Diagnostic Analysis to Determine Critical Stress Distribution in HPHT Openhole MSF Completion

Abstract

Abstract An accurate calculation of the magnitude of tubular stresses on the lower completion is vital for well integrity, especially in wells planned to be completed with openhole multistage frac tools and including multiple openhole packers, frac sleeves, and in some cases openhole anchors. The combination of recurring high pressure and low temperature cycles during multistage well stimulation generates excessive tubular forces and pipe fatigue. In most cases, if this is not estimated early during the planning phase, it may lead to a failure of downhole equipment and compromise well integrity. Seldom is diagnostic analysis done to determine the tubing stresses on individual components of the openhole multistage frac completion, the impact of these stresses on the various components and pipe, and techniques that could be implemented to potentially prevent failure of downhole tools. To analyze and ensure lower completions hold integrity during hydraulic fracturing, in this paper we will focus on the influence of openhole packers and anchors have on completion integrity. To understand this, it is essential to evaluate analytically the effect of these induced axial loads during fracturing on openhole packers that have been set. Hence, this paper encapsulates the study and influence of: 1) thermal loading and pressure prediction across openhole packers; 2) fundamental tribology associated with open hole packers; and 3) variables that contribute to failures, such as packer setting depth reference position of frac sleeves and openhole anchors, bottomhole temperature during treatment, lower completion design, enlarged hole size influence, and application with selective use of openhole anchors. The stimulation fluid injection is modelled using thermodynamic calculations. The openhole packer slipping/movement was investigated using a baseline packer anchoring force calculation derived from lab data. A commercial tubular stress analysis software was then used to analyze different variables that can potentially contribute to lower completion failure. The study indicated that well profile, design, and tool placement in the well had a strong influence on axial load distribution. Several openhole multistage wells have been extensively studied with different constraints to identify occurrence of a failure and possible mitigation during the planning phase. The mode of failure seen in these cases is different than those seen in cemented liners that have been addressed in several papers and do not necessarily fall under the domain of formation movement in geomechanically complex and tectonically active areas. This study provides a unique workflow for calculating downhole stresses on the lower completion. Early identification of a potential multistage completion design failure using analytical models will eliminate serious well integrity issues; and loss of well and associated high well costs. This will further encourage engineers to study the effect of individual variables and downhole tools that effect the completion, and techniques or solutions that can prevent failure.