Jurassic Haynesville Limestones of East Texas: Burial Diagenesis and More Burial Diagenesis

Jeffrey J. Dravis

Progressive loss of primary porosity due to a continuum of pressure solution and associated burial cementation dominated Haynesville porosity evolution. Porosity loss, however, was punctuated at depth by major grain dissolution and microporosity development in oolitic grainstones.

Absence of freshwater precompaction cements allowed incipient burial diagenesis to affect the entire Haynesville sequence. Micritic facies experienced extensive stylolitization and associated cementation, losing their effective porosities relatively early in their burial history. Oolitic grainstones also initially lost porosity due to pervasive suturing of ooids and concomitant interparticle cementation, a relationship confirmed by cathodoluminescence and cement geochemistry. Yet they retained sufficient primary porosity to later reservoir bitumen.

Subsequent to bitumen emplacement, however, ooids underwent extensive burial dissolution which created uniform micromoldic porosity, now the dominant pore type in these gas reservoirs. Dissolution postdated most pressure solution fabrics in these grainstones; adjacent micritic facies were unaffected by this dissolution.

Cathodoluminescence and vertical porosity profiles demonstrate that reduction of some reservoir quality in these oolitic grainstones resulted from renewed pressure solution and cementation, controlled largely by grainstone thickness and proximity to micritic facies. Thin grainstones encased in micritic limestones lost effective porosities due to burial cementation. In contrast, thicker grainstones show a reduction in reservoir quality only near their contacts with micritic facies. These porosity trends suggest that after microporosity was generated, carbonate cements continued to be derived from adjacent micritic limestones still undergoing pressure solution, implying relatively short transport distances before they precipitated.

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