| Related literature showed that there is about33×10~8m~3CBM in Dafosi coal field with agreat exploitation value. A single coal seam and low reservoir pressure, low permeability, lowgas saturation and high absorption characteristics of the coal reservoir, however, make thetechnology of the conventional vertical well can’t obtain a better exploration and developmenteffect.A research on CBM horizontally connected wells drilling technology was carried out inorder to explore a new way to the CBM exploration of Dafosi coal field.The first objective of the study is to present the geographical location and tectoniccharacteristics of Dafosi coal field, to analyze the coal reservoir characteristics and damagemechanism of the case area, and to reveal the importance of drilling fluid in reservoirprotection, laid the foundation for the theory research of CBM horizontally connected wellsand the drilling fluid system. The second goal of this study, using the DFS-C04-H1well as acase study, to optimize the well body structure, to divide the well-path types of CBMhorizontally connected wells, and to provide the application of fixed parameters and adjustparameters in designing well-path. The author also investigated the well-trajectory controltechnologies of horizontally connected wells and optimized drilling assembly and drillingparameters, aimed to provide the technical reference for the later construction of CBMhorizontally connected wells in Dafosi coal field. Finally, the author researched drilling fluidfor different depth of DFS-C04-H1well through the indoor analysis and field test, designedthe more scientific drilling fluid system, and proposed the related maintenance measures fordrilling fluid with the purpose of reservoir protection and safety drilling.The study explored a set of applicable drilling technology of CBM horizontallyconnected wells in order to provide the prerequisites and technical support for thetechnology’s large-scale application in the Dafosi coal field. |
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