Brittleness Evaluation of Glutenite Based On Energy Balance and Damage Evolution

Abstract

Tight glutenite reservoirs are typically characterized by highly variable lithology and permeability, low and complex porosity, and strong heterogeneity. Glutenite brittleness is an essential indicator for screening fracture targets, selecting technological parameters, and predicting the hydraulic fracturing effect of tight glutenite reservoir exploitation. Glutenite formations with high brittleness are more likely to be effectively fractured and form complex fractures. Accurate evaluation of glutenite brittleness facilitates the recovery of oil and gas in a tight glutenite reservoir. Accordingly, two brittleness indexes are proposed in this paper based on energy balance and damage evolution analysis of complete stress–strain curves to evaluate the brittleness of glutenite. Uniaxial and triaxial compression tests of glutenite specimens were carried out and the brittleness indexes were verified by comparison with other existing indexes. The relationships between the mechanical properties and brittleness of glutenite under confining pressure were analyzed based on experimental results and the effects of mechanical and structural parameters on glutenite brittleness are investigated with a numerical approach. The brittleness of glutenite increases with the increase of gravel size and/or volume content. During hydraulic fracturing design, attention should be paid to the brittleness of the matrix and the size and content of gravel. This paper provides a new perspective for glutenite brittleness evaluation from the perspectives of energy dissipation and damage evolution. Our results provide guidance for fracturing layer selection and may also facilitate field operations of tight glutenite fracturing.

Rock Brittleness Evaluation Index Based on Ultimate Elastic Strain Energy

“…Processes 2022, 10, 1367 10 of 16 or 30 Mpa, and both values further decrease when the confining pressure is 50 MPa or 70 MPa. [35], shale 1 [23], shale 2 [23], glutenite [26], granite [36],…”

“…To verify the universality of the proposed brittleness index, BI ES , the CTC test data of six types of rocks (i.e., sandstone [35], shale 1 [23], shale 2 [23], glutenite [26], granite [36], and gneiss [36]) are cited. The corresponding stress-strain curves are exhibited in Figure 7.…”

“…[25] stated that rock brittleness can be represented by the dissipation rate of the failure energy. Ref [26] believed that the additional input energy could be transferred into total elastic strain energy. The aforementioned rock brittleness indices are listed in the Table 1.…”

The Main Controlling Factors of Glutenite Development and Their Impacts on Oil Energy Extraction

“…The glutenite reservoir is a low-permeability tight one [8]. The traditional evaluation methods conventional parameters such as porosity and permeability cannot meet the requirements of fine exploration and productivity improvement [35,36].…”

“…The reservoirs usually have large thicknesses, high productivity per unit area, and great exploration potential [4]. The lithology of glutenite reservoirs changes rapidly, the reservoir connectivity is difficult to describe, and exploration and development are difficult [5][6][7][8]. Therefore, to predict the distribution of glutenite bodies, it is first necessary to systematically study the characteristics and control factors of glutenite development.…”