Basin In New Mexico Research Articles

Estimation of uranium endowment by subjective geological analysis; a comparison of methods and estimates for the San Juan Basin, New Mexico

This study investigates how estimates of uranium endowment made by a geologist using an appraisal system that is based upon a formalization of geoscience and decision rules compare with estimates made by informal and unconstrained intuitive processes. The motivation for this study derives from the premise that formalization of decisions would mitigate the heuristic biases and hedging that may result from the use of unconstrained intuitive processes. Estimates of the uranium endowment of the San Juan Basin of New Mexico by four methodologies are compared in this study. These methods, ranked from top to bottom by degree of decomposition (mitigating of heuristic bias)and control on hedging, are as follows Implicit 2 1.5 × 106 s.t. of U3O8 Implicit 1 1.6 × 106 s.t. of U3O8 NURE (1980) 2.4 × 106 s.t. of U3O8 Appraisal system 3.9 × 106 s.t. of U3O8The magnitude of expected uranium endowment estimated by these methods, ranked from smallest to largest, is in this same order. With the exception of the NURE estimates, the magnitude of the variance (uncertainty)of uranium endowment, ranked from smallest to largest, also is in this same order. These results prompt the suggestion that the more decomposed and formalized the estimation procedure, the greater the expected value and the variance of uranium endowment. Equivalently, predicating U3O8endowment estimation strictly upon that part of the geologist's geoscience that is useful in making U3O8endowment estimates and upon his understanding of the region's history produced larger estimates than have previously been reported. However, this method of estimation also shows that uncertainty about the actual state of U3O8endowment is much greater than previously described.

Gas Recovery From Tight FormationsA Function of Technology and Economics

Summary Three major findings emerge from the study of the technology and economics of recovering natural gas from tight gas formations.1. A minimum threshold price, near $3.00/Mcf (in mid-1977 dollars) and equivalent to approximately $4.50/Mcf (in mid-1981 dollars), is required to make the tight gas resource attractive for investment.2. Beyond the threshold price, improvements in technology have a greater impact in terms of gas recovery than further increases in gas prices.3. The combination of increased gas prices and improved recovery technology provides the most effective means for accelerating production from this vast domestic natural gas resource - calculated at more than 400 Tcf in place.The technology improvements that have the largest impact on ultimate recovery are (1) improved ability to identify the net pay and characterize the reservoir, (2) capacity to stimulate multiple reservoirs from a common wellbore, (3) increased effective fracture length, (4) ability for fractures to intersect sand lens beyond the wellbore, and (5) optimization of field development. Background Large quantities of natural gas exist in tight (low-permeability) formations where the gas flow is too low for economical recovery by means of conventional technology. The basins containing these formations stretch westward from the Cotton Valley trend in Louisiana, through Texas, to the Uinta basin of Utah, and north through the northern Great Plains, crossing the border into Canada (Fig. 1). Declining natural gas production, higher gas prices, and new recovery technologies have focused interest on these resources.In the late 1960's and early 1970's, three attempts were made to stimulate tight formations by nuclear stimulation. Disappointing results ended the nuclear tests.In 1972, massive hydraulic fracturing (MHF) using volumes of fluids and proppants an order of magnitude or more larger than conventional was proposed. As a consequence, a joint government/industry test of MHF was conducted in the Piceance basin in 1974. The results of this test demonstrated that improvements could be achieved in the rate of gas flow. Since that time, MHF technology has been used widely in low-permeability but otherwise geologically favorable settings such as the Wattenberg field (north of Denver), the San Juan basin of New Mexico, and the Cotton Valley trend in east Texas and northern Louisiana.Despite the work to date, challenges posed by difficult geological settings - especially of the deep, tight, lenticular gas pays - have yet to be overcome. Even in the more geologically favorable basins - in the higher permeability and blanket type deposits fundamental improvements in recovery technology need to be pursued. Purpose and Methods This paper examines how improved technology and economics together can accelerate the contribution of the tight gas formations to U.S. energy supply. Overall results are presented for 13 tight gas basins for two levels of technology and three levels of economic incentives (represented by gas prices, although other incentives could be substituted). This is followed by a sensitivity analysis of specific technology improvements. JPT P. 1545^

Mammalian Biochronology of Late Cenozoic Basins of New Mexico: ABSTRACT

The remains of fossil mammals have been collected from the late Cenozoic basins of New Mexico since the middle of the last century. Intensive work in the northern Albuquerque and Espanola basins in this country has resulted in large collections whose lithostratigraphic context has recently been published. Work on the biochronologic significance of these fossils has revealed that these thick basinal deposits preserve a record of the succession of mammalian faunas covering nearly the entire span of Miocene time. The record in each basin is not completely synchronous, but overlaps sufficiently so that the composite succession will eventually yield an important biostratigraphic standard for southwestern North America. It is possible to correlate this faunal succession and many other scattered fossil mammal occurrences within New Mexico with the geochrons of the North American Mammal Ages. Such correlations can be calibrated with a maximum precision of 1-2 m.y. and are thus of significance to historical geology. Geochronologically important fossil mammal remains are known in most of the late Cenozoic basins of New Mexico, but many of these have either gone unrecorded or have not been critically examined. Examples are: late Miocene through early Pleistocene successions in basins drained by the Gila River; early Miocene mammals from the northern Black Range; the Pliocene and Pleistocene faunas of the basins drained by the Rio Grande from Albuquerque south to the border; and early Miocene mammals from re-Santa Fe Group rocks in the Espanola basin. End_of_Article - Last_Page 571------------

Upper Cretaceous Tocito Sandstone Lentil of Mancos Shale, San Juan Basin, New Mexico--Is There Any Oil Left?: ABSTRACT

The Upper Cretaceous Sandstone Lentil of the Mancos Shale consists of a series of northwest-trending linear sandstone bodies in the San Juan basin of New Mexico. This sandstone unit, which has produced most of the basin's crude oil (more than 125 million bbl to date), was referred to as the Sandstone for many years. Recent stratigraphic studies of the by several authors clearly demonstrated that the Sandstone Lentil is a totally different stratigraphic unit from the Gallup; thus, the name was reinstated as a lentil of the Mancos Shale. (Actually, the Tocito was thought to be part of the Gallup years ago and the name was dropped in favor of the name.) Even though hundreds of holes drilled to produce natural gas from th deeper Dakota Sandstone have penetrated the Tocito, these holes cannot be thought of as dry holes because, for many of them, no attempt was made to test the for its possible oil potential. There is still a good chance that significant amounts of oil remain to be found in the Tocito. End_of_Article - Last_Page 559------------

Mammalian biochronology of the late Cenozoic basins of New Mexico

Late Cenozoic mammalian remains have been collected from New Mexico for more than a century. The most important nineteenth-century collections came from the Espanola Basin. Work in this century has continued to focus mainly on the Miocene faunas in that basin and the northern part of the adjoining Albuquerque basin. The lithostratigraphy of these basins has recently been reviewed and revised, but the description of the large collections of fossil remains from the basinal deposits is largely incomplete. Pliocene and early Pleistocene faunas have been found in deposits that mark the development of external drainage of the major rivers of the state. Study of these assemblages has been cursory, although the lithostratigraphy of these deposits has received considerable attention in recent years. The Miocene basinal deposits accumulated under conditions of internal drainage in local structural environments that led to the development of partly synchronous depositional records. Biostratigraphies worked out in each basin overlap sufficiently so that the composite succession forms an important biochronological standard for southwestern North America. The Espanola and Albuquerque-Belen basins contain the only Miocene faunas of importance presently known in New Mexico. Their fossil records complement one another in that the northern Albuquerque basin has the only adequate representation of the early Miocene and the Espanola basin a more complete record of the medial and late Miocene. Synchronous faunas in these basins show a high degree of taxonomic resemblance extending to elements that represent endemic taxa or forms rare elsewhere. Compared with coevel assemblages in the Great Plains, there is considerable generic and specific similarity. This allows easy reference of the New Mexican faunal succession to the sequence of North American mammal ages that are essentially typified by the Great Plains biochronology. In addition to these taxonomic relationships, the New Mexican faunas retain throughout the Miocene characters that may typify a southwestern faunal province. The general features of the latter would include diverse and abundant artiodactyls, especially Camelidae, including a late occurrence of endemic stenomyline genera, and less diverse and abundant perissodactyls, especially horses, when compared with the Great Plains. The fossil vertebrate record of Pliocene and early Pleistocene time in New Mexico is largely confined to the basins of the Rio Grande and the Gila River and is derived from deposits of the axial rivers that were the percursors of the modern streams and from the piedmont slope facies of the basin margins. Sites scattered along the length of the Rio Grande rift from the Santo Domingo basin near Santa Fe south to the international border have yielded Blancan and early Irvington faunas. These assemblages can be arranged in temporal order from their position in local stratigraphic columns, from their biological affinities, and with respect to dated basalts and ashes interbedded in the sediments containing the fossil remains. Important reference sequences are available in adjacent Arizona and Texas, where mammalian faunas and calibrated biochronologies compare closely with those in New Mexico. The New Mexican record supports the southwestern biochronology for Pliocene and early Pleistocene time, including the following events and their calibration: the last appearance of hipparionine horses ( Nannippus ) and the first appearance of the South American immigrants, the glyptodont Glyptotherium and probably the mylodontid sloth genus Glossotherium , were nearly synchronous events close to the Gauss-Matuyama boundary (2.5 m.y. B.P.); at least three species Equus were present in the Southwest by the time of the Nannippus extinction; the first appearance of the Asiatic immigrant Mammuthus in the southwest between 1.2 and 1.4 m.y., postdating the Olduvai Event and, by definition, indicating that the Blancan-Irvingtonian boundary, at least as determined for the Southwest, lies close to the beginning of medial Pleistocene time.

Cenozoic continental deposits of New Mexico: An overview

Cenozoic rocks of New Mexico are wholly continental in origin and contrast markedly with most pre-Cenozoic deposits. Extensive stratigraphic and paleontologic work facilitates correlations and paleoenvironmental reconstructions; less extensive sedimentologic and petrologic studies allow detailed reconstructions of dispersal patterns and provenance locally. The accompanying papers summarizing recent research on the Cenozoic of New Mexico provide many new insights concerning paleontology, sedimentology, stratigraphy, and tectonics. The Cenozoic history of New Mexico can be divided into three phases on the basis of plate-tectonic events affecting the southwestern United States and styles of deformation, magmatism, and sedimentation in local areas. The Paleocene and Eocene were characterized by amagmatic basement deformation (Laramide orogeny), resulting in complex uplifts and basins, followed by widespread beveling. Massive outpourings of intermediate to silicic volcanics characterized much of the state during the Oligocene. The Neogene (Miocene to Holocene) has been characterized by extensional tectonics and bimodal volcanism, best expressed by the Rio Grande rift. Local sedimentary and paleontologic histories of the numerous Cenozoic basins of New Mexico reflect these regional tectonic processes.

Taxonomy and biostratigraphy of the early Tertiary Taeniodonta (Mammalia: Eutheria): Summary

The Taeniodonta is an order of archaic mammals known exclusively from the lower Tertiary of western North America (Schoch and Lucas, 1981a). Their remains are found in Puerean (lower Paleocene) to Uintan (upper Eocene) strata of the Rocky Mountain intermontane sedimentary basins (Figs. 13, 14; Table 12). In the San Juan basin of New Mexico and Colorado, the Puerean to Wasatchian (lower Eocene) sedimentary sequence includes the type localities for the Puerean, Torrejonian (middle Paleocene), and Tiffanian (late Paleocene) land mammal “ages” (Wood and others, 1941) as well as a classic Wasatchian fauna (Lucas and others, 1981). Thus, the San Juan basin mammalian faunas provide a sequence of faunas which can provide the basis for interbasinal correlation. The Taeniodonta are an important element of these faunas; many of: the type specimens and important referred specimens of these animals come from the San Juan basin. However, except for Patterson9s (1949b) brief review, a comprehensive study of this order has not been published for more than 80 years (Wortman, 1897b). Before a group of animals can be used, biostratigraphic correlation, its species- and genus-level taxonomy, and its known stratigraphic occurrences must be well established. In this paper, I revise the species-level taxonomy of the Taeniodonta and document their geographic and temporal (stratigraphic) distribution and I discuss their usefulness and implications for biostratigraphic correlation in western North America. SCope And Methods In this paper, I undertake a complete taxonomic revision at the genus- and species-level of the Taeniodonta based on the majority of the known specimens. The suprageneric classification and phylogeny of the taeniodonts is not considered here. Taxonomic judgments are made solely on the basis of morphology; extrinsic stratigraphic and geographic data, although recorded and considered important, are not used to define taxa.

Four Corners-Intermountain Area

Exploratory drilling in the Four Corners-Intermountain area increased sharply in 1980, with 220 wells drilled. Drilling activity was up in all states. A total of 62 successful wells were completed, yielding a success rate of over 28%, up from 26% in 1979. Total exploratory footage drilled was up nearly 24% from 1979, with 1,103,356 ft drilled in all exploratory categories. Development drilling increased 15% from 1979, with 1,103 holes drilled, most of which were in the San Juan basin, as in previous years. The region's most significant discovery was in the overthrust belt of northern Utah, where the Amoco 1 Bountiful Livestock flowed 4 mmcf gas/d and 1,054 bbl/d from the Jurassic Nugget Sandstone to open up the Anschutz Ranch East field. Amoco also drilled the Cave Creek ield discovery well, the 1 Fawsett and Sons, with initial production of 40 mmcf gas/d and 681 bbl condensate/d from commingled Mississippian, Pennsylvanian, and Permian reservoirs. In southeastern Utah, Wexpro Company opened the Bug field with the 1 Bug well that flowed 608 bbl/d and 1,128 mcf gas/d from the Middle Pennsylvanian Desert Creek pay (Paradox). By year's end, Bug field had five producing wells. One new gas field was discovered in the Uinta basin of Utah and one in the eastern San Juan basin of New Mexico. There were no discoveries in Arizona or Nevada. New drilling depth records were set in Nevada, northern New Mexico, Utah, and Arizona. Exploratory and development drilling trends indicate that activity will remain high in the area for 1981.

Westwater Canyon Member of Morrison Formation: Is it Really One Fan?: ABSTRACT

Three distinct fluvial packages can be recognized within the Westwater Canyon Member along the west side of the San Juan basin in New Mexico. Two of the fluvial packages (lower and upper) persist to the east and can be recognized as far east as Laguna. The middle fluvial package is as thick as the lower and upper on the west side of the basin but thins rapidly to the east; fluvial sandstones cannot be recognized in this interval east of the Gallup area. Cross-bedding studies show that streams of the lower package flowed east-northeasterly, whereas streams of the middle and upper packages flowed generally easterly and southeasterly. Volcanic pebbles are present in abundance only in the middle package. Isopach maps of each separate package, together with maximum pebble-size data, show that major fluvial axes shifted through time. Northeasterly flowing streams of the lower fluvial package had two distinct lobes. One lobe, centered near Thoreau, apparently traversed the area of the present-day Zuni uplift, and the other lobe was centered northwest of the Gallup sag, near Asaayi Lake. The easterly and southeasterly flowing streams of the middle and upper fluvial packages dropped their coarsest bed-load material just east of the Defiance u lift as they entered the basin from the west. Farther east the middle unit changes facies rapidly and loses its fluvial character. The upper package maintains its fluvial character, but contours for maximum pebble size for this interval widen considerably in an eastward direction, suggesting a more constant energy level as the streams traversed the basin. Results of these studies are not compatible with the concept of one fan emanating from the southwest, as has been proposed by previous workers. Separating the Westwater Canyon into discrete packages and treating them separately eliminates the need to have streams enter from the southwest, turn, and then flow southeasterly in the vicinity of the mineral belt. Both northeast and southeast paleocurrent directions occur in the Westwater Canyon, but in different parts of the member. End_of_Article - Last_Page 1502------------

Early Precipitation of Authigenic Clay by Meteoric Water, Pictured Cliffs, San Juan Basin, New Mexico and Colorado: ABSTRACT

The Pictured Cliffs, which is exposed around the San Juan basin in New Mexico and Colorado, was deposited in a variety of nearshore environments during the last of a series of major regressions of the Cretaceous epicontinental seaway. The Pictured Cliffs is a prolific producer of natural gas. The permeability of the Pictured Cliffs sandstones decreases from the southwest to the northeast, apparently in response to a progressive increase in the amount of authigenic grain-coating clay to the northeast. Gas-production trends are oriented parallel to depositional strike and cut across present-day structure contours. Thus, it appears that most of the authigenic clay was precipitated before the formation of the San Juan Basin. Oxygen and hydrogen isotopic analyses of eight samples from different parts of the basin suggest strongly precipitation of the clays by meteoric water. The early precipitation of authigenic clay in marine sandstone by meteoric water has not been previously described. However, there are significant differences between the Cretaceous Western Interior basin and marginal basins such as the Gulf Coast basin which might help explain this occurrence. The highest rates of sedimentation and subsidence in the Cretaceous Western Interior basin were near the adjacent highlands, resulting in the stratigraphic rise of the marine sandstones toward the basin. Also, marine End_Page 1683------------------------------ shales constitute less than half of the thickest part of the basin fill. Thus, compactional fluids were possibly less significant diagenetically than in the Gulf Coast basin. These factors may have contributed to the development of a regional flow system in which large volumes of meteoric water moved basinward through the marine sandstones. End_of_Article - Last_Page 1684------------

Some additional economic aspects of ground water resources and replacement flows in semi-arid agricultural areas

Abstract This article considers some aspects of the integrated model of the demand function for irrigation water with a hydrologic model of a one-cell-aquifer. A comparison between an optimal control and free market is carried out. The issue of the optimal time for introducing imported water to the aquifer is also considered. The results are empirically applied to the Pecos Basin in New Mexico.

San Juan Basin of New Mexico and Colorado, Classic Area of Stratigraphic Exploration: ABSTRACT

The San Juan basin of northwestern New Mexico and southwestern Colorado is a Laramide structural basin with a maximum thickness of 15,000 ft (4,572 m) of Paleozoic to Eocene sedimentary rocks. The basin is elongate north-south, approximately 125 × 100 mi (201 × 161 km); it is structurally asymmetrical, with the deepest part in the north near the New Mexico-Colorado line. Monoclinal basin rims are especially prominent. Petroleum occurs in Pennsylvanian carbonate rocks, End_Page 761------------------------------ Jurassic eolian sandstones, but predominantly in Cretaceous sandstones and fractured shales. The San Juan basin is gas-prone, although significant oil fields are common. The Cretaceous Blanco basin gas field is one of the largest in the United States. The key to exploration in this mature area lies in understanding the complex stratigraphy that controls most of the traps. The San Juan basin area was a part of larger depositional basins prior to the Laramide orogeny. Major sedimentation in the area began during the Pennsylvanian with deposition of shelf-carbonates and flanking arkosic clastics from Ancestral Rocky Mountain uplifts. Regression during the Permian resulted largely in nonmarine clastic deposition. Triassic fluvial red beds were deposited across the area after an erosional interval. After another erosional interval, Jurassic nonmarine clastics and restricted limestones and evaporites were deposited. During the Cretaceous, the sea returned and repeatedly transgressed and regressed across the basin, producing well-developed depositional cycles. Laramide uplift around the San Juan basin during latest Cretaceous and earliest Cenozoic time produc d the structural basin which became partly filled with Paleocene and Eocene nonmarine clastics. End_of_Article - Last_Page 762------------

Detection of Hydraulic Fracture Orientation And Dimensions in Cased Wells

A promising technique for recovering gas reserves combines large hydraulic fractures with multiple-zone completions in a single well. An accurate knowledge of the dimensions, orientation, and spatial characteristics of the fractures is needed. This paper reports research on the use of large hydraulic fractures and multiple completions conducted in conjunction with projects for detecting and measuring fracture dimensions and orientation. projects for detecting and measuring fracture dimensions and orientation. Introduction The need for the nation to expand its natural gas reserves has become increasingly apparent to both the industry and the layman in recent years. Considerable gas in place exists in several Rocky Mountain sedimentary basins in tight reservoirs that are not now included in the nation's reserves because of a lack of means to economically recover this gas. Fig. 1 shows the location of some of the more predominant sedimentary basins in the mountain area of the west. A recent national study estimates that the nation's recoverable natural-gas reserves could be doubled if economic means could be developed to recover about half the gas from the tight sandstones in the Green River, Uintah, and Piceance Basins alone. Many of these potential reserves are contained in large vertical intervals up to 4,000 ft thick. One of the promising techniques for recovering this gas combines promising techniques for recovering this gas combines the use of large hydraulic fractures and multiple-zone completions in a single well. For example, economic completion of a well in the northern Green River Basin may require hydraulic fracturing of more than 100 individual pay sands in a single well in up to 10 completion stages. One proposal would require 8 million gal of fracturing fluid and 15 million lb of sand proppant for a single well. Propped fractures would extend about 1/2-mile from the wellbore. Economic development of such a gas reservoir using these fracturing techniques will require an accurate knowledge of the dimensions, orientation, and spatial characteristics of the fractures. Well spacing must be correlated with fracture orientation to minimize interference of drainage patterns and, thus, maximize economic-recovery potential. Fracture dimensions and spatial characteristics are the key to understanding reservoir exposure and production characteristics. The completion of gas wells in these tight sands will require casing to insure well integrity and to minimize production problems. However, the use of casing limits production problems. However, the use of casing limits the usefulness of the standard tools for defining fracture properties. Casing prevents the use of impression properties. Casing prevents the use of impression packers to determine fracture height and orientation and packers to determine fracture height and orientation and severely limits sonic and electromagnetic techniques. Temperature and radioactivity tools do work at only slightly reduced efficiencies. Even in uncased wells, the plane and direction of a hydraulic fracture can be directly observed only at the wellbore with standard techniques. What is needed is a means to measure the dimensions and orientation of the induced fracture over its entire area. El Paso Natural Gas Co. is presently conducting research in the use of large hydraulic fractures and multiple completions in the Pinedale Unit in the northern Green River Basin. In conjunction with this effort, research projects implemented by El Paso, Sandia Laboratories, and Globe Universal Sciences have the goal of detecting and measuring fracture dimensions and orientation. Exploratory experiments also have been performed in the San Juan Basin in New Mexico. These performed in the San Juan Basin in New Mexico. These sites are shown in Fig. 1. This paper is a progress report on these fracture-detection efforts. P. 1116

EXAMPLES OF THE EFFECT OF SOURCE AND RECORDING SITE PARAMETERS ON THE SEISMIC RESPONSE OBSERVED FROM PLOWSHARE PROJECTS, GASBUGGY AND RULISON

The amplitude and frequency composition of the seismic motions observed over a wide geographic area from Gasbuggy and Rulison, two Plowshare detonations, illustrates the effect which source and recording site parameters have on the resultant ground motion. Gasbuggy (29 kt) and Rulison (40 kt) were detonated, respectively, in the San Juan and Piceance Creek sedimentary basins of New Mexico and Colorado. Because both detonations were emplaced in sedimentary formations to stimulate the flow of natural gas, these detonations were placed at a greater depth of burial than typically required for containment. The effect of source parameters (device depth of burial and energy release) was simulated by seismic scaling theory. This theory (based on an extension of Sharpe’s problem) predicted a smaller elastic radius and, consequently, higher dominant frequency of generation for the elastic waves than would be expected on the basis of Nevada Test Site experience with typically contained events of 29 and 40 kt. Observed effects of the source variables were displayed in the Gasbuggy and Rulison seismic data: (1) a shift of the frequency of maximum spectral response to the high frequency end of the spectrum and (2) enhancement of the peak vector surface particle accelerations and velocities and a decrease in the peak vector surface particle displacements. Some of the Rulison recording sites were located on thin (50 ft thick or less) layers of alluvium which, on the basis of refraction surveys, exhibited a fairly significant contrast in acoustic impedance relative to that of the underlying sedimentary rocks. The effect of the lowvelocity alluvium layers at recording sites of interest was simulated by amplitude amplification modeling (based on the Haskell‐Thompson matrix formulation) using interpreted data from refraction surveys to define the layer physical parameters. These calculations indicated that significant local frequency‐dependent amplification would occur at some locations in the Piceance Creek Basin, a prediction which was verified by the seismic data.

GASBUGGY SEISMIC SOURCE MEASUREMENTS

Gasbuggy, a 29‐kt nuclear experiment, was detonated December 10, 1967, at a depth of 4240 ft in the San Juan Basin in New Mexico. Its purpose was to develop techniques for stimulation of natural gas production from tight gas‐bearing formations. Data from four subsurface instrument stations in a boring 1500 ft from Gasbuggy indicated formation of a spherical cavity of 88 ft radius and a microfracture radius of about 480 ft. The mean peak value of reduced displacement potentials which defined the seismic source was [Formula: see text]. Calculations indicate that about 2 percent of the energy released remained in the seismic source at 1500 ft. Data from surface motion instruments distributed between surface zero and 8400 ft were similar to those observed above any other contained nuclear explosions. Spalling was indicated at all surface stations. Transient vertical displacements indicate a mound about 6.7 inches high near surface zero and extending through the most remote station where uplift was 0.3 inch.

Measurement of Vertical Groundwater Velocity from Temperature Profiles in Wells

Vertically moving groundwater transports heat by convection and causes curvature in the earth's thermal profile. Dimensionless plots of the temperature distribution in wells can be matched with published type curves to obtain solutions for vertical groundwater velocity, if the thermal conductivity of the solid‐fluid complex is known or can be estimated. Rates of upward movement through semiconfining beds determined from temperature studies in the San Luis valley of Colorado and the Roswell basin of New Mexico were in good agreement with rates computed from pumping tests and water budget methods. Limitations of the method result from instability in borehole fluids, measurement detail required, and magnitudes of flow that can be detected.

Optimal Use of Coupled Leaky Aquifers

Aquifers enclosed or confined by sediments that impede or retard the vertical movement of groundwater generally leak. A stochastic dynamic programing model for the optimal operation of a composite system of two coupled leaky aquifers and a surface water subsystem is formulated and applied to the Roswell basin in New Mexico. The optimal operating policies for the two coupled aquifers of the basin are influenced by the values added to the basin by different crops, by the amounts of water in storage in the two aquifers, by the discount factor, and by mutual leakage of the aquifers. Some of these factors tend to increase whereas others tend to decrease the operating policy. The resultant of all these factors determines the final operating decision rule. The magnitude and direction of leakage are determined by the relative storages in the aquifers. Coupled aquifer systems should be considered for conjunctive use only.

Developments in Four Corners-Intermountain Area in 1967

The number of exploratory wells drilled in the Four Corners-Intermountain area during 1967 continued to decline, a trend that has persisted for several years. This decline was greatest in northern New Mexico. Oil discoveries in Utah's Uinta basin and in northeastern Arizona, and a gas discovery in the Salt anticline region of southwestern Colorado, should help to reduce this decline during 1968. Development drilling also decreased during 1967 in all parts of the area except Arizona. The largest decrease was in the San Juan basin of New Mexico followed by the Uinta basin in Utah. Increased leasing activity noted during 1967 should result in an increase of exploratory drilling during 1968, particularly in the Uinta basin, on the Defiance uplift, and throughout the Salt anticline region.

Developments in Four Corners-Intermountain Area in 1966

Exploratory drilling in the Four Corners-Intermountain area was considerably reduced from 1965. Activity was recorded in all major basins of the area, and 2 significant discoveries were made in Utah. These were the Bridger Lake and Indian Ridge discoveries. Development drilling increased in every state but Nevada. The San Juan basin in New Mexico and the Uinta basin in Utah showed the largest increase. Exploratory and development drilling is expected to be equally active in 1967. The north flank of the Uinta Mountains, and the northwest corner of Arizona, particularly, should receive much attention.

Geologic History Of Piceance Creek-Eagle Basins

The Eagle basin occupies a part of the Maroon trough that began to develop in Early Pennsylvanian time. The trough extended across northwestern Colorado and was bounded by the positive elements of the ancestral Front Range uplift on the northeast and the Uncompahgre uplift on the southwest. The early sediments are clastics, carbonates, and evaporites deposited during cyclic marine transgressions and regressions in the narrow trough. The evaporites are of the basin-center type according to Sloss (1958), but are strongly affected by contemporaneous clastic deposition. The growth of the Front Range in Morrowan time and the uplift of the Uncompahgre in Desmoinesian time contributed large volumes of clastic sediments to the trough during the regressions; these sediments are in erbedded with the evaporites. The coarse clastics from the ancestral Front Range and Uncompahgre uplift continued to influence strongly the sedimentary types of the Maroon basin throughout Triassic and Jurassic deposition, the predominant type being redbeds. In Cretaceous time, the area was inundated by a sea in which the sediments being deposited were black shale, marine sandstones, bars, and beach deposits. During Late Cretaceous time, the entire basin became a shallow sea with paludal and lagoonal sediments, including coal, shale, and underclay that were interbedded with shoreline sandstones in response to fluctuations of the sea. Some of the older structural features, such as the Douglas Creek arch, as well as the Uncompahgre uplift, began to influence sedimentation during Late Cretaceous time, as evidenced by thinning in the Mancos Shale over the arch. After prolonged sedimentation, the Eagle basin was uplifted at the end of Mesozoic time, and folded and faulted during the Laramide orogeny. The Sawatch Range, White River uplift, and the Uinta Mountains came into being in successive stages of the orogeny, and separated the Maroon basin into the present tectonic basins, namely, the Piceance basin, Carbondale basin, Axial basin, Coyote basin, and Sand Wash basin. Many of the present-day structural features were formed during the long period of orogeny from Late Cretaceous to early Tertiary time. The types of sediments have been very important in determining the reservoirs for the accumulation of oil and gas after the Laramide orogeny. Virtually all of the oil and gas in the Paleozoic in the Eagle basin has been produced from the Weber Sandstone. It is a facies having some permeability and effective porosity that was, at the same time, sufficiently brittle to fracture. The intergranular porosity and permeability alone in this formation are insufficient in many of the fields to support commercial rates of production. Thus, in addition to the types of sediments, folding and fracturing have been all-important in establishing substantial reserves in the Paleozoic reservoirs. The same control of accumulations by fracturing and sedimentary type applies to Cretaceous and Tertiary reservoirs in the Piceance basin, though folding was not a prime prerequisite to accumulation. All important Cretaceous and Tertiary oil and gas fields are related to the local improvement of porosity and permeability greater than that normal in the sediments encasing the reservoirs. In contrast to the normal relationships of gas, oil, and water found in the Paleozoic reservoirs, many of these relationships are reversed in the Cretaceous and Tertiary reservoirs. The relationships are similar to those in the San Juan basin of New Mexico and may have a similar explanation. More realistically, the explanation may be the indigenous nature of the oil and gas, where the only migration has been to local reservoirs in juxtaposition with the source beds.