A Novel Technique To Acidize Horizontal Extended-Reach Wells

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 90385, "A Novel Technique To Acidize Horizontal Wells With Extended Reach," by H.A. Nasr-El-Din, SPE, and N.S. Al-Habib, SPE, Saudi Aramco, and M. Jemmali, SPE, A. Lahmadi, SPE, and M. Samuel, SPE, Schlumberger, prepared for the 2004 SPE Annual Technical Conference and Exhibition, Houston, 26-29 September. Extended-reach horizontal wells are drilled to maximize reservoir drainage and minimize water production from coning. A problem with these wells is poor acid distribution during matrix acidizing. The full-length paper discusses a new technique that uses mechanical diversion in the wellbore and chemical diversion in the carbonate formation. A hydraulic tractor was used to pull coiled tubing (CT) to the total depth of the well, and a viscoelastic surfactant-based acid system was used to remove formation damage created by drilling fluids. Introduction It is common practice to drill horizontal and multilateral wells to maximize oil recovery in carbonate and sandstone reservoirs. Extended-reach wells are defined as those with a measured-depth (MD) to true-vertical-depth (TVD) ratio greater than 2. Most oil and gas reservoirs are heterogeneous, with significant variations in reservoir permeability. Significant variations in rock permeability in wells with long target zones will cause poor fluid distribution during any chemical treatment. In matrix acidizing treatments, poor fluid placement will adversely affect the outcome of the treatment. Mechanical and chemical means that can enhance fluid placement are available. Mechanical means, including CT, are used to distribute the fluid across the target zone. Chemical means enhance fluid distribution inside the formation. Several chemical diverters have been used in matrix acid treatments including foam and gelled and in-situ gelled acids. Several authors have raised concerns regarding use of polymer-based fluids in tight formations, especially in sour environments. To overcome some of the problems encountered with polymer-based fluids, viscoelastic surfactant-based acid systems have been used successfully in matrix stimulation. Positive field results were reported when viscoelastic surfactant-based acids were used to stimulate oil producers, water injectors, and water-disposal wells.