Compaction Localization in Porous Sandstone: Implications for Reservoir Mechanics

Compaction of porous rocks can occur in two modes: uniform and localized. Recent experimental work has demonstrated that compaction can occur in tabular zones that expand with increasing applied deformation. The appearance of compaction bands and their growth has a strong influence on the measured permeability of the host rock. The rock behind the moving compaction front can be either uniformly compacted or can consist of intercalated bands of uncompacted and compacted material. These three types of compaction would have very different effects on production from reservoirs undergoing compaction. We review the status of experimental results on localized compaction and the bifurcation theory of strain localization for compaction. Introduction Compaction of porous rock is an important process in the oil and gas industry. Compaction caused by changes in effective stresses during production can: (1) cause casing failures, (2) lead to seafloor subsidence having a significant impact on structure design and performance, and (3) squeeze oil from the rock into the borehole, or (4) significantly decrease the permeability of the reservoir rock thus reducing production Ostermeier (2001). When grain crushing is involved, compaction may also contribute to sand production in boreholes (Haimson, 2001). Diagenesis is of course a natural arena where compaction plays an important role but this paper does not touch on that important problem. Naturally occurring, nonhomogeneous compaction, arranged in subparallel, sharply restricted, or localized, layers, unrelated to sedimentary layering was described by Mollema and Antonellini (1966). They demonstrated that compaction had occurred in thin, tabular zones, approximately 1 cm thick, oriented perpendicular to the axis of maximum compression. These zones were characterized by pure normal compression