Discovering the underground structure (6300)

1. Learn the words and word combinations before reading:

pattern - ['pxtn]– образец, пример, структура, форма

density -['densiti] - распределение определенного количества чего-либо на единицу площади, объема, длины, и т.д.; плотность, удельный вес

altitude - ['xltitHd] - высота, высокие места, высота над уровнем моря

subsurface picture – подповерхностная картина

delineation wells - [di"lini'eiSqn] - описательная скважина

geometric frame­work – геометрическая структура

spatial elements - ['speiSql] - пространственные элементы

slicing – нарезание

validate - ['vxlideit] - подтверждать

laterally – горизонтально

selected event – выделенная волна

travel time – время пробега

resolution – разрешение, разрешающая способность

strong acoustic impedance [im'pJdqns] contrast – сильный контраст акустического сопротивления

acquisition configuration – конфигурация сбора, приема

downhole hardware - аппаратное обеспечение скважины

2. Read and translate the text:

Large-scale geological structures that might hold oil or gas reservoirs are invariably located beneath non-productive rocks, and in addition this is often below the sea. Geophysical methods can penetrate them to produce a picture of the pattern of the hidden rocks. Relatively inexpensive gravity and geomagnetic surveys can identify potentially oil-bearing sedimentary basins, but costly seismic surveys are essential to discover oil and gas bearing structures.

Sedimentary rocks are generally of low density and poorly magnetic, and are often underlain by strongly magnetic, dense basement rocks. By measuring 'anomalies' or variations from the regional average, a three-dimensional picture can be calculated. Modern gravity surveys show a generalised picture of the sedimentary basins. Recently, high resolution aero-magnetic surveys flown by specially equipped aircraft at 70 - 100m altitude show fault traces and near surface volcanic rocks.

Initially 3D seismic surveys were used over the relatively small areas of the oil and gas fields where a more detailed subsurface picture was needed to help improve the position of production wells, and so enable the fields to be drained with maximum efficiency. Nowadays 3 D seismic surveys are used for more detailed information about the rock layers, to plan and mon­itor the development and production of a field. The seismic information is integrated with well logs, pres­sure tests, cores, and other engineering/geoscience data from the discovery and delineation wells to formulate an initial field development plan. As more wells are drilled, logged, and tested, and production histories are recorded, the interpretation of the 3-D data volume is revised and refined to take advantage of the new information. Aspects of the interpretation that were initially ambiguous become clear as an under­standing of the field builds, and inferences from the seismic data become more detailed and reliable. The 3-D data volume evolves into a continuously utilized and updated management tool that impacts reservoir planning and evaluation for years after the seismic survey was originally acquired.

Types of 3-D Seismic Analyses

The interpretations that a geophysicist might per­form with 3-D seismic data can be grouped conve­niently into those that examine the geometric frame­work of the hydrocarbon accumulation, those that analyze rock properties, and those that try to monitor fluid flow and pressure in the reservoir.

These analyses affect and significantly improve decisions that must be made about volume of reserves, well or platform locations, and recovery strat­egy.

The first general grouping is geometric framework. It’s a collective term for such spatial elements as the attitudes of the beds that form the trap, the fault and fracture patterns that guide or block fluid flow, the shapes of the depositional bodies that make up a field's stratigraphy, and the orientations of any unconformity surfaces that might cut through the reservoir.

By mapping travel times to selected events, displaying seismic amplitude variations across selected horizons, isochroning between events, noting event termina­tions, slicing through the volume at arbitrary angles, compositing horizontal and vertical sections, optimiz­ing the use of color in displays, and using the wide variety of other interpretive techniques available on a computer workstation, a geophysicist can synthesize a coherent and quite detailed 3-D picture of a field's geometry.

The second general grouping of 3-D seismic analy­ses involves the qualitative and quantitative definition of rock properties. Amplitudes, phase changes, interval travel times between events, fre­quency variations, and other characteristics of the seismic data are correlated with porosity, fluid type, lithology, net pay thickness, and other reservoir prop­erties. The correlations usually require borehole con­trol (well logs, cuttings, cores, etc.) both to suggest initial hypotheses and to refine, revise, and test pro­posed relationships. An interpreter develops a hypoth­esis by comparing a seismic parameter in the 3-D volume at the location of a well to the well's informa­tion, often through the intermediary of a synthetic seismogram or 2-D or 3-D seismic model. The hypoth­esis is then used to predict rock properties between wells, and subsequent drilling validates (or invalidates) the concept. Gas saturation in sandstone reservoirs is probably the rock property that has been most suc­cessfully mapped by 3-D seismic surveys. The pres­ence of free gas typically lowers sharply the seismic velocity of relatively unconsolidated sandstones and creates a strong acoustic impedance contrast with surrounding rock. The contrast produces a seismic amplitude anomaly. Since the early 1970s, this "bright spot" effect has been widely exploited to detect gas saturation with standard 2-D seismic sections. When the effect occurs in 3-D volumes, gas-saturated sand­stones can be accurately mapped laterally across fields at multiple producing horizons.

The third general grouping of 3-D seismic analyses consists of those designed to monitor the actual flow of the fluids in a reservoir. Such flow surveillance is possible if one (1) acquires a baseline 3-D data volume at a point in calendar time, (2) allows fluid flow to occur through production and/or injection with attendant pressure/temperature changes, (3) ac­quires a second 3-D data volume a few weeks or months after the baseline, (4) observes differences between the seismic character of the two volumes at the reservoir horizon, and (5) demonstrates that the differences are the result of fluid flow and pressure/ temperature changes.

The standard 3-D seismic data volume is acquired with source and receivers at the Earth’s surface. It is logistically possible to put sources and/or receivers in boreholes and to record part or all of the 3-D data volume with this downhole hardware. This approach is an active area of research. Depending on the acquisi­tion configuration, one records various kinds and amounts of reflected and transmitted seismic energy, which can then be sorted to provide information on geometric framework, rock properties, and flow sur­veillance, just like surface surveys. Advantages of downhole placement are that higher seismic frequen­cies generally can be recorded, thereby improving resolution, and that surface-associated seismic noise and statics problems are lessened or avoided. The main disadvantages are that source and receiver plants are constrained by the physical locations of available boreholes; borehole seismology can be affected by tube waves and the like, so downhole placement is not noise-free; a borehole source cannot be so strong as to damage the well; and the logistics and economics of operating in boreholes are complex, though not nec­essarily always worse than operating on the surface. One can imagine a time when borehole seismic sources and receivers might be standard components of the hardware run into wells and accepted as routine and valuable devices for reservoir characterization and flow surveillance.

The petroleum industry's twenty-year experience with 3-D seismic surveying is an example of a techno­logical and economic success. Today, the investment in a 3-D survey typically results in fewer development dry holes, improved placement of drilling locations to maximize recovery, recognition of new drilling oppor­tunities, and more accurate estimates of hydrocarbon volume and recovery rate. These outcomes improve the economics of development and production plans and make the surveys cost effective.

Notes:

* to take advantage of - воспользоваться

* "bright spot" effect – эффект «яркого» пятна

2. Find the sentences in the text with the word “drilling” and determine its grammar form.

3. What are ing – forms in the sentence below:

By mapping travel times to selected events, displaying seismic amplitude variations across selected horizons, isochroning between events, noting event termina­tions, slicing through the volume at arbitrary angles, compositing horizontal and vertical sections, optimiz­ing the use of color in displays, and using the wide variety of other interpretive techniques available on a computer workstation, a geophysicist can synthesize a coherent and quite detailed 3-D picture of a field's geometry.

4. Answer the questions:

1. When is 3-D seismic survey used? 2. What interpretations can the geophysicist get with 3-D seismic method? 3. What does geometric framework comprise in? 4. Can you name qualitative and quantitative definitions of the rock structure? 5. Where are the standard 3-D seismic data receivers located? 6. Why 3-D surveying method is more appreciated nowadays?

ADDITIONAL READING

Tasks of a Professional Geologist (11200)

Statement by the National Association of State Boards of Geology (ASBOG®), a non-profit organization comprised of state boards that have developed and administer national competency examinations for the licensure/registration of geologists. (in all the states in the U.S. and the territory of Puerto Rico) The following areas of professional practice contain generalized and some specific activities which may be performed by qualified, professional geologists.

Professional geologists may be uniquely qualified to perform these activities based on their formal education, training and experience. Under each major heading is a group of activities associated with that specific area of geoscience practice. The major areas of professional, geologic practice include, but are not limited to: Research; Field Methods and Communications; Mineralogy; Petrology; Geochemistry; Stratigraphy; Historical, Structural, Environmental, Engineering, and Economic Geology; Geophysics; Geomorphology; Paleontology; Hydrogeology; Geochemistry; and Mining Geology and Energy Resources. These areas are specifically included in the ASBOG® examinations to assure geologic competency. Again, this list represents only a cross-section of possible activities, and does not include all potential professional practice activities.

Also included in this publication is a listing of "Other related activities which may be performed by qualified Professional Geologists." These activities, although not specifically geoscience in content, may be performed by a qualified, professional geologist.

Research, Field Methods and Communications

! Plan and conduct field operations including human and ecological health, safety, and regulatory considerations

! Evaluate property/mineral rights

! Interpret regulatory constraints

! Select and interpret appropriate base maps for field investigations

! Determine scales and distances from remote imagery and/or maps

! Identify, locate and utilize available data sources

! Plan and conduct field operations and procedures to ensure public protection

! Construct borehole and trench logs

! Design and conduct laboratory programs and interpret results

! Evaluate historic land use or environmental conditions from remote imagery

! Develop and utilize Quality Assurance/Quality Control procedures

! Construct and interpret maps and other graphical presentations

! Write and edit geologic reports

! Interpret and analyze aerial photos, satellite and other imagery

! Perform geological interpretations from aerial photos, satellite and other imagery

! Design geologic monitoring programs

! Interpret data from geologic monitoring programs

! Read and interpret topographic and bathymetric maps

! Perform geologic research in field and laboratory

! Prepare soil, sediment and geotechnical logs

! Prepare lithological logs

! Interpret dating, isotopic, and/or tracer studies

! Plan and evaluate remediation and restoration programs

! Identify geological structures, lineaments, or fracture systems from surface or remote imagery

! Select, construct, and interpret maps, cross-sections, and other data for field investigations

! Design, apply, and interpret analytical or numerical models

Mineralogy/Petrology

! Identify minerals and their physiochemical properties

! Identify mineral assemblages

! Determine probable genesis and sequence of mineral assemblages

! Predict subsurface mineral characteristics on the basis of exposures and drill holes

! Identify and classify major rock types

! Determine physical properties of rocks

! Determine geotechnical properties of rocks

! Determine types, effects, and/or degrees of rock and mineral alteration

! Determine suites of rock types

! Characterize mineral assemblages and probable genesis

! Plan and conduct mineralogic or petrologic investigations

! Identify minerals and rocks and their characteristics

! Identify and interpret rock and mineral sequences, associations, and genesis

Geochemistry

! Evaluate geochemical data and/or construct geochemical models related to rocks and minerals

! Establish analytical objectives and methods

! Make determinations of sorption/desorption reactions based upon aquifer mineralogy

! Assess the behavior of dissolved phase and free phase contaminant flow in groundwater and surface water systems

! Assess salt water intrusion

! Design, implement and interpret fate and transport models

! Identify minerals and rocks based on their chemical properties and constituents

Stratigraphy/Historical Geology

! Plan and conduct sedimentologic, and stratigraphic investigations

! Identify and interpret sedimentary structures, depositional environments, and sediment provenance

! Identify and interpret sediment or rock sequences, positions, and ages

! Establish relative position of rock units

! Determine relative and absolute ages of rocks

! Interpret depositional environments and structures and evaluate post-depositional changes

! Perform facies analyses

! Correlate rock units

! Interpret geologic history

! Determine and establish basis for stratigraphic classification and nomenclature

! Establish stratigraphic correlations and interpret rock sequences, positions, and ages ! Establish provenance of sedimentary deposits

Structural Geology

! Plan and conduct structural and tectonic investigations

! Develop deformational history through structural analyses

! Identify structural features and their interrelationships

! Determine orientation of structural features

! Perform qualitative and quantitative structural analyses

! Map structural features

! Correlate separated structural features

! Develop and interpret tectonic history through structural analyses

! Map, interpret, and monitor fault movement

! Identify geological structures, lineaments, fracture systems or other features from surface or subsurface mapping or remote imagery

Paleontology

! Plan and conduct applicable paleontologic investigations

! Correlate rocks biostratigraphically

! Identify fossils and fossil assemblages and make paleontological interpretations for age and paleoecological interpretations

Geomorphology

! Evaluate geomorphic processes and development of landforms and soils

! Identify and classify landforms

! Plan and conduct geomorphic investigations

! Determine geomorphic processes and development of landforms and soils

! Determine absolute or relative age relationships of landforms and soils

! Identify potential hazardous geomorphologic conditions

! Identify flood plain extent

! Determine high water (i.e. flood) levels

! Evaluate stream or shoreline erosion and transport processes

! Evaluate regional geomorphology

Geophysics

! Select methods of geophysical investigations

! Perform geophysical investigations in the field

! Perform geological interpretation of geophysical data

! Design, implement, and interpret data from surface or subsurface geophysical programs including data from borehole geophysical programs

! Identify potentially hazardous geological conditions by using geophysical techniques

! Use wire line geophysical instruments to delineate stratigraphic/lithologic units

! Conduct geophysical field surveys and interpretations, e.g. petrophysical wellbore logging devices, seismic data (reflection and refraction), radiological, radar, remote sensing, electro-conductive or resistive surveys, etc. Includes delineation of mineral deposits, interpretation of depositional environments, formation delineations, faulting, salt water contaminations-intrusion, contaminate plume delineations and other

! Identify and delineate earthquake/seismic hazards

! Interpret paleoseismic history

Hydrogeology/Environmental Geochemistry

! Plan and conduct hydrogeological, geochemical, and environmental investigations

! Design and interpret data from hydrologic testing programs including monitoring plans

! Utilize geochemical data to evaluate hydrologic conditions

! Develop and interpret groundwater models

! Apply geophysical methods to analyze hydrologic conditions including geophysical logging analysis and interpretation

! Determine physical and chemical properties of aquifers and vadose zones

! Define and characterize groundwater flow systems

! Develop water well abandonment plans including monitoring and public water supply wells

! Develop/interpret analytical, particle tracking and mass transport models

! Design and conduct aquifer performance tests

! Define and characterize saturated and vadose zone flow and transport

! Evaluate, manage, and protect groundwater supply resources

! Potentiometric surface mapping and interpretation

! Design and install groundwater exploration, development, monitoring, and pumping/injection wells

! Develop groundwater resources management programs

! Plan and evaluate remedial-corrective action programs based on geological factors

! Evaluate, predict, manage, protect, or remediate surface water or groundwater resources from anthropogenic (man's) environmental effects

! Characterize or determine hydraulic properties

! Interpret dating, isotopic, and/or tracer surveys

! Determine chemical fate in surface water and groundwater systems

! Make determinations of sorption/desorption reactⁱons based upon aquifer mineralogy

! Assess the behavior of dissolved phase and free phase contaminant flow in groundwater and surface water systems

! Assess and develop well head protection plans and source water assessment delineations

Engineering Geology

! Provide geological information and interpretations for engineering design

! Identify, map, and evaluate potential seismic and othergeologic-geomorphological conditions and/or hazards

! Provide geological consultation during and after construction

! Develop and interpret engineering geology investigations, characterizations, maps, and cross sections

! Evaluate materials resources

! Plan and evaluate remediation and restoration programs for hazard mitigation and land restoration

! Evaluate geologic conditions for buildings, dams, bridges, highways, tunnels, excavations, and/or other designed structures

! Define and establish site selection and evaluation criteria

! Design and implement field and laboratory programs

! Describe and sample soils for geologic analyses

! Describe and sample soils for material properties/geotechnical testing

! Interpret historical land use, landforms, or environmental conditions from imagery, maps, or other records

! Conduct geological evaluations for surface and underground mine closure and land reclamation

! Laboratory permeability testing of earth and earth materials

Economic Geology, Mining Geology, and Energy Resources

(including metallic and non-metallic ores/minerals, petroleum and energy resources, building stones/materials, sand, gravel, clay, etc.)

! Plan and conduct mineral, rock, hydrocarbon, or energy resource exploration and evaluation programs

! Implement geologic field investigations on prospects

! Perform geologic interpretations for rock, mineral, and petroleum deposit evaluations, resource assessments, and probability of success

! Perform economic analyses/appraisals

! Provide geologic interpretations for mine development and production activities

! Provide geologic interpretations and plans for abandonment, closure, and restoration of mineral and energy development or extraction operations

! Identify mineral deposits from surface and/or subsurface mapping or remote imagery

! Predict subsurface mineral or rock distribution on basis of exposures, drill hole, or other subsurface data

! Evaluate safety hazards associated with mineral, petroleum, and/or energy exploration and development

! Determine potential uses and economic value of minerals, rocks, or other natural resources

Other related activities which may be performed by qualified Professional Geologists

! Implement siting plans for the location of lagoons and landfills

! Environmental contaminant isocontour mapping

! Conduct water well inventories

! Determine geotechnical aquifer parameters

! Land and water (surface and ground water) use utilized in planning, land usage, and other determinations

! Determine sampling parameters and provide field oversight.

Emergency response activities and spill response planning including implementation and coordination with local, state, and federal agencies

! Develop plans and methods with law enforcement, fire, emergency management agencies, toxicologists and industrial hygienists to determine methods of protection for public health and safety

! Provide training related to hazardous materials and environmental issues related to hazardous materials

! Develop plans and methods with biologists for protection of wildlife during spill events

! Prepare post spill assessments and remediation plans

! Develop and implement site safety plans and environmental sampling plans

! Provide educational outreach related to geological, geotechnical, hydrologic, emergency response and other activities

! Respond to natural disaster events (i.e. floods, earthquakes, etc.) for protection of human health and the environment

! Participate in pre-planning for spill events in coastal or other environmentally sensitive environments

! Develop resource(s) and infrastructure vulnerability assessment plans and reports related to potable and non-potable water supplies, waste water treatment facilities, etc.

Some more information about rocks (3800)

Dykes are intersecting veins. In inclination dykes may vary from vertical to horizontal. Sometimes we may observe them extend, outward from larger masses of intruded rocks.

Effusive or volcanic rocks occur in the forms of domes, sheets and flows. Domes are the names of arched accumulations of lava solidified in the form of beds similar to those of sedimen­tary rocks.

Sheets are formed on the surface from quiet outwelling of highly molten materials through a) localized opening or volcanic vents and hence connected with volcanic eruptions or b) from fissures not connected with volcanic eruptions. Sheets are similar in form to sedimentary strata and extend to large areas.

Flows are formed in the same manner as sheets but they fill negative reliefs such as valleys and flumes. Flows are much smaller in size than sheets.

Igneous rocks are characterized by a holocrystal line (or granular-crystalline)_, glassy and porphyritic structure.

Igneous rocks are subdivided according to their chemical composition. Based upon the silicon oxide content the rocks are divided into ultra acid, acid average, basic and ultra basic. The amount of silica present exercises an important influence on the crystallization of the magma. The many hundreds of analyses that have been made of igneous rocks show them to contain the following principal oxides, silica, alumina, iron oxides, ferric, ferrous, magnesia, lime, soda, and potash. These principal oxides as composing igneous rocks do not exist as free oxides, excepting a few cases with but a few exceptions only in small amounts.

TEXTURE OF IGNEOUS ROOKS.

By texture of an igneous rock is meant size, shape and manner of aggregation of its component minerals. It is considered to be an important means of determin­ing the physical conditions under which the rock was formed at or near the surface or at some depth below and hence is recog­nized to be one of the important factors in the classification of igneous rocks.

Some rocks are sufficiently coarse-grained in texture for the principal mineral to be readily distinguished by unaided eye. In others their minerals are too small to be seen even with the aided eye. There are also those in which no minerals appeared to have crystallized. Instead the magma has solidified as a glass.

KINDS OF TEXTURE.

Expressing so closely the conditions under which rock magmas solidify the texture is recognized to be an important property of rocks and one of the principal factors in their classifications.

In megascopic description of igneous rocks five principal textures were reported to exist. They are glassy, dense or felsitic, porphyritic, granitoid and fragmental.

According to the size of mineral grains we may recognize: 1) fine-grained ; 2) medium-grained; 3) coarse-grained rocks.

DESCRIPTION OF SOME IGNEOUS ROOKS.

Granites are known to be composed of feldspar and quartz usually with mica or hornblende, rarely pyroxene.

The chemical composition of granite is now regarded to be of less economic importance than the mineral composition.

PHYSICAL PROPERTIES.

The usual colour of granite is reported to be some shade of grey though pink or red varieties are likely to occur depending chiefly upon that of the feldspar and the proportion of the feldspar to the dark minerals. Specific gravity ranges from 2.65 to 2.75.The percentage of absorption is very small. Crushing strength is very high ranging from 15.000 to 20.000 pounds per square inch (psi).

These properties render the rock especially desirable for building purposes.

DIORITE. MINERAL COMPOSITION.

The diorites are granular rocks which are known tobe composed of plagioclass as the chief feldspar and hornblende or biotite or both.

Augite is likely to be present in some amount and some ortho - class occurs in all diorites. The name diorite is applied to those granular rocks in which hornblende is found to equal or exceed feldspar in amount. Because of the fine-grained texture it is not possible in manycases to determine by megascopic exa­mination the dominant feldspar.

CHEMICAL COMPOSITION.

The most important points to be ob­served inthe chemical composition of normal diorites are lower silica content but notably increased percentages of the bases, iron, lime and magnesia over the granites.

PHYSICAL PROPERTIES.

Diorites are usually of a dark or greenishcolour, sometimes almost black depending upon the colour of hornblende and its proportion to feldspar. They have a higher specific gravity than granites, ranging from 2.82 to 5.0. They show a high compressive strength and a low per­centage of absorption.