Abstract “Environmental geology” is a term which is becoming widely used and misused. The rocks that contain fluids and through which they pass, together with the fluids themselves, physical conditions such as temperature and pressure, and various chemical and biologic factors, define the subsurface environment. The present characters of rocks and fluids in the subsurface are the result of the influences of many changing environments which affected them during their geologic histories. The papers in this volume discuss important subsurface fluids, their origins, movements, and evolution in geologic environments.

Abstract Subsurface mineral fluids and the substances recovered from them constitute a major part of the value of all minerals produced in this country, increasing from about 48 per cent in 1946 to 58 per cent in 1961, not including ground water. Each mineral fluid has its own preferred habitats, and finding new sources will require ever-increasing knowledge of geologic principles and processes. The predicted annual demand for petroleum and natural gas by the year 2000 is three to four times present domestic production. This increased demand must be balanced by increased rate of production from known fields, by new discoveries, by increased imports, or by synthetic products extractable from coal and oil-shale deposits, or by utilization of other energy sources. Other natural gases that come from subsurface reservoirs include helium, carbon dioxide, and hydrogen sulfide. Helium is in particular demand because of its unique physical and chemical properties; its geologic habitat is becoming better known. About one-sixth of the country's present water supply comes from ground water. In some areas withdrawal exceeds recharge, but in other areas withdrawal can be increased greatly without exceeding potential recharge. Currently about one-third of the ground water withdrawn is not being replaced. The behavior, quality, and quantity of both surface and ground water are geologically intimately interrelated. Increasing water usage will require improved scientific and legal coordination. Subsurface saline waters pose a threat to some fresh-water supplies; but with improved conversion techniques saline water can provide additional fresh water. Some fossil brines are now rich sources of valuable chemicals, and other brines are potential sources. Development of geothermal energy from subsurface thermal water and steam has begun, and further exploration will increase the power output. Recovery of valuable chemicals dissolved in some geothermal fluids is being considered. New uses for low-value fluids include “fluidizing” solids for easier transport and handling, and “solution mining” of low-grade ores.

Abstract Producible petroleum represents only a very small proportion of the source material preserved in the earth. Most of this carbonaceous matter remains in the rocks as a dark-colored, chemically complex, insoluble solid. The marine environment seems to have been the most favorable for the genesis of accumulatable crude oil, and this apparent association may reflect favorable chemical composition of the source material, a favored path of diagenesis, or perhaps merely a higher incidence in the proximity of suitable traps. Most investigators believe that plant and animal detritus is the ultimate source material for crude oils and associated fossil organic matter. The chemical composition of the tissues and metabolic products of marine organisms is not proving to be as different from that of terrestrial organisms as has been assumed on occasion in the past. Present evidence indicates that a long and complex chemistry is involved in the conversion of the constituents of the original plant and animal detritus into crude oils or other fossil organic matter. The conversions, however, proceed along definite reaction pathways which are governed by the subsurface environment. Data are rapidly accumulating concerning the chemical composition and variability of the source material as seen in recent aquatic sediments, the composition of the fossil organics, including crude oil, and the reactions which lead from one to the other in the earth. Ultimately, the geochemist hopes not only to be able to describe how crude oil forms in a given sedimentary environment but also why it has its particular composition.

Abstract The mechanisms and extent of oil and gas migration have long been controversial subjects among petroleum geologists. Acceptance of proposed “primary” migration mechanisms, which involve the initial transfer of oil or gas from source rock to reservoir, is further complicated because several of these hypotheses require that petroleum formation occurs during the primary migration stage. “Secondary” migration, which refers to the movement of oil and gas from one reservoir position to another, is better understood because geochemists have shown that petroleums undergo small but measurable changes in chemical composition during this type of migration. Fortunately, in many instances, these chemical changes can be distinguished from those chemical transformations which stationary petroleums slowly experience in response to reservoir temperatures and pressures over geologic time intervals. In contrast to the relatively minor chemical changes that can be attributed to secondary migration, certain petroleums, produced from distinct but narrowly separated horizons within a single field or limited geographic area, are markedly different in chemical composition. Other chemical characteristics of this group of oils, however, suggest that they were derived from a common source. The observed chemical differences cannot be explained as transformations of the stationary maturation variety. Detailed studies of the compositional differences encountered in such oil sequences imply that these oils must have undergone physical separations of major petroleum fractions prior to, or during, the migration process. This variety of petroleum segregation, capable of producing major chemical changes, is herewith designated as a “separation- migration” mechanism to distinguish it from the typical secondary migration phenomenon, which results in relatively minor petroleum-composition changes. Although the recognition of a new petroleum migration mechanism may appear to complicate further our already strained concepts of petroleum migration and segregation, the existence of a “separationmigration” mechanism is in accord with and a plausible consequence of some of the best-founded hypotheses of petroleum evolution.

Abstract A structural relationship exists in a number of areas in the Southwestern region between rock types in the Precambrian and Paleozoic structural trends. The Ouachita folded belt on the south and east of the Texas craton, which underlies the Southwestern region, was the dominant structural feature during the Paleozoic and probably exercised indirect control over all intracratonic structures. Most of the early and middle Paleozoic oil and gas reservoirs are associated with unconformable surfaces. These reservoirs were formed by weathering of the unconformity surface, particularly where pre-unconformity folded and faulted structures existed. Four Paleozoic continent-wide interregional unconformities are present. The approximate dates of the regressional maxima represented are (1) very late Precambrian, (2) early Middle Ordovician, (3) early Middle Devonian and (4) post-Mississippian. In addition, many regional unconformities are present, the most important in relation to the source, migration, and accumulation of oil and gas being that between the Permian and Pennsylvanian. This regional unconformity is composed of a number of local unconformities associated with structurally positive areas. Early and middle Paleozoic hydrocarbon-source beds were probably organic-rich sediments overlying the unconformities. Late Paleozoic Pennsylvanian and Permian sediments were by far the most abundant sources of hydrocarbons in the reservoirs in the middle and early Paleozoic formations. Within the Pennsylvanian and the Permian, unconformities are important; however, their importance is overshadowed by lithofacies phenomena related to reefs which formed the most prolific oil-producing reservoirs of those two periods.

Abstract Analyses of 310 crude oils from formations ranging in age from Cambrian to Cretaceous were studied to correlate the geologic occurrence of these oils with such characteristics as composition by hydrocarbon type (aromatics, naphthenes, and paraffins), content of gasoline and gas oil (determined by distillation and refractometric methods), distillate yield and residuum, sulfur and nitrogen contents, and cloud points. Five general categories, based on likenesses that may indicate a similar history, include most of the oils, but smaller groupings are also discussed. Average values for each of the categories are given below. Category S N N/S V A V N V P V D Wax Content I 0.16* 0.032 0.20 5.5 7.5 87.0* 84 Medium II 0.35* .059 .17 8.7 30.3* 61.0 79 High III 1.77* .10 .057 19.3* 31.4 49.3 73* High IV 0.16* .125 .78* 6.5 45.6 47.9 76 High V 1.19* .140 .12 6.2* 63.1* 30.7* 63 Low* S and N refer to weight-per cent sulfur and nitrogen; Va, Vn, and Vp to volume-per cent of aromatics, naphthenes, and paraffins in the gasoline; Vd to volume-per cent total distillate. * Items of particular interest. Category I (Ellenburger and Simpson oils).—The Simpson shale is considered as a likely source. Category II (a few Ellenburger and Simpson oils, Fusselman, Devonian, Mississippian, Pennsylvanian, Wolfcamp, a few Yeso oils).—Probable sources are dark basinal shales of Woodford, Mississippian, Pennsylvanian, and Wolfcamp age, commonly associated with unconformities. Category III (Yeso and San Andres oils).—These occur commonly now on the Northwest and Eastern shelves where sulfate content is high. Category IV (Spraberry, Delaware Mountain, some Wolfcamp and Yeso oils).—These are relatively unaltered oils, associated with or derived from basinal shales. Category V (San Andres, Grayburg, Queen, Seven Rivers, Yates, Rustler, Castile, Cretaceous oils). —These oils appear altered. Reaction with sulfur, fresh water leaching of volatile aromatics, and microbial oxidation of wax are suggested as reasons for the alteration.

Abstract From its discovery May 14, 1942 to January 1, 1965 Embar field produced 28,344,573 bbl of oil from pays in the Grayburg, upper Clear Fork, lower Clear Fork, Devonian, Fusselman, and Ellenburger. San Andres production on the Embar structure is not included in this figure as it is incorporated with Martin San Andres field and Andector San Andres field. Up to 1,500 ft of sandstone and red shale of Tertiary, Cretaceous, and Triassic age overlie the Permian, which in turn is about 6,400 ft thick and directly overlies a major unconformity. Beds ranging in age from Pennsylvanian to Precambrian are present beneath this unconformity, but within the limits of Embar Ellenburger field beds no younger than Precambrian, Ellenburger, or basal Simpson are found. The pre-Permian structure of Embar field is an anticlinal fault block which is part of a much larger anticlinorium. The structure was peneplaned following its uplift in late Mississippian or early Pennsylvanian time and again in late Pennsylvanian or the earliest Permian. This structure is gently reflected through the Permian pay horizons owing to drape or to renewed uplift along the old axes. The Devonian is productive on the south flank of the Embar structure, owing to up-dip pinchout complicated by faulting. Although analyses reveal that oils from the different horizons of Embar field are similar, the waters are distinctive. This does not damage the concept that the oils from the upper and lower Clear Fork, Devonian, and Ellenburger are probably from the same source. This source may have been dark shales of Pennsylvanian and Mississippian age which were preserved in structurally lower areas. It is theorized that migration may have started in post-Clear Fork time when all the present reservoirs were covered. From the source beds, the oil may have followed the unconformity at the base of the Permian, then Permian strata, and/or fault planes, until it reached the Ellenburger and Devonian. From these horizons the oil may have gradually migrated vertically to the lower and upper Clear Fork horizons.

Abstract Any application of controversial theories concerning the origin, migration, and alteration of petroleum must be presented as a hypothesis that satisfies known prerequisites, including those demanded by geologic history. Permian shelf-edge carbonates, both reef and nonreef, were deposited near sea level, and time horizons in them can be used as paleolevels in determining the time, direction, and magnitude of tilts which affected the migration of petroleum in the Permian Basin of West Texas and southeastern New Mexico. The geologic prerequisites assumed to be necessary for secondary migration are (1) sufficient depth of burial, (2) carrier beds, and (3) adequate regional tilt. These prerequisites to secondary migration within the Abo formation were best satisfied during the Permian Period. The API gravity of crudes found in the studied Permian formations forms regional patterns which are assumed to reflect secondary migration. The Abo oil-gravity pattern differs from the overlying Grayburg pattern. This is interpreted to mean that secondary migration within the Abo had ceased prior to secondary migration within the Grayburg. The Grayburg migration was caused by post-Grayburg tilt; thus secondary migration within the Abo had ceased by the end of Grayburg time. Levorsen's technique, which involves the study of reservoir pressures and gas saturations as related to depth of burial, was used to estimate the time of final oil accumulation in three fields in southeastern New Mexico. The Vacuum field was found to be an example of accumulation due to secondary migration within the late Leonardian and early Guadalupian Epoch of the Permian. Accumulation during secondary migration probably occurred at the Lovington field also, but a study of trap capacity and an application of Levorsen's technique to both the Abo and overlying San Andres reservoirs indicate that final accumulation did not occur until the late Triassic. The accumulation at the Empire field occurred during the late Tertiary and early Quaternary after regional eastward tilt resulted in the establishment of a favorable hydrodynamic system, and after the erosion of Pliocene, Triassic, and upper Permian strata. Secondary migration within the Abo occurred during the Permian, and two detectable episodes of remigration occurred during and after times of regional unconformity. The stratigraphic sequence of late Permian strata overlain by late Triassic strata, overlain by late Tertiary strata, dates these times of unconformity.

Abstract The Delaware-Val Verde basins lie as a continuous elongate northwest-southeast-trending downwarp extending from Eddy County in southeast New Mexico to Edwards and Kinney Counties, Texas. Deep production is confined primarily to gas-condensate reservoirs in the Ellenburger Group of the Ordovician; the Devonian; the Morrowan, Atokan, and Strawn Series of the Pennsylvanian; and the Wolfcampian Series of the Permian. Significant structures include the Brown-Bassett, Bell Lake, Coyanosa, Hershey, Puckett, Rojo Caballos, Toyah, and Worsham-Bayer Fields. Post-Precambrian geologic history began with a shallow embayment in Cambro-Ordovician time which was followed by the development of the Tobosa basin in the Middle and Upper Ordovician epochs and Siluro-Devonian periods. Epeirogenic uplift in the middle to late Devonian gave rise to a widespread erosional unconformity. Subsequent deposition of Mississippian and early Pennsylvanian sediments was without tectonic incident. In middle to late Atokan time (early Pennsylvanian), severe folding and thrusting occurred in the Ouachita geosyncline and Marathon region, to the south. This rising mountainous area resulted in a flood of Permo-Pennsylvanian clastic sediments which filled the Delaware-Val Verde trough. Renewed uplift of the Diablo and Central Basin platforms and thrusting in the Ouachita- Marathon region in mid-Wolfcampian time culminated the early history of the Delaware-Val Verde basins. Later tectonic influences–which help account for fluid distribution–include the regional upwarp of the Diablo platform, Marathon uplift, and Ouachita folded belt in the Triassic-Jurassic periods, along with late Cretaceous faulting and Tertiary igneous activity. Original distribution of the water salinity in the Ellenburger and Devonian zones appears to have been highly modified by subsequent hydrodynamic movement of meteoric waters in the west, southwest, and south portions of the trough. This flushing, extremely active in early Pennsylvanian, late Permo- Pennsylvanian, and Triassic-Jurassic periods, continued to a lesser degree to the present time. Charged meteoric waters introduced carbon dioxide which had as its major origin the solution of carbonate and bicarbonate components in the exposed rocks of the Ouachita, Marathon, and Diablo platform areas. The most likely periods of generation were early Pennsylvanian, late Permo-Pennsylvanian, and during the Tertiary igneous disturbance. Forceful emplacement of carbon dioxide and methane may have occurred in the Val Verde basin throughout the time of early Pennsylvanian and mid-Wolfcampian folding and thrusting in the Ouachita-Marathon region. Absence of oil production from the deep zones in the Delaware and Val Verde basins appears to be the result of two major factors. The first is the hydrodynamic flushing of crude-oil accumulations from all but the deeper and large closures. This scattering of oil occurred coincident with the major periods of hydrodynamic activity. The second factor is that restored maximum overburden, as well as present overburden in many cases, exceeds the gas-condensate conversion point for Delaware-Val Verde basin oils. These oils, derived from the Simpson, Woodford, and Permo-Pennsylvanian shales, disassociate into gas-condensate and gas below depths of 14,000, 13,000 and 8,000 to 9,000 ft, respectively.

Abstract The Permian Central Basin platform consists in large part of a great carbonate build-up of Wolfcamp to upper Guadalupe age, and within it may be recognized a great many individual but related reefs. One of the best revealed of these reefs is one of late San Andres age which extends for more than 70 mi along the east flank of the Central Basin platform from the Penwell-Jordan pool of Crane and Ector Counties, to the Means pool of northern Andrews County. Isopachand facies studies demonstrate that during late San Andres time this reef grew in relatively shallow water along the then eastern margin of the platform. To the east lay somewhat deeper water of the Midland basin where rocks of the same age are sandstone, limestone, and dolomite. On the opposite or western side of the reef the water was nearly as shallow as over the reef itself, but slightly more saline, and the rock is dolomite with traces of anhydrite. Growth of the upper San Andres reef ceased at the close of San Andres time, but the reef was affected by subsequent post-San Andres crustal movements so that now the southern part of the reef is 600 ft higher thanthe northern end. During reef growth, porosity developed widely throughout its extent and can now be tracedalmost continuously from the southern to the northern extremity, but beyond the reef to the east and to the west, relatively little porosity developed. By the beginning of post-San Andres time the voids had been filled with fluids–gas, oil, and water. These fluids, according to their specific gravities, responded to subsequent structural movements, within the limits of available porosity, so that now the oil is concentrated in the several pools which occupy much of the trend.

Abstract From the axis of the Delaware basin to the western homocline, upper Bell Canyon-sandstone pools exhibit aregular progression from gas-bearing structures down dip to oil-bearing stratigraphic traps up dip–anexample of Gussow's principle of differential entrapment.

Abstract A hydrodynamic study of several stratigraphic unitsin the Permian Basin shows a regional west-toeast dip of the potentiometric surface. The potentiometric surfaces of the Ellenburger and Devonian have both closed lows and closed highs against faults on the Central Basin platform, and that of the Ellenburger is low around the Fort Stockton uplift. Data for the Devonian showa steeper dip of the potentiometric surface in New Mexico than in Texas. The Mississippian data are too sparse to show significant features other than dip to the north, east, and south from Terry County, Texas. The Strawn potentiometric surface has steeper east dip on the east flank of the Midland basin, and approaches hydrostatic conditions around the Central Basin platform. The dip of the potentiometric surface of the Wolfcamp is to the east and north in New Mexico, and east and northeast in Texas. The San Andres shows east dip. The Delaware Mountain group has general east dip, but anomalous conditions are suggested in central Reeves County. The potentiometric surfaces of all units mapped have some common regional characteristics in spite of the wide differences in elevation and location of the outcrops and subcrops. However, locally, there are many variations. Tilting of the hydrocarbon accumulations is a significant factor in a few fields, but much apparent tilting is caused by discontinuous porous lenses and by low permeability. Vertical and horizontal pressure relationships around faults and subcrops, vertical and horizontal continuity of oil, relative permeability to oil, and other hydrodynamic conditions can be critical factors to be considered in exploration in the Permian Basin. Salinity maps of the Basin waters show a northwest-southeast trend of high salinity through the southeast corner of New Mexico. It is separated from a parallel high trend to the north, by a low trend with less than 50,000 ppm total solids. The quality of drillstem-test instrumentation and programming in the Permian Basin needs to be improved to furnish the pressure data that should be available to the industry.

Abstract Ground-water irrigation in the Southwestern Region developed explosively after World War II. Most of the water used is being taken from storage. Reserves are rapidly being depleted and, in the light of present knowledge, changes in the economy of large areas must take place within a generation. The importance of ground water in this area has led to the development of physical and legal ground-water concepts of general application. The Roswell area is now over-developed and the rateof use of ground water there must decrease in the future. The immediate effects of drilling artesian wells in the early years of the century led to the New Mexicolaw adopting the principle of priority for the right to use ground water. Irrigation on the Llano Estacado in Texas is depleting a reserve of perhaps 150,000,000 acre-feet of water at the rate of about 5,000,000 acre-feet a year. Thegreat size and essentially simple character of this aquifer led to the development of a time-dependent theory of ground-water movement, and, together with a dramatic fall of the water table, led to a judicial determination that this water body, and by inference others, is a depleting resource. Pumping of stream-connected alluvial aquifers like those of the Rio Grande and the Pecos depletes the flow of the stream in the same amount at some time in the future. The principle has been recognized in the administration of ground water in New Mexico. At a distance, this effect of pumping is so long delayed that all the water pumped may be considered taken from storage. In Reeves County the water table has fallen as much as 160 feet in eight years. Bolson aquifers have a base perennial yield which is apparently being exceeded in the Salt Basin of Hudspeth County. Bolson aquifers in southwestern New Mexico are being pumped essentially from storage.

Abstract Most saline waters of marine sedimentary rocks wereprobably similar initially to present-day ocean water. Many early diagenetic changes in sediments and waters are related to organic content and bacterial activity;ion exchanges and perhaps some other early changes areinorganic. Diagenetic and later changes in sedimentaryrocks cannot be understood without considering the associated fluids, which are mobile and leave little direct and easily interpretable evidence of their changingcompositions with time. Compaction of sediments and escape of interstitial water start at the time of deposition and probably continue for millions of years. The evidence is now convincing that fine-grained sediments behave as semipermeable membranes, permitting selective escape of water and concentrating dissolved components in remaining porefluids. The initial driving force is lithostatic pressure; after maximum compaction has been attained, salt-filtering may continue under certain circumstances of topography, structure, and lithology, with meteoric water providing the driving energy.

Abstract It has now been established that considerable sulfur-isotope fractionation occurs in the biological sulfur cycle and that the bacterial reduction of sulfate, which leads to the enrichment of S 34 in sulfate and its depletion in sulfide, is largely responsible for the wide fluctuations in isotope ratio which occur in marine sediments. In this regard, present-day ocean-water sulfate is remarkably uniform in sulfur-isotope content, both in depth and in geographical location at a value of δ − S 34 = +20 (20 parts per mil enriched S34 with respect to sulfur in meteorites), and provides a base level in isotope ratio from which fractionation can be reckoned. However, in dealing with ancient sediments and petroleum, we need to know the S34 content of the ancient oceans or seas. Recently (Thode and Monster, 1963) a study of the sulfur-isotope distribution in the marine evaporites of some ten sedimentary basins of several continents was carried out. From this study it has been possible to estimate the sulfur-isotope ratio for the various ancientoceans and to establish the pattern of change throughout geological time. The pattern of change for petroleum sulfur appears to be parallel to that for the evaporites and ancient seas. However, the petroleum sulfur is, in general depleted in S34 by about 15 °/oo with respect to the contemporaneous gypsum and anhydrite deposits. This displacement of 15 °/oo in the S 34 content, which is about the isotope fractionation expected in the bacterial reduction of sulfate, is strong evidence that seawater sulfate is the original source of petroleum sulfur and that it is first reduced by bacterial action in the shallow muds before being incorporated into petroleum. The lack of any sulfur-isotope fractionation in the plant metabolism of sulfate would seem to rule out plant sulfur as a major source of petroleum sulfur. Inasmuch as the δS 34 values for petroleum pools in a given horizon, for example, Devonian (D-2), are fairly uniform over a large sedimentary basin, and as these values vary from one horizon to another depending on the S 34 content of the contemporaneous seas, sulfur isotope studies should be useful in solving migration problems.

Abstract Numerous theories have been proposed to explain theorigin of subsurface carbon dioxide. The conclusion isreached that, although carbon dioxide may be formed in many ways, most of the carbon dioxide, in appreciablylarge accumulations had its origin in the breakdown of impure limestone or dolomite under the heat of igneous intrusion.

Abstract Isotopic enrichments of Xe 132 , Xe 134 , and Xe 136 were found in a number of natural gases and are attributed to the spontaneous fission of U 238 . The ratio of spontaneous-fission xenon to atmospheric xenon and the ratio of spontaneous fission xenon to He are discussed in terms of a solubility model. It is shown that the isotopic enrichments can be explained in terms of the solubility model and a preferential release of He as compared to XegF by a factor ranging up to three. An estimate is made of the present flux of spontaneous-fission xenon into the atmosphere.

Abstract Disposal of radioactive liquid wastes through deep wells may be categorized as containment or confinement. Containment means the placement of wastes under conditions that preclude their movement out of a definablezone. Confinement means the placement of wastes in a zone where movement may take place under restricted conditions that can be controlled or monitored. Disposal of liquid wastes on a continuing basis by containment probably is not practical except for smallquantities and may be possible in only a few areas. Itis probable, therefore, that any deep disposal of radioactive liquid wastes will be by confinement of wastesin certain geologic horizons through which they will move at measured rates. Hydrologic principles applied to the data presently available indicate that there is circulation of fluids in almost all sediments. Movement of fluids tend to be restricted in the basal parts of sedimentary basins, but any assumption that wastes introduced into a basin would not eventually move out of the basin or to the near-surface formations should be carefully scrutinized. Introduction of wastes into an anomalously low-pressure zone should not be considered safe until or unless the reason for the low pressure can be explained. Data necessary to define the hydrodynamics of fluids injected through deep wells will be expensive to obtain, and many of them will have to be collected for each particular disposal site. Geochemical factors may influence greatly the movement of radioactive material in deep formations. A system of monitoring, and possibly removal, is a prime requisite of deep-well disposal of radioactive wastes. Initial disposal activities necessarily will be on an experimental basis pending the results of such monitoring.