Large-Volume Cement Squeezes for Severe-Loss Zones

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 128734, ’Large-Volume Cement Squeezes as Cost-Effective Solu tions for Severe-Loss Zones,’ by Devendra Algu, SPE, Loran Galey, SPE, Myles Barrett, and Mike Humphries, Shell International E&P, originally prepared for the 2010 IADC/SPE Drilling Conference and Exhibition, New Orleans, 2-4 February. Lost circulation is common while drilling wells through depleted intervals. The narrow margin between formation pore pressure and fracture pressure makes lost circulation inevitable in many wells. The full-length paper presents the design strategy, formulations and testing requirements, placement techniques and procedure, and other practices used in successful large-volume cement squeezes to remediate severe, high-rate, large-volume losses. Results from two deepwater case studies are presented to illustrate successful application of this treatment approach. Introduction Induced fractures are a common source of lost circulation when drilling depleted intervals. The average volume of losses for wells in this study was 4,000 bbl. Fracture dimensions (i.e., width, length, and volume) significantly affect lost-circulation-treatment design. Size, type, and concentration of lost-circulation material (LCM) used in the treatment are related directly to fracture width according to bridging theory, which is commonly applied within the industry. Treatment volume and other variables in the placement technique are affected by fracture volume. Estimation of fracture width can be made through a variety of methods. Formation material properties, in-situ stress fields, pressure, flow (loss) rate, and fluid viscosities and efficiencies all affect fracture geometry. Fracture width is directly proportional to fracture height and length. Therefore, most methods for estimating fracture width require a height or length as input. In practice, fracture heights have been determined reasonably from logging information before and after the loss event. Hydraulic-fracturing simulation programs can be applied to these loss conditions to estimate fracture dimensions. Many of these programs include basic-fracture-geometry models widely used in the industry. These models have been adequate for estimating fracture widths for design of effective treatments in lost-circulation conditions. Fracture length often is much greater than fracture height for these conditions, and both drilling fluids and cement slurries have much higher fluid efficiencies than do most fracturing fluids used for completions and stimulation treatments. Consideration of these basic differences may be helpful for selecting the most appropriate fracture-geometry model for estimating fracture width for severe-lost-circulation-treatment design. Cement Slurries for Severe-Lost-Circulation Treatments Bridging materials of a specific size range commonly are added to drilling fluids as lost-circulation treatments. Bridging materials have a range of shapes from granular spheroids to fibers and flakes. Granular or basic spheroid shapes are the most common materials used to bridge fractures. Theory and practice for sizing granular LCMs to bridge a specific fracture width are well known in the industry.