1. The Role of the Annular Gap in Expandable Sand Screen Completions SPE 86463. J. Heiland, J. Cook, A. Johnson, B. Jeffryes. Schlumberger Cambridge Research

2. SPE 86463. The Role of the Annular Gap in Expandable Sand Screen Completions. Outline Where does the gap come from? How does it influence the mechanics of the completion? –experiments –theory How does it influence the hydraulics? Conclusions.

3. SPE 86463. The Role of the Annular Gap in Expandable Sand Screen Completions. Origins of the gap State of the hole after drilling (enlargement, tortuosity, rugosity). Nature of the screen - expansion ratio. Nature of the expansion process - fixed diameter or compliant.

4. SPE 86463. The Role of the Annular Gap in Expandable Sand Screen Completions. Possible consequences of a gap: short- and long-term Rock failure behind screen with gap: generating load on screen. releasing grains and fines. –transport, and erosion of screen –plugging of screen changing permeability (  or  ). Fluid flow in annular gap: intervention or production logging more difficult. This paper addresses the first two of these.

5. SPE 86463. The Role of the Annular Gap in Expandable Sand Screen Completions. Views of the system Collapse; closure; inflow Inflow; fluid and sand transport Transverse Axial

6. SPE 86463. The Role of the Annular Gap in Expandable Sand Screen Completions. Transverse view - experimental Aim: observe how the gap influences closure and collapse using full-size screens in simulated boreholes in weak rock. Sample is 600 mm OD, 215 mm ID, 1000 mm long. NB: no fluid flow through rock pores. Kerosene Pressure Camera Rock Screen

7. SPE 86463. The Role of the Annular Gap in Expandable Sand Screen Completions. Summary of conditions for the screen closure experiments. ExperimentScreen typeGap Conditions 1Open hole 2BasepipeClose fit 3Basepipe + sand filter3 mm (0.125 in) gap 4Full screen type 1Close fit 5Basepipe Zero gap, small outward stress 8Basepipe12 mm (0.5 in) gap 9Full screen type 2Close fit

8. SPE 86463. The Role of the Annular Gap in Expandable Sand Screen Completions. Example: Test 4. Full screen, close fit Pressure in bars (500 bars = 7250 psi)

9. SPE 86463. The Role of the Annular Gap in Expandable Sand Screen Completions. Closure data from all the experiments No.Conditions 1Open hole 2Basepipe, close fit 3Basepipe + filter, 0.125 in gap 4Full screen type 1, close fit 5Basepipe, small outward stress 8Basepipe, 0.5 in gap 9Full screen type 2, close fit

10. SPE 86463. The Role of the Annular Gap in Expandable Sand Screen Completions. Summary of experiments Most stable hole is achieved when movement of both large fragments and grains is prevented; Most of stabilizing effect is by hindering the movement of failed rock; Initial outward radial stress has negligible further effect; Small gap reduces stability of system, if sand grains are free to move out of load-bearing areas; Large gap (~0.5 in) reduces stability of system, by allowing movement of large fragments of rock.

11. SPE 86463. The Role of the Annular Gap in Expandable Sand Screen Completions. Transverse view - modelling Simple rock deformation model, incorporating support stress (isotropic stress, perfect plasticity, no pore pressure gradients). Couples deformation of rock to that of screen. Allows study of effects of stiffness, gap, rock properties….

12. SPE 86463. The Role of the Annular Gap in Expandable Sand Screen Completions. Typical results from modelling Result: Optimum gap for mechanical stability: zero to few mm

13. SPE 86463. The Role of the Annular Gap in Expandable Sand Screen Completions. Summary of modelling Three parameters to optimize system: –loading on screen –closure of hole –disaggregation of rock. Leads to idea of optimum gap for mechanical stability; varies between zero and a few millimetres depending on stiffness of screen.

14. SPE 86463. The Role of the Annular Gap in Expandable Sand Screen Completions. Axial view - modelling Accounts for –radial flow from formation into well –axial flow along gap –radial flow through screen wall –axial flow in basepipe. Tracks movement of sand (if annulus velocity is above threshold value). Allows blockage of screen or annulus.

15. SPE 86463. The Role of the Annular Gap in Expandable Sand Screen Completions. Typical axial model result Toe Heel

16. SPE 86463. The Role of the Annular Gap in Expandable Sand Screen Completions. Effect of gap size: hole ID 0.2 m, screen OD 0.195 m. Toe Heel

17. SPE 86463. The Role of the Annular Gap in Expandable Sand Screen Completions. Effect of gap size: hole ID 0.2 m, screen OD 0.185 m. Toe Heel

18. SPE 86463. The Role of the Annular Gap in Expandable Sand Screen Completions. Conclusions Most stable system when movement of both grains and larger fragments is prevented. Small gap (few mm) allows mobilization of rock strength to assist stability. Sand movement in annulus prevented by smaller gap, because of lower annulus velocity. Sand accumulations, plugged screen sections, and enlarged holes lead to local hotspots and potential erosion. Very small or zero gap is therefore best for long- term integrity of completion.