Sand Control in Steam Assisted Gravity (SAGD) Wellbores

Abstract

Steam Assisted Gravity Drainage (SAGD) is a thermal recovery technology used to produce heavy oil and high viscosity bitumen from Alberta oil sands. The oil sands of Alberta are unconsolidated sands which require sand control within the horizontal wellbores to reduce the erosive power of the sand and plugging of sand control screens. Slotted liners have been extensively used in Alberta’s SAGD wells to provide sand control. Slotted liner slot width specifications can be effectively designed based on the particle size distribution of the in-situ reservoir sands and coupled reservoir parameters. Modified laser particle size analysis can simulate a sieve analysis to determine slot width sand control requirements and provide a means to estimate the particle size for stable arching of sand around a slot during production. The slot must be designed to allow free flow of fines and clays through the slot and near well pore space without plugging. Based on the findings of research documented in this thesis, the minimum slot width for the majority of slotted liners used for sand control in clastic heavy oil and bitumen formations is 0.012” (~300 μm). The results also reveal that a seamed slot, which provides a “keystone” profile, provides anti-plugging characteristics. Slotted liner manufacturing is a complex process of metal-to-metal slotting of an interrupted cut. Pipe grades, process of manufacture, chemical composition and physical properties can dramatically affect the machinability tool-life and sand control. The results of the research also show that machinability of the pipe is largely controlled by the combination of optimal microstructure (manufacture) and chemical composition (specifically sulfur content). Sulphur content has been widely known to improve machinability but too high of a sulphur content can have dramatic effects on the performance of a slotted liner when H2S is present. Tool-life tests proved that the carbon content of the pipe cannot be used as a predictor of the pipe’s machinability. Taylor’s tool-life equation can be successfully applied to blade slotting and a metric developed here, called the Relative Material Machinability Index, has can be used to relate slot manufacturing performance of differing grades of pipe, microstructure, and chemical composition.