Wireline Log Analysis Research Articles

Geophysical response of flood basalts from analysis of wire line logs: Ocean Drilling Program Site 642, Vøring volcanic margin

Analysis of wire line logs at Ocean Drilling Program Site 642, the deepest scientific hole yet drilled in an offshore large igneous province (LIP), reveals the main features of the extrusive complex constructed during formation of a volcanic margin. A characteristic cyclic log response images tholeiitic lavas and thin tuffs corresponding to the seaward dipping reflectors in the seismic record. Flows are 0.6–18.5 m thick, while most sediments are <l m thick. Porosity dependent sonic, density, neutron porosity and resistivity logs respond to gently decreasing porosity in upper 5–7 m of the flow and rapid porosity increase near the flow base. Velocity and density top and bottom gradients are largely independent of flow thickness, with velocity gradients of 400 to 600 s−1 and −1000 to −2000 s−1, respectively. A positive correlation between flow thickness and mean velocity simply reflects increased proportion of massive basalt in thicker flows. There is also an overall increase in mean fine‐grained basalt velocity with depth with a gradient of 0.8±0.3 s−1. Flow velocity‐density relations show a downward velocity strengthening related to a decrease in high aspect ratio voids. High velocities near the flow base correlate with high, >2000 Ω‐m, focused resistivity kicks. The large flow‐scale variations in physical properties show that representative core measurements must be densely sampled. Both on flow and sequence scales Site 642 log responses appears typical for the North Atlantic Volcanic Province and other LIPs but differs from logs in deep ocean crustal holes. Principal differences in log responses reflect mode of crustal emplacement and alteration. Hence Site 642 forms a reference hole for extrusive constructions on oceanic LIPs.

Some Considerations in the Application of Wireline Logging to Environmental Investigations: ABSTRACT

ABSTRACT Wireline log interpretation and analysis techniques were developed by the petroleum industry to identify and quantify pore fluids in petroleum reservoirs, to characterize the properties of reservoirs, to identify lithology, and to facilitate geologic interpretation. In subsurface environmental investigations the information required is almost identical. Such investigations must identify and quantify pore fluids in contaminated media, quantify contaminant concentrations in ground water, determine the hydrologic properties of aquifers, and characterize subsurface geology. Given the great similarity of information required, classical petroleum log interpretation and analysis principles should have direct and useful application to environmental questions. However, attempts to apply these principles have often produced disappointing results that can many times be attributed to differences in the physical environments, primarily hole and formation conditions, in which logging data are acquired by the two disciplines. Classical wireline logging theory is based on central assumptions regarding the physical environment in which tools are operated. Environmental logging may occur both above and below the water table, in formations that contain air and/or fresh water, in holes that may be filled with air, water, or mud, and where the salinity of the formation and borehole fluids may be similar. In these cases those central assumptions are commonly not valid. Geologists and log analysts must be aware of these differences and how they affect the various types of wireline logs. Some of these problems may be resolved by further research, rethinking of existing theory, and the development of new analytical techniques.

Integration of Lithofacies Description, Fracture Characteristics, Micropaleontology and Wireline Log Analysis to Define the Internal Architecture of Chalk Reservoirs in the Norwegian Sector of the North Sea: ABSTRACT

Integration of Lithofacies Description, Fracture Characteristics, Micropaleontology and Wireline Log Analysis to Define the Internal Architecture of Chalk Reservoirs in the Norwegian Sector of the North Sea: ABSTRACT

Log-derived reservoir properties and porosity preservation of Upper Jurassic Arab Formation in Saudi Arabia

Various types of wireline log analysis were conducted for the Arab Reservoirs of Upper Jurassic age in eastern Saudi Arabia. After evaluating the values of the cementation factor m in the Archie equation and the formation water resistivity R w, values such as total, primary and secondary porosities, lithological composition, water (or hydrocarbon) saturation and permeability were estimated using combinations of various logs. Some of the results, such as the estimated porosity and permeability, were then compared with the available core analysis results. The estimated percentage of dolomite was also plotted against the percentage porosity in an attempt to show a possible effect of dolomitization on porosity; dolomitization seems to increase the porosity in the early and intermediate stages, but tends to reduce porosity in the later or near-completion stages of dolomitization. This finding coincides with the earlier work of Power based on petrographical and petrophysical studies. The calculated average porosity of the Arab Reservoirs is up to 30%, which is exceptionally high if the effects of depth of burial between 4000 and 9000 ft and the geological age of about 160 million years (Upper Jurassic) are taken into consideration. To explain such high porosity values for the Arab Reservoirs, probable geological, physical, chemical factors, such as acidic formation fluids, reduced fluid mobility and ion-exchange capacity, tectonic forces and dolomitization are suggested.

Hydrocarbon Generation Potential of the Cretaceous Section from Well ALP-6, Perija Region, Venezuela

Geochemistry and sedimentology have been integrated in order to provide a better understanding of the source rock potential and depositional environments of the La Luna Formation and Machiques Member in Well ALP-6 (Perija region). These two units, the dominant source rocks in the Maracaibo Basin, are mainly shales with high to very high organic content, while thin interbeds of limestones are poor in organic matter. A detailed sedimentological study and sequence analysis indicates that both shaly units represent a period of platform infilling subsequent to drowning. Periods of progressive back stepping culminating in the deposition of organic-rich condensed intervals are recognized, based on sedimentology of cores and wireline log analysis. A succession of fining-upward sequences, 1' to 5' thick, with distinct sedimentological and geochemical signatures have been identified in the La Luna Formation. Phenomena of early diagenesis (intrashale calcite growth due to organic matter degradation; sulfur precipitated in local paleolows) to late diagenesis (pressure-solution effects with development of laterally correlatable cone-in-cone layers) are all indicators that the hydrocarbon generation potential of La Luna is not uniform and can only be assessed by detailed geological, sedimentological and geochemical investigations. Two geochemically distinct facies can be identified in both La Luna andmore » Machiques. A sulfur-rich facies is characterized by Corg/AVSul ratios averaging 1.9 and by exceptionally high concentrations of sulfur-bearing aromatic compounds. A sulfur-poor facies is characterized by Corg/AVSul ratios averaging 9.2 and by trace concentrations or absence of sulfur-bearing aromatic compounds.« less

Assessing the Impacts of Geopressure on Exploration Using Integrated Geological Log Analysis

The occurrence of geopressure anomalies in the El Furrial, Chaguaramal and Boqueron oil fields in the Maturin subbasin of the Eastern Venezuela Basin, and their heterogeneous evolution through geological time has caused significant drilling problems. Identification of these anomalies and isolation of the adjacent subcompacted formations has cost much time and money. There are two main abnormal pressure zones in the Eastern Venezuela Basin. The lower occurs in a thick homogenous marine shale sequence of the Carapita Formation, deposited during late Oligocene-early Miocene times, which was followed by a late Miocene period of uplift and erosion. The upper occurs in marine shales and sandstones of the La Pica Formation, which was transgressively deposited on the eroded Carapita Formation. Using an integrated analysis of lithology and wireline logs, tectonically-influenced sections have been identified within the lower geopressure which have modified its original conditions. Furthermore, the late Miocene unconformity between the two zones controls the occurrence, style and dimension of the upper geopressure. Detailed differential compaction analysis from low to high hydraulic potential intervals through the lithostratigraphic sequence and their association to the unconformity explain the evolution and the current state of geopressure distribution throughout the oil fields. These conclusions are supportedmore » by direct and indirect quantitative pore and fracture pressure gradient analysis. The study identifies areas within these fields (e.g., Central and Eastern Boqueron) which show alterations of the occurrence and behavior of the geopressure. Such knowledge permits rapid modifications to drilling programs, allowing successful exploration and development.« less

INTEGRATED SOURCE, MATURATION AND MIGRATION ANALYSIS, GIPPSLAND BASIN, AUSTRALIA

Biomarker geochemistry, maturation modelling and migration pathway analysis have been used in a new, integrated analysis of the Gippsland Basin. The analysis has resulted in the development of a predictive model for hydrocarbon charge and oil versus gas split. The study was carried out in 4 parts: analytical geochemistry, source distribution mapping, maturation modelling and migration pathway analysis.New geochemical biomarker studies confirm a non-marine source for the oils, but place peak oil generation in the upper part of the traditional oil window. Gas in the basin is mainly derived from overmature source rocks. Coals were recognised to contribute significantly to oil generation.The source rock thickness and distribution for the entire basin were mapped using analytical techniques plus wireline log analysis, coupled with seismic structural mapping and facies analysis. Prime oil-prone source rocks were found to be located in the lower coastal plain depositional environment. Extrapolations were necessary for older rocks, using stratigraphic models.Maturation modelling modelling of selected wells and synclines was carried out and an overall basin model constructed. Post-structuring yields of oil and gas were also derived. A key result was the lack of post-structuring overmature gas generation in the oil prone southeastern part of the basin, owing to high palaeo-temperatures associated with earlier rifting.Analysis of present day and palaeo-migration pathways gave an excellent match between predicted oil versus gas ratios and discoveries, both geographically and stratigraphically. The tool is now being used in a predictive mode to highgrade basin prospectivity.

The petrophysical characteristics of the Brent sandstones

Abstract The commonly occurring ranges and the principal controlling factors of the porosity, permeability, capillary characteristics and fluid saturations of the Brent sandstones are presented. Whilst there is insufficient space to discuss these parameters in specific detail, their variability and the degree to which they are influenced by the geological characteristics of the Brent sandstones is reviewed. The paper shows, through the use of examples, that a thorough understanding of the petrophysical characteristics of a reservoir rock requires the integration of several types of data into a single model. The wireline log and laboratory core analyses provide a quantitative input, whilst geological factors such as mineralogy, diagenetic history, and sedimentary fabric provide a most necessary framework within which the pore geometry variability, detected by log and core data, can be examined. An appendix summarizes the principal quantitative techniques involved.

The Effect of Anhydrite on Oil Production in Dolomite Reservoirs -- Some Early Observations

Results from wireline log analysis of recently drilled wells in the San Andres dolomite of the Slaughter and Levelland fields, west Texas, suggested a correlation between the presence of anhydrite and poor oil production. Log data from wells in the North-Central Levelland, Wright and Boyd Mallet units show that a high percentage of wells that perform poorly all have significant amounts of anhydrite in their reservoirs. Preliminary indications suggest that more than 20% anhydrite in the reservoir will severely reduce porosity and permeability and cause higher than average water saturations. In addition, the spacing of new wells indicates that reservoir degradation by anhydrite may be sporadic and areally restricted, allowing a poorly performing well to be located no more than 1500 ft from better performing wells that have low amounts of anhydrite. These observations imply that uneconomic infill well locations could be minimized by mapping the percent of anhydrite within the reservoir section. On a practical basis, the only way to acquire a sufficiently large enough database for good anhydrite prediction in west Texas is to refine log analysis to yield accurate mineralogy from cased hole logs.

The third age of wireline log analysis: application to reservoir diagenesis

Abstract Geophysical well logs were first developed to identify the porosity and fluid composition of potential petroleum reservoirs. Subsequently their use was extended to include diagnosing the depositional environment of reservoirs, as an aid to predicting their geometry. Both these techniques are now routine. A new age of the application of geophysical logs now dawns due to the enhanced understanding of the diagenetic processes that affect petroleum reservoirs, including cementation which destroys porosity and solution which enhances it. These ideas can be used to interpret both conventional porosity logs and the new types of log that, when carefully interpreted, allow vertical variations in mineralogy to be measured. Three main diagenetic effects can be recognized in geophysical well logs: facies-related diagenetic phenomena; cemented and leached zones related to migrating diagenetic fronts of acid meteoric or deep connate fluids; and diagenetic effects related to petroleum migration and entrapment.

Integrated High-Resolution Palynomorph Biostratigraphy and Wireline Log Analysis as a Tool for Basin Analysis and Depositional Environment Interpretation

In Cabinda, Angola, serious correlation problems are encountered in thick Cenomanian and Albian successions of mixed clastics and carbonates. Rapid lateral and vertical facies changes result from the close proximity of diverse depositional environments, ranging from shallow marginal marine to deep open marine. Lithological miscorrelations can result from reliance solely on wireline logs. Foraminiferal and nannofossil distributions are strongly modified by these facies by palynomorphs, particularly pollen and spores and some microplankton, are less subject to facies control. A stratigraphic framework within which the facies relationships can be correctly resolved is provided by a high-resolution palynomorph can be correctly resolved is provided by a high-resolution palynomorph biozonation. Palynomorph assemblages from 30 offshore wells were analyzed. Biozones are defined on selected first downhole occurrences (tops), concurrent ranges, and relative abundances of regional key zone forms. Palynomorphs were selected by the criteria: readily recognizable morphology, relative abundance, stratigraphic range, and known stratigraphic value. Fifteen biozones are defined: four are Cenomanian, ten are Albian, and one is Aptian. Specific environments that were identified in conventional cores produced characteristic populations of environmentally sensitive palynomorphs. These distinctive assemblages can now be used to identify open marine, upper shoreface to foreshore, shallow lagoon, and tidal flatmore » environments in cuttings. Application of the high-resolution palynomorph biozonation is illustrated in a depositional setting characterized by rapid facies changes. Correlation using sonic, density, gamma ray, and resistivity logs is improved when constrained by the biozonal framework.« less

Depositional Environment of the Upper Cretaceous Mokelumne River Formation, Sacramento Basin, California: ABSTRACT

The Upper Cretaceous Mokelumne River formation of the southern Sacramento basin is a fluvial-deltaic sequence deposited during the late Maestrichtian epoch. Quartzose-feldspathic sediments, sourced from the rising proto-Sierra Nevada terrain toward the east, were deposited within a fore-arc basin tectonostratigraphic setting. The Mokelumne River formation contains interbedded sands and shales in the northern area which grade into massive sands in the southern area, indicating a change in depositional environments. The upper contact of the unit is an unconformity which separates the Mesozoic and Cenozoic eras. The lower contact is an unconformity in the north which grades into a conformable contact with the underlying strata toward the south. The present study examines the depositional characteristics of the Mokelumne River formation in the northern area. Wireline log analysis indicates the presence of the following lower delta-plain deposits: distributary channels, natural levees, crevasse splays, and marshes with associated lignite beds, Subaqueous delta-plain deposits include the basal sand unit, locally termed the Bunker sand. The Bunker sand exhibit a coarsening-upward sequence on wireline logs and is interpreted to represent a prodelta distal bar. The sand-shale ratio decreases northward and westward and increases toward the south. The Modelumne River formation is productive in 29 fieldsmore » and has produced in excess of 500 bcf of natural gas. Hydrocarbon accumulations are formed by updip fault truncation, stratigraphic traps, and updip erosional traps sealed by overlying clays.« less

Computerized Wireline Log Analysis in the Mining Industry: ABSTRACT

Computerized Wireline Log Analysis in the Mining Industry: ABSTRACT

Cerro Prieto Case History: Use of Wireline Logs to Characterize a Geothermal Reservoir

Abstract The Cerro Prieto geothermal field is located in Baja California, Mexico, in the Salton Trough–a rift basin filled mainly with Colorado River sediments. A comprehensive wireline log analysis was undertaken as part of a multidisciplinary study of this geothermal system. It established (1) the physical properties of the various sedimentary units; (2) the depositional environment and hydrothermal alteration of the units; (3) the location, attitude, and displacement of faults; and (4) the subsurface circulation of the geothermal fluids. Presented are the methodology that was used and the application of the results to further exploration and development of this high-temperature geothermal resource.

Pressure Prediction with Flowline Temperature Gradients

The procedure described here is applicable anywhere in the world, from the Louisiana Gulf Coast to the South China Sea. However, in using this method to predict the existence of overpressured shale and the first overpressured sand below a shale interval, one must carefully consider many factors affecting flowline temperature response to changes in geotemperature. Introduction Abnormal pore pressure is found at very shallow depths in several areas of the world and very short pressure transition zones are often encountered. At pressure transition zones are often encountered. At one time, all methods of determining the presence of abnormal pressure depended upon drilling data accumulated after the bit had reached the transition zone or upon after-the-fact analysis of wireline logs. All methods have inherent limitations that create additional difficulties in detecting higher pressure either as the depth of abnormal pressure decreases, or as the length of the transition zone decreases, or both. A complementary procedure was needed that would not be dependent upon the amount of mud weight overbalance, upon penetration far into the transition zone, upon the nature of the rock matrix, or upon correlations of log parameters with pressure values. A method satisfying these requirements was suggested by variations observed in surface mud temperature. Detailed studies resulted in the development of a pressure prediction and detection procedure that pressure prediction and detection procedure that utilizes relationships between pore pressure and mud flowline temperature. This paper reviews theory presently associated with the flowline temperature presently associated with the flowline temperature method, discusses data collection and interpretation, and suggests further exploitation. Theory The geothermal gradient or the rate at which subsurface temperature increases with depth can be defined by ...........(1) where the gradient is expressed in F per 100 ft of depth. For any given area, the geotemperature gradient is usually assumed to be constant. While the average gradient across normal pressured horizons may be constant, higher-than-normal geothermal gradients have been found to be associated with pore-pressure gradients greater than normal. Lewis and Rose presented a theory to explain how high-pressure zones presented a theory to explain how high-pressure zones relate to departures of the geothermal gradient from the normal value. Practically all heat flowing within the earth moves outward from the molten core and is radiated into space. The total heat flowing across all depth increments is constant, but the temperature differential across any increment depends upon the ability of materials in the increment to conduct beat. Below a formation whose conductivity is relatively low, heat builds up until the temperature differential across the formation allows heat flow through the insulator to equal the flow of incoming heat. Accordingly, higher geothermal gradients must exist across insulating formations and relatively lower temperature gradients are present in formations with relatively higher conductivities. JPT P. 135

Well-driven seismic: 3D data processing solutions from wireline logs and borehole seismic data

Steve Morice, product champion, well-driven seismic, WesternGeco, Jean-Claude Puech, borehole seismic co-ordinator, Schlumberger, Europe, CIS and Africa, and Scott Leaney, geophysics advisor, Schlumberger describe how new integrated seismic data processing techniques, combined with a rich borehole geophysics dataset, offer opportunities to significantly enhance 3D seismic preconditioning, prestack imaging and inversion to elastic properties. Meeting the demands for higher resolution, signal-tonoise ratio, positional accuracy and amplitude fidelity from 3D seismic data requires enhanced algorithms and techniques throughout the entire data processing sequence. Well data, in the form of wireline logs and vertical seismic profiles (VSPs), provide unique constraints on key seismic data processing parameters as well as a calibration of the 3D processing sequence in terms of wellto- seismic ties. New methods for the combined analysis of wireline logs, VSPs and prestack seismic data provide invaluable information about seismic velocities (P and S), anelastic attenuation (Q) factors, velocity anisotropy (of various symmetry axes) and multiples. The logs, VSPs and seismic data should be processed and analysed together - reconciling differences due to the basic geophysics of the various measurements, the range of resolution scales, and different source of errors and uncertainties - for a unified and self-consistent borehole and surface-seismic dataset. The derivation of seismic properties from well logs and VSPs is covered extensively in the geophysical literature (see Further Reading below). The purpose of this article is to describe and illustrate how these properties can be applied to address some of the major challenges in conventional 3D seismic data processing.