Study on induced stress of hydraulic fracturing in fractured‐porous elastic media

Abstract

The study on induced stress of hydraulic fracturing is an important part of hydraulic fracturing design, temporary plugging and steering fracturing design, and completion design in oil and gas development. Based on fracture continuum method (FCM), cohesive unit method, and finite volume method (FVM), the propagation behavior of multiple hydraulic fractures (HFs) in fractured‐porous media reservoir is simulated from the perspective of fluid and geological stress coupling. The influence of natural fractures (NFs) on stress distribution and stress inversion sensitive factors are studied. NFs in the model are equivalent to physical models controlled by tension and shear bonds. The proposed model can deal with any number of NFs, which greatly improves the computational efficiency of the model. Then PKN analytic solution and Abaqus software results were used to verify the correctness of our model. The results show that the NF will make the reservoir stress show strong heterogeneity after fracturing, and the prominent feature is the regional stress mutation. The sudden change of stress shows the sudden increase or decrease in stress; with the increase in the initial stress difference, the stress inversion becomes more difficult. When the stress difference exceeds 3 MPa, the stress inversion area is almost 0. The stress interference increases with the decrease in cluster spacing. The stress inversion region between HFs decreases, while the external stress inversion region increases; Biot coefficient has great influence on stress and stress inversion. With the decrease in Biot coefficient, stress inversion region will decrease obviously. When the Biot coefficient is 0.4, there is no stress inversion area in the whole reservoir. Poisson's ratio has little influence on stress inversion. When Poisson's ratio changes between 0.1 and 0.3, the change range of stress is within 1 MPa, and the stress inversion area is almost unchanged. Our results can be helpful for understanding the stress distribution after hydraulic fracturing in fractured‐porous media.

Three‐dimensional complex fracture propagation simulation: Implications for rapid decline of production capacity

“…For unconventional reservoirs, especially low-permeability fractured reservoirs, under certain conditions, hydraulic fracturing can take advantage of developed NFs and the coupling effect of fluid flow and geological stress to form a highly permeable fracture network. [3][4][5][6] Microseismic field data confirmed that some reservoir fracture zones can be formed after hydraulic fracturing. 7 The corresponding capacity analysis showed that the larger the SRV, the larger the initial capacity.…”

“…In the development of shale, tight oil, and tight gas, and in the refracturing of old wells, hydraulic fracturing technology is generally adopted for reservoir reconstruction. For unconventional reservoirs, especially low‐permeability fractured reservoirs, under certain conditions, hydraulic fracturing can take advantage of developed NFs and the coupling effect of fluid flow and geological stress to form a highly permeable fracture network 3‐6 . Microseismic field data confirmed that some reservoir fracture zones can be formed after hydraulic fracturing 7 .…”

“…The ⟨⟩ symbols represent Macaulay brackets, indicating that the pure extrusion deformation or stress state does not cause damage. Equation (6) indicates that damage begins when the sum of squares of the total nominal stress ratio reaches 1. The nominal stress component and the elastic parameters are determined by the linear elastic constitutive relation and the material properties of the CE.…”

Variation law of roof stress and permeability enhancement effect of repeated hydraulic fracturing in low‐permeability coal seam

“…Figure 8 shows the seam roof stress cloud diagram of water injection for 200 seconds, 800 seconds, 1000 seconds, and 2000 seconds during the first hydraulic fracturing, and the stress accumulation and stress transfer of the coal roof during the entire fracturing process. 34 At the beginning of fracturing, the coal seam is still in the stage of water pressure accumulation, and the roof is less affected by water injection, and only the stress around the water injection hole increases. As the fracturing progresses, the stress rapidly increases in the area centered on the water injection hole and results in a stress concentration zone.…”