Porosity Formation in Deep-Burial Environment: Overview, with Examples, from Permian Basin

S. J. Mazzullo, P. M. Harris

Deep-burial diagenesis in carbonates includes complex processes and products that are commonly similar to those known from eogenetic environments. It has often been stressed that porosity reduction rather than enhancement is the dominant trend observable in deeply buried carbonates. Our studies in the Permian basin, however, suggest that porosity formation within the deep subsurface environment may in fact be more important than previously appreciated.

Porosity formation accompanying deep burial is ubiquitous and widespread in the Permian basin, particularly but not exclusively in offshore platform and resedimented basinal carbonates of Pennsylvanian and Permian age. Hydrocarbon reservoirs in such platform carbonate examples locally contain evidence of subaerial exposure and meteoric diagenesis. Commonly, much of the porosity formed during exposure is ultimately reduced by compaction and cementation during early burial. By contrast, no evidence of meteoric diagenesis is observed in associated basinal carbonates, although compaction and cementation accompanying progressive burial are readily evident. In both cases, however, such early diagenesis is overprinted by late burial dissolution, sometimes coincident with hydrocarbon emplacem nt, creating rocks of high porosity. The formation of porosity by cement dissolution may exhume occluded pores or enhance relict pores that formed in the eogenetic zone, the result being a preponderance of interparticle and moldic pores and residual cements that mimic vadose and phreatic products. In other cases, nonfabric selective dissolution, locally associated with fractures or stylolites, creates vuggy porosity which may resemble that formed during eodiagenesis. Multiple phases of deep-burial dissolution and partial cementation or replacement (by calcite or dolomite) are indicated for many of these diagenetic systems and result in a complex suite of different pore types.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.