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.
Highlights
During the production, the optimal arrangement and post-adjustment of the well pattern are crucial to the efficient development of coalbed methane (CBM) resources (Crosdale et al, 1998; Li, 2005; Zhang and Liu, 2008)
When fracturing the heterogeneous reservoir, the artificial fracture is easier to communicate with natural fracture system, forming crisscross fracture network and improving the reservoir permeability (Blanton, 1982; Fan et al, 2014; Jeffrey et al, 2009; Liu et al, 2019; Valko and Economides, 1994)
Based on the characteristics of hydraulic fracture under the control of coal petrology, the relationship between well pattern, well pattern density and different coal macrolithotypes were analyzed according to the characteristics of gas pressure transmission in different coal macrolithotype, and the model of well pattern optimization and adjustment under the control of coal petrology was established
Summary
The optimal arrangement and post-adjustment of the well pattern are crucial to the efficient development of CBM resources (Crosdale et al, 1998; Li, 2005; Zhang and Liu, 2008). Due to the influence of coal reservoir heterogeneity, there are obvious differences in the propagation rules of hydraulic fractures in all aspects, resulting in strong anisotropy of permeability, and affects the determination of the well pattern and spacing (Diamond and Oyler, 1987; Jeffrey et al, 2009; Xu et al, 2014; Zhang and Liu, 2008).when developing the coal reservoirs, the completion technologies and production measures should adapt to different types of coal reservoirs, the adjustment and optimization of the pre-production and post-well wells should be tailored to local conditions (Karacan and Mitchell, 2003; Li et al, 2017; Pan et al, 2014). Based on the characteristics of hydraulic fracture under the control of coal petrology, the relationship between well pattern, well pattern density and different coal macrolithotypes were analyzed according to the characteristics of gas pressure transmission in different coal macrolithotype, and the model of well pattern optimization and adjustment under the control of coal petrology was established
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