Abstract

The Elk Sands in Clearfield and Cambria Counties of Southwestern Pennsylvania have been difficult to successfully fracture stimulate. Treatments successfully applied to the upper Devonian Sands resulted in screenouts and little productivity increase when applied to the Elks. This paper discusses various studies that have been conducted, including net pressure analysis and three-dimensional modeling, to understand the fracturing behavior of these formations. Recommendations are made for improving future treatments of these formations.

Background

Dry gas wells have been under development in Southwestern Pennsylvania since the late 1800's. The initial areas of activity were in the western counties of Armstrong, Westmoreland, Jefferson, and Indiana. The predominate production came from shallow (1500 to 3500 ft), tight gas sands. By the late 1970's, many of the proven fields in these counties had been developed and the economic environment had led to some exploration in the eastern counties. At the same time, deep exploratory wells being drilled on the edge of the Pennsylvania Plateau revealed shallow gas sands Pennsylvania Plateau revealed shallow gas sands below the typically drilled formations. These formations, appearing below the Bradford and Kane Sands, became known as the Elk Sands. Although Elk Sands had been reported in northwestern counties as early as 1920, this was the first active development of them.

The first completions of Elk Sands in Centre County during the early 1980's demonstrated that techniques previously proven to work on the Bradford and other previously proven to work on the Bradford and other upper sands would not work on the Elk Sands. Eventually, techniques were developed for and successfully applied to these formations. This led to the development of several economic fields.

However, as development of the Elks began in Clearfield Co. during the late 1980's, some operators began to question the poor results obtained from hydraulic fracturing treatments. Also during this period, advances in fracturing interpretation, well logging, and coring were applied to further improve the production from the tight gas sands of Southwestern Pennsylvania, specifically the Elk Sands. Although any improvements in production are to date unproven due to the small amount of data available for comparison and the production data being short term, this paper will describe the techniques and technologies applied to Elk Sands during the late 1980's and the early 1990's.

In addition, results of the various studies conducted will be discussed and recommendations for the improvement of future fracturing treatments in the Elk Sands will be made.

GEOLOGY

In general, the upper Devonian gas sands of Pennsylvania consist of deltaic deposits such as Pennsylvania consist of deltaic deposits such as channels, bars, and sloughs. The locations of the wells discussed in this paper are shown on the map of Fig. 1 and the sandstone formations discussed are summarized in Fig. 2. In this figure, the geological column is displayed only as an aid in visualizing the respective positions of the formations, with the cross section and depths presented merely for the reader's reference. presented merely for the reader's reference. The lenticular nature of the Elk Sands makes formation mapping rather difficult. In addition, the geologic formation names of southwestern Pennsylvania vary among producers. For example, a Pennsylvania vary among producers. For example, a Balltown-D formation for one producer is a Sheffield or Tiona to another producer.

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