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To evaluate compaction as a factor in porosity evolution, a plot of intergranular volume vs. depth was constructed using data from relatively uncemented reservoir sandstones from a variety of depths, ages, and geographic locations. The resulting intergranular-volume-decline curve reveals that sands compact mechanically and intergranular volume declines rapidly, from about 40 to 42% at the surface, to about 28% at 1500 m. Between about 1500 and 2500 m, intergranular volume continues to decline slowly, until the framework stabilizes at around 26% (maximum potential porosity in the absence of cement or matrix). No further significant decrease in intergranular volume is observed to the depth limits of the data set at 6700 m. Comparison of intergranular volume and volume of quartz cement for different formations reveals no obvious balance between intergranular pressure solution (as monitored by intergranular volume) and quartz cementation. This indicates that grain-to-grain pressure solution and quartz cement precipitation do not proceed concomitantly on the thin-section scale. Moreover, grain compaction is limited (to about 26% intergranular volume) in rigid-grain sandstones, which suggests that the occurrence and distribution of deep porosity is a function of the volume of cement available to fill the intergranular pores. Therefore, deep, porous sandstones are relatively uncemented rather than undercompacted.
Stan Paxton is an assistant professor of geology at Oklahoma State University (OSU). Prior to joining OSU in 1999, he was employed by Exxon Production Research Company where he was actively involved in the development of reservoir-quality technology. He was recipient of AAPG's Best International Poster Award for work presented at the Rio International Conference and Exhibition held in 1998. In 2001, Stan served as an AAPG International Distinguished Lecturer to China and Southeast Asia. At OSU he is working closely with colleagues to promote his petroleum-related research and apply petroleum technology to the exploration and production of ground water in Oklahoma and South Africa.Janos Szabo worked with Exxon Production Research Company from 1959 (then Jersey Production Research Company based in Tulsa) to 1986. Janos's areas of expertise include sedimentary petrography, heavy mineral analysis, and reservoir diagenesis. Throughout his career with Exxon, Janos was a key driving force behind many of the Exxon sandstone diagenesis research projects, including the first deep sandstone porosity study, initiated in 1967.
Joanna Ajdukiewicz is employed at ExxonMobil's Upstream Research Center in Houston, Texas. Since 1980, she has been involved in developing integrated techniques for reservoir quality assessment and prediction. She was leader of the Reservoir Quality Assessment and Prediction Group from 1991 to 1995. Her current research deals with the causes of preserved porosity and permeability in deeply buried reservoirs.
Robert Klimentidis is a member of the Reservoir Quality Group at ExxonMobil Upstream Research Company in Houston, Texas. Bob works to quantify mineral diagenesis and burial compaction for the purpose of predicting porosity, permeability, and water saturation in different hydrocarbon-bearing stratigraphic intervals. A current project entails the integration of special core and well-log analyses with detailed description of the reservoir pore network.