Changes

==Production from channelized systems==

==Production from channelized systems==

The channel axes may act as pathways for the preferential ingress of water. This can result in the stranding of banked oil along the channel margin pinch-out edges (Figure 194a) (Clark et al., 1997).

The channel axes may act as pathways for the preferential ingress of water. This can result in the stranding of banked oil along the channel margin pinch-out edges ([[:File:M91FG194.JPG|Figure 2a]]) (Clark et al., 1997).

[[FIGURE 194.]] Features influencing fluid flow in deep-marine sandstones.

[[File:M91FG194.JPG|thumb|300px|{{Figure number|2}}Features influencing fluid flow in deep-marine sandstones.]]

Channel fills can show differing degrees of amalgamation laterally and vertically (Figure 193). The degree of sandstone continuity is influenced by the stacking patterns. In channelized systems, this can be a critical parameter in assessing economic feasibility for reservoir appraisal, e.g., as in the appraisal of the Schiehallion field, offshore United Kingdom (see Chapter 3, this publication) (Leach et al., 1999). Eubanks (1987) described channelized turbidites from the Oligocene lower Hackberry sands of the North Sabine Lake field, Louisiana. Stacking of individual channels resulted in a large amalgamated reservoir interval with pressure communication throughout. Isolated channels also occur, but these have shown rapid depletion within 2 months following production start-up.

Channel fills can show differing degrees of amalgamation laterally and vertically ([[:File:M91FG193.JPG|Figure 1]]). The degree of sandstone continuity is influenced by the stacking patterns. In channelized systems, this can be a critical parameter in assessing economic feasibility for reservoir appraisal, e.g., as in the appraisal of the Schiehallion field, offshore United Kingdom (see Chapter 3, this publication) (Leach et al., 1999). Eubanks (1987) described channelized turbidites from the Oligocene lower Hackberry sands of the North Sabine Lake field, Louisiana. Stacking of individual channels resulted in a large amalgamated reservoir interval with pressure communication throughout. Isolated channels also occur, but these have shown rapid depletion within 2 months following production start-up.

Connectivity between individual channels will depend on how much shale is present. The effect of increasing shale content is to reduce vertical connectivity through sand-on-sand contacts and also to increase lateral variability (Weimer and Slatt, 2004).

Connectivity between individual channels will depend on how much shale is present. The effect of increasing shale content is to reduce vertical connectivity through sand-on-sand contacts and also to increase lateral variability (Weimer and Slatt, 2004).

Shales may be present either as extensive late-stage channel-fill shales or as shale drapes at the base of the channels. They may be composed of mudstone, siltstone, or heterolithic sediments (Figure 194b) (Beaubouef et al., 1999). Simulation modeling indicates that shale drapes may be a significant feature reducing connectivity between channel complexes and impairing the recovery efficiency (Larue, 2004). This mechanism has been invoked to explain why channel margins in the Forties field, UK North Sea, appear to act as baffles to fluid flow (Vaughan et al., 2007).

Shales may be present either as extensive late-stage channel-fill shales or as shale drapes at the base of the channels. They may be composed of mudstone, siltstone, or heterolithic sediments ([[:File:M91FG194.JPG|Figure 2b]]) (Beaubouef et al., 1999). Simulation modeling indicates that shale drapes may be a significant feature reducing connectivity between channel complexes and impairing the recovery efficiency (Larue, 2004). This mechanism has been invoked to explain why channel margins in the Forties field, UK North Sea, appear to act as baffles to fluid flow (Vaughan et al., 2007).

According to Weimer and Slatt (2004), the width to thickness ratio of channels typically ranges from 10:1 to 300:1.

According to Weimer and Slatt (2004), the width to thickness ratio of channels typically ranges from 10:1 to 300:1.