Computational Fluid Dynamics of HCl Single and Two-Phase Oil Flow in a Multi-Stage Vertical and Horizontal Acid Fractured Well

Abstract

Currently, the oil industry is using hydraulic fracture as a tool to exploit tight and ultra-tight oil formations. In carbonates, acid fracturing is common, unlike proppant fracturing in sandsones. The main objective of this paper is to study the behaviour of HCl injected and oil flow back from a horizontal well with multi-stage acid fractures (fractured hydraulically). For a vertical well, a single acid fracture is common. The 2D fracture model and psedo-3D fracture model are incorporated in this integrated program for acid fracturing with all geomechanics and operational constraints. With five stages of fractures, post-fracture oil production from an acid fractured horizontal/vertical well is generated from this integrated model. Program is written in MATHCAD to observe the volumetric flow rate in steady-state, transient, and pseudosteady regime. ANSYS Fluent is used to carry out a computational fluid dynamics (CFD) for oil flow back along the fractures. CFD is applied to observe production rates where sequential pad fluid and acid injection is performed until the desired fracture dimensions are reached. Results from production model shows, for steady-state, production increased from 44 to 60 STB/D and from 113 to 124 STB/D with P-3D-C and 2D-PKN-C fracture model respectively. CFD simulation is performed using a viscous model with gravitational and turbulent effects and the results show an increase in radial turbulence at the outlet of the fracture. The absolute pressure exerted on the walls is 1700 psi and the flow velocity increased from the tip at 39.4 ft/min covering a fracture length of 500 ft in both steady-state and transient flow. This paper investigates the effect of acid fracturing on oil production using a predetermined fracture model and dimensions. The flow characteristics are challenged in multi-stage fractures in horizontal and vertical well. The outcome of CFD will assist in upscaling the simulation to a 3D model with field values from existing wells for validity. A further development with fracture simulation are carried out for vertical and horizontal fracture to understand the deformation behavior on the predetermined zone. This paper will contribute to advanced well stimulation techniques of acid fracturing that are representative of actual field applications.