Analysis of hydraulic fracture behavior and well pattern optimization in anisotropic coal reservoirs

Abstract

Macrolithotypes control the pore-fracture distribution heterogeneity in coal, which impacts stimulation via hydrofracturing and coalbed methane (CBM) production in the reservoir. Here, the hydraulic fracture was evaluated using the microseismic signal behavior for each macrolithotype with microfracture imaging technology, and the impact of the macrolithotype on hydraulic fracture initiation and propagation was investigated systematically. The result showed that the propagation types of hydraulic fractures are controlled by the macrolithotype. Due to the well-developed natural fracture network, the fracture in the bright coal is more likely to form the “complex fracture network”, and the “simple” case often happens in the dull coal. The hydraulic fracture differences are likely to impact the permeability pathways and the well productivity appears to vary when developing different coal macrolithtypes. Thus, considering the difference of hydraulic fracture and permeability, the CBM productivity characteristics controlled by coal petrology were simulated by numerical simulation software, and the rationality of well pattern optimization factors for each coal macrolithotype was demonstrated. The results showed the square well pattern is more suitable for dull coal and semi-dull coal with undeveloped natural fractures, while diamond and rectangular well pattern is more suitable for semi-bright coal and bright coal with more developed natural fractures and more complex fracturing fracture network; the optimum wells spacing of bright coal and semi-bright coal is 300 m and 250 m, while that of semi-dull coal and dull coal is just 200 m.

A study on moment tensor inversion of acoustic emission response on damaging localization of gas-bearing coal under load

“…Under the loading stress, the damage and deformation of coal mass lead to the final dynamic failure, which is the essential reason for the dynamic disaster in mining engineering. The weaker non-chemical bonds will break during the coal rupture process 8 – 10 . Microcosmically, the internal microcracks initiate, expand, coalesce and gradually form a crack gathered zone from the weak structural plane under loading stress.…”

Quantitative evaluation indexes of the spatial steering effect of directional perforation hydraulic fractures

“…The morphology of hydraulic fractures generated by directional perforation is the key to evaluating whether this technique has been successfully implemented. However, due to reservoir stress differences, mechanical properties of reservoir rock, wellbore radius, perforation parameters and injection pressure, hydraulic fractures deflect to different degrees after initiation at the perforation hole (Chen et al, 2017;Duan et al, 2021;Guo et al, 2020;Liu et al, 2021;Lu and He, 2020;Lu et al, 2020b;Lyu et al, 2020;Song et al, 2020). It is very important to quantitatively evaluate the influence of these factors on the fracturing effect of directional perforation hydraulic fracturing.…”