Dolomite‐rock textures and secondary porosity development in Ellenburger Group carbonates (Lower Ordovician), west Texas and southeastern New Mexico

Abstract

Pervasive early‐ to late‐stage dolomitization of Lower Ordovician Ellenburger Group carbonates in the deep Permian Basin of west Texas and southeastern New Mexico is recorded in core samples having present‐day burial depths of 1.5–7.0 km. Seven dolomite‐rock textures are recognized and classified according to crystal‐size distribution and crystal‐boundary shape. Unimodal and polymodal planar‐s (subhedral) mosaic dolomite is the most widespread type, and it replaced allochems and matrix or occurs as void‐filling cement. Planar‐e (euhedral) dolomite crystals line pore spaces and/or fractures, or form mosaics of medium to coarse euhedral crystals. This kind of occurrence relates to significant intercrystalline porosity. Non‐planar‐a (anhedral) dolomite replaced a precursor limestone/dolostone only in zones that are characterized by original high porosity and permeability. Non‐planar dolomite cement (saddle dolomite) is the latest generation and is responsible for occlusion of fractures and pore space. Dolomitization is closely associated with the development of secondary porosity; dolomitization pre‐and post‐dates dissolution and corrosion and no secondary porosity generation is present in the associated limestones. The most common porosity types are non‐fabric selective moldic and vuggy porosity and intercrystalline porosity. Up to 12% effective porosity is recorded in the deep (6477 m) Delaware basin. These porous zones are characterized by late‐diagenetic coarse‐crystalline dolomite, whereas the non‐porous intervals are composed of dense mosaics of early‐diagenetic dolomites. The distribution of dolomite rock textures indicates that porous zones were preserved as limestone until late in the diagenetic history, and were then subjected to late‐stage dolomitization in a deep burial environment, resulting in coarse‐crystalline porous dolomites. In addition to karst horizons at the top of the Ellenburger Group, exploration for Ellenburger Group reservoirs should consider the presence of such porous zones within other Ellenburger Group dolomites.

The Lower Miocene Nukhul Formation (Gulf of Suez, Egypt): microfacies and reservoir characteristics

“…The classification is descriptive, but carries genetic implications, since size distribution and crystal boundary shape is controlled by nucleation and growth kinetics (Sibley and Gregg 1987;Amthor and Friedman 1991).…”

Beyreli - Çamiçi (Hadim-Konya) Dolayındaki Jura Yaşlı Dedebeleni Formasyonu Dolomitlerinin Sedimantolojik ve Jeokimyasal İncelenmesi

“…İnce partiküller hacimleriyle karşılaştırıldığında çok büyük yüzey alanına sahiptir ve bu yüzden çekirdekleşme oranı hızlıdır. Eğer çekirdekleşme oranı, büyüme oranıyla karşılaştırıldığında yüksek ise sonuçta kristal boyu küçük olacaktır [20]. Dedebeleni formasyonundaki ince kristalli dolomitler de erken diyajenezde sığ gömülme ortamında oluşmuştur.…”

“…İri -çok iri kristalin anhedral dolomit orijinal kireçtaşı ya da dolomitin ornatılmasıyla oluşur [20]. Bu tip replase genellikle bütün orijinal depozisyonal dokuları yokeder.…”

Integrated Synthesis of the Permian Basin: Data and Models for Recovering Existing and Undiscovered Oil Resources from the Largest Oil-Bearing Basin in the U.S.

“…Diagenesis of the Ellenburger Group is complex, and the processes that produced the diagenesis covered millions of years (e.g., Lucia, 1971;Loucks and Anderson, 1985;Lee and Friedman, 1987;Kerans, 1988Kerans, , 1989Kerans, , 1990Kupecz and Land, 1991;Amthor and Friedman, 1991;Loucks, 1999Loucks, , 2003. Several studies have presented detailed diagenetic analysis of the Ellenburger (Kerans, 1990;Kupecz and Land, 1991;Amthor and Friedman, 1991).…”

“…Several studies have presented detailed diagenetic analysis of the Ellenburger (Kerans, 1990;Kupecz and Land, 1991;Amthor and Friedman, 1991). A paragenetic chart is presented in Figures 14.…”