ROP Control instantaneous drill rate to avoid overloading annulus with cuttings
Pump Failure Stop drilling and circulate until full pump capacity is restored
Slide Drilling Conduct rotary wiper trip after prolonged periods of sliding
Viscous Pills Use only when essential. Take special care with lo-vis pills to maintain high flow rate
Dense Pills Use only when essential. Limit volume to avoid fracturing formation
Tripping Circulate the hole clean with rotation prior to tripping. A single bottoms up is not sufficient
Overpull Pull through tight spots ensuring the pipe is free to go down. Work gradually up to predetermined maximum overpull limit
Backream Only when essential. Use DEAP to control maximum backreaming rate
ROP Increasing ROP will result in more cuttings being generated at the bit and so increase the cuttings loading in the annulus. Higher penetration rates require higher flow rates to clean the hole. It is good practice to maintain steady ROPs and to avoid high instantaneous penetration rates. Mud properties and flow rates should be adjusted to ensure the hole is cleaned as fast as it is drilled. This is a primary criteria (total pump capacity) to consider when selecting the rig.
Rig Site Indicators There are a number of rig site indicators that should be used to monitor the hole condition. These should normally be examined for trends and sudden departures rather than absolute values.
• The shape and size of the cuttings coming over the shaker should be regularly monitored. Small rounded cuttings indicate that cuttings have been spending extended periods downhole being reground by the BHA. The cuttings return rate at the shakers should also be measured and compared with the volume predicted from ROP.
• Torque and drag can be used to determine whether cuttings beds are adding to the wellbore friction. Simulations should be conducted in
the normal trend line can be indicative of cuttings beds forming. Erratic signals in torque or SPP can also be an early warning of cuttings beds.
• Record pickup, slackoff and off-bottom rotating torque regularly at connections to establish actual trends for comparison to predicted trends.
Cutting size & shape
Rounded cuttings indicate poor carrying capacity
Cuttings Return Use ROP to estimate anticipated cuttings rate at shakers
Torque & Drag Use DEAP to predict torque and drag. Look for deviations from trend
Erratic Torque / SPP
Look for indicators of cuttings beds & packing-off
Trend Analysis Compare drag trends on subsequent trips to indicated presence of cuttings beds
Hole Fill Monitor string weight for indications of fill on bottom
Operational Practices Successful hole cleaning relies upon integrating optimum mud properties with best drilling practices. When difficulties are encountered, it is essential to understand the nature and causes of the problem. This allows options to be focused to determine the most appropriate actions. This list below should be used as a guide to identifying possible courses of action:
• Poor hole cleaning will result in high cuttings loading the annulus. When circulation stops these cuttings can fall back and pack-off the BHA. When packing-off occurs, the flow rate is too low or the well has not been circulated for sufficient time.
• Typical volumes (50+bbl for 17-1/2 inch; 30-50 bbl for 12-1/4 inch; 20 bbl for 8-1/2 inch). It is not advisable to use low viscosity pills in weakly consolidated formations.
Limit the use of viscous pills to supplement hole cleaning. Control the mud in circulation properties to provide sufficient hole cleaning.
Typical Volumes:
Hole Size Volume
17-1/2 inch 50+bbl
12-1/4 inch 30-50 bbl
• Treat the hole gently. Avoid sudden mechanical or hydraulic shocks which may cause cuttings to avalanche.
• Control tripping rates to avoid pulling rapidly into a cuttings beds or causing excess swab/surge pressure.
• Pulling through tight spots is OK, provided the pipe is free going down. Agree to a maximum allowable overpull in advance with the Company Man/Drilling Superintendent. Do not go immediately to the maximum overpull, but work up progressively ensuring that the pipe is free to go down on every occasion.
• Stop and circulate the hole clean if overpulls become excessive. • Avoid precautionary backreaming - only backream when essential from
torque and drag trends. Use DEAP to determine the maximum allowable backreaming rate.
• Anadrill’s on-line drillstring simulator using data from the drilling mechanics sub is capable of calculating the variations in friction factors and can provide early indications of hole cleaning problems.
• The use of downhole torque and downhole WOB at Wytch Farm has proved to be an important tool in qualitatively assessing hole cleaning efficiency. Trend analysis can clearly indicate the condition of the hole while drilling, as well as the effectiveness of any remedial action such as reaming, circulating and wiper tripping.
• The response of these parameters to hole cleaning efficiency is very dependent upon the formation drilled. It has been established that while drilling mudstones inefficient hole cleaning is indicated by an increasing drag trend with very little increase in drilling torque as shown in the following figure. However, both torque and drag will increase with poor hole cleaning while drilling the Sherwood sandstone resevoir section. Analysis is not always straightforward though, as a decrease in wellbore lubricity with increasing amounts of sandstone cuttings may play a significant role in determining the drillling mechanics response.
DWOB DWOB 0 80 1 % 0 80 100 0 20 0 20 0 150 0 100 0 100 0 200 ROP M/hr STORQ DTORQ SURFACE RPM DRAG FRIC API GR %
CIRC HOLE CLEAN 35 STD WIPER TRIP @ 3168m 3150m 3150m Drill String RPM Guidelines
Normal range of drill pipe RPM's is typically 90-180 rpm (up to 120 rpm on bottom, up to 180 rpm off bottom). In practice, there needs to be a balance between good effects for hole cleaning versus possible detrimental effects (e.g. vibration causing premature failures of downhole equipment). High rpm should also be avoided in unstable formations since the string action can knock off loose sections of the wellbore. Limitations on downhole tool components (e.g. downhole motors) can also restrict the maximum allowable rpm.