This article will explain the overall of how to transform organic matter into petroleum. Chemical processes will take place in order to transform organic matter preserved in source rocks into petroleum. This can be called a cooking process. Three phases regarding maturation of the organic matter to form petroleum are diagenesis, categenesis and metagenesis.
Oil and gas that we are drilling today comes from a biogenic origin and it is formed with proper time and temperature. Organic matter is one of the most important parts of hydrocarbon generation. This topic will give you an overview of how organic matter will be transformed to hydrocarbon.
Starting with plants and algae, take carbon (CO2) from the atmosphere and process it to form glucose and this starting process is called photosynthesis. Glucose is transformed into more complex organic compounds. Trees, for example will grow bigger because they use photosynthesis to convert into energy. When animals and trees die, the organic matter is typically oxidized and this will create CO2 and put water back into environment again. However, in some situations when organic matter is buried quickly in areas where there is no oxygen, the organic matter may be preserved. If the organic matters are buried in proper conditions, petroleum may be formed. Continue reading
Geological time scales help us to know the age of formations and three types of time scales are relative, absolute time and magnetic polarity scales. Relative time scale relates to an order in which a specific rock sequence occurs, but absolute time is an actual time that is derived from the chemical half-life of minerals in rocks. Magnetic polarity uses a concept of magnetic sequences to age the rocks.
Clastic deposition covers about 75% of the Earth’s surface and clastic sedimentary rocks can be categorized into 3 groups based on grain size. Table 1 demonstrates grain size and type of sedimentary rocks.
Table 1 – Grain Size and Sedimentary Rock
(Ref: http://www.takenote.it/blog/wp-content/uploads/2012/01/table13.jpg)
Mudstone is a fine grain sedimentary rock and this is the most abundant type of sediments. Its grain size is less than 1//16 mm, so people cannot differentiate it with normal eyesight. Typical mudstones are siltstone, claystone and shale and the most common minerals are quartz, feldspar, calcite and clay. The fine grained rock can show the least about its formation because of a very small grain size. Mudstone is defined as sediment with a large component of clay sized material. Mudstone occurs due to slow settling from slow currents. This fine grain sediment is typically formed on blanketing ridges, continental shaves, seafloor, abyssal plain and in trenches. Continue reading
Clastic sediment rocks are rocks which are formed from broken pieces of other pre-existing rocks by physical weathering. Then, rock particles are transported to lower lying areas. Mechanically eroded small pieces of rocks are usually formed in an angular shape because of a natural fracture point when erosion takes place initially.
When rock particles are transported, their shapes become rounded because of abrasion. Figure 1 demonstrates the shape of clastic particles. Furthermore, rock particles will be sorted due to conditions; for example, the flow rate of water transporting particles, size and weight of rocks, and the hardness of each rock. Eroded rock particles will be more rounded and well sorted as time progresses. Figure 2 shows the definition of clastic particle sorting.
Figure 1 – Shape of Clastic Particles
Figure 2 – Sorting of clastic sedimentary rocks
(Ref Image: http://www.tankonyvtar.hu/hu/tartalom/tamop425/0038_foldrajz_mineralogy_Da/images/Fig_2_7.jpg) Continue reading
