Sedimentary Structures in Petroleum Geology

Sedimentary structures

These are formed by mechanical and physicals process. It includes -

1.  Bedding 
2. Cross Bedding (Current Bedding)
3. Ripple Marks
4. Graded Bedding
5. Mud Cracks
6. Cruscentic marks
7. Rain Drops
8. Convolute Bedding
9. Scour Marks

1. Bedding

It is the arrangement of the rock mass, into distinguish layer, these are 3 types of bedding. 1. Lamination bedding - whose thickness is less than 1 cm. , 2. Stratum - whose thickness greater than 1 cm and 3. Massive Beddive :- Which is apparently structure less.

2. Cross Bedding / Current Bedding  

It is the sedimentary structures, the various layer line one or another are not parallel, but bear an irregular relationship to each other. This structure indicates rapid changes - Velocity and direction of the wind caring the sediment. In cross bedding the minor beds are inclined and stacked up in the direction of the prevailing wind. 

3. Ripple Marks

These are wavy undulations seen on the surface of the bedding plains. These structures may be form on the surface of the deposit formed by wind. Ripple marks are two types -

• Symmetrical RM 
• Asymmetrical RM

4. Graded Bedding

Here each bed shows of, variation ingrain size, from coarse below to fine above  -- When the sequences of rock is made up of such graded layer. This structure is known as graded bedding. Normally such perfectly graded beds are the result of the sedimentation, In bodies of standing water, where the factor of gravitative settling from a mixed sediments loud is the predominant process. This structure is generally found in Graywacks ( Gray-wacks )

5. Mud Cracks 

The structure consist of polygonal or irregular cracks which straight along the surface of an exposed sedimentary layer mud cracks are developed due to dissication ( state of extreme dryness ) at close and compact of water saturated body sediment. The size of the polygon varry in with  from a few mm to over 30 cm, they make penetrate to a depth of 1 to 2 cm of several tons of metre.

6. Rain Drops Imprints

Rain drops falling on soft sediment surface makes small impact craters, which is circular If the rain falls vertically downward & slightly elliptical if the path is obliged to the surface.

This may get dried up and subsequently preserved, this imprints became a part of deposition.

7. Crescentric Marks 

These are produced on the consolidated sediment surface around obstacles such as peddles, shells, or wood fragments. In the path of water flow the obstacle line on the way of the current tend to deflect the flow-line, which results either a erosion or deposition or both below the obstacle.

8. Scour Marks 

These are produced as a result of erosion of sediment surface by the current flowing over it. The soft but cohesive type sediment generally mud, id sculptured by the scouring action of current.

9. Convolute Bedding

Con volute bedding shows crumbling or complicated folding layer. Con volute bedding shows more or less sharp crest, alternating with bladder  trough.

It is generally develop fine grain non cohesive sediment.

Notes:- Data is collected from different university class notes . Main purpose to write this articles is to help peoples.

Article Written by-

Ritu Raj Medhi

Founder & President

Chief technical & editorial officers 

Petroleumbuddy websites and initiatives

 

Pore Morphology || Petroleum Engineering and Geology

Pore Morphology

A minute opening or tiny hole between the constituent grain of particles of a body. Which admits the passage of fluid (Oil, gas, water ). Theoretically the measure of void space is defined as porosity of the rock.

Classification of porosity types  

1. Primary / pre depositional porosity 

• Inter granular Porosity
• Intragranular Porosity

2. Secondary/ Post depositional Porosity

• Intercrystalince Porosity
• Fenestrial Porosity
• Mouldic Porosity
• Vuggy porosity
• Fracture Porosity

Primary Porosity

Primary Porosity is that which by definition forms when sediment is towards take down. It is the natural porosity types found in petroleum reservoir sands or rocks. It is characterized or recognised by two types -

1. Inter-Granular Porosity 

  

It occurs in the spaces between the detridal grain which form the frame work. of a sedimentary rocks, It is the very important porosity type. It is present initially in almost all sediment, It is generally progressively reduced by diagenesis in many carbonate, But it is dominated porosity types found in sand stone.

2. Intragranular / Inter Particle Porosity 

In carbonate sands particularly those of skeleton origin , Primary porosity may be present within the grains. For example - Cavities of Molluscs , Bryo Zoans, Ammonites and macro fossils etc can all be classes as intra granular / Intra particular porosity.

             However the Chemical instability of the carbonate host grains of an leads to their intra particle pores being modified or obliterated by subsequent diagenesis.

3. Secondary Porosity ( Post Depositional Porosity)

It is that which by definition which form after the sediment was deposited , It is a result of Geological Process Like diagenesis after deposition of sediment, It is more diversed in Morphology, and more complex in genesis then primary porosity.

       The magnitude, shape, size, interconnection of the pores may have no direct relation to the form of original sedimentary particles. It is more commonly found in carbonates.

1. Inter-crystalline porosity

It means the porosity between crystal of approximately equal size although the simple definition would apply, in a strict sense to almost all porosity in carbonate. Intercrystalline normally restricted to porosity between the Individual crystal, It is charecteristics of dolomite.

2, Fenestrial Porosity

Lens shape porosity develop in carbonate due to the presence of fenestrial porosity, rocks with fenestrial porosity will not form good reservoir rocks unless the penestry we interconnected, to permit a good  permeability to be establish. Elongated fenestrial pores may developed into rotting of organic material.

3. Mouldic Porosity

Mould are pores form by the selective disolution of individual constituent grains  of coasals in carbonate rock, it is all the grains of a particular type that is dissolved. It is typically found in carbonate.

4. Vuggy Porosity  

Vuggs are larger size than moulds. Porosity produced by dis-solution of the rock by the formation water, to generate patchy cavity. Vuggs tend to larger than moulds. It is most common in carbonates.

5. Fracture Porosity

Porosity resulting from fracture develop by tectonic forces between the rock, is Called fracture porosity. This porosity type is charecteristics of rocks , that we strongly lifted. Therefore they are generally form, later than the other varieties of porosity. It is important to knows that fracture porosity is not only found in well cemented sand stone and carbonate but may also be present in shales and igneous and metamorphic rock.

Notes:- Data is collected from our universities notes-books and persons experienced. Main purpose of this article is to help peoples.

Articles written & composed by -

Ritu Raj Medhi

Founder & President

Chief technical & editorial officers

Petroleumbuddy websites & initiatives

Origin Of Petroleum || Geology || Petroleum Engineering

Origin of petroleum

Two theory are available that try to describes origin of petroleum. First on is Inorganic origin theory and second one is organic origin theory. we will discuss each theory briefly  one by one in this article.

Inorganic Origin Theory of Petroleum

According to Demitrive Mendelive (1877) metalic carbrides deep within the earth reacted with water to form accetylic (C2H2), This acetylene later condensed to form heavier hydrocarbon, This theory was modified by-  Berthelot and Mendeleen.   

    

          According to their theory the earth contain Iron Carbide ( Mantle of the earth contain ), IRON Carbide ( Mantle of the earth contain ) Iron Carbide Which reacted (CH4). In recent time Thomas Gold has revived the Inorganic  origin of petroleum, According to him:- From the Earliest time there was an inexhaustible store of Hydrocarbon, In the interior of the earth. Gold argued that Meteors contain Inorganic Hydrocarbon, Initially when the earth was very hot and liquid state millions of Meteoroids showered on earth, stretching million of  years, This Meteoroids  melted and mixed with liquefied layers of earth. As a results all the hydrocarbon within meteoroids mixed and spread all over the liquids layers , When the earth cool later the liquid layers solidified and form different types of rock and it is rock and Hydrocarbon Was Distributed 

Organic Origin Theory of Petroleum

According to this theory petroleum originated from the remains of various type of mixture marine floating organism known as plankton. Like the mosses which float on the ponds, Algae mixed with other plants and animals, leaves, spores, pollens etc. floated on the sea after wards countless million of this organism died and sunk to the bottom of the ocean  and began to accumulated from 100-1000 years. This types of accumulation continues over the sea floor. Before this remains where decomposed, they were sealed in the mud, anaerobic bacteria acted upon them in the absence of air. There was perhaps some chemical reaction with the salt in the water + weight of the over-line sediment. Converted this mud into shale, this source material of oil was this finally in prison. Due to chemical reaction and action of microbes the accumulated remains of plants and animals were transform into blacking, glue like compact mass known as kerogen. Later due to disturbance in the earth, It went down to greater depths due the pressure and temperature of the earth kerogen was transformed into oil and gas throughout the centuries. In this respect a good co-relation is found between the occurrence of oil with depth. Maximum amount of oil and gas is orginated at a depth of 3000 meter to 5,000 meter respectively. And the temperature remains between 50 degree to 250 degree.

Notes:- Data is collected from various university notebook , different books , e&p websites and person own experience in Industry. Main purpose of this article is to help peoples