What kind of rocks store petroleum

The grains originally came from other rocks that had been eroded. The sample is exceedingly porous and permeable. Thegrains are loosely packed and there is very little cement filling the space between the grains. The arrow indicates possible pathways for fluid movement. Figure 2b --A thin-section photomicrograph of a Pennsylvanian limestone taken from a core sample of a producing zone in Victory field, haskell County, Kansas.

This particular sample comes from an interval that is not a good reservoir rock. Circular grains composed of calcite finely crystalline, reddish-stained areas in a grain and dolomite clear, coarse crystals are completely cemented by medium crystalline calcite.

No porosity is visible. Figure 2c --A thin-section photomicrograph of a Pennsylvanian limestone. A source rock is defined as mature when it is reached to generate hydrocarbons.

A rock that does not reach to the level of generation of hydrocarbons is defined as an immature source, and that which passed the time of significant generation and expulsion, it is considered as over-mature source rock. Generally, various parameters have been used for estimating source rock maturation. These parameters include vitrinite reflectance Ro and rock-eval pyrolysis data such as T max and production index PI.

The study of thermal maturation of source rocks is one of the main steps in the source rocks evaluation in the study area. This is because it is possible from the maturation stage to determine the position of the sediments with the respect to the oil generation.

It can also help in oil exploration from knowing the relation between hydrocarbon generation, migration, and accumulation with the tectonics, which lead to the development of the structural traps in the study area. The most common method used for determining the stage of maturation is the vitrinite reflectance Ro , which was discussed by several workers.

Hood et al. Tissot and Welte [ 2 ] considered the vitrinite reflectance as the most powerful tool for detecting maturation of organic matter. It measures the ability of tiny vitrinite particles called macerals in kerogen to reflect incident light. This method depends on the separation of the organic macerals and measuring its vitrinite reflectance in oil immersion lens using a reflecting polarizing microscope connected with a photometer.

The vitrinite macerals are increased in its reflectivity, as the maturation of their host rocks increases. In the Sayun-Masilah basin, the vitrinite reflectance values ranges from 0. These reflect that Madbi and Shuqra Formations are mature stage, whereas the samples in L.

Qishn Member and Nayfa Formation lie mainly in the mature stage Figure 7. The lowering of the values of vitrinite reflectance in the studied samples from Sunah field, in spite of their occurrence at greater depths, may be related to the presence of high content of unstructured lipids of the type II kerogen [ 31 ]. Rock-eval pyrolysis. Plot of vitrinite reflectance data Ro versus depths showing thermal maturity stages of the Source rocks samples in the study area.

The values in the Nayfa and Shuqra Formations reflect immature to mature stages. The production index PI data plotted against depth in Figure 1 indicate that the phases of maturation of kerogen of these rock units are in the immature to mature stages.

Most of the studied samples in the Madbi Formation at Sayun-Masilah basin lie in the mature stage Figure 1. Reversely, the L. Qishn and Nayfa samples reveal a marginal mature stage. Qishn and Nayfa formations. Geohistory diagrams [ 32 ] and similar diagrams have been widely used in geology, particular in hydrocarbon exploration.

These diagrams were adapted to perform numerical modeling of burial, erosion, and thermal histories in sedimentary basins, e. This method has become an important tool and successfully applied to search for new petroleum plays or for the evaluation of exploitable oil and gas accumulations around the world e.

In this chapter, quantitative one-dimensional basin modeling is performed for evaluating the thermal histories and timing of hydrocarbon generation and expulsion of the Nayfa, Madbi, and Shuqra source rocks in the Sayun-Masilah basin.

Sunah exploration well was created as a result of geochemical, well log, and further geologic data were used. The geologic model consisting of the depositional, nondepositional, and erosional events in absolute ages was compiled using stratigraphic data that were provided from well reports and previous stratigraphic studies, e.

The tectonic evolution of the region has significantly influenced burial and thermal history of the study area. The burial subsidence and thermal histories are necessary in order to predict the timing of hydrocarbon generation and expulsion. To describe the resulting models clearly, we review first the results of our reconstruction of the subsidence curves [ 40 ].

Based on well profile, subsidence curves Figure 8 were first constructed for the studied well by decompacting the sedimentary section using formation thicknesses present day thickness and lithologies assigned from mud logs and composite well log.

The subsidence curves and basin history filling of one representative well is shown in Figure 8 , it illustrate that the Upper Jurassic section have a long burial history although it has thin sedimentary cover m , due to thick sedimentary sections m precipitated during the Cretaceous and Tertiary epoch Figure 8 ,which help oil generation in this area.

However, the Madbi source rocks during that time were buried deeply, and the petroleum generation can be generated in this time. Burial history modeling for investigated well in the Sayun-Masilah basin. The thermal history of the source rocks in the sedimentary basins can be evaluated based not only on the deposition and erosion history but also on the heat-flow evolution [ 41 , 42 ].

The borehole temperatures increase systematically with depth in the Earth and were used to calibrate the present day heat-flow regime. The increase of temperatures, indicating that heat is transferred through sediment layers to the surface. The transfer of heat is mainly controlled by thermal conductivity of the formations and geothermal gradient. Therefore, the thermal conductivity and geothermal gradient need to be determined to estimate the heat-flow history [ 43 , 44 , 45 ].

The present day geothermal gradient of borehole location was calculated using BHTs that were corrected for the circulation of drilling fluids. The heat-flow is an important value in the input of the basin modeling, but needs to be determined for the geological past [ 45 , 46 ].

Therefore, the reconstruction of the thermal history of the basin is simplified and calibrated with thermal maturation measurements e. Vitrinite reflectance was measured from maturity measurements of three stratigraphic units Upper Jurassic , including Naifa, Madbi, and Shuqra formations Table 1 , and used to predict paleo-heat flow.

Heat-flow model Figure 10b is used to calculate maturity, which is generally calibrated with a thermal maturity parameter such as vitrinite reflectance, e.

In the Sayun-Masilah basin, paleo-heat flow was affected by the tectonic evolution and rifting phase. The rift influenced heat-flow model, which incorporates a higher heat flow episode during the rift phase and an exponential reduction during the post-rift phase [ 50 ]. Based on the geological evolution of the Sayun-Masilah basin, the two rifting phases were incorporated in the heat flow model by peaks of heat flow during the periods of rifting Figure 10b.

Paleo-temperature modeling in well calibrated using borehole temperature. Notice that there is a good correlation between measured data and calculated curves of temperature and measured vitrinite reflectance.

In thermal history reconstructions of the study area, the influence of the tectonic evolution on the heat-flow distribution through time was applied. The detailed maturity history model of source rocks was used to determine the time when source rocks passed through the oil window. The detailed maturity history of source rocks in the Upper Jurassic source rocks is modeled for the representative well in the Sayun-Masilah basin Figure Based on the thermal maturity model, the hydrocarbon generation history of the source rocks in the model are different because of the variation in thermal and buried history Figure The Madbi Formation has reached the required levels of maturity in the model probably due to the temperatures Figure Because these rocks are cemented together from such small components, they are porous, full of spaces in which energy-rich carbon compounds can settle, later to be liberated in the form of either oil or gas.

Shale is a sedimentary rock frequently mentioned as a natural fuel source, likely because of its abundance 42 percent of all sedimentary rock is estimated to be shale and its composition.

It is produced when layers of carbon-rich mud are compressed until they harden into rock that retains those layers. Other types of especially porous rocks often form above shale beds, trapping the low-density carbon compounds that may rise through the mud that becomes shale in their spaces. Sandstone is one such rock, created from grains of minerals like quartz bound by other compounds, such as silica. Within sandstone beds, carbon compounds generally exist in liquid form, as crude oil, that in some cases also releases natural gas when brought to Earth's surface.

As a result, its main industry is agriculture. Corn, soybeans, and wheat are globally exported from this region and serve as the main economy. On the other side of the spectrum, the desert southwestern region of the United States depends on the Central Arizona Project canals to transport water from the Colorado River in order to support agriculture and urban areas.

Use these materials to explore the interconnected nature of resources and their distribution. Students discover how geologists use the composition and location of rocks to find deposits of oil and natural gas.

They use an interactive computational model to explore how hydraulic fracturing releases natural gas from deep shale formations. See how hydraulic fracturing, or fracking, releases petroleum or natural gas trapped in shale rock formations. Petroleum, or crude oil, is a fossil fuel and nonrenewable source of energy.

Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Skip to content. Twitter Facebook Pinterest Google Classroom. Encyclopedic Entry Vocabulary. Oil shale is a type of sedimentary rock that is rich in kerogen. Kerogen is a part of rock that breaks down and releases hydrocarbons when heated. Hydrocarbon s are substances made entirely of hydrogen and carbon. Petroleum and natural gas are probably the most familiar hydrocarbons.

The hydrocarbons in oil shale can be used as an alternative to petroleum or natural gas. Like traditional petroleum, natural gas, and coal, oil shale and kerogen are fossil fuels. Fossil fuel s developed from the remains of algae, spores, plants, pollen, and a variety of other organisms that lived millions of years ago in ancient lakes, seas, and wetland s.

When these organisms died and drifted to the seabed, they were buried under new layers of plants and sediment. They encountered intense pressure and heat, decomposed, and slowly transformed into the waxy substance known as kerogen. There is not a consistent chemical composition of kerogen, because it has a variety of origins.

Kerogen that formed from land plants called humic kerogen usually has a higher oxygen content than kerogen formed from plankton called planktonic kerogen. However, all types of kerogen consist mainly of hydrocarbons; smaller amounts of sulfur, oxygen, and nitrogen; and a variety of mineral s. Oil shale can be thought of as a precursor to oil and natural gas. A sedimentary rock, oil shale is found all over the world, including China, Israel, and Russia.

The United States, however, has the most shale resources. Spanning the U. Although not all of this can be extracted, it is more than three times the proven petroleum reserves of Saudi Arabia. Oil shale, shale oil, and oil-bearing shale are three different substances.

Oil shale is a sedimentary rock. As it reaches its oil window, oil shale releases a liquid known as shale oil. Oil shale is the rock from which shale oil is extract ed. Shale oil is similar to petroleum, and can be refined into many different substances, including diesel fuel, gasoline , and liquid petroleum gas LPG. Companies can also refine shale oil to produce other commercial products, such as ammonia and sulfur.

The spent rock can be used in cement. Oil-bearing shale s are underground rock formations that contain trapped petroleum. Companies extracting tight oil often use hydraulic fracturing fracking , while companies extracting shale oil most often use heat. The Bakken formation , for example, is made of oil-bearing shale. It is a series of layered shale rocks with a petroleum reservoir trapped between the layers.

The Bakken formation stretches from the province of Saskatchewan, Canada, through the U. Improved drilling technologies have allowed companies to extract oil from the Bakken formation, creating an economic boom in the region.

Oil shales are often classified by their depositional history and mineral content. The depositional history of an oil shale includes the organisms and sediments that were deposited, as well as how those deposits interacted with pressure and heat. The van Krevelen Diagram is a method of classifying oil shales based on their depositional history. The diagram divides oil shales according to where they were deposited: in lakes lacustrine , in the ocean marine , or on land terrestrial.

Oil shales from lacustrine environments formed mostly from algae living in freshwater, saltwater, or brackish water. Lamosite and torbanite are types of oil shales associated with lacustrine environments.