Carbonate Petrography

Carbonate petrography is the study of limestones, dolomites and associated deposits under optical or electron microscopes greatly enhances field studies or core observations and can provide a frame of reference for geochemical studies.

25 strangest Geologic Formations on Earth

The strangest formations on Earth.

What causes Earthquake?

Of these various reasons, faulting related to plate movements is by far the most significant. In other words, most earthquakes are due to slip on faults.

The Geologic Column

As stated earlier, no one locality on Earth provides a complete record of our planet’s history, because stratigraphic columns can contain unconformities. But by correlating rocks from locality to locality at millions of places around the world, geologists have pieced together a composite stratigraphic column, called the geologic column, that represents the entirety of Earth history.

Folds and Foliations

Geometry of Folds Imagine a carpet lying flat on the floor. Push on one end of the carpet, and it will wrinkle or contort into a series of wavelike curves. Stresses developed during mountain building can similarly warp or bend bedding and foliation (or other planar features) in rock. The result a curve in the shape of a rock layer is called a fold.

Showing posts with label energy. Show all posts
Showing posts with label energy. Show all posts

Download Geoscience Books

Geoscience Books:

We are grateful to Qazi Sohail Imran for providing Geoscience books to our community. Qazi is from Islamabad Pakistan and is a Former Research Geophysicist at King Fahd University of Petroleum and Minerals. He is contributing to his oil and gas community with the believe that "Knowledge is power and knowledge shared is power multiplied".Follow the link above the images to download the books. However if the link is not working or you have any other query, just mention it in comment or email us here , we will fix it for you.

1. Name: Sedimentology and Stratigraphy by Gary Nichols 
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2. Name: Physical Geology- Earth Revealed. 9th Edition by C.C. Plummer   
     Download Here


3. Name: An Introduction to Structural Geology and Tectonics by Stephen Marshak
    Download Here

4. Name: 3-D Structural Geology by R.H.Groshong
     Download Here

5. Name: Structural Geology of Rocks & Regions 3rd Edition - Davis Reynolds
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6. Name: Geological Field Techniques Edited By Angela L. Coe
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7. Name: Seismic Stratigraphy, Basin Analysis and Reservoir Characterisation_Vol37       by Paul C.H. Veeken
    Download Here

8. Name: General Dictionary of Geology by Alva Kurniawan, John Mc. Kenzie,                  Jasmine Anita Putri
    Download Here

9. Name: The Handy Geology Answer Book
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10.   Name: Sedimentary Basin Formation-Presentation
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11. Name: Facies Models Response to Sea Level Change by Walker and James
       Dowload Here


12. Name: AAPG Memoir 33 - Carbonate Depositional Environments
      Download here

13. Name: Petroleum Formation and Occurrence by Tissot, B.P. and Welte, D. H        Download Here

14. Name: Basin Analysis-Principles and Applications by Allen     
       
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15. Name: Sedimentary Rocks in the Field by Tucker
         Download Here


16. Name: Exploration Stratigraphy 2nd Edition - Visher
      Download Here

17. Name: Petroleum Geology of Pakistan by Iqbal B. Kadri
      Download Here

18. Name: The Geological Interpretation Of Well Logs by Rider
      Download Here


19. Name: Digital Signal Processing Handbook by Vijay K. Madisetti
      Download Here

20. Name: AAPG Memoir 88 - Giant Hydrocarbon Reservoirs of the World                           Download Here

21. Name: Deep-Water Processes and Facies Models-Implications for Sandstone               Reservoirs by  Dr. Shanmugam
      Download Here

               
      

Different shale distributions in low resistivity log response.


                   First, we will start with a small introduction about the resistivity logs                                           


Resistivity log


Technique : produce a current in the adjacent formation and measure the response of the formation to that current.


Resistivity logs are used to:


• determine hydrocarbon-bearing versus water bearing zones

• indicate permeable zones

• determine porosity


By far the most important use of resistivity logs is the determination of hydrocarbon-bearing versus water-bearing zones. Because the rock’s matrix or grains are non-conductive and any hydrocarbons in the pores are also non-conductive, the ability of the rock to transmit a current is almost entirely a function of water in the pores. As the hydrocarbon saturation of the pores increases (as the water saturation decreases), the formation’s resistivity increases. As the salinity of the water in the pores decreases , the rock’s resistivity also increases.


Resistivity tools principle : there are two types of resistivity tool , The dual lateral log ( DLL ) and the induction log ( DIL ) both types measures the resistivity in three zones simultaneously.


LLD looks deep into reservoir


LLS Looks shallow into the reservoir



MSFL reads the resistivity close to the wellbore.




Low Resistivity response :


High deep resistivity means : HCs or Tight streak  { low porosity }


Low deep resistivity means : Shale or wet sand.




Shale: Shale is defined as a fine-grained, indurated detrital sedimentary rock formed by the consolidation (by compression or cementation) of clay, silt, or mud.

It is characterized by a finely stratified structure of laminae ranging from 0.1 to 0.4 mm thick. Shale contains an appreciable content of clay minerals or derivatives from clay minerals, with a high content of detrital quartz; containing at least 50% silt, with 35% clay or mica fraction, and 15% chemical or authigenic materials

In petrophysical analysis, shale volume is one of the key answers used later to correct porosity and water saturation for the effects of clay bound water, (CBW).



Shale distribution in shaly sand :

 

Shale can be distributed in several different ways, as shown below.

Laminated shale is a special case in petrophysical analysis. Standard models for porosity and saturation do not work.

Dispersed shale is usually composed of from clay minerals that form in place after deposition due to chemical reactions between the rock minerals and the chemicals in the formation water.

Structural shale is usually deposited as particles, grains, or clasts during the initial depositional phase. For example, the flooding of a river valley can carry mud or shale from surrounding areas.

Different shale distributions have different effect on the sand reservoir.

In a sand reservoir contain structure shale : it will affect the reservoir porosity

In a sand reservoir contain laminae shale : it will affect only the net pay of the reservoir

In a sand reservoir contain : it will affect the porosity and permeability of the reservoir and also it will lead to a shortcut in the resistivity log response , which may result in a miss lead in the interpretation of the reservoir porosity and saturation  , it could be interpreted as sand bearing water instead of a sand contain dispersed shale.

So, the question here is how to differentiate between them and to avoid this wrong interpretation ?!

Let’s assume that you have a 100% clean sand reservoir. So the total porosity of this reservoir is 30% and the sand grains will represent 70% of the volume of the reservoir

Hint : Porosity of sandstone is 30 % and porosity of shale is 10%


Case 1 :

In the case of the presence of structure shale ,

So in this case shale grains will replace sand grains ( volume of 70% ) , the shale will bring its 10% porosity with it.

In other words , The porosity will be enhanced by 10% in the volume of 70% of the sand

So , the porosity will increase by 70/10 and the total porosity will be = 37 %


Case 2 :

In the case of the presence of laminae shale , in this case shale will replace the whole reservoir ( 100 & ) and also will bring its own 10% porosity.

In other words , the porosity will be reduced from 30% to 10%
Case 3 :

In the case of the presence of dispersed shale , in this case shale we will replace the porosity  volume it self ( 30 % ) and as usual it will bring its own porosity.

 
In other words , the porosity will be reduced into 3% ( 30 / 10 )Summarized figure for the different shale distributions in shaly sand reservoir and it’s effect on the reservoir porosity.
Shale distribution model proposed by Thomas and Stieber (Tyagi et al. 2009). Here Vshale is the volume of shale, φtotal is the total porosity, φmax is the maximum porosity, and φsh is the porosity in shale

Conclusion :


 

So, we can differentiate between the three different types of shale distribution and according to the type we can make the right interpretation for the porosity and the saturation of the sand reservoir , also we will avoid the miss leading interpretation in the shortcut in the resistivity log.


Photo Credits: Ahmed Adel
Originally blog is written by Ahmed Adel 










Raging Waters

Raging Water

Raging waters causes lots of damages that cannot be avoided.

The Inevitable Catastrophe 

Up to now, in recent posts we have focused on the process of drainage formation and evolution and on the variety of landscape features formed by streams. Now we turn our attention to the havoc that a stream can cause when flooding takes place. Floods can be catastrophic they can strip land of forests and buildings, they can bury land in clay and silt, and they can submerge cities. A flood occurs when the volume of water flowing down a stream exceeds the volume of the stream channel, so water rises out of the channel and spreads out over a floodplain or delta plain, or fills a canyon to a greater depth than normal. 
Floods happen 

  1. during abrupt, heavy rains, when water falls on the ground faster than it can infiltrate and thus becomes surface runoff; 
  2. after a long period of continuous rain, when the ground has become saturated with water and can hold no more; 
  3. when heavy snows from the previous winter melt rapidly in response to a sudden hot spell; or 
  4. when a dam holding back a lake or reservoir, or a levee or retaining wall holding back a river or canal, suddenly collapses and releases the water that it held back. 
Examples of seasonal floodplain flooding.
Geologists find it convenient to divide floods into two general categories. Floods that occur during a “wet season,” when rainfall is heavy or when winter snows start to melt, are called seasonal floods. Floods of this type typically take place in tropical regions during monsoons, and in temperate regions during the spring when storms drench the land frequently and or a heavy winter snow pack melts. When seasonal floods submerge floodplains, they produce floodplain floods, and when they submerge delta plains they produce delta-plain floods (figure above a–c). 

Flash floods can occur after torrential rains.

Events during which the flood waters rise so fast that it may be impossible to escape from the path of the water are called flash floods (figure above a, b). These happen during unusually intense rainfall or as a result of a dam collapse (as in the 1889 Johnstown flood) or levee failure. During a flash flood, a canyon or valley may fill to a level many meters above normal. In some cases, a wall of water may slam downstream with great force, leaving devastation in its wake, but the flood waters subside after a short time. Flash floods can be particularly unexpected in arid or semiarid climates, where isolated thundershowers may suddenly fill the channel of an otherwise dry wash, whose unvegetated ground allows runoff to reach the channel faster. Such a flood may even affect areas downstream that had not received a drop of rain.

Case Study: A Seasonal Flood 

In the spring of 1993, the jet stream, the high-altitude (10–15 km high) wind current that strongly affects weather systems, drifted southward. For weeks, the jet stream’s cool, dry air formed an invisible wall that trapped warm, moist air from the Gulf of Mexico over the central United States. When this air rose to higher elevations, it cooled, and the water it held condensed and fell as rain, rain, and more rain. In fact, almost a whole year’s supply of rain fell in just that spring some regions received 400% more than usual. Because the rain fell over such a short period, the ground became saturated and could no longer absorb additional water, so the excess entered the region’s streams, which carried it into the Missouri and Mississippi rivers. Eventually, the water in these rivers rose above the height of levees or broke through levees, and spread out over the floodplain. By July, parts of nine states were underwater (see a in first figure). 
The roiling, muddy flood uprooted trees, cars, and even coffins (which floated up from inundated graveyards). All barge traffic along the Mississippi came to a halt, bridges and roads were undermined and washed away, and towns along the river were submerged. For example, in Davenport, Iowa, the river front district and baseball stadium were covered with 4 m (14 ft) of water. In Des Moines, Iowa, 250,000 residents lost their supply of drinking water when flood waters contaminated the municipal water supply with raw sewage and chemical fertilizers. Row boats replaced cars as the favoured mode of transportation in towns where only the rooftops remained visible. In St. Louis, Missouri, the river crested 14 m (47 ft) above flood stage. 
For 79 days, the flooding continued. When the water finally subsided, it left behind a thick layer of sediment, filling living rooms and kitchens in floodplain towns and burying crops in floodplain fields. In the end, more than 40,000 square km of the floodplain had been submerged, 50 people died, at least 55,000 homes were destroyed, and countless acres of crops were buried. Officials estimated that the flood caused over $12 billion in damage. Comparable flooding happened again in the spring of 2011, in the Mississippi and Missouri drainage basins. 

Case Study: A Flash Flood 

On a typical sunny day in the Front Range of the Rocky Mountains, north of Denver, Colorado, the Big Thompson River seems quite harmless. Clear water, dripping from melting ice and snow higher in the mountains, flows down its course through a narrow canyon, frothing over and around boulders. In places, vacation cabins, camp grounds, and motels line the river. The landscape seems immutable, but as is the case with  so many geologic features, permanence is an illusion.
On July 31, 1976, easterly winds blew warm, moist air from the Great Plains toward the Rocky Mountain front. As this air rose over the mountains, towering thunder heads built up, and at 7:00 P.M. rain began to fall. It poured, in quantities that even old-timers couldn't recall. In a little over an hour, 19 cm (7.5 inches) of rain drenched the watershed of the Big Thompson River. The river’s discharge grew to more than four times the maximum recorded at any time during the previous century. The river rose quickly, in places reaching depths several meters above normal. Turbulent water swirled down the canyon at up to 8 m per second and churned up so much sand and mud that it became a viscous slurry. Slides of rock and soil tumbled down the steep slopes bordering the river and fed the torrent with even more sediment. The water undercut house foundations and washed the houses away, along with their inhabitants (see above figure b). Roads and bridges disappeared, and boulders that had stood like landmarks for generations bounced along in the torrent like beach balls, striking and shattering other rocks along the way. Cars drifted downstream until they finally wrapped like foil around obstacles. When the flood subsided, the canyon had changed forever, and 144 people had lost their lives.

Living with Floods 

Flood Control  

Holding back rivers to prevent floods.
Mark Twain once wrote of the Mississippi that we “cannot tame that lawless stream, cannot curb it or confine it, cannot say to it, ‘go here or go there,’ and make it obey.” Was Twain right? Since ancient times, people have attempted to control courses of rivers so as  to prevent undesired flooding. In the 20th century, flood-control efforts intensified as the population living along rivers increased. For example, since the passage of the 1927 Mississippi River Flood Control Act (drafted after a disastrous flood took place that year), the U.S. Army Corps of Engineers has laboured to control the Mississippi. First, engineers built about 300 dams along the river’s tributaries so that excess run-off could be stored in the reservoirs and later be released slowly. Second, they built artificial levees of sand and mud, and built concrete flood walls to increase the channel’s volume. Artificial levees and flood walls isolate a discrete area of the floodplain (figure above a–c). 
Although the Corps’ strategy worked for floods up to a certain size, it was insufficient to handle the 1993 and 2011 floods when reservoirs filled to capacity, and additional run-off headed downstream. The river rose until it spilled over the tops of some levees and undermined others. “Undermining” occurs when rising water levels increase the water pressure on the river side of the levee, forcing water through sand under the levee. In susceptible areas, water begins to spurt out of the ground on the dry side of the levee, thereby washing away the levee’s support. The levee finally becomes so weak that it collapses, and water fills in the area behind it. In some cases, the Corps of Engineers intentionally dynamites levees along a relatively unpopulated reach of the river upstream of a vulnerable town. This diverts water out onto a portion of the floodplain where the water will do less damage, and prevents the flood waters from over topping levees close to the town.
Another solution to flooding in some localities may involve restoration of wetland areas along rivers, for wetlands can absorb significant quantities of flood water. Also, where appropriate, planners may prohibit construction within designated land areas adjacent to the channel, so that flood water can fill these areas without causing expensive damage. The existence of such areas, which are known as flood ways, effectively increases the volume of water that the river can carry and thus helps prevent the water level from rising too high.

Evaluating Flooding Hazard  

When making decisions about investing in flood-control measures, mortgages, or insurance, planners need a basis for defining the hazard or risk posed by flooding. If flood waters submerge a locality every year, a bank officer would be ill advised to approve a loan that would promote building there. But if flood waters submerge the locality very rarely, then the loan may be worth the risk. Geologists characterize the risk of flooding in two ways. The annual probability of flooding indicates the likelihood that a flood of a given size or larger will happen at a specified locality during any given year. For example, if we say that a flood of a given size has an annual probability of 1%, then we mean there is a 1 in 100 chance that a flood of at least this size will happen in any given year. The recurrence interval of a flood of a given size is defined as the average number of years between successive floods of at least this size. For example, if a flood of a given  size happens once in 100 years, on average, then it is assigned a recurrence interval of 100 years and is called a “100-year-flood.” Note that annual probability and recurrence interval are related:
    annual probability = 1/recurrence interval 
For example, the annual probability of a 50-year flood is 1/50, which can also be written as 0.02 or 2%. 
Unfortunately, some people are misled by the meaning of recurrence interval, and think that they do not face future flooding hazard if they buy a home within an area just after a 100-year flood has occurred. Their confidence comes from making the incorrect assumption that because such flooding just happened, it can’t happen again until “long after I'm gone.” They may regret their decision because two 100-year floods can occur in consecutive years or even in the same year (alternatively, the interval between such floods could be, say, 210 years).

The conceptual relationship between flood size and probability.
The recurrence interval for a flood along a particular river reflects the size of a flood. For example, the discharge of a 100-year flood is larger than that of a 2-year flood, because the 100-year event happens less frequently (figure above a). To define this relationship, geologists construct graphs that plot flood discharge on the vertical axis against recurrence interval on the horizontal axis (figure above b).
Knowing the discharge during a flood of a specified annual probability, and knowing the shape of the river channel and the elevation of the land bordering the river, hydrologists can predict the extent of land that will be submerged by such a flood. Such data, in turn, permit hydrologists to produce flood-hazard maps. In the United States, the Federal Emergency Management Agency (FEMA) produces maps that show the 1% annual probability (100-year) flood area and the 0.2% annual probability (500-year) flood risk zones (figure above c).
Figures credited to Stephen Marshak.

Sources of energy in the Earth System

Energy sources in the Earth system

What comes to mind when someone asks you to name an energy resource? Perhaps you think about the many kinds of fuel, materials that burn or react to produce heat. Alternatively, you may think of windmills and hydroelectric dams, or arrays of solar panels, because they are appearing on the landscape with increasing frequency. Where does the “energy” (the capacity to do work) in these energy resources originally come from? Let’s consider the underlying sources: 
  • Energy directly from the Sun: Solar energy, resulting from nuclear fusion reactions in the Sun, bathes the Earth’s surface. It may be converted directly to electricity, or it may be used to heat water.
  • Energy directly from gravity: The gravitational attraction of the Moon, and to a lesser extent, the Sun, helps cause ocean tides, the daily up-and-down movement of the sea surface. The flow of water during tidal changes can drive turbines. 
  • Energy involving both solar energy and gravity: Solar radiation heats the air, which becomes less dense. In a gravitational field, this warm air rises, while cool, denser air sinks. The resulting air movement, wind, powers sails and windmills. Solar energy also evaporates water, which enters the atmosphere. When the water condenses, it rains on the land, where it accumulates in streams that flow downhill in response to gravity. This moving water can drive waterwheels and turbines.
  • Energy via photosynthesis: Algae and green plants absorb some of the solar energy that reaches the Earth’s surface. Their green colour comes from a pigment called chlorophyll. With the aid of chlorophyll, plants produce sugar through a chemical reaction called photosynthesis. Plants use the sugar to manufacture more complex organic chemicals. Burning plant matter releases potential energy stored in the chemical bonds of organic chemicals. During burning, the molecules react with oxygen and break apart to produce carbon dioxide, water, and carbon (soot). People have burned plant material (biomass) to produce energy for centuries. More recently, plant material has been used to produce ethanol, a flammable alcohol. 

While a portion of our energy comes from recently living biomass (wood, sugar cane, etc.) even more comes from the remains of organisms that lived either by carrying out photosynthesis or by eating algae or plants, and were then buried and preserved in sediment after they died. Because the energy stored in these substances was trapped by photosynthesis long ago, and has been preserved in rock over geologic time, we refer to these materials as fossil fuels. 
  • Energy from chemical reactions: A number of inorganic chemicals can burn to produce light and energy. A dynamite  explosion is an extreme example of such energy production. Recently, researchers have been studying electrochemical devices, such as hydrogen fuel cells, that produce electricity directly from chemical reactions. 
  • Energy from nuclear fission: Atoms of radioactive elements can split into smaller pieces, a process called nuclear fission. During fission, a tiny amount of mass transforms into a large amount of energy, called nuclear energy. This type of energy runs nuclear power plants and nuclear submarines. 
  • Energy from Earth’s internal heat: Some of Earth’s internal energy dates from the birth of the planet, while some comes from radioactive decay in minerals. This internal energy heats underground water. The resulting hot water, when transformed to steam, provides geothermal energy, which can drive turbines. 
Sources of energy used by people. The proportion of sources changed through time, but the total quantity used increases. Industrialization in Asia is now driving growth.
During the course of civilization, the sources of energy that people use have changed (figure above). Prior to the industrial age, direct burning of wood and other biomass provided most of humanity’s energy. But by the second half of the 19th century, deforestation had nearly destroyed this resource, and energy needs had increased so dramatically that other fuels came into use. 
Figures credited to Stephen Marshak.