An Analysis Accounting for the Combined Effect of Drillstring Rotation and Eccentricity on Pressure Losses in Slimhole Drilling

Abstract

Knowledge of the distribution of pressure losses is a key factor to the design of a slimhole well. However, predicting annular pressure losses-the major partis difficult because drillstring motion makes nonnegligible complex contributions that have not been accounted for up to now.Flow in <an eccentric annulus with eccentricity varying in the axial direction is studied. The effect of rotation induced transverse vibrations is included by allowing time periodic variations of eccentricity. The resulting model predictions can reproduce trends observed in field data. INTRODUCTlON*The potential for better economics is the basic reason behind the gaining popularity of slimhole drilling. In fact, reducing the borehole diameter is expected to result in significant cost savings I , associated with the use of more compact and easier to transport rigs, faster mobilisation of equipment and accelerated drilling programs.However, reducing the borehole diameter may lead to reconsider existing knowledge on some technical issues, whose impact was' either negligible or well accounted for by common practices and techniques of the drilling industry. *References and illustrations at end of paper 871 One such issue is hydraulics, in relation with solid free fluids that are required for slimhole drilling.As pointed out by Bode et al 2 , the distribution of pressure losses in the well is completely modified for small annular clearances contrary to conventional drilling, the major part of pump pressure-more than 90% in some cases-is lost to friction in the slimhole annulus. Accurate modeling of annular pressure losses pecorr.:cs therefore an important issue, especially in cases where small margins exist between optimal drilling parameters and well bore stability.One critical situation that comes to mind concerns hole cleaning. Requirements on cuttings transport in conjunction wi th fluid properties and drilling geometry fix a lower bound for flow rate. The upper bound is dictated by how close the resulting equivalent density is to formation fracture gradients. Reliable predictions on annular pressure losses are therefore needed in order to successfully adjust the whole set of drilling parameters.The slimhole specific geometry and drilling parameters impose severe restrictions on the design of drilling fluids. Formulations should be solids' free or at least contain minimal amounts of fine particles. Under these conditions it is difficult to efficiently control the filtrate, to adjust densities and to obtain gels that are capable of sustaining cuttings when circulation is stopped. Low annular clearances also imply that high shear rates may exist at moderate flow rates. This may induce prohibitive pressure losses, if fluid's viscosity is 2 AN ANALYSIS ACCOUNTING FOR THE COMBINED EFFECT OF DRILLSTRING ROTATION SPE 25769 AND ECCENTRICITY ON PRESSURE LOSSES IN SLIMHOLE DRILLING not low enough. So, fluid's rheology must also be adapted according to criteria provided by hydraulic predictions. structure and examine how they can be accounted for by...

Experimental study and predictions of pressure losses of fluids modeled as Herschel–Bulkley in concentric and eccentric annuli in laminar, transitional and turbulent flows

“…Harnett and Kostic (1990) reported that the best approach for turbulent flow of power-law fluids in pipes was through the use of the approach of Metzner and Reed graph (1955). The majority of published data and flow predictions of Herschel-Bulkley fluids in concentric and eccentric annuli concern oilwell drilling (Bode et al, 1989;Cartalos and Dupuis, 1993;McCann et al, 1995;Ribeiro and Podio, 1994;Uner et al, 1989;Wang et al, 2000). This reflected the need in the last few decades of a more accurate modeling of annular pressure losses due to an increasing application of new drilling technologies, such as slim hole and coil tubing, characterized by narrower annuli between drill string and borehole or casing walls compared to standard drilling.…”

Hole-cleaning performance comparison of oil-based and water-based drilling fluids

“…Several researchers investigated the drill string rotation effect on the annulus pressure drop by ascribing to the flow regime (laminar or turbulent), formation of Taylor vortices, drill pipe eccentricity and various other parameters (Ahmed and Miska, 2008;Cartalos and Dupuis, 1993;Erge et al, 2015;Erge et al, 2014;McCann et al, 1995;Ozbayoglu and Sorgun, 2010;Saasen, 2013;Sorgun et al, 2011).…”

Evaluation of Commonly Used Fluid Rheological Models Using Developed Drilling Hydraulic Simulator

“…Different authors [8][9][10] remarked that concentric annulus models overestimate actual pressure losses in laminar and fully turbulent flow regimes by a percentage of 35-50 depending on the flow parameters. Haciislamoglu and Langlinais 11 presented a model that simulates flow in skewed narrow annular geometries for laminar, transition and turbulent non-Newtonian flow.…”