Characteristics and key technologies of multi-round fracturing transformation of deep coal in Daning-Jixian Block
LIU Chuanqing
WEI Xiaochen
BAI Kunsen
LIU Tong
ZHU Weiping
LIANG Lixi
ZHEN Huaibin
TANG Hanlin
Abstract：In the deep coalbed methane(CBM)development in Daning-Jixian block,the application of multi-stage fractur-ing has significantly increased the gas production and EUR(Estimated Ultimate Recovery)of vertical wells,achieving stable production along with enhanced production.This successful practice has important engineering guidance value for the efficient development of deep CBM.However,the current understanding of reservoir modification characteristics due to multi-stage fracturing is still unclear,and there is a lack of a comprehensive understanding regarding the initiation/propagation pressure and the propagation pattern of subsequent hydraulic fractures following the initial fracturing stage.Therefore,it is essential to clarify the mechanisms of multi-stage fracturing for enhanced production and develop system-atic methods for optimizing multi-stage fracturing parameters in different reservoir conditions.Well DJ55 was selected as the research object,and theoretical analysis was combined with numerical simulation to investigate fracture propagation characteristics and stress evolution induced by fracturing in deep coal seams.A stress-fluid flow coupling model for cleated coal is constructed to reveal the reservoir permeability evolution and key technology of multi-stage fracturing.The results show that the induced stresses generated by each fracturing stage lead to a continuous increase in the horizontal minimum principal stress as the number of fracturing stages increases.The fracturing stress shadow causes local stress re-direction,changing the orientation of the horizontal minimum principal stress from east-west to nearly north-south.Influ-enced by both the magnitude and direction of the induced stresses,subsequent hydraulic fractures tend to propagate to-wards areas that were inadequately modified during the first fracturing stage.Additionally,the fracture initiation pressure gradually increases with each fracturing stage,and the range of permeability increase continues to expand with fracturing stages.Under different fracturing fluid combinations,the stress disturbance range significantly increases after the second fracturing stage in the guar gum-slickwater-guar gum scheme,with a rising fracturing pressure curve indicating effective complex fracture creation.In contrast,the fracturing pressure curve for the guar gum-guar gum-guar gum and slickwater-guar gum-guar gum schemes in the second stage are both descending.Thus the selection of working fluid for the second stage is crucial for multi-stage fracturing.The promotion of multi-stage fracturing technology needs to consider specific reservoir characteristics.Well DJ55 has strong stress shielding capabilities from its roof(limestone)and floor(mudstone),with good horizontal stress equilibrium,resulting in significant effects using multi-stage fracturing.Besides the fracture enhancement effect of multi-stage fracturing,further in-depth research is needed on the physical property changes of cleated coal and gas desorption,as well as comprehensive evaluation of the technical applicability range.
Keywords：deep coal rocksmulti-round fracturinginduced stressdamage-seepage couplingfracture redirectionDaning-Jixian Block
Publication Date：2025-09-27
Online Publishing Date：2025-10-22(First online date of this platform, not the publication date of the document)
Pages：16( 4416-4431 )