Slotted liners are used extensively in the majority of steam assisted gravity drainage operations conducted in Western Canada due to their superior mechanical strength and integrity in contrast to other mechanical sand control devices. These liners are required due to the generally poorly or unconsolidated nature of the majority of formations in which SAGD applications are conducted. These liners can have a variety of configurations with varying slot density, slotting patterns, slot apertures and slot internal geometries. The overall objective of a successful slotted liner design is to ensure that the liner allows the maximum production of bitumen and other fluids with a minimum pressure drop, while retaining the majority of the formation sand and preventing infill of the horizontal section of the well with solids and erosion and failure of downhole pumps and surface equipment. This paper describes a detailed lab test protocol which was successfully developed over a number years for the design and evaluation of slot geometry for SAGD applications, describes test procedures used and quantifies some of the major mechanisms discovered that lead to the plugging of slots. It has been found that in addition to grain size of the sand under consideration and slot geometry, that clay content of the formation, flow velocity, wetting phase type and pH play crucial roles in the plugging mechanism of slotted liners. Clay plugging at the top portion of the slots has been found to be the dominant damage mechanism.
Steam assisted gravity drainage (SAGD) is being used extensively in Western Canada and other areas in the world as an effective and economic means for the recovery of heavy oil and bitumen reserves and represents the current primary technology for the exploitation of this large hydrocarbon resource(1–5). Key factors in the successful operation of a SAGD process include;
Keeping the differential pressure between the lower (production) horizontal well and the upper (injection) well very low to prevent steam coning between the two spatially adjacent wellbores. This allows effective vertical propagation of the steam chamber upwards from the injector, and gravity motivated drainage of the mobilized bitumen down the sides of the steam chamber to the production well.
Retaining the formation sand to prevent infill of the producing well (and injection well during periods of possible backflow) with solids which may result in wellbore plugging or mechanical issues with various types of artificial lift systems.
Slotted liners have proven to be the sand control device of choice in most SAGD applications to date due to their superior mechanical integrity for long horizontal well completions. Different slotting methods have been developed over the past decade, including (Figure 1);
Conventional ‘straight’ cut slots prepared using a single blade plunge into the liner.
‘Keystone’ cut slots prepared using two separate blade plunges to form a single slot, with the blade angle differing between each plunge to form a slot with an ‘aspect’ ratio that has the top of the slot smaller than the base of the slot to aid in the passage of any sand grains/fines that may enter the slot
