Shu'Aiba Porosity Types, Saudi Arabia

Robert F. Lindsay¹ and Peter K. Swart^2
1Geological Technical Services Division, Saudi Aramco, Dhahran, Saudi Arabia
²University of Miami, Miami, FL

A study of Shu’aiba porosity was conducted to determine the abundance and types of porosity and their effects upon reservoir performance. The Shu’aiba was found to contain four types of porosity that include microporosity, mesoporosity, macroporosity, and megaporosity. Surprisingly, the Shua’aiba contains little microporosity, but contains considerable amounts of mesoporosity (common throughout the section), macroporosity (most common up-section), and lesser amounts of megaporosity (more common up-section). These were determined by core description, petrography, high-pressure mercury injection capillary pressure, image analysis, and SEM (regular and relief pore cast views) of the pore and pore throat system.

Microporosity and mesoporosity are similar, but cannot be distinguished petrographically. They vary in size, and reside within peloid intraparticle porosity and carbonate mud as micrite and microspar intercrystal pores and micro-molds. Macroporosity is present as interparticle and moldic pores, with moldic pores being the most common. Interparticle pores have been reduced, but not eliminated, by calcite cement. Megaporosity is present where rudist bivalve shells have dissolved to create large moldic to vugular pores.

Microporosity and mesoporosity are considered to result from dissolution of peloids and other grains followed by precipitation of micrite and an abundance of microspar calcite crystals. Early stages of dissolution preferentially affected the margins of peloids and micritized rims of bioclasts. Interiors of peloids display progressively increasing microporosity and mesoporosity dissolution leading to macroporosity.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas