Ronald F. Broadhead

Stratigraphic and Sedimentologic Controls of Gas in Shale--Example from Upper Devonian of Northern Ohio

The gas-bearing Devonian Ohio and Chagrin Shales along Lake Erie have produced marginally commercial volumes of gas for over 100 years. These shales thin depositionally westward from a maximum of 2,000 ft (600 m) at the Pennsylvania-Ohio border to less than 500 ft (180 m) near Sandusky, Ohio. West of Sandusky, they have been truncated by Holocene and preglacial erosion on the Findlay arch. Westward thinning is accompanied by a facies change from gray shale and siltstone in the east to black shale in the west. The Ohio and Chagrin Shales were deposited on a turbidite slope and basin plain and all were derived from the Catskill delta on the east. The Late Devonian epeiric sea was at least 700 ft (215 m) deep and was poorly oxygenated. There are three major lithologies--black bituminous shale, greenish-gray shale, and siltstone. Black bituminous shale is most abundant in the west, whereas gray to greenish-gray shale and siltstone are most abundant in the east, where they constitute 75% of the section. Zones productive of natural gas occur most commonly in the greenish-gray shale and siltstone. These rocks contain abundant thin silt laminae which probably act as permeable conduits and reservoirs for gas. This gas appears to have had its origin in underlying black shales. Sedimentologic study helps explain the origin of both small- and large-scale interbedding of the greenish-gray and black bituminous shale and provides guides for improved gas exploration in the Appalachian basin.

Play Analysis and Digital Portfolio of Major Oil Reservoirs in the Permian Basin: Application and Transfer of Advanced Geological and Engineering Technologies for Incremental Production Opportunities

The Permian Basin of west Texas and southeast New Mexico has produced >30 Bbbl (4.77 x 10{sup 9} m{sup 3}) of oil through 2000, most of it from 1,339 reservoirs having individual cumulative production >1 MMbbl (1.59 x 10{sup 5} m{sup 3}). These significant-sized reservoirs are the focus of this report. Thirty-two Permian Basin oil plays were defined, and each of the 1,339 significant-sized reservoirs was assigned to a play. The reservoirs were mapped and compiled in a Geographic Information System (GIS) by play. Associated reservoir information within linked data tables includes Railroad Commission of Texas reservoir number and district (Texas only), official field and reservoir name, year reservoir was discovered, depth to top of the reservoir, production in 2000, and cumulative production through 2000. Some tables also list subplays. Play boundaries were drawn for each play; the boundaries include areas where fields in that play occur but are 1 MMbbl (1.59 x 10{sup 5} m{sup 3}) was 301.4 MMbbl (4.79 x 10{sup 7} m{sup 3}) in 2000. Cumulative Permian Basin production through 2000 from these significant-sized reservoirs was 28.9 Bbbl (4.59 x 10{sup 9} m{sup 3}). The top four plays in cumulative production are the Northwest Shelf San Andres Platform Carbonate play (3.97 Bbbl [6.31 x 10{sup 8} m{sup 3}]), the Leonard Restricted Platform Carbonate play (3.30 Bbbl 5.25 x 10{sup 8} m{sup 3}), the Pennsylvanian and Lower Permian Horseshoe Atoll Carbonate play (2.70 Bbbl [4.29 x 10{sup 8} m{sup 3}]), and the San Andres Platform Carbonate play (2.15 Bbbl [3.42 x 10{sup 8} m{sup 3}]).

Underdeveloped oil fields — Upper Pennsylvanian and lower Wolfcampian carbonate reservoirs of southeast New Mexico

Carbonate reservoirs in the Cisco and Canyon (Upper Pennsylvanian) and lower Wolfcampian (Permian) sections in the Permian Basin of southeast New Mexico, U.S.A. are significant reservoirs for oil and gas. The approximately 400 fields that have produced from these reservoirs have yielded a cumulative production of 490 million bbls oil (MMBO; 78 million m3) and 3.2 trillion ft3 (91 billion m3) gas, 12% of the oil and 16% of the gas produced in southeast New Mexico. Sixteen of these fields have been identified that were underdeveloped at some stage in their history. Cumulative production ranges from Milnesand West (0.210 MMBO; 0.033 million m3) to Dagger Draw (31 MMBO; 4.9 million m3).Although initially underdeveloped, subsequent redevelopment of these 16 fields added significantly to reserves and production. Statistical analysis of production decline curves was used to estimate reserves developed during initial drilling of these fields and during subsequent phases of redevelopment. For the 16 fields studied, redevelopment accounted for a total of 65% of developed reserves. Redevelopment accounted for more than 90% of total reserves at Dagger Draw and 99% at Baum.Redevelopment in these fields was generally in undrilled portions of the fields, and not in bypassed pay zones. The fields are formed by stratigraphic traps but were initially thought to be structural traps and were developed on structural culminations. Because initial development was based on the premise of structural entrapment, the majority of reserves in these fields remained unproduced until redevelopment. Redevelopment generally resulted in a fivefold to tenfold increase in numbers of producing wells and productive acreage. Because 84% of Upper Pennsylvanian and lower Wolfcampian fields have less than 10 producing wells and 57% have less than three producing wells, it would appear that significant reserves may remain undeveloped in most existing fields. For those fields that have been developed only on structures, additional study of carbonate facies and environments is needed to fully delineate the reservoirs and identify full potential.

PLAY ANALYSIS AND DIGITAL PORTFOLIO OF MAJOR OIL RESERVOIRS IN THE PERMIAN BASIN: APPLICATION AND TRANSFER OF ADVANCED GEOLOGICAL AND ENGINEERING TECHNOLOGIES FOR INCREMENTAL PRODUCTION OPPORTUNITIES

A play portfolio is being constructed for the Permian Basin in west Texas and southeast New Mexico, the largest petroleum-producing basin in the US. Approximately 1300 reservoirs in the Permian Basin have been identified as having cumulative production greater than 1 MMbbl of oil through 2000. Of these major reservoirs, approximately 1,000 are in Texas and 300 in New Mexico. On a preliminary basis, 32 geologic plays have been defined for Permian Basin oil reservoirs and assignment of each of the 1300 major reservoirs to a play has begun. The reservoirs are being mapped and compiled in a Geographic Information System (GIS) by play. Detailed studies of three reservoirs are in progress: Kelly-Snyder (SACROC unit) in the Pennsylvanian and Lower Permian Horseshoe Atoll Carbonate play, Fullerton in the Leonardian Restricted Platform Carbonate play, and Barnhart (Ellenburger) in the Ellenburger Selectively Dolomitized Ramp Carbonate play. For each of these detailed reservoir studies, technologies for further, economically viable exploitation are being investigated.

ABSTRACT: Upper Pennsylvanian and Lower Permian of Southeastern New Mexico—Rejuvenation of Underdeveloped Fields Yields Major Reserves

Carbonate reservoirs in the Cisco and Canyon (Upper Pennsylvanian) and lower Wolfcamp (Permian) sections in the Permian Basin of southeastern New Mexico are significant reservoirs for oil and gas. The 400 fields that produce from the reservoirs have yielded a cumulative 508 million bbls of oil and 3.2 TCF of gas. Sixteen of these fields have been identified that were underdeveloped at some stage in their history. For the 16 fields studied, redevelopment accounted for 65% of developed reserves, Redevelopment in the late 1980’s and 1990’s accounted for more than 95% of total reserves at Dagger Draw, and turned this seemingly insignificant field into the most productive field in New Mexico. Redevelopment of Dagger Draw has reversed the production decline in southeast New Mexico. Redevelopment in these fields was generally in undrilled portions of the fields and not in overlooked pay zones. Most of these fields are formed by stratigraphic traps, but initially were thought to be structural traps and were developed as such. Because initial development was on structure and off-structure areas were undrilled, most reserves remained unproduced until redevelopment. Because 9 1% of the Upper Pennsylvanian and lower Wolfcampian fields have less than 10 producing wells and have been developed primarily on structures, significant reserves may remain undeveloped in existing fields. Although initially underdeveloped, subsequent redevelopment added significantly to reserves and production.

Petroleum Geology of Santa Rosa Sandstone (Triassic), Northeastern New Mexico: ABSTRACT

The Santa Rosa Sandstone (Triassic) occurs at depths of less than 2,000 ft (610 km) over most of northeastern New Mexico. Two major, presently unproductive heavy oil accumulations are known to exist in the Santa Rosa Sandstone in New Mexico: the Santa Rosa tar sands near the town of Santa Rosa in central Guadalupe County and a subsurface accumulation near the town of Newkirk in northeast Guadalupe County. The Santa Rosa Sandstone is 67-350 ft (20-107 m) thick in northeastern New Mexico. It overlies the Artesia Group (Permian) with regional angular unconformity and is subdivided into three regionally recognizable units: a lower sandstone unit 18-140 ft (5-43 m) thick, a middle mudstone unit 0-144 ft (0-44 m) thick, and an upper sandstone unit 7-150 ft (2-46 m) thick. The lower and upper units are blanket deposits of braided streams and consist mostly of fine to medium-grained porous sandstones and minor red mudstones. The middle unit is lacustrine, consisting chiefly of red mudstones and minor sandstones. Structures on the Santa Rosa Sandstone are mostly northwest to northeast-trending gentle folds superimposed on a southeast regional dip of 0.4°. The two heavy oil accumulations occur in the upper sandstone unit. Shows of asphaltic hydrocarbons occur in the lower unit. Stratigraphic and petrographic studies indicate that good reservoirs are widespread in the lower and upper sandstone units in northeastern New Mexico. The blanket geometry of the lower and upper sandstone units indicates that structure should play an important or even dominant role in the trapping of undiscovered hydrocarbons in the Santa Rosa Sandstone. End_of_Article - Last_Page 844------------

Gas-Bearing Ohio Shale along Lake Erie--Stratigraphy, Petrology, and Sedimentology: ABSTRACT

Increased interest in low-yield gas-bearing strata has led to reexamination of the Ohio Shale in the vicinity of Lake Erie where it has had a history of marginal commercial production for over a century. These strata thin depositionally westward from a maximum of 2,000 ft (600 m) at the Pennsylvania border to less than 600 ft (180 m) near Sandusky where they are truncated by erosion on the Findlay arch. Common lithotopes are black and gray shale, siltstones, and rare carbonate rocks. Black shales are most abundant in the west where gray shales and siltstones are rare. In the east, gray shales and siltstones constitute 75% of the section and the remainder is mainly black shale and minor carbonate rocks. Thin-section petrology revealed that the black shale commonly contains, by volume, less than 20% silt-size quartz and feldspar, 30 to 60% clay and mica, and 15 to 35% organic material. Gray shale commonly contains less than 30% silt-size quartz and feldspar, 50 to 90% clay and mica, and less than 10% organic material. Much of the silt is concentrated in discrete laminae a few grains thick. Production records are related to facies distribution to provide an exploration tool. Cross sections and paleocurrents indicate that the Upper Devonian prodeltaic muds and turbidite siltstones were deposited episodically in a euxinic basin. End_of_Article - Last_Page 1576------------