Lithological Components Research Articles

Estimating Thermal Conductivity in Sedimentary Basins Using Lithologic Data and Geophysical Well Logs (1)

A method for estimating in-situ thermal conductivity profiles in oil and gas wells is advanced to rectify a major shortcoming in thermal analyses of sedimentary basins. Thermal conductivity estimates are made in a two-stage procedure and are based on a model for the conductivity of mixtures and input data from lithological and geophysical logs. First, rock matrix conductivity for an arbitrary depth interval (i.e., drill cuttings sample interval, which is about 3 m) is determined from the laboratory-calibrated conductivities and volumetric representation of its individual lithologic components using a geometric mean model. In-situ conductivity is then estimated by a second application of the model, correcting for temperature and porosity determined from geophysical logs. > The method is illustrated for three Uinta basin (Utah) wells that penetrate a series of Tertiary sandstones, shales, and muddy carbonates. Detailed lithologic descriptions, together with sonic and neutron logs, were digitized and used for estimating in-situ conductivity. The validity of the method was tested by comparing the prediction against laboratory measurements on 565 samples from the same wells. Rock matrix thermal conductivity ranges from 1.6 to 6.8 W/m/K and is predicted within 20% of the actual measurement for 90% of the samples. Both in-situ conductivity values and variations for a given lithologic unit are reduced at increased porosity and increased temperature. Thermal conductivity nomograms are presented as useful tools to predict directly the in-situ thermal conductivit of a formation from a well log signal.

Metasomatic products of the lunar magma ocean: The role of KREEP dissemination

The origin of the incompatible element-rich lunar component, KREEP, is in the Lunar Magma Ocean (LMO). The fractionated residual melt after crystallization of the LMO represents “urKREEP” (after Warren and Wasson, 1979). The percentage of this residual melt is low enough to be within the realm of silicate liquid immiscibility (SLI). This process has the ability to split the KREEP signature into K- and REEP-Fractions, which are manifest as lunar granite (K) and phosphate phases present in highland lithologies or as quartz ferrotroctolite in lunar soils (REEP). We envisage this as a localized, but significant process since only a small portion of urKREEP undergoes SLI. Norms of experimental and Apollo 15 basaltic immiscible glasses suggest that thevREEP-Fraction found in the lunar highlands has undergone post-SLI fractionation of at least fayalite. This significantly reduces the density of the REEP-Fraction and coupled with its low viscosity (10–15 poise), it can percolate upward, metasomatizing the lunar crust. The higher viscosity of the granitic melt (=∼30000 poise) inhibits its mobility, and it forms “pods” in the lower rust (as required for VHK basalt petrogenesis). With the identification of KREEPy components, the composition of urKREEP can be calculated. Using experimental evidence, the KREEP components may be recombined to give the pre-SLI composition, or liquid-liquid Kd's can be used to calculate a pre-SLI composition from lunar granite. Both calculated urKREEP compositions are lower in MgO and Al 2O 3 and higher in FeO and P 2O 5 than reported low- and high-K KREEP compositions. The calculated REE abundances are higher and the REE profiles are slightly more LREE-enriched than the previously reported KREEP compositions. However, the REE profile calculated using liquid-liquid Kd's is concave-upwards, compared to the LREE-enriched profile produced by recombining the KREEP components. Pre-SLI whitlockite/apatite fractionation occurred prior to immiscibility in order to generate the concave-upwards profile. The LREE-enriched profile represents the pre-SLI magma prior to phosphate fractionation. The presence of “superKREEPy” rock types can be accounted for by K- and REEP-Fraction assimilation, and the compositions of olivine vitrophyres can now be modeled using analyzed lunar rock types without the inference of a mythical “high-Mg” component. Other, more widespread KREEPy rocks ( e.g., Apollo 14 breccias, Apollo 15 KREEP basalts, LKFM basalts) are produced by incorporation of the more widespread pre-SLI urKREEP component. The splitting of KREEP into identifiable lithological components allows the petrogenesis and role of KREEP in lunar evolution to be better understood.

An analysis of statistical average velocities in a horizontally layered earth

For a medium consisting of two lithologic components, we analyze relationships among various velocity statistics that have appeared in the literature. We then address the problem of using stacking velocities to estimate the lithologic content.

Sedimentologic Controls on Brittle Deformation of Siliceous and Dolomitic Mudstones: Pismo Fromation, California: ABSTRACT

Sedimentologic parameters and diagenetic history are important factors influencing the brittle behavior of fine-grained rocks in a given structural environment. The complexity of these relationships is high-lighted by the fact that different parameters influence the level of fracturing in different rock types of the same depositional sequence. This can be illustrated with data collected from 23 outcrop stations from the upper Miocene to lower Pliocene Miguelito member of the Pismo formation in the Pismo basin. The samples were divided into two lithologic groups based on outcrop description, x-ray diffraction data, and thin-section analysis. Bed thickness was measured in the field, and matrix porosity determined in the laboratory. The magnitude of brittle deformation was estimated by calculating the fracture intensity (fracture surface area per unit rock volume) of individual bedding units. For the 16 opal-CT siliceous mudstone samples, the d-spacing values determined by x-ray diffraction have the highest correlation coefficient with fracture intensity (0.65). The ratio of biogenic to detrital silica, which has been shown to influence d-spacing values, has a correlation coefficient of 0.59. Other variables that have lower correlation coefficients with fracture intensity include matrix porosity (0.49), the detrital content (0.48), and the biogenic silica content (0.40). The bestmore » two-variable model for predicting fracture intensity of these mudstones combines d-spacing and matrix porosity (R-squared equals 0.72). For the seven dolomite samples, individual lithologic components exhibit the best correlation coefficients with fracture intensity, including detrital content (0.74), dolomite content (0.64), and biogenic silica content (0.59). Bed thickness has a reasonable correlation coefficient with fracture intensity (0.59), but matrix porosity has a very low correlation (R-squared equals 0.23).« less

Paleozoic gneissic granitoids in the Shoo Fly Complex, central Sierra Nevada, California

Paleozoic gneissic granitoids are an important lithologic component of the Shoo Fly Complex of the central Sierra Nevada, California. Field relations and petrographic and geochemical studies indicate that the gneisses were intruded as a series of plutons ranging in composition from gabbro (oldest) to granite (median age) to syenite (youngest), with the granitoid types predominating. Compositionally they represent a calc-alkalic suite and a younger alkalic rock suite. The plutons and related smaller injections truncate an early S1 foliation in the Shoo Fly. During regional D2 and D3 deformational events, the granitoids were isoclinally folded and foliated under peak epidote-amphibolite grade conditions, and they were deformed into augen gneiss, blastomylonite, and ultramylonite. The gneisses contain porphyroclasts of feldspar, quartz, mica, and amphibole, and granitic aggregates, surrounded by an anastomosing foliation of quartzose ribbons and recrystallized quartz, feldspar, amphibole, mica, and stilpnomelane. Later deformational phases (D4–D7) typically involved open folding with the development of a spaced biotite schistosity (S4) and nonpenetrative cleavage (S5, S6, S7), and recrystallization of older fabric elements. Available geochronologic data of Sharp and others (1982) and H. K. Brueckner and W. D. Sharp (1985, personal communs.) suggest that the protoliths of the gneissic granitoids were intruded in Late Devonian time, thus establishing a pre–Late Devonian depositional age for the Shoo Fly Complex. D1 and intrusion of the orthogneiss protoliths may have been precursors of the Late Devonian to Early Mississippian Antler orogeny. Collectively, the gneisses may represent scattered remnants of a Paleozoic plutonic belt.

Role of clays in the disposal of nuclear waste: A review

Applied and basic sciences of clay mineralogy have played significant roles in radioactive waste disposal practices. Clays and clay minerals as in situ lithologic components and engineered barriers are characterized by favorable properties from the viewpoint of radioactive-waste emplacement. Their high sorptivity, longevity, and low permeability make them promising candidates for retaining most natural and anthropogenic long-lived radionuclides within the contaminated and engineered disposal sites. In this review the following subjects are discussed: (1) source-term classification and current and proposed disposal methodology of low-level and high-level wastes: (2) selected physicochemical properties of clays pertinent to site characterization, grouting, and impermeable barrier components; (3) application of clays in current and future waste disposal practices.

THE NATURE, DISTRIBUTION AND RELATIONSHIP OF ARCHAEAN TERRANES IN EASTERN BRAZIL

This is a study of the general geological characteristics, distribution and relationship of the major Archaean terranes of eastern Brazil. It also íncludes a concise descriptíon of several líthostratigraphic sequences of typical greenstone signature and associated granite-gneisses belonging the São Francisco Craton, which is interpreted as the only Archaean cratonic area within the region under consideration. The greenstone successions, however, present a poorly preserved stratigraphy, due mainly to the emplacement of gneissic tonalite, and granite plutons, and to the proportion of volcanics, particularly of komatiític composition, ís low, while aquagene tuffs and associated sediments form the most important lithological components. The high-grade metamorphic terranes, subjected to granulite facies of regional metamorphism most1y during the late Archaean (~ 2.7 Ga), are represented by the Jequié and Goiás mobile belts, and the Santa Catarina and Santa Maria Chico complexos. In the first two belts, graníte-greenstone nucleus display relatively well preserved stratigraphic sequences exist within the high-grade metamorphites as isolated remnants, while adjaceut areas have been reworked by a intense tectono-thermal evento. In comparison to Archaean terranes in other parts of the world, the Brazilian counterparts are rather different in features such as transitional boundaries, fragmentary patterns and poorly preserved greenstone sequences.

Tectonic development and stratigraphy at the western margin of the Caledonides: Islay and Colonsay, Scotland

ABSTRACTIslay and Colonsay occupy a crucial position in the Caledonian frontal zone S of the Great Glen fault in western Scotland. However, some of the stratigraphical units which comprise these islands are of doubtful age as they have tectonic boundaries and contain no fossils or distinctive lithological components. New information is presented here on the deformational histories and styles of the rocks and this has prompted a reassessment of their stratigraphical position and a major reinterpretation of t0he tectonism of this frontal zone.In contrast to the conventional view, all the stratigraphical units have been deformed together during a regional shearing event. The Colonsay Group contains intrafolial and sheath folds and has a pronounced linear fabric which is parallel to grain elongations in parts of the Bowmore and Dalradian sequences. Most junctions between the Colonsay Group and basement of the Lewisian complex are highly sheared. The junction between the Bowmore Group and Dalradian Supergroup is also tectonised and is normally referred to as the Loch Skerrols thrust but here as a shear zone. This structure is shown not to be a profound discontinuity, alone representing the Caledonian front S of the Great Glen fault, but one element in a major flat-lying NW-directed ductile shear zone. The Caledonian front therefore lies to the W of the islands.The Bowmore Group is suggested to be a lateral equivalent of the Crinan Grits in the Dalradian Supergroup, lying in the overturned sheared limb of the Islay anticline. The age of the Colonsay Group remains enigmatic; the identification of previously unrecognised early structures which may precede shearing in the Grampian episodes of the Caledonian orogenic cycle allows the possibility of a pre-Caledonian deformation of the Group.

Analyse critique des extractions sequentielles a travers l'etude de quelques constituants des residus d'attaque critical analysis of sequential extractions through the study of several attack constituent residues

Abstract Analysis of lithologic components (Fe, Mn, COP, CaCO3) dosed in extraction residues of a muddy estuarine sample revealed the insufficient specificity of the sequential extraction method.

Lunar volcanic glasses and their constraints on mare petrogenesis

Volcanic glasses from the Apollo 11, 14, 15, and 16 landing sites have been analyzed for major elements and Ni by electron microprobe. The 19 varieties of volcanic glass define two distinct chemical arrays that provide new insights into (a) the petrogenesis of mare basalts and (b) the structure of the deep lunar interior. A simple model is proposed whereby mare basaltic liquids may have been derived from two isolated, cumulate systems occurring at depths of ~300 km and ≳ 400 km. Each system was itself composed of two lithologic components (low-Ti vs high-Ti) that underwent hybridization, assimilation, or mixing to generate the large compositional range of magmas observed within each array. While the distribution of the two components within each system was locally heterogeneous, data indicate that the components themselves were chemically uniform on at least a regional scale. The surface-correlated volatiles associated with the lunar volcanic glasses seem to have come from some other reservoir within the Moon. The simplicity of the chemical relationships observed among the lunar volcanic glasses allow specific-predictions to be made. We believe that they should readily reveal any strengths or weaknesses of this new model.

Composition of the lockett conglomerate lake Sylvester area, North-West Nelson

Abstract In its type area, the Lockett Conglomerate of north-west Nelson, New Zealand has a much greater variety of lithological components than has previously been described. The;e components include, in addition to the dominant basic volcanic detritus, ultrabasic, basic, and intermediate plutonic; intermediate, and acid volcanic; acid plutonic; sedimentary; and metamorphic detritus. The metamorphic material appears largely confined to the matrix and is possibly of distant derivation, but the other material, particularly serpentinite, is more locally derived.

6: The Dalradian rocks of the northern Loch Awe district

Introduction In this guide accessible exposures of Middle and Upper Dalradian rocks (now respectively classified as the Argyll and Southern Highland Groups [Harris and Pitcher 1975]) in the northern Loch Awe district are described. The localities have been chosen so as to allow examination of each of the major lithological components of the succession. Furthermore, the outcrops allow the major structures of the region to be detected. Examination of the localities described requires two days. The best centre on which to base an excursion is Oban although Kilchrenan, Taynuilt and Connel also provide accommodation within the area. General Geology Within the present area (Fig. 2) the outcrop pattern of the Dalradian stratigraphy is controlled by the Loch Awe Syncline, a structure which was first described by Bailey (1913). The most north-easterly part of this structure is shown by the synclinal distribution of stratigraphic units shown in Figure 2. In detail the Loch Awe Syncline is a compound structure consisting of two synclines and an intervening anticline. These quite tight folds are slightly overturned to the south-east (Borradaile 1973) in contrast with the single broad, open, upright syncline indicated by Bailey. The axial traces of the component folds to the Loch Awe Syncline strike NE.-SW. and the more prominent syncline is the Kilchrenan Syncline. Its axial trace passes just to the west of Kilchrenan and the syncline appears to continue as the Tayvallich Syncline in the area to the south–west of that indicated in Figure 2. The Loch Awe-Tayvallich district . . .

Ordinal Data and the Gamma Statistic in Geology

ABSTRACT An ordinal scale is one which comprises rank-ordered data, where the differences between the ranks are not (and commonly cannot be) specified. Examples include the Mohs' hardness scale, biostratigraphic stages and zones, metamorphic grade, and absent-rare-common-abundant estimates of lithologic components. Correlations and trends in ordinal information can be investigated in a manner analogous to linear regression using a measure of association, the gamma statistic. A significance test for gamma is provided. These statistical measures are applied to the following illustrative examples: distribution and correlation of mineral components in some modern lake sediments, variation of grain size with distance in some detrital limestones, and the distribution in time of sedimentary structure assemblages in a deltaic succession. Use of gamma (and in certain cases multivariate techniques such as cluster analysis) is valuable if time or other limitations prevent the acquisition of data on an interval or ratio scale. For many types of data, ordinal statistics are the only type suitable but have been largely ignored by geologists in the past.

Application of some correlation coefficient techniques to time-series analysis

Application of the sliding correlation technique has permitted detailed stratigraphic correlation over entire basins. The main values of the technique are to (1) demonstrate correlation statistically, (2) extend the range of visual correlation, and (3) establish precise correlation where correlation is known to exist but is difficult to establish visually. The technique is especially valuable in aiding correlation of stratigraphic sequences such as varves and turbidites, which are characterized by monotonous repetition of two or more lithologic components. The moving correlation technique is a valuable aid in examining variations in degree of correlation between correlative sections, and in analysis of component associations within a single stratigraphic sequence.

Petrology of Carbonate Rocks of the Green River Formation (Eocene)

ABSTRACT Lacustrine carbonate rocks of the Green River Formation contain a diversity of lithologic components and sedimentary features that are comparable to carbonate formations of marine origin. Fossils (algal plates, ostracodes, molluscs), coated grains (ooliths, pisoliths, circumcrusts), and polygenetic microcrystalline carbonate aggregates (intraclasts, peloids) are the main rock-forming carbonate grains. No genetic difference between ooliths and pisoliths was found. Both grain types display probable algal cell molds and are believed to be algal precipitates. Microcrystalline carbonate is more abundant than sparry carbonate in most rocks, although well-washed, grain-supported sparites are not uncommon. Dolomicrite is ubiquitous in the formation and petrographic evidence indicates that it ormed as a selective replacement product of calcium carbonate mud during early diagenesis prior to lithification. Admixed terrigenous constituents are an important component in most of the carbonate rocks; siltstone and sandstone are transitional with silty and sandy carbonate rocks. The similarity of lacustrine and marine carbonate rocks indicates that the two types can not be differentiated solely on the basis of petrographic relations. Sedimentary structures and stratification types are especially well developed in many of the carbonate rocks and greatly aid in the interpretation of subenvironments of deposition. The use of structures and stratification types in conjunction with lithologic variations and associations permits the recognition of several lacustrine subenvironments: mudflat, beachbar, lagoonal, shoal, transitional and offshore. Algal stromatolite bioherms locally are present in rocks of the shoal facies.

Genetic Units and Delta Prospecting: ABSTRACT

Deltas generally are formed at river mouths during stillstands of sea level under conditions of either cyclic transgression or regression. Consequently, they are rarely isolated phenomena, but are present in multiples in a predictable fashion. Reservoir facies consist of both continuous and discontinuous, bifurcating channel sandstones that thicken downward at the expense of the underlying prodelta clays. All the lithologic components of a deltaic complex are related to each other and are collectively referred to as one type of increment of (GIS). The GIS is a sequence of strata in which each lithologic component is genetically related to all the others. It is defined at the top by a time-lithologic marker bed (such as a thin limestone or bentonite), and at the base by either a time-lithologic marker bed, an unconformity, or a facies change from marine to nonmarine beds. It generally consists of the sum total of all marginal marine sediments deposited during one stillstand stage of a shoreline, or it may be a wedge of sediments deposited during a series of cyclic subsidences or emergences. An isopach map of a GIS clearly shows the bifurcating trends of the individual d stributaries and the shape of the delta, regardless of the variable lithology of the channel fills. A genetic sequence of strata (GSS) consists of two or more GIS's and, when isopached, clearly defines the shelf, hinge line, and less stable part of a depositional basin. An isopach map of the McAlester Formation of the Arkoma basin is a good example of a GSS. The oil-productive Booch Sandstone is a good example of a deltaic complex occurring within a GIS of this GSS. The upper Tonkawa, Endicott, and Red Fork Sandstones of the Anadarko basin are deltaic accumulations within different GIS's. A hypothetical model serves to establish the criteria for (1) recognizing successive stillstand positions of a shoreline, (2) predicting paleo-drainage courses, (3) predicting positions of a series of deltaic reservoirs, (4) locating isolated channel sandstone reservoirs, and (5) tracing related beach sandstone reservoirs. End_of_Article - Last_Page 152------------

Genetic Units in Delta Prospecting

Deltas generally are formed at river mouths during stillstands of sea level under conditions of cyclic transgression or regression. Consequently, they are rarely isolated phenomena, but form in multiples in a predictable fashion. Reservoir facies consist of continuous and discontinuous, bifurcating channel sandstones and delta-front sheet sandstones. The channel sandstones generally thicken downward at the expense of the underlying prodelta clays and may replace selected parts of the delta-front sheet sandstones. The lithologic components of a deltaic complex are interrelated and are referred to collectively as one type of Genetic Increment of Strata (GIS). The GIS is a vertical sequence of strata in which each lithologic component is related genetically to all the others. It is defined at the top by a time-lithologic marker bed (such as a thin limestone or bentonite) and at the base by either a time-lithologic marker bed, an unconformity, or a facies change from marine to nonmarine beds. It generally consists of the total of all marginal marine sediments deposited during one stillstand stage of a shoreline, or it may be a wedge of sediments deposited during a series of cyclic subsidences or emergences. An isopach map of a GIS clearly shows the bifurcating trends of the individual distributari s and the shape of the delta, regardless of the variable lithology of the channel fills. A Genetic Sequence of Strata (GSS) consists of two or more contiguous GIS's and, when isopached, clearly defines the shelf, hinge line, and less stable part of a depositional basin. An isopach map of the McAlester Formation of the Arkoma basin is a good example of a GSS. The oil-productive Booch sandstone is a good example of a deltaic complex occurring within a GIS of this GSS. The upper Tonkawa, Endicott, and Red Fork sandstones of the Anadarko basin are identified as deltaic accumulations within different GIS's. A hypothetical model serves as a basis for establishing the criteria for (1) recognizing successive stillstand positions of a shoreline, (2) predicting paleodrainage courses, (3) predicting positions of a series of deltaic reservoirs, (4) locating isolated channel sandstone reservoirs, and (5) tracing related beach sandstone reservoirs.

Principles of Deltaic Prospecting: ABSTRACT

Deltas generally are formed at river mouths during stillstands of sea level under conditions of either cyclic transgression or regression. Consequently, they generally are not isolated phenomena, but rather occur in multiples in a predictable fashion. Reservoir facies consist of both continuous and discontinuous bifurcating channel sandstones, which thicken downward at the expense of the underlying prodelta clays. All the lithologic components of a deltaic complex are related and are collectively referred to as type of genetic increment of (G.I.S.). The G.I.S. is a sequence of strata in which each lithologic component is genetically related to all the others. It is defined at the top by a marker bed (such as a thin limestone or bentonite) and at the base by either a marker bed or an unconformity. It generally consists of the total of all marginal marine sediments deposited during a stage of either cyclic subsidence or emergence. An isopach map of a G.I.S. clearly shows the bifurcating trends of the individual distributaries and the shape of the delta, regardless of the varied lithology of the channel fills. A genetic sequence of (G.S.S.) consists of 2 or more G.I.S. and, on an isopach map, the shelf, hinge line, and less-stable parts of a depositional basin are clearly defined. An isopach map of the McAlester Formation in the Arkoma basin is a good example of a G.S.S. The oil-productive Booch Sandstone is a good example of a deltaic complex occurring within a G.I.S. of this G.S.S. The upper Tonkawa, Endicott, and Red Fork Sandstones of the Anadarko basin are identified as deltaic accumulations within different G.I.S.'s. A hypothetical model serves as a basis for establishing the criteria for (1) recognizing successive stillstand positions of a shoreline, (2) predicting paleodrainage courses, (3) predicting positions of a series of deltaic reservoirs, (4) locating isolated channel sandstone reservoirs, and (5) tracing related beach-sandstone reservoirs. End_of_Article - Last_Page 839------------

Computer Processing of Log Data Improves Production In Chaveroo Field

Abstract Computer log analysis has proved quite successful in the Chaveroo field of Roosevelt County, N.M., in a carbonate section of low permeabilities, low porosities and variable water saturations. Production in this field occurs at about 4,300 ft in the San Andres formation, a Permian carbonate with a mixture of dolomite, anhydrite and gypsum, and lesser amounts of silica, limestone and silt. Sonic, density and neutron logs, all of which respond differently to porosity and lithology, enable a mathematical solution that defines the fractions of major lithologic components and gives the correct porosity. The Laterolog and Microlaterolog are used to solve for a movable oil relationship. The computer output is a log of bulk volume percentages of porosity, dolomite, anhydrite, gypsum and silica, and a movable oil plot. The record shows that wells completed on the basis of this computer log analysis statistically have higher initial productions and lower water cuts than wells completed on the basis of less diagnostic logging techniques. Introduction The Chaveroo pool is characterized by conditions generally considered hostile to effective log interpretation. Porosities are low-about 5 percent in most producing intervals. The intervals are predominantly dolomite, but contain unpredictably varying fractions of anhydrite, gypsum, chert, silt and limestone. Formation resistivities are high, and most wells are drilled with salt mud. However, in spite of these difficult conditions, modern logs and interpretation methods are giving information needed for efficient completion in the Chaveroo pool. The more efficient completions are obtained by avoiding water-productive intervals interspersed among the pay section of the pool. The produced water fraction is important in Chaveroo because it usually determines whether a well will flow or will require pumping. Thus, better completions are possible when water-productive intervals are distinguished from pay zones. Logs both define pay sections and identify water-productive intervals. Porosity information from logs is used with resistivity data to define fluid saturations. However, because the lithology is variable, no single log defines porosity with sufficient accuracy to reliably distinguish between pay and water. Sonic, neutron and density logs, all of which respond differently to porosity and lithology, are used in a mathematical solution that identifies major lithologic components and thus affords a reliable value of porosity. Office-based electronic computers are used to perform the mathematical solutions. The output of the computer is a log of percentages of major lithologic components and porosity, and an index of movable oil and water saturation. Statistics show that wells selectively completed on the basis of these computer logs are more efficient producers than other wells of the Chaveroo pool. These wells generally flow with higher initial oil production and produce less water. The logs and interpretation methods presented in this article are not entirely new. Earlier papers have described the primary logs, the basic interpretation methods and typical applications of computers to log studies. This study is presented to show how the various logs and methods are combined for improved well completion in the Chaveroo pool. The methods are not restricted to Chaveroo; they are similarly appropriate for other areas of complex lithology. Chaveroo Field Chaveroo field straddles the line between Chaves and Roosevelt Counties of eastern New Mexico (Fig. 1). Production is from the Slaughter zone of the San Andres formation. The main producing interval is about 650 ft below the top of the San Andres, and is at an approximate depth of 4,150 ft. The Slaughter zone, situated between two massive anhydrite sections, is 200 to 250 ft thick. It is described as a fractured, vuggy dolomite having some intercrystalline and oolitic porosity. In addition to interbedded and nodular anhydrite, the zone also contains variable but lesseramounts of gypsum, chert, silt and limestone. JPT P. 889ˆ

Time Surfaces, Vacuity, and Mappability in Stratigraphy: ABSTRACT

Recognition of regional lithologic marker beds is accelerated by refined mechanical logging techniques and adequate drilling density. These correlative punctuations are considered to be geologically instantaneous, and to yield surfaces bounding reliable End_Page 484------------------------------ stratigraphic units. The enclosed units represent longer intervals of time, and their lithologic gradations represent the diluted total environmental impress. Markers represent (1) widespread, essentially contemporaneous deposition of thin lithologic components, and (2) virtually contemporaneous contact phenomena resulting from halmyrolic chemical alteration, replacement, and syngenetic emplacement proximal to the sediment-water interface during times of non-deposition. Time markers may indicate such short-interval lithologic inflictions as changes in water depth, climatic variations, migration of shoreline, and influx of suspensoids with chemical or physical character sharply differing from that of sediments within the body of the marker-bounded unit. Unit thickness of sediment deposited at any locale is dependent on sediment availability, fluxes of the scattering agent, rate of regional variation in chemical impress of depositing medium, nd amplitude of local and regional structural change. Lithologic variations occur in any unit, but the mechanical-log characters of the units are remarkably consistent through an entire sedimentary basin. If log character of unit sequence is similar, one may consider the unit to be areally equivalent not only in duration but in simultaneity. Log character is a function of space and environment, and the markers signal massive changes in the vertical continuity of these environmental controls. Stratigraphic analysts are able to use these time slices to create isopachous and lithofacies maps of short-interval synchronous units. These maps are rigidly controlled for unit initiation, termination, and span. Thickness variations represent a measure of competitive sedimentation resulting from an interplay of environmental factors which involve the allogens and syngens in sedimentary prisms of a marine basin. Paleontologic and sedimentologic characteristics in these geosynchronous units yield environmental and geographic patterns important in the delineation of porosity trends. Geosynchron maps permit analysis of intra-basin structural growth which influences first-phase oil migration. Time-length vacuity becomes susceptible to quantitative analysis. If the generally accepted concepts of uniformitarian geology are approximately correct, these maps systematize haphazard lithologic patterns into geographic and time-controlled stratal units whose internal characteristics make it possible to determine rates of sedimentation, facies gradation, lateral intensities of environmental impress, origins of sediments, depth of water, distance to shore, and a host of other sedimentational variables not otherwise easily susceptible to quantification. End_of_Article - Last_Page 485------------