Introduction Tectonics

Tectonics

From Wikipedia, the free encyclopedia

Tectonics, (from the Greek for "builder", tekton), is a field of study within geology concerned generally with the structures within the crust of the Earth (or other planets) and particularly with the forces and movements that have operated in a region to create these structures.

Tectonics is concerned with the orogenies and tectonic development of cratons and tectonic terranes as well as the earthquake and volcanic belts which directly affect much of the global population. Tectonic studies are also important for understanding erosion patterns in geomorphology and as guides for the economic geologist searching for petroleum and metallic ores.

A subfield of tectonics that deals with tectonic phenomena in the geologically recent period is called neotectonics

Tectonic studies have application to lunar and planetary studies, whether or not those bodies have active tectonic plate systems.

Since the 1960s, plate tectonics has become by far the dominant theory to explain the origin and forces responsible for the tectonic features of the continents and ocean basins.

There are three main types of tectonic regime

• Extensional tectonics
• Thrust (Contractional) tectonics
• Strike-slip tectonics

Extensional tectonics is concerned with the structures formed, and the tectonic processes associated with, the stretching of the crust or lithosphere.

Areas of extensional tectonics are typically associated with:

• The development of continental rifts, with or without the effects of mantle upwelling
• The gravitational spreading of zones of thickened crust formed during continent-continent collision
• Tensional flexures along strike-slip faults
• On passive margins where an effective basal detachment layer is present at the upper end of a linked system

Extensional structures

The main structures formed in areas of extensional tectonics are normal faults and graben structures.

Prominent examples include:

• The East African Rift, a major continental rift system
• The Basin and Range province of western North America
• The global mid-ocean ridge system
• The Dead Sea basin formed at a releasing bend along a continental transform boundary

Thrust tectonics is concerned with the structures formed, and the tectonic processes associated with, the shortening of the crust or lithosphere.

Areas of thrust tectonics are typically associated with:

• The collision of two continents or a continent and an island arc at a destructive plate boundary
• Restraining bends on strike-slip faults
• On passive margins, balancing up-dip extension, where an effective detachment layer is present

Strike-slip tectonics is concerned with the structures formed by, and the tectonic processes associated with, zones of lateral displacement within the crust or lithosphere.

Areas of strike-slip tectonics are associated with

• Continental transform (conservative) plate boundaries
• Lateral ramps in areas of extensional or contractional tectonics accommodating lateral offsets between major extensional or thrust faults
• Zones of oblique continent-continent collision
• The deforming foreland of a zone of continent-continent collision, a process sometimes known as escape tectonics

Introduction geology

From Wikipedia, the free encyclopedia

Geology (from Greek: γη, gê, "earth"; and λόγος, logos, "speech" lit. to talk about the earth) is the science and study of the solid matter that constitutes the Earth. Encompassing such things as rocks, soil, and gemstones, geology studies the composition, structure, physical properties, history, and the processes that shape Earth's components. It is one of the Earth sciences. Geologists have established the age of the Earth at about 4.6 billion (4.6x10⁹) years, and have determined that the Earth's lithosphere, which includes the crust, is fragmented into tectonic plates that move over a rheic upper mantle (asthenosphere) via processes that are collectively referred to as plate tectonics. Geologists help locate and manage the Earth's natural resources, such as petroleum and coal, as well as metals such as iron, copper, and uranium. Additional economic interests include gemstones and many minerals such as asbestos, perlite, mica, phosphates, zeolites, clay, pumice, quartz, and silica, as well as elements such as sulfur, chlorine, and helium. Geology is also of great importance in the applied fields of civil engineering, soil mechanics, hydrology, environmental engineering and geohazards.

Planetary geology (sometimes known as Astrogeology) refers to the application of geologic principles to other bodies of the solar system. Specialised terms such as selenology (studies of the moon), areology (of Mars), etc., are also in use. Colloquially, geology is most often used with another noun when indicating extra-Earth bodies (e.g. "the geology of Mars").

The word "geology" was first used by Jean-André Deluc in the year 1778 and introduced as a fixed term by Horace-Bénédict de Saussure in the year 1779. The science was not included in Encyclopædia Britannica's third edition completed in 1797, but had a lengthy entry in the fourth edition completed by 1809.An older meaning of the word was first used by Richard de Bury to distinguish between earthly and theological jurisprudence.

Introduction stratigraphy

Stratigraphy, a branch of geology, studies rock layers and layering (stratification). Stratigraphy, from Latin stratum + Greek graphia, is the description of all rock bodies forming the Earth's crust and their organization into distinctive, useful, mappable units based on their inherent properties or attributes in order to establish their distribution and relationship in space and their succession in time, and to interpret geologic history. Stratum (plural=strata) is layer of rock characterized by particular lithologic properties and attributes that distinguish it from adjacent layers.

History of stratigraphy begin by Avicenna (Ibn Sina) with studied rock layer and wrote The Book of Healing in 1027. He was the first to outline the law of superposition of strata:^[1] "It is also possible that the sea may have happened to flow little by little over the land consisting of both plain and mountain, and then have ebbed away from it. ... It is possible that each time the land was exposed by the ebbing of the sea a layer was left, since we see that some mountains appear to have been piled up layer by layer, and it is therefore likely that the clay from which they were formed was itself at one time arranged in layers. One layer was formed first, then at a different period, a further was formed and piled, upon the first, and so on. Over each layer there spread a substance of differenti material, which formed a partition between it and the next layer; but when petrification took place something occurred to the partition which caused it to break up and disintegrate from between the layers (possibly referring to unconformity). ... As to the beginning of the sea, its clay is either sedimentary or primeval, the latter not being sedimentary. It is probable that the sedimantary clay was formed by the disintegration of the strata of mountains. Such is the formation of mountains."

The theoretical basis for the subject was established by Nicholas Steno who re-introduced the law of superposition and introduced the principle of original horizontality and principle of lateral continuity in a 1669 work on the fossilization of organic remains in layers of sediment.

The first practical large scale application of stratigraphy was by William Smith in the 1790s and early 1800s. Smith, known as the Father of English Geology, created the first geologic map of England, and first recognized the significance of strata or rock layering, and the importance of fossil markers for correlating strata. Another influential application of stratigraphy in the early 1800s was a study by Georges Cuvier and Alexandre Brongniart of the geology of the region around Paris.

In the stratigraphy you can find term of

- Stratigraphic classification. The systematic organization of the Earth's rock bodies, as they are found in their original relationships, into units based on any of the properties or attributes that may be useful in stratigraphic work.

- Stratigraphic unit. A body of rock established as a distinct entity in the classification of the Earth's rocks, based on any of the properties or attributes or combinations thereof that rocks possess. Stratigraphic units based on one property will not necessarily coincide with those based on another.

- Stratigraphic terminology. The total of unit-terms used in stratigraphic classification.It may be either formal or informal.

- Stratigraphic nomenclature. The system of proper names given to specific stratigraphic units.

- Zone.Minor body of rock in many different categories of stratigraphic classification. The type of zone indicated is made clear by a prefix, e.g., lithozone, biozone, chronozone.

- Horizon. An interface indicative of a particular position in a stratigraphic sequence. The type of horizon is indicated by a prefix, e.g., lithohorizon, biohorizon, chronohorizon.

- Correlation. A demonstration of correspondence in character and/or stratigraphic position. The type of correlation is indicated by a prefix, e.g., lithocorrelation, biocorrelation, chronocorrelation.

- Geochronology. The science of dating and determining the time sequence of the events in the history of the Earth.

- Geochronologic unit. A subdivision of geologic time.

- Geochronometry. A branch of geochronology that deals with the quantitative (numerical)measurement of geologic time. The abbreviations ka for thousand (103), Ma for million (106), and Ga for billion (milliard of thousand million, 109) years are used.

- Facies. The term "facies" originally meant the lateral change in lithologic aspect of a stratigraphic unit. Its meaning has been broadened to express a wide range of geologic concepts: environment of deposition, lithologic composition, geographic, climatic or tectonic association, etc.

- Caution against preempting general terms for special meanings. The preempting of general terms for special restricted meanings has been a source of much confusion.

CHALLENGES AND SOLUTIONS IN PLANNING AND OPTIMIZING A HORIZONTAL WELL IN SOUTH SUMATRA, INDONESIA

PROCEEDINGS, INDONESIAN PETROLEUM ASSOCIATION
Twenty-Eighth Annual Convention & Exhibition, October 2001

CHALLENGES AND SOLUTIONS IN PLANNING AND OPTIMIZING  A HORIZONTAL WELL IN SOUTH SUMATRA, INDONESIA

John Wasson*
John Pairaudeau*
Rahmad Wibowo*
Suwardji*
Hidayat Abqory*
Mike Pearson**

ABSTRACT

JOB Pertamina-Seaunion Energy (Limau) Ltd. drilled its first horizontal well in the Q-51 Block of the Limau Oil Field, South Sumatra, Indonesia in September, 1999. The primary objective was to improve production performance and oil recovery from a mature oil field that faces escalating water cuts and production decline. The reservoirs are massive stacked channel / alluvial sandstones, with excellent porosity and permeability, occurring in thick, stacked- sand sequences. Water coning in vertical wells has been partially controlled in recent years with reverse coning installations (dual oil-leg/water-leg completions).

Reservoir numerical simulation modeling was used to history match existing vertical wells and to forecast production from possible horizontal well locations across the top of the remaining oil pay. A detailed drilling plan was prepared for drilling a horizontal sidetrack through a “window” cut in the casing of an existing vertical well. The well was successfully drilled and a 215-meter horizontal section of excellent oil pay was completed open-hole, with an uncemented pre-perforated liner.

The well produced clean oil during the first five weeks of production; however, after that, the water- cut steadily increased. A bottomhole flowing and shut-in pressure survey was conducted and the test analysis indicated that the pressure drawdown was very low, that only 5-10% of the total pay section was effectively producing, and that the wellbore skin was negative. Later, a mud clean-out job and production logging survey was performed, which showed no improvement and that all of the production was coming from a short section at the toe of the well. It was concluded that the wellbore has encountered a very high permeability layer that is causing the water problem and that it may be possible to close this off. It was also concluded that a completion method allowing more isolation control of the wellbore should be utilized on future horizontal wells of this nature.

 

* JOB Pertamina-Seaunion Energy (Limau) Ltd. ** Schlumberger Oilfield Services