Chapter 5 Drilling Techniques and Drilling Problems. Part 1 Drilling Techniques. Straight hole. Well deviates < 3 deg. per 100 ft (30m) Cone with a maximum angle of 5 deg.
Straight hole Well deviates < 3 deg. per 100 ft (30m) Cone with a maximum angle of 5 deg
If the bit hits a subsurface rock layer with a dip greater than 45 deg., the bit tends to be deflected down dip. If rock layer dip less than 45 deg., the bit tends to be deflected updip. A well with an excessive angle in it that has not been drilled on purpose that way is call a crooked hole.
Directional Drilling or Deviation Drilling Modern rotary rigs can be controlled so that the well is drilled out at a pre-determined angle during directional or deviation drilling and ends up in a pre-determined location called target.
Directional Drilling (Patterns) • Directionally drilled wells will usually be drilled according to one of three basic hole patterns.
Directional Drilling (Patterns) • After making an initial deflection from vertical, the well may be drilled to the target, or deflected once more to allowed the bottom of the hole to be drilled vertically (“double dogleg”).
Directional Drilling • The deviation begins when the hole is deflected using one of several techniques: • (1) downhole hydraulic motors with a “bent sub”(井底馬達 與 彎曲接頭) • (2) jet bits(沖鑽頭) • (3) whipstocks (導斜具)
A steerable downhole assembly (可控式井下總承)is a combination of stabilizers, bent subs, downhole turbine motor, and diamond bit that can maintain, drop, or build angle.
Plot of well survey data showing paths of directionally drilled wells
Extended Reach Well and Horizontal Drain Well
Problems while drilling • Fishing 打撈 • Stuck pipe 卡鑽 • Sloughing shale 頁岩崩落 • Lost circulation 喪失循環 • Formation damage 地層損傷 • Corrosive gases 腐蝕性氣體 • Abnormal high pressure 異常高壓
Comment situations requiring fishing jobs • Differential sticking 差壓黏卡 • Key seating 匙孔卡鑽 • Sloughing shale 頁岩崩落（泥坑） • Poor mud properties 鑽屑停滯或糊鑽 • Fatigue failures 金屬疲勞破壞 • Foreign objects 外來的掉落物件
Equipment used for a fishing job • For stuck drillpipe （卡鑽） • Overshot 打撈碗 • Spear 打撈矛 • For foreign objects （掉落物） • Junk baskets 打撈籃