Abstract
Hydraulic fracturing has been applied in the cave mining industry with the purpose of re-creating an orebody rock mass condition that is suitable for caving. Prescribed hydraulic fracturing was proposed in a previous study as a supplement to the conventional hydraulic fracturing strategy. In this paper; dimensional analysis is used to project laboratory scale numerical modelling results to field scales in order to study the applicability of creating prescribed hydraulic fractures (PHFs) under field conditions. The results indicate that field scale PHFs are feasible if the stress shadows of the pre-located fractures are properly utilized. Water can be used to create the pre-located fractures that induce the local stress change in a low differential stress state; and the use of more proppants and a shorter pre-located fracture spacing lead to PHFs propagating more quickly towards the pre-located fractures. For field condition having high differential stresses, more viscous fluid must be used to create the pre-located fractures in order to enhance the stress shadows. In this case, a shorter pre-located fracture spacing does not necessarily result in the re-orientation of PHFs towards the pre-located fractures and may even lead to unsatisfactory pre-conditioning. A sufficiently high pre-located fracture net pressure to the differential stress ratio (close to 0.5) is the prerequisite for creating PHFs.
Highlights
Hydraulic fracturing was invented in the 1940s and its first two commercial trials were realized by the Halliburton Oil Well Cementing Company in Oklahoma and Texas, respectively, in 1949 [1].Since this technique has been introduced into other industries for various purposes, such as improving gas production in the shale gas industry [2] and generating additional flow paths in enhanced geothermal systems [3]
In this paper, validated laboratory scale numerical modelling results on prescribed hydraulic fractures (PHFs) are transformed with dimensional analysis to predict PHF behaviour in field conditions as proof of the plausible practical feasibility of the concepts developed in lieu of field trials
Prescribed hydraulic fracturing was proposed in a previous study as a supplementary to the existing hydraulic fracturing strategy [4]
Summary
Hydraulic fracturing was invented in the 1940s and its first two commercial trials were realized by the Halliburton Oil Well Cementing Company in Oklahoma and Texas, respectively, in 1949 [1]. He et al [4] discussed the state of the art of cave mining hydraulic fracturing and established the requirement for creating HFs that are not perpendicular to the minimum in-situ principal stress orientation in some geotechnical conditions This is vital for ensuring that HFs form an additional joint set to increase the probability of achieving a blocky rock mass to improve caveability. These HFs that are forced to deviate from their theoretically predicted propagation directions are termed prescribed hydraulic fractures (PHFs) by He et al [4]. In this paper, validated laboratory scale numerical modelling results on PHFs are transformed with dimensional analysis to predict PHF behaviour in field conditions as proof of the plausible practical feasibility of the concepts developed in lieu of field trials
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