Dipmeter

The method of dip sequence analysis presented here was developed for the structural analysis of dipmeter logs by Bengtson (1981a) but is equally informative whether the traverse is down a well or along a stream. Major problems with the structural interpretation of dip data are the high stratigraphic noise content and the complexity of the ...

This video presents the basics of a Solid State Dip Meter, which is the more "modern" equivalent of the old classic Grid Dip Meter (GDO). The GDO was simply...Dipmeter Borehole Geometry Sonde BGS Multi Button Dipmeter MBD Precision Strata Dipmeter PSD Scratcher Dipmeter Sonde SDC Production Fluid Conductivity Sonde FCS Logging Fluid Density Sonde FDS Services Full Bore Flowmeter Sonde FFS In Line Flowmeter Sonde IFS Pressure Gauge Carrier PGC ...... dipmeter data. The tilt axis are mainly trending N–S in sandstones, associated to Westward transport of sediments. The sliding surfaces S1 and S3 correspond ...The Standard Dipmeter is a lightweight water level measuring instrument, designed for routine groundwater monitoring. BENEFITS. • Cost effective. • Reliable.Shallow neural networks and classification methods for approximating the subsurface in situ fluid-filled pore size distribution. Siddharth Misra, Jiabo He, in Machine Learning for Subsurface Characterization, 2020. 2.2 Petrophysical basis for the proposed data-driven log synthesis. NMR logging tool is generally suited for uniform boreholes of diameter greater than 6.5 inches run …Abstract. Geoscientists use a robust arsenal of tools to expand their knowledge of reservoir characteristics and to model reservoir behavior. Borehole imaging offers geologists the high-resolution ...

Author: S. Luthi Publisher: Springer Science & Business Media ISBN: 366204627X Format: PDF, Kindle Release: 2013-03-14 Language: en View Their Use in Reservoir Modeling S. Luthi. Ronningsland TM (1990) Structual interpretation of dipmeter results in the Gullfaks field. Hurst A, Lovell MA, Morton A (eds) Geological Applications of Wireline Logs.The Dipmeter has become a reliable tool for defining structure and stratigraphy in many areas. Computer processing has enabled quick results to be provided. Decisions on these results may entail very large expenditures. If the readings vary, then two possibilities exist: an instrumentation or hole condition problem, or geological conditions ...The DIPMETER ADVISOR program is an application of Al and Expert System techniques to the problem of inferring subsurface geologic structure. It synthesizes techniques developed in two previous ...The new HDT (High Resolution Dipmeter Tool) was designed to obtain a very high vertical resolution while maintaining a reasonable recording speed. This was achieved through the development of: A new micro-resistivity sensor capable of a resolution of 0.2 inches. An entirely new telemetry system capable of handling the information acquired at a ...Dipmeter interpretation in thrust belts can be difficult because thrust belt structure is often complicated. However, interpreters can construct reliable transverse sections by combining statistical curvature analysis techniques (SCAT) with the geometric techniques for constructing thrust belt sections. By itself, the simplistic tadpole plot ...Product overview. Abcam's Lipolysis Assay Kit (Colorimetric) (ab185433) is simple and easy-to-use. The assay measures glycerol released from 3T3-L1 cells after induction of lipolysis using colorimetric method. The color intensity is directly proportional to the amount of glycerol. This assay kit can detect less than 200 pmol of glycerol.Abstract. The resistivity dipmeter tool uses three or four horizontal, equally-spaced, microresistivity measurements to determine formation dip magnitude and direction. The accurate determination of in-place formation dip is a two-part problem. First, the relative dip of formation beds, expressed in bed displacement along the borehole wall, is ... Although these dip measurements are at a lower vertical resolution than those from an image tool or dipmeter, they are sufficiently robust to provide critical structural information and detect major events such as unconformities or faults crossing the borehole. Additional stratigraphic insight results from pairing dip measurements from Rt ...

The dipmeter is a tool with arms arranged radially around a central mandrel with pads pressed against the borehole wall by a spring mechanism. Each pad measures the microresistivity of the formation. By correlating a microresistivity feature across the borehole, a plane can be defined and its dip and strike computed.NHBS started life as the Natural History Book Service in 1985 as a mail-order supplier of 500 ornithology books based in London. After two years we moved to Totnes in Devon, where we have remained as an independent, privately held company. In May 1995 we began the transition from mail-order catalogue to online, with the launch of our website ...Acoustic logging. Petroleum applications of acoustic-wave-propagation theory and physics include both: Surface-geophysical methods. Borehole-geophysical methods. Acoustic logging is a subset of borehole-geophysical acoustic techniques. Historically, the primary and the most routine uses of acoustic logs in reservoir engineering have been:@article{osti_6144633, title = {Detailed reservoir analysis using EPT-Cyberlook and dipmeter computations}, author = {Standen, E}, abstractNote = {In recent years, a tremendous amount of work by oil companies has been done to evaluate tertiary flood programs in heavy oil reservoirs. One of the keys to understanding how a flood will behave, and therefore an input to the modeling, is a basic ...HSN Code 9026. Instruments and apparatus for measuring or checking the flow, level, pressure or other variables of liquids or gases, e.g. flow meters, level gauges, manometers, heat meters (excluding instruments and apparatus of heading 9014, 9015, 9028 or 9032) HS Code. Description. GST%.Although these dip measurements are at a lower vertical resolution than those from an image tool or dipmeter, they are sufficiently robust to provide critical structural information and detect major events such as unconformities or faults crossing the borehole. Additional stratigraphic insight results from pairing dip measurements from Rt ...

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Dipmeter with 30, 50, 100, 200, 300m Tape. A simple measuring tape with a sensor at the tip for borehole water level readings. Dipmeter, a water level indicator, to measure the depth of water levels in boreholes, standpipes …The response of an induction dipmeter and standard induction tools to dipping beds Geophysics. Multiple Applications of Dipmeter Curves for Analyzing Evaporite Formations: Examples from Paleogene of Bresse Trough, France AAPG Bulletin. Integrated use of well data for structural control of seismic interpretation ...NHBS started life as the Natural History Book Service in 1985 as a mail-order supplier of 500 ornithology books based in London. After two years we moved to Totnes in Devon, where we have remained as an independent, privately held company. In May 1995 we began the transition from mail-order catalogue to online, with the launch of our website ...Liu Wenbin, Chen Yingtai, Wang Duoyun, Zheng Chengguang, Huang Gang. STUDY ON THE CHARACTERISTICS OF PALAEOCURRENTS BY USING DIPMETER LOGGING DATA[J]. Chinese ...The dipmeter is a tool with arms arranged radially around a central mandrel with pads pressed against the borehole wall by a spring mechanism. Each pad measures the …A natural inclinationfor geotechnical andstructural monitoring. Sisgeo is the global leader in the production of cutting-edge technologies applied to inclinometers. We design, produce, and install a wide range of high precision instruments conceived to provide added value to geotechnical and structural engineering in any possible application.

56 May 2003 B1, B2--1.5 V AA or AAA cell. C1--75 pF variable, OSE AVC75 or 365 pF variable BC14400. C2, C8--5 pF disc capacitor, Digi-Key P11408CT-NF,The Dipmeter Advisor was an early expert system developed in the 1980s by Schlumberger with the help of artificial-intelligence workers at MIT to aid in the analysis of data gathered during oil exploration.The Advisor was generally not merely an inference engine and a knowledge base of ~90 rules, but generally was a full-fledged workstation, running on one of Xerox's 1100 Dolphin Lisp machines ...Using a good reference capacitor, form a resonant circuit and dip the meter. Note the frequency. Then tune the dip meter down until you find the frequency where the meter reads about 30% higher ...Reclaiming And Remediating Abandoned Mine Drainage For Clean Water Use. Coal mining began in Pennsylvania over 250 years ago, and today it still supplies 60 per cent of the fuel for the state's electric power generation—the fourth largest coal-producing state in the U.S.Quite a bit! The dipper is one piece of test equipment that can replace a whole shelf of expensive gear-if you know how to use it. As radio amateurs we are often interested in resonance.Long dipmeter logs from the wells allowed to determine the directions of recent horizontal compression by analysis of the failure of the borehole wall, called breakouts (Bell and Gough, 1979; Gough and Bell, 1981). The breakouts analysis method provides the unique opportunity for almost continuous observations of the horizontal stress ...ELGI Air Compressor Operations and Maintenance Manual. ELGI_OM_Manual_AirCompressor.pdf. Last updated on March 22, 2017. ELGI_OM_Manual_AirCompressor.pdf.Present-day stress directions interpreted from well bore breakouts adjacent to two crastal-scale, active, strike-slip faults (the San Andreas fault in California and the Great Sumatran fault in Sumatra) indicate that the maximum horizontal stress direction (S H) is oriented at a high angle (70°–90°) to both faults.The regionally defined stress fields …Press Down on the White Terminals on the Circuit Board and Insert the Tape Leads. With the probe in a glass of tap water, turn the Water Level Meter to the 'ON' position. If the connections are correct the buzzer and light will activate. If they do not activate, check all connections and the polarity of the battery.Well Log Analysis Centre Geofizyka Toru Sp. z o.o. fHISTORICAL DATES The dipmeter methods had been employed for 60 years by 2002. The most important dates in their evolution are given below: 1942 - the 1st 3-arm dipmeter (a perimeter) used to continuous recording of spontaneous potentials (SP); 1943 the 3-arm dipmeter (with a photoclinometer ...Dipmeter: Borehole Televiewer Correlation and lithology. Correlation devices are used to identify common formations between wells and to distinguish potential reservoir rocks from nonreservoir rocks. These devices make use of three different physical phenomena: spontaneous potential, gamma rays, and photoelectric effect. Table 2 …

The main purpose of the dipmeter measurement is to obtain structural dips of the layers traversed by the borehole. This is achieved by recording variations in the rocks’ electrical properties along tracks of the borehole wall, and by correlating these curves. Dips are measured with respect to the borehole (“apparent dips”) or with respect ...

The sinusoidal taces on the image are planes computed from dipmeter processing of the image microresistivity curves. Each sinusoid peak azimuth is the updip direction; the sinusoid trough azimuth is the downdip direction. The thin limestone at the base (see gamma-ray log) is the white band at the bottom of the image log.Grid dip oscillator ( GDO ), also called grid dip meter, gate dip meter, dip meter, or just dipper, is a type of electronic instrument that measures the resonant frequency of nearby unconnected radio frequency tuned circuits. It is a variable-frequency oscillator that circulates a small-amplitude signal through an exposed coil, whose ...... dipmeter data. The tilt axis are mainly trending N–S in sandstones, associated to Westward transport of sediments. The sliding surfaces S1 and S3 correspond ...31 พ.ค. 2559 ... Dipmeter Data, Borehole Image Logs and Interpretation - Download as a PDF or view online for free.The dipmeter offers a relatively low cost, highly effective alternative for defining geologic features. The 60{double_prime}= 100{prime} scale playback of the raw dipmeter data may be an oil field {open_quotes}dinosaur,{close_quotes} but it is also the key to assessing the reliability of a dipmeter.dipmeter log A down-hole geophysical log designed to measure the dip and dip direction of dipping surfaces in a borehole. The logging tool consists of four ...Piezometers are used for measuring pore water pressures. They are generally installed in boreholes but can also be placed in fill. Pore water pressures are important because they are a fundamental component of the effective stress, which is the cornerstone of soil mechanics. The principle of effective stress states that all measurable effects ...About Geotech's Dipmeter · Highly portable · Delivery included · 30m, 60m, and 100m lengths · Lightweight · Buzzer · Light indicator · 20,000 units sold worldwide ...dipmeter log A down-hole geophysical log designed to measure the dip and dip direction of dipping surfaces in a borehole.The logging tool consists of four resistivity logging devices set at 90° to one another, and held against the side of the borehole (see RESISTIVITY LOG; and RESISTIVITY METHODS).When wound back to the surface they respond instantly to layers of differing electrical ...

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Un Dipmeter es, en esencia, un oscilador capaz de funcionar en un amplio margen de frecuencias y en cuyo circuito se encuentra un instrumento que mide la amplitud de la energía de RF generada. Al acercar la bobina del Dipmeter a un circuito resonante sintonizado a la misma frecuencia del Dip-meter, se produce una disminución de la amplitud de ...The resistivity dipmeter tool uses three or four horizontal, equally-spaced, microresistivity measurements to determine formation dip magnitude and direction. The accurate determination of in-place formation dip is a two-part problem. First, the relative dip of formation beds, expressed in bed displacement along the borehole wall, is measured ...A very useful instrument into the every respectable ham workshop is, without any doubts, the grid-dip-meter. This name came from the golden age of tubes, but today, in the era of semiconductors, that name became gate-dip-meter, dip-meter or simple, dipper. Under various appearances, the GDM, in essence, is just a variable frequency oscillator ...The sequences tend to be uniform and lack discernible coarsening- or fining-upward trends and, thus, exhibit blocky to weakly serrated gamma ray, SP, and resistivity log profiles The well-bedded and high angle cross stratified nature of eolian sandstones promotes reliable results from dipmeter logs. Dune and interdune deposits can often be ...The DIPMETER ADVISOR program is an application of Al and Expert System techniques to the problem of inferring subsurface geologic structure. It synthesizes techniques developed in two previous ...Nov 13, 2022 · A dip meter or a grid dip meter can be considered as a kind of frequency meter whose function is to determine the resonant frequency of an LC circuit. For this, the circuits don't have to 'radiate' any waves or frequency across each other. Instead, the procedure is implemented simply by placing the coil of the dip meter close to the external ... The system is currently being used in a small number of. Schlumberger Field Log Interpretation Centers as an aid to human dipmeter interprcters. In this paper, ...On 8/14/2019 5:13 PM, rchadwick7 via Groups.Io wrote: I always thought Grid Dip meters were cool, but it seems a VNA can be used as a Grid Dip meter.Dipmeter data can provide valuable insights into the structural and depositional features of a reservoir, such as faults, fractures, bedding planes, and sedimentary facies. However, acquiring and ... ….

Well logging, also known as borehole logging is the practice of making a detailed record (a well log) of the geologic formations penetrated by a borehole.The log may be based either on visual inspection of samples brought to the surface (geological logs) or on physical measurements made by instruments lowered into the hole (geophysical logs).Some …The con- sequence of poor imaging is volumetric and well targeting uncertainty. Structural interpretation of dipmeter and image logs is an essential technique to locally calibrate seismic maps and ...Based on the results from a dipmeter from this well, it was revealed that discontinuities located between depth of 620 and 650 m, have highly varied dip angles, proving no major trend. Below that depth and until 825 m, low dip angles (\(< 10^{\circ }\)) were registered. Between 825 and 875 m depth, dip angle increased to \(20^{\circ }\).The sinusoidal taces on the image are planes computed from dipmeter processing of the image microresistivity curves. Each sinusoid peak azimuth is the updip direction; the sinusoid trough azimuth is the downdip direction. The thin limestone at the base (see gamma-ray log) is the white band at the bottom of the image log.The dipmeter is a tool with arms arranged radially around a central mandrel with pads pressed against the borehole wall by a spring mechanism. Each pad measures the microresistivity of the formation. By correlating a microresistivity feature across the borehole, a plane can be defined and its dip and strike computed. Jan 18, 2022 · 1 Dipmeter data acquisition; 2 Thin bed resolution; 3 Dip computation; 4 Dipmeter presentations; 5 Applications of dipmeters. 5.1 Structural applications; 5.2 Stratigraphic applications; 6 Examples of use; 7 See also; 8 External links Beli Meteran 50 Meter terbaik harga murah Oktober 2023 terbaru di Tokopedia! ∙ Promo Pengguna Baru ∙ Kurir Instan ∙ Bebas Ongkir ∙ Cicilan 0%.The standard dipmeter is a water level measuring instrument designed for routine groundwater monitoring. Lightweight design, reliable and with a simple operation for use by drilling contractors, fruit and vegetable farmers, and people using it in landfill and remediation applications Within the first category, salient advances include the continuing improvement of the borehole televiewer, refinement of the electrical conductivity dipmeter for fracture characterization, and the development of a gigahertz-frequency electromagnetic propagation tool for water saturation measurements. Dipmeter, Cons. Not bright enough for the outdoors. 6. Hima Nanovna-F Vector Network Analyzer. All of the above-mentioned antenna analyzers are quite compact in their construction, whereas the Hima Nanovna-F Vector Network Analyzer is unapologetic about its bulkier construction and a large 4.3-inch LCD touchscreen., The dipmeter tool records microresistivity measurements which are used to determine the dip and strike of resistive features in the subsurface. The modern tool is a four-arm device, in which the arms are arranged radially around a central mandrel and are pressed against the borehole wall by a spring mechanism. Small electrodes are embedded in a ..., Dip Meter, 50m ... A simple and very accurate device for measuring the depth of wells and boreholes. The sensor is lowered on […] ... CAN'T FIND WHAT YOU NEED? We ..., 12-11-2021 Using NanoVNA for SWR Measurement – Step by Step KJ7ROX . Page | 1. This procedure is for the use of a NanoVNA for measuring SWR of an antenna directly on the NanoVNA device. There are different hardware versions of the NanoVNA – The one used here is called the “NanoVNA-H 4” and it has a 4 inch, Jan 18, 2022 · 1 Dipmeter data acquisition; 2 Thin bed resolution; 3 Dip computation; 4 Dipmeter presentations; 5 Applications of dipmeters. 5.1 Structural applications; 5.2 Stratigraphic applications; 6 Examples of use; 7 See also; 8 External links , Advanced measurements with a VNA RIGOL Technologies Inc. 07.08.2020 Advanced measurements with a Vector Network Analyzer In our wireless world the need of RF component testing is one of a key factors to bring a product to market., Currently, more than 800 wells of various depths penetrate multiple reservoirs; over 30 dipmeter logs have been run during the past 34 years. Although structure contour maps of individual stratigraphic horizons have been drawn simply from conventional well data, more subtle features of deformation are interpreted from the use of dipmeter logs., Dipmeter Advisor: Digunakan oleh Schlumberger untuk analisis data dalam pengeboran minyak. 4. XCON & XSEL : Membantu konfigurasi sistem komputer besar. Dikembangkan oleh Digital Equipment Corporation (DEC) dan Carnegie Mellon Universitas (CMU), akhir 70 an. Untuk sistem komputer DEC VAC 11 1780 5. Sophie : Analisis sirkit elektronik 6., Applications Structural geology Structural dip, even in frac- tured and conglomeratic formations Faults Sedimentary features Sedimentary dip Paleocurrent direction Sedimentary bodies and their boundaries Anisotropy, permeability barriers and paths Thin-bedded reservoirs Rock texture Qualitative vertical grain- size profile Carbonate texture, The dipmeter, on the left, has sensors on four actuated arms, which are shown in their fully extended position. Attached to the bottom of one of its four arms is an additional electrode array embedded in a rubber “pad.” It is followed by a sonic logging tool, characterized by a slotted housing, and then a density device with its, Homebrew RF Circuit Design Ideas "There is no such thing as a new idea. It is impossible. We simply take a lot of old ideas and put them into a sort of mental kaleidoscope., Dipmeter Advisor: Digunakan oleh Schlumberger untuk analisis data dalam pengeboran minyak. 4. XCON & XSEL : Membantu konfigurasi sistem komputer besar. Dikembangkan oleh Digital Equipment Corporation (DEC) dan Carnegie Mellon Universitas (CMU), akhir 70 an. Untuk sistem komputer DEC VAC 11 1780 5. Sophie : Analisis sirkit elektronik 6., Symmetry, which regulates the symmetry against the datum, is measured using a caliper, micrometer, or a coordinate measuring machine. This page explains the advantages and disadvantages of using these instruments. “Learning GD&T From Scratch,” provided by KEYENCE, walks you through the basics of geometric dimensioning and tolerancing, datums, …, Within the first category, salient advances include the continuing improvement of the borehole televiewer, refinement of the electrical conductivity dipmeter for fracture characterization, and the development of a gigahertz-frequency electromagnetic propagation tool for water saturation measurements., The DIPMETER ADVISOR program is an application of Al and Expert System techniques to the problem of inferring subsurface geologic structure. It synthesizes techniques developed in two previous ..., The con- sequence of poor imaging is volumetric and well targeting uncertainty. Structural interpretation of dipmeter and image logs is an essential technique to locally calibrate seismic maps and ..., A very useful instrument into the every respectable ham workshop is, without any doubts, the grid-dip-meter. This name came from the golden age of tubes, but today, in the era of semiconductors, that name became gate-dip-meter, dip-meter or simple, dipper. Under various appearances, the GDM, in essence, is just a variable frequency oscillator ..., Currently, more than 800 wells of various depths penetrate multiple reservoirs; over 30 dipmeter logs have been run during the past 34 years. Although structure contour maps of individual stratigraphic horizons have been drawn simply from conventional well data, more subtle features of deformation are interpreted from the use of dipmeter logs., Dipmeter logs were developed to resolve the "3-points define a plane" problem in a single well bore by measuring some physical property of the rocks in at least three directions around the borehole. Since the borehole is typically only 8 inches in diameter, considerable precision in measurement was required., Dipmeter Log The dipmeter includes a variety of wall-contact microresistivity devices that are widely used in oil exploration to provide data on the strike and dip of bedding planes. The most advanced dipmeters employ four pads located 90° apart, oriented with respect to magnetic north by a magnetometer in the sonde., The dipmeter is truly a jambalaya of geologic information. Consider the many situations where knowledge of inclination and direction would be useful. Determination of structural dip and identification of faults and unconformities caused by abrupt changes in that dip are well-known uses. Furthermore, bending of beds resulting from drag of ..., Seeing the shape of formation-resistivity variations often provides understanding of the lack of coherent dip found by a dipmeter computation program. Halliburton's Electromagnetic MicroImager (EMI) tool is a six-arm resistivity borehole imager tool. Its principle of operation is similar to the FMI tool., The direction of the maximum horizontal in situ stress is 275° by a comprehensive analysis of the dipmeter log data and micro resistivity scanning imaging. The fracture pressure gradient is 1.7 MPa/100 m, and the strata pressure gradient is 1.3 MPa/100 m. The relative normal probability functions of tectonic stress coefficient A and B are:, Umzimvubu catchment is located in the southeastern part of South Africa and covers an area of 19845 km² (Fig. 1). The study area is mainly determinated by triassic sedimentary strata belonging to ..., 1. Mengelola prospek. Melansir laman Job Hero, salah satu tanggung jawab utama dari seorang sales advisor adalah mengelola prospek perusahaan. Mereka harus mencari tahu pelanggan yang mungkin tertarik dengan produk-produk milik perusahaan. Mereka juga harus menghubungi calon klien dan membuat presentasi untuk menggaet minat para pelanggan., Waterproof 52mm Water Level Gauge + Fuel Sender Unit Sensor 0~190ohm Liquid Water Tank Level Indicator Meter 7 Color Backlight. ₱1,213 - ₱1,645. 47 sold. Mainland China. Fuel & Water Level Gauge Sensor Boat Motorcycle Car Fuel Sending Unit 0~190 ohm/240~33 ohm with 100mm 125mm ,150mm, 200mm,450mm. ₱570 - ₱1,600., Dipmeter logs available in the area are collected by a three-arm slimline dipmeter tool that samples at 0.5 cm. The correlation step of the dipmeter log is 0.26 m and the vertical resolution is about 1 cm, so the dataset does not have the ability to resolve small sedimentary features such as ripples or micro-fractures. However, dipmeter ..., The Defining Series: Basic Well Log Interpretation. Well logs present a concise, detailed plot of formation parameters versus depth. From these plots, interpreters can identify lithologies, differentiate between porous and nonporous rock and quickly recognize pay zones in subsurface formations. The ability to interpret a log lies in …, Consider the Dipmeter Advisor (Smith and Baker 1983), started at Schlumberger in the early 1980s and based on the knowledge of the legendary oil finder, Al Gilreath, shown in figure 7. And the Dipmeter Advisor was both data driven, converting raw signals to patterns, and model driven, using rules to classify stratigraphie and tectonic features ..., The dipmeter data set consists of a series of measurements of elevation, azimuth and dip angle of stratigraphic bedding surfaces (e.g. Annex 1).Processing is based on a multi-spectral analysis, where the changes of bedding attitude are compared and tracked between various scales (Fig. 1).It is important to note that this processing only applies to stratigraphic surfaces., The nature and origin of borehole elongation recorded by the four-arm dipmeter calipers is studied utilizing information obtained from hydraulic fracturing ..., Jul 1, 1994 · There are a number of ingredients in successful dipmeter interpretation. More than with any other logging technique, quality control is critical. However, aside from a solid knowledge of local geology, the key attribute of a dipmeter interpreter is a good sense of perspective. , dipmeter log and core description from a turbidite The interval is interpreted as a convergent margin channel reservoir. Abrupt changes in dip azimuth drape associated with a channel story element. The and magnitude mark the position of erosional dis- example shown in Figure 13A consists of a 1.25-m conformities or probable channel-base surfaces.