Most common Factors causing troublesome Trips

(Reading time 15 Minutes)

In the drill operations, running in (RIH) & pull out of hole (POOH) are the crucial steps, time taken on these have a visible impact on over all well performance, if hole condition is good then trip can be performed smoothly on elevator without taking additional time, otherwise significant amount of time would be spent on the trips. If trips are not smooth, hole condition is not favorable then these steps shall add excess time on well graph and it can be worrying step for all drilling? team also because tight trips can be converted in to stuck pipe conditions easily, there may be several contributing factors to the tight hole conditions, ?most of the time drilling team consider MW as a solution to get out of that situation which is not always necessary & correct. Many factors can be the contributing cause of Tight hole and unstable trips, most common causes are mentioned below by address these appropriately we may smoothen the running in and pull out of hole.

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1.????? Poor Hole cleaning

Poor hole cleaning is most common cause of tight hole conditions, before final POOH it must be ensured the hole is clean, good viscosity Hi-vis pills (Required Viscosity is relative to the hole size and cutting load, Volume should be adjusted as rule of thumb it height should ≥ 500ft) can be pumped and its response can be monitored on shale shakers, as a Rule of thumb during drilling cutting load in hole must be less than 3% then hole cleaning shall not be a challenge, hole cleaning can be monitored by keep on eyes on circulating? pressure & Torque values. When hole would be loaded with cutting then pumping pressure tend to be high similarly cuttings inside the bore hole can create torque/erratic torque. As good practice before POOH, hole should be cleaned, if any kind of cuttings and cavings are observed on shakers then circulation need to be continued till shakers become clean, there can be minor amounts of cuttings on shakers, don’t be confused it does not mean hole is not clean, observation of cuttings traces is common even after complete hole cycle so one should not be confused with minor volume of cuttings. During POOH at any depth in case of tight hole, reaming/back reaming may be performed if the reamed interval and time is slight then POOH or RIH can be continued, but if reaming interval & time is notable then it is necessary to Pump His pill(s), circulate at that bit depth to ensure hole clean before further trip, poor hole cleaning during reaming/back reaming is common cause of stuck pipe.

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2.????? Unstable bore hole & formations

Unstable bore hole is second most cause of tight trips, the borehole instability can be of different types & different challenges have a different solutions, one solution can be against other phenomenon so understanding of real cause is very important for example if one thinks to increase MW to stabilize a bore hole in the presence of depleted formations then there are chances of differential stucking, similarly in case of fissile shales with micro fracs shall be destabilized with increasing MW as it will increase the fluid invasion as a result of which cavings may be induced so the treatment decision making is very important in case of unstable shale/formations, the formations prone to heave and plastic in nature needs optimum MW, and similarly formation with Geomechanical stress also needs optimum MW and well direction to keep bore hole stable.

Following are most common cause of unstable bore hole which need to be addressed correctly.

Plastic formation: Certain formation which are plastic in nature may cause tight hole conditions which shall be resulting troublesome trips, some classical examples of Plastic formations are Salt and Shales, for such formations we need to maintain optimum MW.

Fissile and Microfracture shales: Fissile and Microfracture shales are also cause of bore hole instability and tight trips, during drilling through this type of formation not only Drilling fluid system should be compatible but Drilling practice also should be optimized, for example shock & vibration, well angle, turbulence of fluid due to high GPM can cause such formation to frac and cave in. Micro fractured formations need to be stabilized with Micro and nano sealants, for such type of shales Gilsonite, Sulfonated asphalt, Latex, recently developed nano sealants, and resilient carbon products can be used at optimum concentration, there are certain drawbacks of these additives also, if these are added in high volume in system then PV shall be increased and sometime high-volume of solids can impact the cake quality and fluid loss.

Reactive formation: The formation which are reactive in nature may hydrate and swell which can cause tight trips for such type of formation a good inhibitive mud system is needed, in the wild cat well best guess system based on Geological prognosis can be employed but once cuttings are available then different lab tests can be performed to optimize mud system to inhibit such formations.

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3.????? Well profile/well Geometry:

Well profile is also a major cause of tight trips, with certain Geometry of a bore hole, one side trip can be smooth and other may be troublesome, so this factor must be considered from start of well planning and guidelines to be made part of Drilling Program so that well site team remain prepared for such challenges.

High DLS, Tortuosity, Key seat, washouts, high angle, and high angle wells with frequent change in azimuth can cause tight trips. In such scenario wiper trips, lubricity in Mud and extra precautions during trips can help.

When wiper trips are avoided for longer section the micro DLS/DLS and edges in bore hole will be formed, especially on wells where high ROPs are achieved, these can cause tight trips, many companies save times of wiper trips but at the end they spend more time on trips to smoothen the bore hole and on such wells logging tools stuck issues are common so when talking about well bore geometry a whole picture should be kept in mind, not only angle, azimuth and DLS, over all well tortuosity should be evaluated and operations should be planned accordingly.

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4.????? Balling of Bit & BHA

Bit and string balling can also be a cause of tight trip, once these are balled up then trip in & trip out shall be like moving full gauge pistol in a bore with high friction forces which can cause tight conditions, this condition not only can cause tight trip but stuck pipe also. For the prevention of Balling certain basic requisite shall be fulfilled then it shall not be a problem, use of Optimum Bit design, Optimum GPM, proper break in Bit, use of good inhibitive mud system while drilling reactive formations, tight fluid loss, use of certain anti accretion additives can prevent the balling. With high inhibitive mud system bore hole may be in gauge which also can be cause of tight trip (discussed later) that factor also should be considered.

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5.????? Gauge or under gauge bore hole.

Gauge or under gauge bore hole may cause tight trips, most common reason of these factor is heaving/mobile/plastic formations which can under gauge the bore hole, entering in an open hole which was drilled with previous bit that came to be under gauge when pulled out and highly inhibitive mud system like Silicate Polymer mud with minimum lubricity can cause tight hole condition due to Gauge bore hole.

For under gauge bore hole due to plasticity of formation one can ream, open hole and increase required MW so that it keeps formation pushed back and under gauge bore hole drilled with under gauge bit can be reamed & opened to the required hole size with new bit.

The Gauge hole, as result of inhibitive mud system like silicate is considered a good sign as it may save Cement Volume & cost and keep hole stable but moving through gauge bore hole can be troublesome and a cause nuisance for well site team so to prevent such conditions three things can be done, add Certain percentage of lube in mud, use under gauge stabs and drill with little bit higher GMP to wash the bore hole so that BHA can pass easily without tight hole condition. Please note high wash outs are not desired and are considered bad for hole and so decision to increase GPM is tricky.

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6.????? Change in the drill string/BHA

When a bore hole is drilled with certain BHA, it make a profile and during wiper trips hole become slick with reference to that BHA, when we make any change in a BHA then tight trip is common, one should keep patience only while trip in/trip out with changed BHA, better option is not to change BHA but if it’s necessary then components of new BHA should be matching with previous one to avoid tight hole conditions, for example in place of Motor/Directional component we can add the collar(s) of similar OD, ideally after performing trip with changed BHA hole should be slick, if not then other factors also should be considered.

Above mentioned factors are the most common causes of tight trips which came in my mind, if I missed some then kindly mention those in comments section.