The Laverda Field is an offshore waterflooded field developed with two long horizontal producers targeting two stacked high quality sandstone units. The oil producer LAV02ST2 is completed with sand screens and Inflow Control Devices (ICDs). Elevated Gas Oil Ratios (GORs) were experienced during start-up, which indicated free gas production downhole, raising concerns over ICD erosion and sand production. While the ICDs have defined operating limits in the presence of single-phase flow, the safe operating range in multi-phase flow conditions was highly uncertain. Given the significant risk of well failure due to erosion, additional bean up was halted pending studies to understand and quantify the erosion risk.
Erosion risk was influenced by:
the distribution of gas along the well (concentrated vs dispersed inflow),
the presence of an open annulus and associated erosion risk due to solids production, and
tolerance of the ICDs to higher velocities under three-phase flow.
Collaboration between subsurface and completions disciplines was required to understand the source of the gas and assess the risk to completions. Initially, production trends were analysed in conjunction with a review of geological data and numerical simulation insights to identify likely sources of gas and which areas within the well were more susceptible to gas exposure.
Near-wellbore modelling using NETool® and GAP was undertaken to understand the range of feasible gas inflow scenarios and eliminate scenarios inconsistent with observed production data. The most likely scenario was then used to establish the relationship between total well rate and peak velocities in the ICDs, for a worse-case erosion outcome.
To understand the risk of ICD erosion under multi-phase flow and potential for loss of well integrity, Computational Fluid Dynamics (CFD) modelling was conducted on a range of expected production scenarios to establish safe operating limits. Both, ICD slot erosion and housing erosion behaviour was investigated, as a function of peak ICD gas rate/velocity, well liquid rate and well GOR.
The CFD study helped to establish a relationship between erosion rate and total downhole rate at reservoir conditions for various production scenarios, thus allowing calculation of erosion over the course of field life. A revised safe operating envelope was recommended for the oil producer in multi-phase conditions that allowed the production rate to be doubled without compromising well integrity.
Traditionally, industry physical erosion testing of the ICDs by the vendor is restricted to single-phase, liquid conditions only. Successfully benchmarking the CFD model to the single-phase physical tests allowed quantification of erosion rates in multi-phase flow and establishment of a safe operating envelope over the life of the well.