Development and Validation of a Hydraulics Simulator for Estimating Subsurface Reverse Cementing Placement Pressures

Abstract

This paper covers the development and validation of a hydraulic simulator for subsurface reverse cementing placement in which fluids are placed down drillpipe and diverted into the annulus through a crossover tool above a liner hanger. Returns are taken up the liner inner diameter and are re-diverted through the crossover tool back to surface. Since commercially available cementing simulators are unable to model cement placement through this flow path with a crossover tool, a simulator was developed and validated using downhole pressure data collected during large-scale flow testing and a reverse cementing field trial. Development of this simulator is a major step forward to implementing a subsurface reverse cementing system in deep water. This custom simulator determines the magnitude of equivalent circulating density (ECD) reductions and identifies opportunities in which subsurface reverse cementing is advantageous with regard to pressure. Traditionally, placement through reverse cementing results in reduced bottomhole ECDs compared to conventional cementing. This pressure reduction is not uniform throughout the annulus, and a placement simulator that takes into account wellbore geometry, a crossover tool, fluid properties, and cementing hydraulics is required to assess viability of reverse cementing for specific deepwater wells. Computational fluid dynamics (CFD) modeling was conducted using specific crossover tool geometry and various fluid properties to develop a lumped-pressure loss model mimicking local pressure drops. This lumped model was incorporated into a hydraulics system-level solver to estimate surface and downhole pressures. The hydraulics solver was initially validated by comparing model output with downhole pressure data collected from large-scale flow testing and a field trial in which a liner was cemented using the crossover tool. The resulting subsurface reverse cementing simulator is able to simulate incompressible, multi-fluid placement through a crossover tool. Current capabilities of the simulator include incorporation of a crossover tool to divert flow into the annulus directly above the liner hanger in a deepwater well; estimation of surface pressures, bottomhole pressures, and downhole ECDs at any specified depth; and estimation of u-tubing effect from free fall of fluids. During a large-scale closed-system flow test, model output matched pressure gauge readings to within 11%. Comparisons of field trial surface and downhole pressures correlated with model output for cement placement. This paper will present comparisons of simulator pressure output and collected downhole data used for validation, along with simulator output for an example subsurface reverse cementing job for a deepwater liner.