Completion optimization Yes
management method
Sand exclusion • Gravel pack
• High-rate water pack • Frac and pack
• Openhole gravel pack • Expandable screens
Customized integrated technologies Manage sand at surface Screenless completions
• Artificial lift • Downhole desander
• Oriented perforating • Selective perforating • Screenless fracturing • Consolidation
> Completion options to balance sand control with production requirements. If formation-stability concerns exist, operators can choose between downhole sand-exclusion technologies or screenless-completion methods. They may also choose to manage existing sand production by careful selection of arti cial-lift techniques and practices.
Sand-
Formation- stability issues
No
Stimulated or natural
Customized integrated technologies Natural
Stimulated
(previous page, top). This work has greatly enhanced sand-prediction modeling, which is based on the peak strength of a rock in a perfora- tion tunnel or wellbore. Schlumberger uses this information to optimize completions to ensure that wells produce at economic rates with an acceptable risk of sand production.
Similar to wellbore-stability analysis, sand- production analysis differs in that the perforation-tunnel pressure is less than reservoir pressure, allowing fluid flow. Or, in the case of openhole completions, wellbore pressure is less than reservoir pressure. Stress calculations are made at the appropriate perforation orientation and phasing to determine minimum drawdown that does not promote shear failure, or the maximum sand-free drawdown. This drawdown is then used to calculate production rates and to establish whether minimum production requirements are achieved. If they are not, the completion design must be modifi ed. Schlumberger developed proprietary software
called Sand Management Advisor to accomplish this analysis. This 3D sand-prediction modeling software requires MEM inputs and exploits the outputs from other analysis tools, such as SPAN Schlumberger perforation analysis and ProCADE well analysis software tools. It also links to the Formation Completion Selection Tool (FCST), a proprietary knowledge-based completion-plan- ning tool, so that experts can optimize completions by screening and ranking the most appropriate completion technologies available.
The sand-prediction tool calculates the critical drawdown pressure for different user-provided completion scenarios and identi- fies the sand-free production window. Two models are used in computing the critical draw- down pressure at which a formation will fail. A wide range of methods has been used in the past for sand production prediction, for example, using elastoplastic models.18
Sand Management
Advisor uses a proprietary method developed by Schlumberger that takes into account the well-known increase in the strength of holes in rocks as their diameters decrease. The sand-free window defines completion and artificial-lift design limits, for example the maximum allow- able drawdown produced by an electrical submersible pump (ESP). Uncertainty can also be considered on six input parameters: Poisson’s ratio, unconfined compressive strength, mini- mum horizontal stress, minimum horizontal stress direction, ratio of the maximum and mini- mum horizontal stresses, and grain size. For a given completion scenario, this sand-free window is displayed graphically by plotting reservoir pressure versus bottomhole flowing pressure (BHFP), highlighting the sand-free drawdown window and the various levels of uncertainty (previous page, bottom). This and other tools can also be used in the selection of sand- management candidate wells.
From Prediction to Practice With knowledge of a reservoir, its stresses and the probability of encountering sand production, operating companies can make informed deci- sions about the best approach to optimize well completions and limit the impact of producing sand (above). Initially, the question is whether to control or to prevent sand production. Sand- exclusion methods may be required when sand production is certain, or when the risk associated with unforeseen sand production is high— for example, in subsea completions or high-rate gas wells. One of a variety of screenless-completion methods may offer the best option when sand production can be avoided or at least limited. Regardless of the method, proper sand manage- ment is the vehicle needed to balance sand control with the desired production results through optimized completions.
Gravel packing is a common sand-exclusion technique that has been used since the 1930s.19 This procedure involves pumping a designed slurry, comprising gravel of a specifi c size and an appropriate carrying fluid, to fill the annular
18. Bradford IDR and Cook JM: “ A Semi-Analytic Elastoplastic Model for Wellbore Stability with Applications to Sanding,” paper SPE 28070, presented at the SPE/ISRM Rock Mechanics in Petroleum Engineering Conference, Delft, The Netherlands, August 29– 31, 1994.
19. Ali S, Dickerson R, Bennett C, Bixenman P, Parlar M, Price-Smith C, Cooper S, Desroches L, Foxenberg B, Godwin K, McPike T, Pitoni E, Ripa G, Steven B, Tif n D and Troncoso J: “ High-Productivity Horizontal Gravel Packs,” Oil eld Rev iew 13, no. 2 (Summer 2001): 52– 73.
Carlson et al, reference 7.
Spring 2004
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