Oil migration
Petroleum: Migration through carrier bedsThe hydrocarbons expelled from a source bed next move through the wider pores of carrier beds (e.g., sandstones or carbonates) that are coarser-grained and more permeable. This movement is termed secondary migration. The distinction between primary and secondary migration is based on pore size and rock type. In some cases, oil may migrate through such permeable carrier beds until it is trapped...
The yellow layer indicates a carrier bed
Wednesday, May 27, 2015
What are Carrier Beds? | Petroleum Geology
What is Kerogen?
Kerogen (Greek κηρός "wax" and -gen, γένεση "birth") is a mixture of organic chemical compounds that make up a portion of the organic matter in sedimentary rocks.[1] It is insoluble in normal organic solvents because of the high molecular weight (upwards of 1,000 daltons or 1000 Da; 1Da= 1 atomic mass unit) of its component compounds. The soluble portion is known as bitumen. When heated to the right temperatures in the Earth's crust, (oil window ca. 50–150 °C, gas window ca. 150–200 °C, both depending on how quickly the source rock is heated) some types of kerogen release crude oil or natural gas, collectively known as hydrocarbons (fossil fuels). When such kerogens are present in high concentration in rocks such as shale they form possible source rocks. Shales rich in kerogens that have not been heated to a warmer temperature to release their hydrocarbons may form oil shaledeposits.
The name "kerogen" was introduced by the Scottish organic chemist Alexander Crum Brown in 1906.[2][3][4][5]
Formation of kerogen
With the demise of living matter, such as diatoms, planktons, spores and pollens, the organic matter begins to undergo decomposition or degradation.[6] In this break-down process, large biopolymers from proteins and carbohydrates begin to dismantle either partially or completely. (According to Tucker (1988), this break-down process is basically the reverse of photosynthesis[7]). These dismantled components are units that can then polycondense to form polymers. This polymerization usually happens alongside the formation of a mineral component (geopolymer) resulting in a sedimentary rock like kerogen shale.
The formation of polymers in this way accounts for the large molecular weights and diverse chemical compositions associated with kerogen. The smallest units are the fulvic acids, the medium units are the humic, and the largest units are the humins. When organic matter is contemporaneously deposited with geologic material, subsequent sedimentation and progressive burial or overburden provide significant pressure and a temperature gradient. When these humic precursors are subjected to sufficient geothermal pressures for sufficient geologic time, they begin to undergo certain specific changes to become kerogen. Such changes are indicative of the maturity stage of a particular kerogen. These changes include loss of hydrogen, oxygen, nitrogen, and sulfur, which leads to loss of other functional groups that further promote isomerization and aromatization which are associated with increasing depth or burial. Aromatization then allows for neat molecular stacking in sheets, which in turn increases molecular density and vitrinite reflectance properties, as well as changes in spore coloration, characteristically from yellow to orange to brown to black with increasing depth.[8]
Composition
As kerogen is a mixture of organic material, rather than a specific chemical, it cannot be given a chemical formula. Indeed its chemical composition can vary distinctively from sample to sample. Kerogen from the Green River Formationoil shale deposit of western North America contains elements in the proportions carbon 215 : hydrogen 330 : oxygen 12 : nitrogen 5 : sulfur 1.[3]
Types
Labile kerogen breaks down to form heavy hydrocarbons (i.e. oils), refractorykerogen breaks down to form light hydrocarbons (i.e. gases), and inertkerogen forms graphite.
A Van Krevelen diagram is one example of classifying kerogens, where they tend to form groups when the ratios of hydrogen to carbon and oxygen to carbon are compared.[9]
Type I: Sapropelic
Type 1 oil shales yield larger amount of volatile or extractable compounds than other types upon pyrolysis. Hence, from the theoretical view, Type 1 kerogen oil shales provide the highest yield of oil and are the most promising deposits in terms of conventional oil retorting [10]
- containing alginite, amorphous organic matter, cyanobacteria, freshwateralgae, and land plant resins
- Hydrogen:carbon ratio > 1.25
- Oxygen:carbon ratio < 0.15
- Shows great tendency to readily produce liquid hydrocarbons.
- It derives principally from lacustrine algae and forms only in anoxic lakes and several other unusual marine environments
- Has few cyclic or aromatic structures
- Formed mainly from proteins and lipids
Type II: Planktonic
Type II kerogen is common in many oil shale deposits. It is based on marine organic materials, which are formed in reducing environments. Sulfur is found in substantial amounts in the associated bitumen and generally higher than the sulfur content of Type I or III. Although pyrolysis of Type II kerogen yields less oil than Type I, the amount acquired is still sufficient to consider Type II bearing rocks as potential oil sources
- Plankton (marine)
- Hydrogen:carbon ratio < 1.25
- Oxygen:carbon ratio 0.03 to 0.18
- Tend to produce a mix of gas and oil.
- Several types:
- Sporinite: formed from the casings of pollen and spores
- Cutinite: formed from terrestrial plant cuticle
- Resinite: formed from terrestrial plant resins and animal decomposition resins
- Liptinite: formed from terrestrial plant lipids (hydrophobicmolecules that are soluble in organic solvents) and marine algae
They all have great tendencies to produce petroleum and are all formed from lipids deposited under reducing conditions.
Type II: Sulfurous
Similar to Type II but high in sulfur.
Type III: Humic
- Land plants (coastal)
- Hydrogen:carbon ratio < 1
- Oxygen:carbon ratio 0.03 to 0.3
- Material is thick, resembling wood or coal.
- Tends to produce coal and gas (Recent research has shown that type III kerogens can actually produce oil under extreme conditions) [11][citation needed]
- Has very low hydrogen because of the extensive ring and aromatic systems
Kerogen Type III is formed from terrestrial plant matter that is lacking in lipids or waxy matter. It forms from cellulose, the carbohydrate polymer that forms the rigid structure of terrestrial plants, lignin, a non-carbohydrate polymer formed from phenyl-propane units that binds the strings of cellulose together, and terpenes and phenolic compounds in the plant. Type III kerogen involving rocks are found to be the least productive upon pyrolysis and probably the least favorable deposits for oil generation
Type IV: Residue
Hydrogen: carbon ratio < 0.5
Type IV kerogen contains mostly decomposed organic matter in the form of polycyclic aromatic hydrocarbons. They have no potential to produce hydrocarbons.[12]
Origin of material
Terrestrial
The type of material is difficult to determine but several apparent patterns have been noticed.
- Ocean or lake material often meet kerogen type III or IV classifications.
- Ocean or lake material deposited under anoxic conditions often form kerogens of type I or II.
- Most higher land plants produce kerogens of type III or IV.
- Some coal contains type II kerogen.
Extra-terrestrial
- Carbonaceous chondrite meteorites contain kerogen-like components.[13]Such material is thought to have formed the terrestrial planets.
- Kerogen materials have been detected in interstellar clouds and dustaround stars.[14
Source: Wikipedia
Tuesday, May 26, 2015
Geologic Structures Diagrams
This graph shows the response to increasing stress as applied to two different rock types: BRITTLE vs. DUCTILE/PLASTIC
Definitions:
- STRESS: The force applied to a plane divided by the area of the plane.
- COMPRESSIVE STRESS: The stress generated by forces directed toward one another on opposite sides of a real or imaginary plane.
- TENSILE STRESS: The stress generated by forces directed away from one another on opposite sides of a real or imaginary plane.
- SHEAR STRESS: Stress (force per unit area) that acts parallel to a (fault) plane and tends to cause the rocks on either side of the plane to slide by one another.
- STRAIN: The result of stress applied to a body, causing the deformation of its shape and/or a change of volume.
- ELASTIC RESPONSE: The deformation of a body in proportion to the applied stress and its recovery once the stress is removed.
- ELASTIC LIMIT: The maximum amount of stress a material can withstand before it deforms permanently.
- DUCTILE RESPONSE: The permanent deformation, without fracture in the shape of a solid.
- BRITTLE RESPONSE: The fracturing of a rock in response to stress with little or no permanent deformation prior to its rupture.
- FOLD: Permanent wavelike deformation in layered rock or sediment.
- FAULT: A fracture in bedrock along which rocks on one side have moved relative to the other side.
- JOINT: A fracture on a rock without noticeable movement.
This Diagram depicts the types of stresses available.
Modified from: Page 374
George H. Davis: Structural Geology of Rocks and Regions Copyright C 1984, by John Wiley & Sons, Inc.
This diagram depicts some common fold types.
Acetate 54 (Figure 14-13)
Syncline and Anticline
C 1992 West Publishing Company
This diagram depicts an adjacent ANTICLINE and SYNCLINE with their representative FOLD AXIS and AXIAL PLANES.
Figure 1.4
Press and Siever: Understanding Earth Copyright C 1994 W. H. Freeman and Company
This Diagram depicts some of the differences between Asymmetrical, Symmetrical, and OVERTURNED folds.
More Fold types
Figures 11.17 and 11.18 from
George H. Davis: Structural Geology of Rocks and Regions Copyright C 1984, by John Wiley & Sons, Inc.
These diagrams show the affect of plunge on the fold axis.
More Fold Types
59 Strike and Dip Diagram
Plummer, Charles C., and David McGeary, Physical Geology, 6/e. Copyright C 1993 Wm. C Brown Publishers, Dubuque, Iowa. All Rights Reserved.
DIP: The angle formed by the intersection of a bedding or fault plane and the horizontal plane; measured in a vertical plane perpendicular to the strike.
This diagram uses Strike and Dip of repeating rock units to produce a geologic map and to infer the underlying fold.
Notice the differential weathering of different rock layers, especially on the right side of the image. This differential weathering allows the tilted/dipping limbs to be more noticeable. Notice the V-shape of the outcrop pattern. This ANTICLINE is plunging toward the top of the picture, therefore, it is a PLUNGING ANTICLINE!
Folding produced by fault action typically produces angular and/or box-folds
Notice the affect of differential weathering on the joints in the background on the left side of the image.
Fault Nomenclature
Fault Types
A and B are REVERSE faults and C is a low-angle reverse fault, typically called a THRUST fault.
A, B, and C depict Normal Faulting. In D, normal faulting has produced HORSTS and GRABENS. Horsts are the up-thrown blocks and the Grabens are the down-thrown blocks. In other words, the Horsts are the ridges and the Grabens are the valleys.
Strike-Slip Faults typically have near-vertical fault surfaces. They also come in two varieties: Left-Lateral Strike-Slip and Right-Lateral Strike-Slip Faults. Notice the pond in C. This is a SAG POND, which is usually due to INTERSEISMIC SUBSIDENCE. Following the release in stress as the result of an Earthquake, the rocks/ground relaxes and subsides, thus forming sag ponds in some situations.
التراكيب الجيولوجية | Geological Structures "Arabic"
التراكيب الجيولوجية هي المظاهر أو الملامح الهندسية التي تتواجد علها الصخور وتنتج أما في نفس زمن تكوينها أو نتيجة لقوى مؤثرة بعد التكوين ، ولهذا تنقسم التراكيب إلى نوعين : التراكيب الأولية Primary structure و التراكيب الثانوية Secondary structure .
التراكيب الأولية :
وهي التي تتشكل أو تتكون أثناء الترسيب للطبقات الرسوبية وتكون ناتجة عن العمليات الفيزيائية (الطبيعية ) أي أنها تعكس ظروف الترسيب مثل طبيعة وسط الترسيب العمق قوة وسرعة التيار وكذلك اتجاه التيارات القديمة وهي أكثر انتشاراً في لصخور الرسوبية الفتاتية ، ومنها :
التطبق المستوي Flat-bedding شكل(1)
التطبق المستوي Flat-bedding شكل(1)
شكل ( 1 )
التطبق المتقطع Cross-bedding شكـل (2)
في بعض الحالات تبدو الطبقات على شكل رقائق مائلة بالنسبة لمستويات التطبق الرئيسية بين الطبقات ، ويعرف هذا النوع من التراكيب بالتطبق المتقاطع أو الكاذب .
شكل (2)
والتدرج الحبيبي graded-bedding شكل (3)
يمثل نوع آخر من التطبق وفيه يتغير حجم الحبيبات في الطبقة الواحدة تدريجيا من حبيبات خشنة إلى حبيبات دقيقة ( عند السطح العلوي للطبقة ) وهي خاصية تمثل الترسيب السريع من ماء يحتوي على قطع فتاتية من الصخور مختلفة الأحجام بفعل التيارات المائية .
شكل ( 3 )
وكذلك علامات النيمRipple marks شكل (4 )
يوجد هذا التركيب على شكل تموجات صغيرة على أسطح التطبق وينشأ بفعل الرياح أو التيارات الشاطئية .
يوجد هذا التركيب على شكل تموجات صغيرة على أسطح التطبق وينشأ بفعل الرياح أو التيارات الشاطئية .
شكل ( 4)
وتشققات الطين Mud Cracks شكل (5 )
عندما تجف الرواسب الطينية تتشقق بطريقة يظهر معها سطح الطبقة الطينية على شكل خلية نحل ، وعندما تمتلىء هذه الشقوق برواسب جديدة غير الطين نتيجة لترسيب طبقات جديدة فوقها ، فإنها تحافظ على هذا الشكل . ووجود مثل هذه في الصخور الطينية القديمة تدل على أن المنطقة ساد فيها الجفاف والفيضان خلال العصور القديمة .
شكل ( 5 )
التراكيب الثانوية :
تنتج التراكيب الثانوي نتيجة تأثير قوى داخلية تؤثر على الصخور المختلفة هذه المؤثرات تأخذ صورا متعددة مثل قوى الضغط الجانبي وقوى الشد والقوى الرافعة والقوى الهابطة بتأثير الجاذبية الأرضية . ومن هذه التراكيب :
1- الطيات : تعرف الطية على أنها التركيب الذي ينشأ عندما ينحني أو يتقوس سطح الطبقة الذي كان في الأصل مستويا ، نتيجة تأثير القوى عليه ، والطيات كثيرة الانتشار في صخور القشرة الأرضية .انظر الشكل
الطيات
2 - عدم التوافق : عبارة عن سطح متعرج نسبيا والذي يمثل مجموعتين من الطبقات ، السفلى منها مطوية أو مجعدة والعليا أفقية .
أنواع عدم التوافق :
- عدم التوافق الزاوي Angular Unconformity : يمثل سطح يفصل بين طبقات مائلة وأخرى مائلة ولكنهما مختلفتين في الميل .
عدم التوافق الزاوي
- عدم التوافق الانقطاعي Disconformity : يكون على شكل سطح متعرج بين طبقات متوازية أو مائلة أو أفقية .
عدم التوافق الانقطاعي
- لا توافق Nonconformity :يتكون هذا النوع من عدم التوافق عندما يتم ترسيب مجموعة من الطبقات الرسوبية فوق صخور نارية أو متحولة .
اللا توافق
- شبه توافق Paraconformity يتكون هذا النوع من عدم التوافق عندما يتم ترسيب مجموعتين من الطبقات الرسوبية لهما نفس الميل ، ويفصلهما سطح تعرية غير واضح .
شبه توافق
3- الصدوع Faults : وهو كسر في صخور القشرة الأرضية يعقبه حركة لإحدى الكتل المكسورة بالنسبة للأخرى .
أنواع الصدوع :
- الصدع العادي Normal Fault : ينشأ هذا الصدع بتأثير قوى الضغط ، وفيه يكون ميل الصدع في عكس اتجاه الرمية ، أو يتحرك الكائط العلوي لأسفل بالنسبة لمستوى الصدع .
- الصدع المعكوس Reverse Fault وفيه يتحرك الحائط العلوي لأعلى بالنسبة لمستوى الصدع .
- الصدع الرأسي Vertical Fault :ويكون فيه مستوى الصدع رأسيا أي أن زاوية ميل الصدع تصبح 90 درجة وبالتالي لا توجد إزاحة .
Monday, May 25, 2015
How to Draw a Contour Map
Petroleum geologists make all kinds of contour maps. Contouring is not especially difficult, but it is easy to make small mistakes when the map gets very large. Your small mistakes might make the map invalid! It does take lots of practice and patience to make a nice-looking map.
In a large part of the United States, the Township and Range System is used to spot wells. This system is part of the Public Land Survey, that was established when the country was young.
How to make a countour map: Let’s assume we are making a map in one of the western states that uses the Township and Range system. In this area, a “section” of land is one mile on each side (one mile square). This also happens to be exactly 640 acres.
Step 1 - Spot The Wells
(1) You start by “spotting,” or drawing, all the wells on a one-square mile section of land. You need to know the distance of each well from a common boundary (the section line, in this case). You might get the exact locations from a scout ticket. Here’s a single section of land, with our wells spotted on it.
Step 2 - Put The Mapping Value On Each Well
(2) Next, you look at the electric logs for each well. We are going to make an
“isopach” map. An isopach map is a map that shows the thickness of something. In this case, it is the thickness of a limestone formation. Count the number of feet of sand in the zone you are interested in. Then, put the number of feet of sand below each well spot.
“isopach” map. An isopach map is a map that shows the thickness of something. In this case, it is the thickness of a limestone formation. Count the number of feet of sand in the zone you are interested in. Then, put the number of feet of sand below each well spot.
Step 3 - Start Contouring The Largest Values
(3) Start contouring with the highest values. Use a pencil. Start with a “contour interval” that is slightly less than the biggest values. In this case, the first line drawn is the 40-foot contour. As you draw your line, look carefully when you pass between two wells. Try to use your eye like a “ruler,” and position the line at the proper distance between the two wells. Notice the well with a footage of “38.” Since 38 is very close to 40 (the contour we are drawing), you should “pull” the 40-foot contour over close to the 38-foot line, like I did here. Actually, I should have pulled it a just little closer!
If there is a “40” on the map (there is on this one), you will draw the 40-foot line right through that well.
Step 4 - Draw The 30-Foot Contour
(4) Now draw the 30-foot contour (contour lines are usually at some even interval, like 10 feet, 20 feet, 50 feet). “Eyeball” the map and be sure to leave the proper amount of room for the remaining contour lines. Use a pencil, and draw light lines, because you have to erase a lot!!
Step 5 - "Eyeball" The Rest Of The Countours
(5) Finish the map by drawing the 10-foot, and zero contour lines. Label the “contour interval” you used at the bottom of the map. In this case, the contour interval is 10 feet. You’re done!
It takes quite a bit of practice to draw decent contour maps by hand. The one we just did was a “quickie”. Normally, you would draw this in light pencil, then go back and make it better with ink.
The little map shown in the last step would still require a lot of erasing and reworking to get it looking just right.
It’s important to know how to contour a map, but these days, geologists use computers to do a lot of their contouring. However it still requires quite a bit of “help” from the petroleum geologist to make a good-looking map. Many geologists use computer contouring for everyday work, but draw it by hand when it must look nice.
When you’re done, after erasing and re-drawing quite a bit, the countours will look nice and even, like the map below:
Hand-Drawn Structure Map
Giant's Causeway beautiful columnar basalt
Photographer: John Adam
Summary Author: John Adam
A crude and simplistic mathematical model (neglecting all the physics) would involve the regular tessellation of the Euclidean plane by hexagons, which (of the three regular polygons, equilateral triangles, squares and hexagons) have the minimum perimeter for a given area. This is superficially similar to the mud crack phenomenon, although that occurs on a much smaller scale and is limited to the surface layers of the mud. Physically, as cooling proceeds, the cracks (which started at the top and base of the flow) propagate inwards and solidify as three-dimensional polygonal columns. However, although hexagonal patterns are very common, there exist many irregular polygonal columns with 3-7 sides on the horizontal surface. The columns also shrink along their length and produce ball and socket convex/concave joints, dividing the columns vertically.
Friday, May 22, 2015
Subscribe to:
Posts (Atom)