Geology and CO2-EOR Potential in the Bradford Oil Field, McKean County, PA and Cattaraugus County, NY
John A. Harper
Pennsylvania Geological Survey, 400 Waterfront Drive, Pittsburgh, PA, [email protected]
Bradford oil field, encompassing approximately 85,000 acres in north-central McKean County, PA, and south-central Cattaraugus County, NY, is the world’s first giant oil field. It has produced >681 million bbl of Penn Grade crude oil since it first went into production in 1871. The Bradford Third sand, a sequence of interbedded sandstones, siltstones, and shales within the Upper Devonian Bradford Group, is a medium- to fine-grained sublitharenite (greywacke) with subordinate interbedded siltstone and shale layers averaging 38 ft in thickness. Porosity generally ranges from one to 26 percent throughout the sandstone; in the pay interval, it varies from 1.4 to 19 percent, averaging 14.5 percent. Permeability ranges from <0.1 to >350 mD.
Bradford field has been the site of numerous enhanced recovery activities almost since the field was discovered, with water flooding producing the most success. Unintentional water flooding began very early, and intentional flooding began ca. 1890, but the impact on production wasn’t noticeable until 1907. Extensive water flooding, initiated in 1928, resulted in production of 416 million bbl of oil through the 1990s when secondary recovery went into general decline. The field is now considered to be watered out. Bradford field has also been the site of various tertiary recovery field tests, including a combined liquid-CO2-and-gasoline project in the 1950s. Subsequent attempts included chemical floods and thermal methods, but all ended with disappointing or mixed results.
Many experts assert that, if a field has been water flooded successfully, much of the remaining oil can be produced through CO2 flooding. The Bradford Third sand is too shallow (generally <2,000 ft deep) for miscible CO2 flooding, but it should respond well to a modern immiscible CO2 flood. It will require significant time, effort, and capital to develop a CO2 flood due to the necessity of locating and plugging many old wells. The payoff, however, will be in potentially recovering a substantial portion of the remaining OOIP, estimated in the 1940s at about 1,075 million bbl. AAPG founding member Sydney Powers once estimated that primary and secondary recovery methods would ultimately produce about 28 percent of the OOIP in Bradford field. Considering the total amount of oil recovered to date, if Powers were correct, that would revise the OOIP upward to almost 2,500 million bbl of oil, of which 1,750 million bbl remain to be produced. The field’s reservoir characteristics, as well as the information amassed during its long history of secondary and tertiary recovery efforts, makes Bradford oil field an ideal location for a case study to evaluate the modern use of CO2 for EOR.
AAPG Search and Discovery Article #90154©2012 AAPG Eastern Section Meeting, Cleveland, Ohio, 22-26 September 2012