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lADC/SPE 35099 Hole Cleaning Modelling: What’s ‘n’ Got To Do With It?
Patrick Kenny and Egil Sunde, Statoil A/S, and Terry Iiemphill,
SPE and IADC Members

Baroid Drilling Fluids

Copyrjghl 1996 .Scaety of Petroleum Engineers, Inc Thm paper was presented for presentatmn at the 1S9S lAOC/SPE Chlling Conference held m New Orleans, Loumana 12.15 March 19S6. Thos papsr wasselected for presentation by an SPE Program Commrtt.sa following rev!ew of mformetmn contained m an abstract submitted by the authm(s). 10 correcfmn by Ihe author(s), Contents of the paper, as presented, have not been revhswed by the Society of Petroleum Engineers and me sh@cted The mate flal, as presented, does not necessarily reflect any Papem presented posmon by the SWIety of Petroleum Engineers,,1sofficer% or Its membvrs

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at SPE meetings are subject to publication review by Edlforial Committees of the Society of Petroleum Engtneem. Petmmwon to cow IS restricted to an abstract of not more than 300 lllustratm”s may not LM cop!ed. The abstract should contain conspicuous words. acknm’dedgemenf of where and by Worn thepaper was pfe$ented. Write Lfbrarwm, SPE, P O. Box 833S36, Richardson, TX 750S3-3836, U. S.A., fax 01 -214.9W-9435.

Abstract Efficient hole cleaning is vitally important in the drilling of directional and extended-reach (ERD) wells. In previous works, the importance of fluid velocity/pump output has been emphasised, while in others, the importance of individual fluid theological parameters has beenstressed. Drillpipe eccentricity and rotation directly affect hole cleaning as well. Recent work on particle settling velocity has accelerated the understanding of the behaviour of drilled cuttings in wellbores. This paper presents a new model to the industry, which combines recent developments in the fields of particle settling and rheology. This model provides a useful tool for the planning ofhole cleaning for highly deviated wells through the use of Lift Factors under the eccentric drillpipe. Information from deviated wells in the field is used to illustrate the usefulness of this hole cleaning model. Importantly, analysis of the data indicates that fluid ‘n’ factors calculated using the yield-power law [HerschelBulkley] theological model play a greater role in promoting good holecleaning in ERD wells than has previously been recognised.

Bern et al’2 include in their model a dimensionless Rheology Factor based on [he API plastic viscosity [PV] and yield point [YP] from the Bingham plastic theological model. Included in the model are calculations for critical flowrates (CFR) required to drill deviated wellbores. It is stated that under Iaminar flow conditions, muds witheither very high or very low YP values are preferred for hole cleaning and that YP is the dominant factor in deviated wells. In their earlier paper, fluid theologies were described using the power law model, but as the PV and YP terms are simpler and more commonly used, the authors applied them in the later paper. It is noted that this model assumes a rotating drillstring. Clark and Bickham3 use amechanistic model to describe hole cleaning. This model considers the various mechanisms involved in the transport of cuttings out of a well (i.e., rolling, lift, and parlicIe settling). This paper concurs with industry opinion in classi~ing flow rate as the most important factor in hole cleaning, and it considers fluid density and rheology as the most important drilling fluid properties that affecthole cleaning. The Herschel-Bulkley theological model is used in this paper with the fluid’s yield stress being the dominant factor. The influences of the other theological parameters (ie. consistency index and flow index) are unclear. Rasid investigated the rate of cuttings bed development and in his modeling efforts focused on predictions of cuttings bed height in eccentric wellbore. [n an...