Well Productivity Optimisation with Tailored Hole Spacing in Smart Liners

Abstract

AbstractOptimum productivity from long horizontal wells requires effective stimulation. The Smart Liner lower completion addresses shortcomings of other matrix-acid stimulation techniques in regards to acid placement along the reservoir section. The concept relies on a limited number of small holes (orifices) drilled through the liner itself to distribute acid over the entire drain length. Different hole spacings can yield similar flow distributions but may result in different stimulation efficiencies. What is best, a few deep wormholes with acid washing in between, or many, less penetrating but closer wormholes? The objective of this work is to investigate which parameters influence the optimum hole spacing leading to the most improved overall reservoir contact.We derive a radial wormhole growth model as a function of time and initial jet velocity, which honors the observation that incremental penetration depth tapers off versus time. This model is specifically tailored to account for the substantial jet velocities generated by the limited-entry liner completion, often in the range of 15-50 m/s, occasionally higher. It qualitatively matches field observations showing that the maximum required acid coverage often lies in the range 0.4-0.5 bbl/ft. Exceptions to this trend have been observed and they deserve further investigation. The hole spacing generally increases with well length to ensure sufficient jetting towards the toe of the well.Work is ongoing to convert the number and length of all wormholes combined to an average overall injectivity improvement for the well. This effort will lead to a more qualitative match to the real-time stimulation data. Field data suggest that the typical transient injectivity is improved by a factor 2-3, sometimes more, if the initial skin prior to stimulation is very high. Larger improvements have been observed during stimulation of dolomite rocks with 28 wt% HCl, possibly due to more drilling-induced damage.