Discussion of this paper is invited. Three copied of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Abstract

The prospect of higher gas prices has triggered new interest in deep drilling below 10,000 feet in the huge Appalachian Basin. Scant past exploration of known deep structures is evidenced by the fact that only 42 wells have been drilled below 10,000 feet in the seven state area. Drilling costs have been high due to some problems peculiar to this area. A sectional hole analysis of these problems and recommended practices based on past experience shows ways to reduce these costs and encourage additional exploration.

Introduction

Prospective higher gas prices, nearness to market, and large unexplored structures are the incentives that have renewed deep drilling in the Appalachian basin. Several major operators are now drilling wells below 10,000' in the seven state area. This has encouraged the application of new drilling techniques in an attempt to reduce high costs of these deep wells.

This paper will (1) review briefly the past and present deep drilling activity in this past and present deep drilling activity in this basin, (2) present a generalized drilling plan that can be of help to new operators entering this area, (3) discuss drilling problems and solutions, and (4) review some special contract and environmental problems peculiar to this area.

The Appalachian Basin covers all or a portion of the seven states of New York, portion of the seven states of New York, Pennsylvania, Ohio, Maryland, Virginia, West Virginia, Pennsylvania, Ohio, Maryland, Virginia, West Virginia, and Kentucky (Figure 1). Covering an area of about 175,000 square miles, the basin contains many deep geologic structures which have been recognized for years and discussed in numerous articles. Scant attention had been paid to these deeper prospects, however, until recent encouragement of higher gas prices triggered the leasing of millions of acres by several major companies new in the area.

It is ironic that the birthplace of the commercial oil industry should have been overlooked so long as to exploration below 10,000'. A survey shoves only forty-two wells have been drilled in the entire area to date (Figure 1). Several wells currently are being drilled to these deep structures, and new depth records have been set. These efforts are very expensive as to drilling costs, and encourage application of cost reducing procedures. Problems causing the high costs of drilling range from surface glacial drift and boulders to extremely hard quartzites, salt sections, and "trapped pressure shales." Dry hole costs in the basin can range from $27/foot for an 11,000' hole drilled to TD on air with no problems to as high as $150/foot for a typical 20,000 foot well which will encounter several problems, including at least one sidetrack operation.

How Deep Can We Find Economic Oil and Gas Accumulations?

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Hunt, John M., Woods Hole Oceanographic Institution

Copyright 1974 American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.

This paper was prepared for the Deep Drilling and Production Symposium of the Society of Petroleum Engineers of AIME, to be held in Amarillo, Texas, Sept. 8–10, 1974. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the Journal of presented. Publication elsewhere after publication in the Journal of Petroleum Technology or the Society of Petroleum Engineers Journal is Petroleum Technology or the Society of Petroleum Engineers Journal is usually granted upon request to the editor of the appropriate journal provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copied of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Abstract

The development of drilling equipment with increasingly greater depth capability should take into account the maximum depths at which economic hydrocarbon accumulations will be found. The origin, accumulation and destruction of hydrocarbons is controlled primarily by temperature and time. Most hydrocarbons form at subsurface temperatures ranging from 125 degrees F to 350 degrees F, equivalent to depths of 3,500 ft. to 20,000 ft. in a typical basin. High temperatures >350 degrees F), or long exposure to moderate temperatures will ultimately destroy oil yielding mainly graphite and methane. Eventually, even commercial accumulations of methane are absent. Each sedimentary basin has a characteristic hydrocarbon limit, beyond which drilling is futile.

ECONOMICS OF DEEP DRILLING

In 1973 there were 506 wells drilled deeper than 15,000 ft. at a cost of over half a billion dollars. The average deep well cost $1,107,000 compared with about $900,000 in 1972. Although deep drilling costs have increased rapidly in recent years, this has not always been so. From the early 1950's until about 1966 the average cost oscillated around $40 per foot, as shown in Figure 1. This was partly due to the remarkable improvements in drilling technology, particularly in the number of bits required for particularly in the number of bits required for deep drilling. This decreased from a high of around 200 bits per well in the late 1940's to only 38 bits per well last year. Since 1966 improvements in drilling technology have not been sufficient to offset rising costs, and for the ultradeep wells below 20,000 ft., the cost rise has been particularly steep. Today six wells can be drilled to 15,000 ft. for each well that is drilled to about 30,000 ft. as shown in Figure 2.

There is no question that drilling in the 15,000 to 20,000 ft. range is justified. Last year 31% of the wildcats were successful, which is high by most standards. The real question is, how much deeper than 20,000 ft. can we drill profitably? profitably? From 1944 through 1958 the deepest production generally lagged behind the deepest well production generally lagged behind the deepest well by about 3,000 ft. as shown in Figure 3. In 1959, this gap began to approach 5,000 ft. and this year it exceeded 8,000 ft.

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