The Jurassic coal measure gas block in Tuha Basin is located in a piedmont high-steep structure with large formation dip and complex geological conditions.It is the coal measure gas reservoir onshore in China with the deepest burial depth.However,the technology of horizontal-well drilling is still blank in such reservoir,and there exist some prominent problems during this drilling,namely well deviation,slow ROP,drilling drag and sticking.It is urgent to study horizontal-well drilling and completion technologies for these sort of gas reservoirs.Thus,some studies were conducted from aspects of casing program and borehole trajectory optimiza-tion,deviation control and faster drilling techniques,and safe drilling and completion in horizontal intervals.A pilot test on KX1H well reveals that(i)the three-section casing program facilitates the safe horizontal-well drilling,while it can be further optimized;(ii)with better performance in some coal measure reservoirs less than 2,500 m in depth,the vertical drilling technology provides a means for deviation control while fast drilling in middle and upper strata;(iii)as a basic condition,to ascertain the casing setting depth is critical for success drilling in horizontal intervals;and(iv)such tools of multi-target trajectory design,tracking lithology while drill-ing,single-bending screw drilling without centralizer + shrinking out diameter of BHA,bi-directional pigging means,and high-inhi-bition and high-plugging drilling fluid can be used to reduce sticking risks in these intervals,thereby to ensure casing while drilling in good order in those horizontal intervals over 1,000 m.
Deep coal measure gasCollapse mechanismCasing programDeviation control while fast drillingCasing setting depthSafe drilling
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