Experimental study on fracture propagation of hydraulic fracturing for tight sandstone outcrop

Abstract

The tight sandstone oil reservoirs characterized by the low porosity and permeability must be hydraulically fractured to obtain the commercial production. Nevertheless, the post-fracturing production of tight oil reservoirs is not always satisfactory. The influence mechanism of various factors on the fracture propagation in the tight oil reservoirs needs further investigation to provide an optimized fracturing plan, obtain an expected fracture morphology and increase the oil productivity. Thus, the horizontal well fracturing simulations were carried out in a large-scale true tri-axial test system with the samples from the Upper Triassic Yanchang Fm tight sandstone outcrops in Yanchang County, Shaanxi, China, and the results were compared with those of fracturing simulations of the shale outcrop in the 5th member of Xujiahe Fm (abbreviated as the Xu 5th Member) in the Sichuan Basin. The effects of the natural fracture (NF) development degree, horizontal in-situ stress conditions, fracturing treatment parameters, etc. on the hydraulic fracture (HF) propagation morphology were investigated. The results show that conventional hydraulic fracturing of the tight sandstone without NFs only produces a single double-wing primary fracture. The fracture propagation path in the shale or the tight sandstone with developed NFs is controlled by the high horizontal differential stress. The higher stress difference (<12MPa) facilitates forming the complex fracture network. It is recommended to fracture the reservoir with developed NFs by injecting the high-viscosity guar gum firstly and the low-viscosity slick water then to increase the SRV. The low-to-high variable rate fracturing method is recommended as the low injection rate facilitates the fracturing fluid filtration into the NF system, and the high injection rate increases the net pressure within the fracture. The dual-horizontal well simultaneous fracturing increases the HF density and enhances the HF complexity in the reservoir, and significantly increases the possibility of forming the complex fracture network. The fracturing pressure curves reflect the fracture propagation status. According to statistical analysis, the fracturing curves are divided into types corresponding to multi-bedding plane (BP) opening, single fracture generation, multi-fracture propagation under variable rate fracturing, and forming of the fracture network through communicating the HF with NFs. The results provide a reference for the study of the HF propagation mechanism and the fracturing design in the tight sandstone reservoirs.

Experimental Study on Hydraulic Fracturing of Bedding Shale Considering Anisotropy Effects

“…Several experimental studies have been conducted on influencing factors such as the in situ stress, natural fracture, temperature, fracturing fluid, and pumping mode in hydraulic fracturing. 23 , 24 …”

“…Along with the development of theory, hydraulic fracturing experiments have also achieved remarkable results. Several experimental studies have been conducted on influencing factors such as the in situ stress, natural fracture, temperature, fracturing fluid, and pumping mode in hydraulic fracturing. , …”

Experimental and Numerical Investigation of Characteristics of Highly Heterogeneous Rock Mechanical Responses in Tight Sandy Conglomerate Reservoir Rock Under Tri-axial Compression

“…It is widely accepted that the quality of hydraulic fracturing in tight and heterogeneous is jointly governed by stress shadows, in-situ stress, brittleness, fracability, clay and organic matter, and fracturing parameters (Guo et al, 2018a;Guo et al, 2018b;Dahi Taleghani et al, 2018;Li et al, 2018;Lecampion et al, 2018;Guo et al, 2019;Mao et al, 2020;Hou et al, 2019;Wang et al, 2019;Chen et al, 2021). To better characterize the hydraulic fracture network, tri-axial tests can provide essential measurements for rock mechanical properties (Guo et al, 2020;Duan et al, 2021). In addition, gravels in conglomerates introduce heterogeneities and increase the complexity of hydraulic fracture propagation.…”

Directional hydraulic fracturing technology for prefabricated longitudinal guide seams in a coal mine tight sandstone roof

“…S. V. Serdyukov (2016) uses a special fracturing device to generate tension in the rock along the axis of the hole, resulting in transverse cracks. There are also hydraulic fracturing methods that use multiple boreholes to achieve directional hydraulic fracturing; for example, dense boreholes have been used to change the stress state and form free surfaces to achieve through fractures for multiple boreholes (Duan et al, 2021;Song et al, 2019). There are also transverse guide seam fracturing methods (Deng et al, 2016;Lin et al, 2016), longitudinal guide seam fracturing methods (Cheng et al, 2018(Cheng et al, , 2020Ge et al, 2019;Zhong et al, 2021), guide seams, and directional hole fracturing methods (Lu and He, 2020).…”