Optimal design of old well stimulation in the Weibei CBM Field and its application

In the Weibei CBM Field, traditional directional wells and vertical wells are faced with several production difficulties, e.g. poor fracturing stimulation effect and low single-well production. In order to deal with these difficulties, this paper proposed a horizontal well deployment scheme suitable for the old well stimulation of Weibei CBM Field based on well pattern arrangement and geological characteristics of coal beds. In view of the drilling difficulties of horizontal well in the Weibei CBM Field (e.g. circulation loss in the upper formation, great variation of coalbed burial depth and thickness in the lower part, and caving coal bed), the geological modeling was carried out using the software Petrel, so as to calibrate the horizons of coal beds accurately. The chart for calculating target-entering deviation-frontal distance from target point-hole dogleg was prepared accurately using the drilling engineering design software Landmark, so as to optimize the design of wellbore trajectory at different formation dips and thicknesses. The matched circulating micro-foam drilling fluid was selected to deal with the circulation loss in the upper formation and the serious coalbed collapse. Field application indicates that when the horizontal section is set 3 m above the coal bed, the circulation loss in the whole horizontal well is low and the rate of penetration is high. And combined with the staged fracturing stimulation technology, horizontal well can stimulate six low-efficiency production wells laterally in the principal coal bed (11# coal bed) in one time, leading to obvious interference between hydraulic fracture networks and between wells, which is conducive to increase the drainage area and improve the single-well production of horizontal wells.