AAPG Bulletin Research Articles

The source rock potential of the Karroo coals of the south western Rift Basin of Tanzania

For many years geoscientists believed that coals (Type III Kerogen) generate gas only. The geochemical study of Durand and Parrante ( Petrolum Geochemistry and Exploration of Europe, pp. 255–265, 1983) revealed that coals have reasonable potential for oil generation. On this basis forty outcrop samples of Lower and Upper Permian age, i.e. coals and carbonaceous shales, were collected from the south western Rift Basin of Tanzania. The aim of the study was to determine the richness, type, maturity and hydrocarbon potential of the above samples. These samples were subjected to both geochemical and petrological analyses. Geochemical analyses included solvent extraction, TOC, GC, GC-MS and pyrolysis. The petrological analysis included vitrinite reflectance, spore fluorescence and maceral content. The geochemical analyses showed all samples to be rich in organic matter of Types II and III and samples from Songwe Kiwira, Namwele, Mbamba Bay, Njuga and Mhukuru coalfields were in an early mature-mature stage of hydrocarbon generation. Whereas samples from Ketewaka and Ngaka coalfields showed a GC-trace of early generated waxy oil. All samples contained organic matter derived from terrestrial material which was deposited under oxic environment. The Hydrogen Index of most coals and carbonaceous shales was greater than 200 indicating that they can generate oil or light oil. Petrological observations showed all samples to be in the range of 0.47–0.67% Ro and some of them were rich in both liptinite and vitrinite macerals. From both geochemical and petrological observations it was concluded that the Lower and Upper Permian coals and carbonaceous shales under study are probably capable of generating oil. The oil generated has the same characteristics as that generated by Cretaceous and Tertiary coals discovered from other parts of the world, i.e. Adjuna and Kutei Basins in Indonesia and the Gippsland Basin in Australia (Kirkland et al., AAPG Bull. 71, 577, 1987).

Karst-Controlled Reservoir Heterogeneity in Ellenburger Group Carbonates of West Texas: Discussion (1)

A discussion is presented on a paper by Charles Kerans (AAPG Bull. 1988). The paper dealt with karst-associated porosity and hydrocarbon reservoir heterogenity in Ellengurger (Lower Ordovician) carbonates in the Permian basin of west Texas. The purpose of this paper is not to dispute the model presented by Kerans, but instead to present some alternative models of reservoir occurrence that are not considered in his paper and that are also widely applicable to the Ellenburger and correlative strata in the Mid-Continent. The discussion is based on regional lithostratigraphy and subsurface mapping studies of the Ellenburger in the southern Midland basin, specifically in Irion, Reagan, Crockett, Schleicher, and Sterling counties (Texas).

Uncertainties are Better Handled by Fuzzy Arithmetic (1)

Uncertainties in the estimates of hydrocarbon volumes are traditionally given by the Monte Carlo method, which is based on classical probability theory. A new and better way to achieve the same objective is to use fuzzy arithmetic. This new math is based on possibility theory derived from fuzzy set theory. A comparison of these two approaches is given, using an example from a recent AAPG Bulletin paper. The fuzzy mathematics approach is more advantageous because, unlike the Monte Carlo method, it does not have to assume the (statistical) distributions of geologic variables, and also because of its parsimonious computations. Furthermore, this new approach has revealed that the estimates of the volumes of petroleum available for entrapment are unreliable where the ratio of he volume expelled from source rock over the volume lost during migration is near unity.

Arbuckle Source for Atoka Formation Flysch, Ouachita Mountains Frontal Belt, Oklahoma: New Evidence from Paleocurrents: ABSTRACT

In the abstract by Charles A. Ferguson and Neil H. Suneson, entitled Arbuckle source for Atoka Formation Flysch, Ouachita Mountains Frontal Belt, Oklahoma: New Evidence for Paleocurrents (AAPG Bulletin, v. 72, p. 184-185), the final sentence of the second paragraph should read, The bounding faults would be the southernmost of a series of northward-younging south-side-down growth faults. End_of_Article - Last_Page 647------------

White Rim Trail, Island in the Sky: ERRATUM

The cover photograph by Jacqueline E. Hunton for the January 1988 (v. 72) AAPG Bulletin should have read: Rim Trail, Island in the Sky. View of top of cliff-forming White Rim Sandstone (Permian) and Green River from top of Junction Butte, Canyonlands National Park, Utah. Photography by Jacqueline E. Huntoon, Pennsylvania State University, University Park, Pennsylvania. End_of_Article - Last_Page 647------------

Lateral Fluid Flow in a Compacting Sand-Shale Sequence: South Caspian Basin

The article Lateral Fluid Flow in a Compacting Sand-Shale Sequence: South Caspian Basin by John D. Bredehoeft, Rashid D. Djevanshir, and Kenneth R. Belitz (AAPG Bulletin, v. 72, no. 4, April 1988, p. 416-424) needs the following corrections. There are several typographical errors that were the author's error. Equation 2 should be EQUATION (2) Equation 3 should be EQUATION (3) Although the equations were incorrect in the article, the associated discussion and equations 4 and 5 are based upon the correct expressions, as shown above. Table 3, the calculated regional sand permeabilities, is also incorrect. The hydraulic conductivity, which in our case has the units of meters per second, was incorrectly converted to millidarcys; values in meters per second were multiplied by the standard conversion 1 m/sec equals 1.04 × 108 md. In retrospect, this conversion was a conceptual error. Table 3 should read Table 3. Calculated Regional Sand Permeabilities Acknowledgment: We appreciate the comments of Stan Lohman, who brought our attention to these errors. End_of_Article - Last_Page 1525------------

Porosity Reduction in Sandstone by Quartz Overgrowth: REPLY

In "Porosity Reduction in Sandstone by Quartz Overgrowth," by Frederic Leder and Won C. Park (AAPG Bulletin, v. 70, no. 11, November 1986, p. 1713-1728), the fluid velocities reported are low by about 35%. However, because of a cancellation of errors, the results published for porosities are correct. The following derivation should be substituted for the published text, beginning with equation 11 (p. 1716): EQUATION (11) where ^ngr = fluid viscosity and ^nablaP = pressure gradient. EQUATION (12) where EQUATION (13) Equation 14 is correct as published. EQUATION (15) Neglecting ^dgrvv ^dgrvy and ^dgrv2P ^dgrvy2 , EQUATION (16) Rearranging and integrating gives equation 17 as published. The left side of equation 18 is correct as published; the right side, however, should be: EQUATION (18) and equation 19 becomes EQUATION (19) Equations 20-22 are correct. EQUATION (23) EQUATION (24) Considering fluid velocities, equation 40 should be EQUATION (40) The subscript zero is required since ^Thgr is a function of time. Equation 42 should be EQUATION (42) and EQUATION (43) Using equation 39, [EQUATION] Therefore, substituting equation 24 into equation 19, [EQUATION] and [EQUATION] By equation 40, [EQUATION] This is the correct expression for use in calculating porosity. Equation 40, as it was published, substituted as above into the published equations 19 and 24, will produce the same equation. This fortuitous result preserves the value of the calculations; however, the derivation presented in this erratum is correct and should be used. End_of_Article - Last_Page 483------------

Hydrodynamics of Minnelusa Formation, North Powder River Basin, Wyoming: ERRATUM

William V. Maloney's abstract for the AAPG Rocky Mountain Section Meeting, Hydrodynamics of Minnelusa Formation, North Powder River Basin, Wyoming (AAPG Bulletin, v. 71, no. 8, August 1987, p. 1011), contains an error. The next to last sentence should be read as follows: Hydrocarbon migration syn/post hydrodynamics will result in the majority of hydrocarbons moving toward the area of minimum potential energy. End_of_Article - Last_Page 1439------------

Hydrodynamics of Minnelusa Formation, North Powder River Basin, Wyoming: ABSTRACT

William V. Maloney's abstract for the AAPG Rocky Mountain Section Meeting, "Hydrodynamics of Minnelusa Formation, North Powder River Basin, Wyoming" (AAPG Bulletin, v. 71, no. 8, August 1987, p. 1011), contains an error. The next to last sentence should be read as follows: "Hydrocarbon migration syn/post hydrodynamics will result in the majority of hydrocarbons moving toward the area of minimum potential energy." End_of_Article - Last_Page 1439------------

Strike-Slip Offset Along the McKittrick Fault, Western Kern County, California: ERRATUM

In the AAPG Annual Convention abstracts (AAPG Bulletin, v. 71, no. 5, May 1987, p. 533), the first sentence of Strike-Slip Offset Along the McKittrick Fault, Western Kern County, by J. R. Bowersox and Deborah M. Olson, should read as follows: Reconstructions of offset Miocene strata in McKittrick and northern Midway-Sunset fields, western Kern County, California, show about 7 mi (11 km) of post-Miocene left-lateral offset along the McKittrick fault. End_of_Article - Last_Page 1018------------

Episodic Rifting and Subsidence in the South China Sea: ERRATUM

In Ke Ru and John D. Pigott's paper, Episodic Rifting and Subsidence in the South China (AAPG Bulletin, v. 70, no. 9, September 1986), two paragraphs on p. 1147 were scrambled. Text on p. 1147 should read as follows: occurred (Tang Xin, 1980). Because Mesozoic volcanism is absent in eastern Indochina (cf., Tang Xin, 1980), the Andean-type volcanic arc would have been located off the east coast of Indochina. We endorse Holloway's (1982) interpretation of a transcurrent fault in southwest Indochina required to offset this subduction system. Kinematically, the 20° clockwise rotation of China and Indochina, and the 45°-50° counterclockwise rotation of southwest Borneo (Hamilton, 1979) are considered by fixing mainland Asia and by placing Borneo in a position about 70° clockwise from today's position. The western edge of this arc-trench system may have formed a zone of crustal weakness, which could later be reactivated during a period of tectonic extension. However, later crustal ex ension in China is not limited to the Mesozoic accretional domain, as Cenozoic extension occurred throughout eastern and southeastern China (Tang Xin, 1980; Wang, 1982; Zhang et al, 1982; Li, 1984). Late Cretaceous The first rifting episode of the South China Sea (Figure 19B) began during the Late Cretaceous with widespread volcanic activity in southeast China, the Natuna arch, and in southwest Borneo (Tang Xin, 1980; Wang, 1982). Tectonic uplift generally characterized the entire region as documented by a regional Late Cretaceous unconformity. However, in the grabens of mainland and offshore China, thick sedimentary successions record this first episode of rifting and continental crustal extension (Wang, 1982). This rifting system trended predominantly northeast-southwest, corresponding to the general strike of the numerous and widespread normal faults on the China margin. As a consequence, the direction of extension is southeasterly. By the close of the Late Cretaceous, Borneo had started its counterclockwise rotation (Hamilton, 1979) with an approximate rotation center being offshore of the southwestern tip of present-day Borneo. Owing to the joint effect of the rotation and the southeastward extension of the continental crust to the northwest, the subduction of the preexisting oceanic crust along the Lupar line of northwestern Borneo, as evidenced by ophiolite outcrops (cf., Haile, 1973; Hutchinson, 1975; Hamilton, 1979), had begun. We infer that the major strike-slip fault southwest of Indochina End_of_Article - Last_Page 119------------

Porosity Reduction in Sandstone by Quartz Overgrowth: ERRATUM

In Porosity Reduction in Sandstone by Quartz Overgrowth, by Frederic Leder and Won C. Park (AAPG Bulletin, v. 70, no. 11, November 1986, p. 1713-1728), the fluid velocities reported are low by about 35%. However, because of a cancellation of errors, the results published for porosities are correct. The following derivation should be substituted for the published text, beginning with equation 11 (p. 1716): EQUATION (11) where ^ngr = fluid viscosity and ^nablaP = pressure gradient. EQUATION (12) where EQUATION (13) Equation 14 is correct as published. EQUATION (15) Neglecting ^dgrvv ^dgrvy and ^dgrv2P ^dgrvy2 , EQUATION (16) Rearranging and integrating gives equation 17 as published. The left side of equation 18 is correct as published; the right side, however, should be: EQUATION (18) and equation 19 becomes EQUATION (19) Equations 20-22 are correct. EQUATION (23) EQUATION (24) Considering fluid velocities, equation 40 should be EQUATION (40) The subscript zero is required since ^Thgr is a function of time. Equation 42 should be EQUATION (42) and EQUATION (43) Using equation 39, [EQUATION] Therefore, substituting equation 24 into equation 19, [EQUATION] and [EQUATION] By equation 40, [EQUATION] This is the correct expression for use in calculating porosity. Equation 40, as it was published, substituted as above into the published equations 19 and 24, will produce the same equation. This fortuitous result preserves the value of the calculations; however, the derivation presented in this erratum is correct and should be used. End_of_Article - Last_Page 483------------

Paleogeographic and Sedimentologic Significance of Mississippian Sequence at Mt. Darby, Wyoming: ABSTRACT

AAPG Bulletin, v. 69, no. 5 (May 1985), Rocky Mountain Section abstracts. Add two co-authors, D. W. Boyd, Univ. Wyoming, Laramie, WY, and W. J. Sando, USGS, Washington, D. C., to abstract by Jeff DeJarnett, Paleogeographic and Sedimentologic Significance of Mississippian Sequence at Mt. Darby, Wyoming. End_of_Article - Last_Page 1042------------

Mosquitia Trip — February 1960

Snyopsis During the turbulent times of the Bay of Pigs invasion of Cuba, the authors made an extended trip into the jungles of the Mosquitia Territory located on the Caribbean Coast of Honduras and Nicaragua. No aerial photos or maps were available for the region, so we made a 190-mile traverse, largely on foot, using the pace-compass method. The trip resulted in mapping the updip exposed Cretaceous carbonates of the Mosquitia Basin in a reconnaissance fashion and, most important, gaining an understanding of the Mesozoic stratigraphy of the region. The results were published in two articles in the AAPG Bulletin. The story here is more about the personal adventures of the two geologists while making the arduous trip during a politically dangerous time in this part of the world. In addition to Fer-de-Lance snakes and Jaguars, the authors encountered the Nicaraguan Army which was very sensitive to intruders from Honduras during their preparation, a short distance down the Coast at Puerto Cabezes, for the Bay...

Metallic Sulfide Deposits in Winnfield Salt Dome Louisiana ...: ERRATUM

AAPG Bulletin (September 1984), v. 68, no. 9, p. 1221, first column. Abstract, Metallic Sulfide Deposits in Winnfield Salt Dome Louisiana. . ., by Mark R. Ulrich, should include the additional authors, J. Richard Kyle and Peter E. Price. End_of_Article - Last_Page 1931------------

Introduction to Stratigraphy, Structure, and Geologic Problems in Big Horn Basin, Wyoming and Montana: ABSTRACT

End_Page 1342------------------------------As the cumulative production of oil from the Big Horn basin approaches the 2 billion bbl mark, it is appropriate that we look at the geology once again. The Big Horn basin, located in northwestern Wyoming and south-central Montana, is bordered on the east by the Big Horn Mountains; on the south by the Owl Creek Mountains; on the west by the Absaroka and Beartooth Mountains; and on the north by the Nye-Bowler lineament. The combination of a great reservoir-source duet in the Paleozoic rocks and the creation of large anticlines during the Laramide orogeny has been the key to the Big Horn basin's success as an oil producer. Stratigraphy of the Big Horn basin can be divided generally into (1) the Middle Cambrian clastics, (2) the Paleozoic shelf carbonates, (3) the Mesozoic clastics, (4) the Late Cretaceous to Tertiary synorogenic clastics, and (5) the Tertiary post-orogenic clastics and volcanics. By far the most economically important formations have been the Permian Phosphoria and Pennsylvanian Tensleep Formations. This dynamic duo consists of porous eolian and shallow marine, quartz sandstones of the Tensleep overlain by shallow marine, oil-rich carbonates of the Phosphoria. The two have combined to produce over 1.5 billion bbl of oil in the Big Horn basin alone. The draping of the Tensleep and Phosphoria over large Laramide structures (closures of over 5,000+ ft, 1,500 m, and areal extents up to 15 mi2, 40 km2) was the final key. An upcoming afternoon session of papers will explore the proposed anatomies and mechanisms of folding in the Cordilleran foreland. There is a controversy over the morphology of the folds in the foreland. Put simply, there is some disagreement over how much the horizontal or thrusting component contributes to these folds. Stearns, who described the fold at Rattlesnake Mountain in the 1971 Wyoming Geological Association guidebook, favors drape folding over near-vertical faults in the Precambrian. Berg in the 1962 AAPG Bulletin and Gries in the 1983 AAPG Bulletin favor a more thrusted model with reverse fault planes dipping 60° to 30°. Sales in the 1968 AAPG Bulletin agrees with the morphology of Berg and Gries, but feels that the folds in the foreland were generated by faults with strong lateral components. Concerning other problems, Stone in the October 1967 AAPG Bulletin pointed out that the Paleozoic reservoirs often have a common oil-water contact (OWC) within individual structures. He attributed the common OWC to fractures joining the reservoirs. The OWC is commonly tilted; this he attributed to hydrodynamic flow. An understanding of fractures and tilted oil-water contacts is imperative for successful exploration and production programs in the Big Horn basin. End_of_Article - Last_Page 1343------------

Selected Structural Basins of the Midcontinent, USA: ERRATUM

AAPG Bulletin, v. 67, no. 9 (September 1983), p. 1484. Review of Selected Structural Basins of the Midcontinent, USA, edited by Paul Dean Proctor and John W. Koenig. Corrected address: Department of Geology, 208 Norwood Hall, University of Missouri-Rolla, Rolla, Missouri 65401. Corrected price: $7. End_of_Article - Last_Page 2160------------

Middle East: Stratigraphic Evolution and Oil Habitat: DISCUSSION

The paper, Middle East: Stratigraphic Evolution and Oil Habitat, by R.J. Murris (AAPG Bull. v. 64, p. 597-618) is discussed. Problems with the time-stratigraphic units used in the article are pointed out, along with the source rocks of the petroleum deposits, the depositional cyclicity, subsidence and sea level fluctuation, and the Middle East geosyncline. (JMT)

Geology of New England Passive Margin: ERRATUM

AAPG Bulletin, April 1980, v. 64, no. 4, Geology of New England Passive Margin, by James A. Austin, Jr., et al. The captions for Figures 19-23 were incorrectly positioned. Figure 19 should have the Figure 23 caption, Figure 20 the Figure 19 caption, Figure 21 the Figure 20 caption, Figure 22 the Figure 21 caption, and Figure 23 the Figure 22 caption. We regret the error. End_of_Article - Last_Page 1124------------

Resource Appraisal Predictions and Exploration Performance--Case Studies for Onshore United States: ERRATUM

AAPG Bulletin, March 1979, v. 63, no. 3, p. 511. Corrected abstract by Richard B. Powers. POWERS, RICHARD B., U.S. Geol. Survey, Denver, Colo. Resource Appraisal Predictions and Exploration Performance--Case Studies for Onshore United States Geologic estimates of undiscovered recoverable oil and gas resources in the United States were published in U.S. Geological Survey Circular 725 in mid-1975, based on data through 1974. In the 1975 study, 47 onshore provinces, included within 11 regions, were evaluated. Three of these geologic provinces, (1) West Texas-Eastern New Mexico, (2) North Slope, Alaska, and (3) the Overthrust belt of Idaho-Utah-Wyoming, were selected as case studies to show the relation between the 1975 resource assessments and subsequent exploration results. U.S. Geological Survey resource estimates for the maturely explored West Texas-Eastern New Mexico province range from 4 to 14.4 billion bbl of oil and 35 to 100 Tcf of gas, based on the 95% and 5% probability percentiles. Exploration wildcat drilling from 1975 through 1977 resulted in more than 417 oil and gas discoveries, mainly of small field size. Exploration results in this province, based on finding-rates and the amounts of oil and gas discovered, do not appear to have met the resource predictions. Resource estimates for the immaturely drilled North Slope province range from 5 to 16 bbl of oil and 14 to 49 Tcf of gas. About 30 wildcats were drilled from 1975 through 1977, resulting in 3 successful oil or gas wells. Two oil discoveries appear to be in the >50 million-bbl field-size (A class). Resource predictions appear to have been met or exceeded for the North Slope, based on this recent exploration performance. Estimates of resources for the Overthrust belt, the most recently successful of the three provinces, range from 0 to 0.2 bbl of oil and 0 to 1.1 Tcf of gas. Thirteen gas and oil fields were discovered out of 64 total wildcats drilled from 1975 through 1978; at least five of which are estimated to be of A field-size class or greater. Exploratory performance to date has exceeded the earlier resource estimates in the Overthrust belt. End_of_Article - Last_Page 1148------------