Abstract
When using hydraulic fracturing techniques to stimulate production from an oil or gas well, successful job placement is often jeopardized by near-wellbore (NWB) problems. Many times, these problems are specifically related to the perforation entry or to the width of the fracture near the wellbore. A likely conclusion is that insufficient width generation in the NWB region is the result of a tortuous (rapidly turning or twisted) path for the first few inches or feet of the fracture. Within this near-wellbore region, such fractures must overcome rock stresses greater than the least principle stress. In other instances, the inadequate width problem may result from the generation of a large number of independent near-wellbore fracture planes (starter fractures) instead of only one fracture (or at least only a few). Additionally, the hydraulic fracture may initiate from a fluid-filled microannulus rather than the perforations, which can lead to significant proppant-pumping limitations.
During the early 1990's, the oil industry began to consider these NWB problems more seriously. Procedures to help identify the problems were developed, and techniques involving proppant slugs and viscous gel slugs were used to mitigate such problems before or during a fracture-stimulation treatment. Alterations of the well completion plan proved to be a major part of successfully reducing the occurrence of similar problems in future wells in that reservoir. This paper discusses this technology and its evolution through recent years, as well as current applications of these techniques.
