Changes

==Problems in characterizing deep-water marine sandstones==

==Problems in characterizing deep-water marine sandstones==

Deep-water marine sandstone systems can be difficult to characterize in the subsurface. The basic problem is in trying to differentiate sheet sandstones from channel complexes. Sheet sandstones are typically well connected laterally and can be very productive. By contrast, the large-scale reservoir connectivity of channel complexes can vary between good, where they have coalesced into connected bodies, and none at all, where they are depositionally isolated.

Deep-water marine sandstone systems can be difficult to characterize in the subsurface. The basic problem is in trying to differentiate sheet sandstones from channel complexes. Sheet sandstones are typically well connected laterally and can be very productive. By contrast, the large-scale reservoir connectivity of channel complexes can vary between good, where they have coalesced into connected bodies, and none at all, where they are depositionally isolated.

Channel complex connectivity will depend upon whether the individual channels show extensive sand-sand contacts with each other or not. It is not always easy to assess this with limited well control. This is a particular problem when it comes to the costly appraisal of deep-marine sandstone reservoirs offshore (Steffens, 2004).

Channel complex connectivity will depend upon whether the individual channels show extensive sand-sand contacts with each other or not. It is not always easy to assess this with limited well control. This is a particular problem when it comes to the costly appraisal of deep-marine sandstone reservoirs offshore (Steffens, 2004).

Weimer and Slatt (2004) gave guidelines on how to differentiate between sheet and channelized deep-marine sandstones. If the log patterns and net-to-gross ratios vary considerably over short distances between wells, then the chances are that this is a channelized system (Chapin et al., 1994). A typical pattern is for channels to have high net-to-gross values and a blocky log response in the channel axis, with lower net-to-gross values and a serrated log response toward the margins (Figure 193). In core, channel-fill sandstones can show erosional features such as erosional bases, shale clasts, and an abundance of chaotic looking sediments.

Weimer and Slatt (2004) gave guidelines on how to differentiate between sheet and channelized deep-marine sandstones. If the log patterns and net-to-gross ratios vary considerably over short distances between wells, then the chances are that this is a channelized system (Chapin et al., 1994). A typical pattern is for channels to have high net-to-gross values and a blocky log response in the channel axis, with lower net-to-gross values and a serrated log response toward the margins ([[:File:M91FG193.JPG|Figure 1]]). In core, channel-fill sandstones can show erosional features such as erosional bases, shale clasts, and an abundance of chaotic looking sediments.

 

Sheet sandstones and their associated shale interbeds are more layered and massive both at the core and interwell scale. Erosive features are relatively rare with few or no shale rip-up clasts. Post-production formation tester data can help to recognize the high degree of lateral continuity likely to be present here.

==Production from channelized systems==

==Production from channelized systems==