Modelling Slugging Induced Flow Instabilities and its Effect on Hydraulic Fractures Integrity in Long Horizontal Wells

Abstract

ABSTRACT: Unconventional reservoirs are developed by drilling long horizontal wells of up to 20,000 ft laterals and produced using multistage hydraulic fracturing (HF) operations. The production profile of such wells has a steep decline at early life (3 to 12 months) during which the flow rates decrease with a diminishing bottom hole pressure and the flow starts oscillating at an increasing amplitude. After reaching the bubble point value, the gas starts releasing at the lateral section and slugs start to form, merge and travel through the vertical section before reaching the wellhead. This flow instability affects the downhole pressures with large variations, reaching several hundreds of psi at the sand face part. The pressure variations have an impact on the hydraulic fracture’s integrity and need to be considered for the safety operations envelop (SOE). In this study the effects of pressure variations have been studied by integrating the transient multiphase flow simulation results of the Bakken well LINSETH 13-12HWinto a dynamic 3D reservoir and geomechanical model. Mid-life production performances were considered to capture the flow and pressure oscillation at their maximum rates. Using the reservoir model, the pressures, and saturations were calculated at different time steps. Also, the geomechanical model was built and calibrated using core data. The model was used to evaluate potential proppant dis-embedment which may lead to proppant settlement at the lower part of the fractures and closes the upper part, resulting in reduced productivity, and contributing to further production decline. The result of this study is used for improved production management of unconventional plays and extended-reach wells. 1. INTRODUCTION Unconventional wells are characterized by a steep initial decline, of flow rates, and pressures during the first 1 to 12 months, requiring operating companies to pre-install artificial lift equipment, usually a mix of Gas lift, ESPs, HJP, and Rod Pumps are used in North Dakota.