Coiled-Tubing Radials Placed by Water-Jet Drilling: Field Results, Theory, and Practice

Abstract

Introduction The URRS makes multiple 25 to 150 R (8 to 46 m) radials in one or more layers. The range of stable production enhancement with multiple radials in both light and heavy oil wells in various formations varies from a two times (200%) to as much as a ten times (1,000%) improvement depending on reservoir and wellbore conditions. The average production improvement is two times to four times (200% to 400%). The comparison is made with respect to either (a) the production in a well after radial placement compared to the production prior to radial placement or (b) the production in a new well with radials compared to similar offset vertical wells. This paper examines the value of multiple radials in penetrating skin or near wellbore damage (Figure 1); the calculated magnitude of oil production improvement by penetrating near wellbore damage; and typical light oil field results involving stable production in a newwell with radials, and a reentered well with radials. II. Theory and Definition Formation damage usually refers to reduction in permeability of a formation around a wellbore caused by extraneous solid particles in the interstices of formation sand, rock, particles, and asphalt. The damage is evaluated by means of a skin factor which can be calculated from an analysis of pressure buildup or falloff data. The skin factor determined in this way may include factors other than simple formation damage. The buildup test yields a skin factor that includes the effect of any restriction to flow into a wellbore. Besides permeability reduction, other factors such as partial penetration and partial well completions (not perforating the full interval) can also restrict the flow. Thus, in order to properly design a stimulation job such as acidizing, tracing, or drilling horizontal radials, it is necessary to determine the contribution of other factors to the total skin determined from a buildup analysis. These factors are discussed below. P. 343^