Aspects of Petroleum Geology of Lockport Formation in Western Crawford County, Northwest Pennsylvania

Samuel T. Pees

A study of more than 700 wells in a 700-mi² sector of northwest Pennsylvania found that recorded natural shows of gas and oil in the Silurian Lockport Formation are more frequent in certain drilled areas than in others. Black water shows also seem to be concentrated and do not necessarily share the same areas with wells having gas shows, although this sometimes happens. The geographic distribution of shows may partly reflect the degree of attention given by various operators to the reporting process or to wellsite geology in the Lockport interval, since it is not the current drilling objective. Nevertheless, patterns of Lockport shows are discernible. They may relate to particular lithofacies and porosity types. Dip reversals and natural fractures seem to also have been a factor at places.

Many shows are found in log-observed porosity zones ("Newburg") in the main Lockport Formation dolomite sequence. However, occasional shows are reported in relatively tight zones on the log. Rare shows have been noted in the DeCew Member, the basal unit in the formation.

The average thickness of the Lockport Formation (including the DeCew Member) is 291 ft (89 m). The main dolomite sequence averages 256 ft (78 m) and is quite variable.

In view of the number of hydrocarbon shows reported and the suspected presence of unreported or unnoticed shows in other wells, the Lockport Formation deserves more attention as a potential prospect locally. Selective testing and cores would be of great value in helping to locate the preferential loci of Lockport hydrocarbons in this area.

AAPG Search and Discovery Article #91041©1987 AAPG Eastern Section Meeting, Columbus, Ohio, October 7-10, 1987.