This paper investigates the performance of horizontalwells under the combined influence of wellbore friction,wellbore storage, and formation damage. A new model isproposed wihich couples wellbore, reservoir, and non-uniformskin, and takes into account the change in flow regime fromlaminar to turbulent along the wellbore.In the conventional perspectives, wellbore damagemay be viewed as an additional pressure drop, is correct onlyfor infinite-conductivity wellbore with uniform damage. It isshown in this paper that the wellbore damage may not beviewed merely as an additive pressure drop due to skin in thepresence of friction inside the long horizontal section of thewell. Wellbore hydraulics change the flux distribution (inflowprofile) along the wellbore and, thus, result in additionalpressure drop in the reservoir and across the skin zone.Horizontal wells, for a number of reasons, are unlikely to havesmooth distributions of damage along their trajectories. Thus,segmented well testing would be ideal tool to estimate theskin, Si, of each segment especially in the zone where moresevere damage is expected, because it delivers a detailedpicture of the skin distribution along an extended horizontalwell.Finite conductivity solution approaches to infiniteconductivity solution at high conductivity values and highwellbore radius. The appearance of bi-linear, linear, and radialflow regimes depends upon the length of the well; for longwells, linear and bi-linear flow regimes are observed, and theyare masked in the case of short wells. The perforation numbereffect appears only in the damaged case, when the open-holescenario deviates from the two other cases. Another importantfactor, that affects the behavior of the pressure, is thedimensions of altered permeability region; the higher theradius of filtrate penetration, the higher the volume of affectedregion and therefore, the higher the loss in pressure. The effect of k/ks is more severe in small wells. Another correlationwhich allows determine kx directly from the intersection pointwith the half slope is presented using a new method ofinterference test interpretation of different segments with eachother in the same well. Isolated segment testing would lead tothe estimate the local skin factor, a possible indication ofuneven damage distribution and a necessary variable for theoptimization of matrix stimulation. Thus designing of aremedial treatment, both the type and the location ofpermeability damage must be considered.Several examples are included to illustrate the use ofthe model developed.
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