Wednesday, December 13, 2017

The Sand Control Completion

Sanding is a problem in weak or unconsolidated sandstones. The objective of a sand  control completion is to eliminate sanding while maintaining a production rate that is economic, minimizes reservoir damage and thus maximizes recovery. Near the wellbore , sand movement can reduce permeability locally. Produced sand can erode downhole and surface equipment and its removal can be costly. In sufficient quantities, san can plug the completion or surface facilities. 

An objective of perforating in these highly productive and often unconsolidated sands is to reduce the near-wellbore pressure gradient during production.  There are two schools of thought on the best way do this. The established method is to perforate in a way that takes advantage of protection afforded by subsequent gravel packing. Theoritical studies show that perforation geometry can sometimes be optimized to obviate gravel packing. 

For gravel packing, many large-diameter perforations are preferred to few small holes. This is because larger holes provide a larger are open to flow and therefore less pressure drop on production. To achieve this, perforators producing large diameter holes and high shot density are used. A uniform shot distribution further reduces formation stress in addition to preserving casing strength.

To create large, clean perforation tunnels, these wells are typically shot underbalance with TCP using high shot density guns. The ideal underbalance will sufficiently clean perforation tunnels without breaking down the formation. Sand control could perhaps be provided by maintaining production rates low enough to prevent collapse of the perforation tunnel's stable arch - interlocking grains, like a keystone arch over a doorway. But such a low production rate is generally uneconomical and arches are unstable when flow conditions change. Instead, the arch is usually stabilized by filling the perforation with gravel. 


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