The Pennsylvania Petroleum Source Rock Geochemistry Database


Christopher D. Laughrey, Jaime Kostelnik, John A. Harper, and Kristin M. Carter

 

This database contains petroleum source rock geochemistry data collected by the Pennsylvania Geological Survey between the late 1970s and today. Petroleum source rocks are organic-rich fine-grained rocks that in their natural setting have generated and released enough hydrocarbons to form a commercial accumulation of oil or natural gas (Hunt, 1996). Most petroleum source rocks are calcareous, dolomitic , siliceous or phosphatic shales or argillaceous limestones . Rocks with the finest grain size have the highest amount of organic material.

In conventional petroleum geology, the source rock is one component of the petroleum system . A petroleum system comprises an active source rock, the oil and natural gas it generates, and all of the essential elements and processes required for a petroleum accumulation to exist ( Magoon and Dow, 1994). The essential elements of a petroleum system are the source rock, reservoir rock, seal rock, and overburden rock. The essential processes are trap formation and the generation, migration, and accumulation of oil and gas in a reservoir. These processes are very inefficient in sedimentary basins. Hunt (1996) notes that the ratio of oil accumulated in reservoirs to the amount of petroleum generated in place in a source rock is usually less than 15% in typical petroliferous basins (p. 392). Yet finding and extracting that small amount of accumulated petroleum in sedimentary basins has provided for much of the world's energy demand and economic growth throughout the 20 th and 21 st centuries. As oil and gas become harder and more expensive to find, petroleum geologists endeavor to reduce exploration risk by using modern technology to the extent possible. They not only hunt for traps and petroleum accumulations, but also try to assess the probability that oil and gas were generated in a particular source rock and migrated into those traps. They work to determine if the petroleum generated in a source rock might have escaped from a trap or been destroyed by thermal processes during deep burial. The answers to these questions are best provided by data from organic geochemistry.

Today, the organic-rich, fine-grained source rocks themselves are the target of intense exploration and drilling for natural gas. So-called thermogenic shale-gas reservoirs comprise an exciting new kind of unconventional energy resource. The organic-rich shale is a self-contained petroleum system in which the shale serves as source, reservoir, trap, and seal. The discipline and data of petroleum geochemistry provide the essential foundation for finding and measuring natural gas resources in these rocks.

The relative ability of a source rock to generate oil and gas is dictated by the quantity of organic matter (total organic carbon or TOC), the quality or type of organic matter (hydrogen content), and the thermal maturity of the organic matter in the rock. The information compiled in this database address these specific three parameters. The analyses available in this database for determining the three petroleum source rock parameters – quantity , quality , and maturity-- of organic matter - consist of various values measured in the laboratory by different chemical and optical means. Interested readers can refer to numerous textbooks for the details of the various analytical methods. We recommend Miles (1994), Hunt (1996), and Peters and Moldowan (1996). Tables 1, 2, and 3 list the interpretive guidelines recommended by Peters and Casa (1996) for the three principal source rock parameters. All of the data were obtained at various commercial and private laboratories.