Chapter 5Chapter 5

Drilling Techniques and Drilling ProblemsDrilling Techniques and Drilling Problems

Well deviates < 3 deg. per 100 ft (30m)

Cone with a maximum angle of 5 deg

Straight hole

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.

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 or Deviation Drilling

Directional DrillingDirectional Drilling Directionally drilled wells will usually be Directionally drilled wells will usually be

drilled according to one of three basic hole drilled according to one of three basic hole patterns.patterns.

Directional DrillingDirectional Drilling After making an initial deflection from After making an initial deflection from

vertical, the well may be drilled to the vertical, the well may be drilled to the target , or deflected once more to allowed target , or deflected once more to allowed the bottom of the the bottom of the

hole to be drilled hole to be drilled

vertically vertically

(“double dogleg”).(“double dogleg”).

Uses of Directional Drilling

Situation Requiring Directional DrillingSituation Requiring Directional Drilling

Directional DrillingDirectional Drilling

The deviation begins when the hole is The deviation begins when the hole is deflected using one of several techniques:deflected using one of several techniques:

(1) downhole hydraulic motors with a (1) downhole hydraulic motors with a

“ “bent sub”bent sub” (2) jet bits(2) jet bits (3) whipstocks(3) whipstocks

Downhole hydraulic Downhole hydraulic motors with a “bent motors with a “bent

sub” sub”

Device used to kick off a well

Jet bitJet bit

Jet bitJet bit

WhipstockWhipstock

WhipstockWhipstock

A steerable downhole assembly 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 Plot of well survey data showing paths of directionally drilled wellsdirectionally drilled wells

Extended Reach Well and Horizontal Drain Well

Depth of a Well

Problems while drillingProblems while drilling

FishingFishing Stuck pipeStuck pipe Sloughing shaleSloughing shale Lost circulationLost circulation Formation damageFormation damage Corrosive gasesCorrosive gases Abnormal high pressureAbnormal high pressure

Differential sticking Differential sticking of drillpipe because of drillpipe because of heavy mud weightof heavy mud weight

Crooked wellbore Crooked wellbore showing view of “key showing view of “key

seated” drillpipeseated” drillpipe

Three types of junk baskets for retrieving foreign Three types of junk baskets for retrieving foreign objects from holeobjects from hole