ABSTRACT: Differential Compaction Influences on Structure in West Cameron Block 225 Field

William R. Finley

The idea of gravitational compaction as discussed by Gay described the concept of lateral variations in compactibility within a stratigraphic section. "This concept was expanded on by Teas (1923)," stated Gay. He continued with "I knew of no published stratigraphic study in the intervening 65 years that has attempted to document this type of compaction structure from well data, although these structures undoubtedly exist." This paper is an attempt to rectify the omission and illustrate that they do indeed exist.

The concept to be illustrated here is the influence on structural configuration of differential compaction caused by lateral variations in stratigraphy, specifically, changes from sand to shale within the same stratigraphic interval. The example chosen to illustrate this concept is West Cameron Block 225 field. As seen in structural stratigraphic cross sections as well as net sand maps constructed in the example field, several channel sands are seen to strongly influence the structural configuration.

The basic structure within the field as defined by well and seismic data consists of a gentle, southerly dipping, north-south-oriented ridge, bounded by a down-to-the-east fault on the west flank and a down-to-the-south fault to the north. Gentle roll into these faults closes the north flank of the structure.

The stratigraphic section consists of alternating sands and shales of Miocene and Pliocene age. Several of these sands map out as linear sand bodies interpreted to be channels. These channels, representing thickened sand bodies that grade laterally into predominantly shale facies, are oriented in a general east-west direction.

The juxtaposition of the basic structural orientation with the orientation of the channel sand(s) sets up a crossing point(s) on the southern flank of the structure. With the advent of differential compaction between the channel sands and the bounding shale faces, a stratigraphic structure is generated. This resulting compaction structure maps out as a double-lobed or saddled high. This effect is amplified as channels in the shallower section stack out over the southern flank of the structure until the southern crest dominates over the northern one. The overall result is one of migrating structural crests caused by variations in compactibility within the stratigraphic section.

Although differential compaction around isolated sand bodies is generally understood to be a valid phenomenon, I do not believe that adequate attention has been focused on its potential importance.

AAPG Search and Discovery Article #90999©1990 GCAGS and Gulf Coast Section SEPM Meeting, Lafayette, Louisiana, October 17-19, 1990