Fracture Propagating Shapes in Gravel-Supported Conglomerate Reservoirs of Upper Wuerhe Formation on Manan Slope, Mahu Sag

doi:10.7657/XJPG20210107

Abstract

Abstract:

The tight conglomerate reservoirs with complicated lithofacies in the Wuerhe formation on the Manan slope are strongly heterogeneous, resulting in complicated fracture shapes after hydraulic fracturing, and insufficient theoretical basis for optimizing fracturing design. Taking the gravel-supported conglomerate as a research object, the mechanical properties of the gravel and the matrix were measured through nanoindentation experiments, and then hydraulic fracturing experiments were carried out to characterize the hydraulic fracture propagation and pressure curves after injecting different fracturing fluids. The research results show that, on a nanometer scale, the gravel underwent elastoplastic deformation, while the matrix underwent plastic deformation after injecting fracturing fluid; the elastic modulus, hardness, fracture toughness and stored elastic energy of the gravel are all higher than those of the matrix. With a wide gap in mechanical properties between gravel and matrix, the fracture propagation in the gravel-supported conglomerate is mainly controlled by gravel, and the extension around gravel is the main form of fracture propagation. Slick-water fracturing tends to initiate fractures at multiple points near wellbore, forming a radial propagation of multiple fractures. Guar-gum fracturing tends to induce tortuous double-wing vertical fractures, but the fractures are easy to branch when encountering gravels, forming tortuous fractures with horizontal and vertical branches communicating with each other. There is no obvious fracture initiating pressure on the bottom-hole pressure curve, but the extension pressure of guar-gum fracturing is higher and more fluctuant than that of slick-water fracturing.

Key words: Mahu sag, upper Wuerhe formation, tight conglomerate reservoir, hydraulic fracturing experiment, rock mechanical property, fracture propagating shape, pressure curve

CLC Number:

TE357.1

YU Tianxi, YUAN Feng, ZHOU Peiyao, HAO Lihua, ZOU Yushi, MA Xinfang, ZHANG Zhaopeng. Fracture Propagating Shapes in Gravel-Supported Conglomerate Reservoirs of Upper Wuerhe Formation on Manan Slope, Mahu Sag[J]. Xinjiang Petroleum Geology, 2021, 42(1): 53-62.

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