Assessment and Prediction of Erosion in Completion Systems under Hydraulic Fracturing Operations Using Computational Fluid Dynamics

Abstract

High rate injection or production of fluids with sand particles places wellhead components and downhole assemblies at risk of erosion damage. Depending on the severity and location of the material loss, this may pose a significant well loss or blow-out hazard. For this reason, assessment and mitigation of erosion can be critical for such applications.

In this work, Computational Fluid Dynamics (CFD) was used in conjunction with erosion models to assess the erosion damage characteristics associated with the operating conditions and equipment for a high-rate, shale gas reservoir fracturing application. The work was based on the severe erosion damage experienced by EnCana as a result of high rate hydraulic fracturing operations performed in horizontal shale gas wells at their Horn River, BC field development. Material losses were observed within the wellhead equipment as well as in the LTC couplings of the production casing string near surface in several wells. CFD models were developed for the existing wellhead and wellbore geometries and used to simulate a range of hydraulic fracture operating conditions in an effort to predict the locations and degree of material loss in the components in each case. The models were calibrated with caliper log data and measurements taken from casing samples retrieved from several wells. The analyses suggested that well head system modifications, such as tubing head spool changes and use of spacer spools, could be effective in substantially reducing material losses in the tubular connections. In addition, sensitivity analyses were performed for different wellhead configurations and variations in the hydraulic fracturing parameters to determine the factors that likely had the most influence on the connection material losses. The results served to demonstrate that it is possible to use CFD with erosion models as predictive tools to identify locations of severe erosion in completion systems, and, when calibration data is available, to quantify the amount of material loss in wellhead and downhole components. This information can aid in designing optimum completions systems, and in defining operating conditions which can reduce the risk of equipment failure, potential blow-outs, and associated safety and environmental hazards.

Introduction

Oil well operations involving either high rate injection or production of fluids with sand particles places wellhead components and downhole assemblies at risk in terms of erosion damage. Severe material loss due to erosion could result in well failures and blow-outs, both of which can have severe impacts on the safety of personnel, the environment and the well or development economics (Enform, 2009 and VanderKlippe, 2010). EnCana reported severe erosion occuring in the vicinity of the tubing hanger and the first casing connection below the wellhead as a result of the hydraulic fracturing operations performed in several wells at their Horn River shale gas development in BC, Canada. Erosion locations and the degree of wall material loss were first determined by caliper logs and later confirmed through physical retrieval of the damaged connections from the ground. In order to better understand the mechanisms and factors associated with the severe wall losses and to identify measures that could be taken to mitigate the erosion risk, it was decided to model the equipment and hydraulic fracturing operation using Computational Fluid Dynamics (CFD). This is emerging as a viable technique to study erosion problems in a number of applications including surface piping and downhole completions systems. CFD simulations can be used to determine impact locations of sand particles, and to quantify both the velocities and angles of the sand particle impacts on the component surfaces. These two parameters have the most influence on erosion damage potential and rate. The analyses took into consideration flow through the well-head equipment installed for slurry injection and down through the top casing segment including the near surface connections.

Author: Farahani, R., Lastiwka, M., Langer, D., Demirdal, B., Matthews, C., Jensen, J., & Reilly, A.

Publisher: SPE Annual Technical Conference and Exhibition, 30 October-2 November, Denver, Colorado, USA

Year: 2011

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