c) Part of fracturing fluid enters the interface crack and makes it extend
A numerical model of hydraulic fracture and cement formation interface (CFI) crack propagation is established, and the propagation law of interface crack under the influence of hydraulic fracture in the process of hydraulic fracturing is shown in this paper
Summary
The “unconventional oil and gas revolution” in the United States has realized the rapid growth of shale oil and gas production and promoted unconventional oil and gas development into a new stage. According to the data of the U.S Energy Information Administration (EIA) and Advanced Resources International Inc [3, 4], by the end of 2017, the recoverable resources of shale oil in China had reached 4.393 billion tons, accounting for about 6% of the global total, ranking third in the world (Figure 1). Large-scale segmented hydraulic fracturing stimulation technology is usually used to improve the production of shale oil and gas [7,8,9], which has become the main technology for the commercial development of unconventional resources [10]. The matching perforation completion technology and large-scale hydraulic fracturing in the later stage will
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