Risk Assessment in Sand Control Selection: Introducing a Traffic Light System in Stand-Alone Screen Selection

Abstract

Sand control and sand management require a rigorous assessment of several contributing factors including the sand facies variation, fluid composition, near-wellbore velocities, interaction of the sand control with other completion tools and operational practices. A multivariate approach or risk analysis is required to consider the relative role of each parameter in the overall design for reliable and robust sand control. This paper introduces a qualitative risk factor model for this purpose. In this research, a series of Sand Retention Tests (SRT) was conducted, and results were used to formulate a set of design criteria for slotted liners. The proposed criteria specify both the slot width and density for different operational conditions and different classes of Particle Size Distribution (PSD) for the McMurray oil sands. The goal is to provide a qualitative rationale for choosing the best liner design that keeps the produced sand and skin within an acceptable level. The test is performed at several flow rates to account for different operational conditions for Steam Assisted Gravity Drainage (SAGD) and Cyclic Steam Stimulation (CSS) wells. A Traffic Light System (TLS) is adopted for presenting the design criteria in which the red and green colors are used to indicate, respectively, unacceptable and acceptable design concerning sanding and plugging. Yellow color in the TLS is also used to indicate marginal design. Testing results indicate the liner performance is affected by the near-wellbore flow velocities, geochemical composition of the produced water, PSD of the formation sand and fines content, and composition of formation clays. For low near-wellbore velocities and typical produced water composition, conservatively designed narrow slots show a similar performance compared to somewhat wider slots. However, high fluid flow velocities or unfavorable water composition results in excessive plugging of the pore space near the screen leading to significant pressure drops for narrow slots. The new design criteria suggest at low flow rates, slot widths up to three and half times of the mean grain size will result in minimal sand production. At elevated flow rates, however, this range shrinks to somewhere between one and a half to three times the mean grain size. This paper presents novel design criteria for slotted liners using the results of multi-slot coupons in SRT testing, which is deemed to be more realistic compared to the single-slot coupon experiments in the previous tests. The new design criteria consider not only certain points on the PSD curve (e.g., D50 or D70) but also the shape of the PSD curve, water cut, and gas oil ratio and other parameters.

An Improved Set of Design Criteria for Slotted Liners in Steam Assisted Gravity Drainage Operation

“…Subsequently, several researchers investigated and proposed the design criteria of the As the unconsolidated oil-bearing sands are inherently loose, SAGD wells require the implementation of stand-alone screens to support the wellbore and control sand production [11][12][13][14][15][16]. The slotted liner is currently widely used in Canada's SAGD process due to its economy and adequate mechanical integrity [17][18][19][20]. Figure 2a illustrates the slotted liner configuration, and Figure 2b shows different slot geometry designs, which can be manufactured into the straight cut, keystone cut, and seamed profiles.…”

“…The maximum slot size in this criterion is 3.5 times D50, and the minimum slot size is two times D70. Other researchers conducted prepacked SRT experiments to determine the proper slot size [17][18][19]29,30].…”

“…Thus, researchers believe prepacked SRT reasonably represents the SAGD wellbore condition [31][32][33][34][35]. Past experimental works recognized a few factors that should be incorporated in the slotted liner design criteria, including slot size, slot density, fluid velocity, fluid phase and PSD [18,19,30,36]. However, these factors were only partially incorporated in their experimental study.…”

“…However, the fluid phase change is not considered in their work. Mahmoudi et al [19] and Wang et al [30] presented their design criteria graphically by using the "Traffic Light System" (TLS). In the TLS, traffic light colors (green, yellow and red) are employed to a linear axis to indicate the optimal slot size window.…”

“…In the TLS, traffic light colors (green, yellow and red) are employed to a linear axis to indicate the optimal slot size window. The green color in the TLS means an acceptable slot size, in which the amount of sand production is lower than 0.12 lb/ft 2 , and retained permeability (RP) is greater than 70% [19,30]. The yellow zone indicates a marginal performance, defined with sand production between 0.12 and 0.15 lb/ft 2 , and RP between 50 and 70%.…”