Ultrasonic Measurements Evaluate and Qualify Annular Creep Barriers

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 208782, “Annular Creep Barrier Evaluation and Qualification Using Ultrasonic Measurements,” by Eric van Oort, SPE, The University of Texas at Austin, and Akshay Thombare, SPE, and Munir Aldin, SPE, Metarock Laboratories, et al. The paper has not been peer reviewed. Creep barriers can simplify well abandonments, particularly in high-cost offshore environments. Evaluation and qualification of creep barriers in the field, however, have proven challenging and labor-intensive when casing is perforated and annular rock material is pressure-tested to verify its sealing ability. This work seeks to eliminate the need for pressure testing by allowing the barrier to be qualified using only cased-hole log measurements. Creep Barrier Formation and Stimulation Plastically deforming shale and salt or evaporite formations under certain conditions can move into uncemented or poorly cemented annular spaces, filling them and contacting the casing to form an effective pressure-tight barrier. Supporting evidence overwhelmingly points toward creep as the fundamental rock-mechanical mechanism behind this type of barrier formation. Creep barriers have, in fact, become commonplace considerations in the plugging and abandonment of offshore wells in the UK and the Norwegian sectors of the North Sea, leading to simplified and more-cost-effective rigless offshore well-plugging operations. The latter is accomplished by eliminating the need for casing cutting and pulling or casing milling followed by setting openhole abandonment plugs. Materials that present alternatives to ordinary Portland cement (OPC) for well plugging-and-abandonment barrier construction include the use of shale or salt as a barrier (SAAB). Comparison of category scores for SAAB with other materials reveals that SAAB offers a well-rounded performance envelope with no weaknesses in any categories, whereas the other materials, including cement, show weaknesses in one or more categories. A main advantage of SAAB is that it offers the ability to “replace” the caprock, the desired goal in most well abandonments. Moreover, for many materials including OPC, long-term (i.e., hundreds or thousands of years and beyond) sealing performance is unknown for well abandonment. The only category in which SAAB technology appears to lag is in its technology readiness level score. This, then, provides motivation for further research.