What type of rock is petroleum

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 The model also shows that the source rock in this unit has reached the required levels of thermal maturity to onset of the oil window 0.

Burial and thermal maturity histories of the Upper Jurassic source rocks for the studied well showing the positions of the oil window. The timing of petroleum generated and expelled from the Upper Jurassic source rocks were modeled Figure The modeled hydrocarbon generation and expulsion of the studied well shows that the Madbi source rocks were generating hydrocarbon with oil as the main product Figure In general, the hydrocarbon generation and expulsion history of the Madbi source rock in the studied model was represented by only two stages Figure The first stage of hydrocarbon generation of the Madbi source rock was occurred during Late Cretaceous-Early Eocene time at 70— This stage is the early phase of oil generation without any expulsion.

The second stage approximately Plots of evolution of the transformation ratio and rate of hydrocarbon generation with age from the Madbi source rocks in the studied well. Oil is a complex mixture containing a large number of closely related compounds [ 2 ]. The compounds present and their relative amounts are controlled initially by the nature of the organic matter in the source rock. With more specific words, the relative amounts of normal alkanes, isoprenoids, aromatics, and sulfur compounds are characteristic of the source and should be essentially the same for all oil derived from a particular source rock.

The fact that variations in crude oil composition are to a certain extent inherited from different source rocks. For instance, coaly material in general yields more gaseous compounds, whereas high wax crude oils are commonly associated with source material containing high proportions of lipids of terrestrial higher plants and of microbial organisms [ 2 ].

High-sulfur crude oils are frequently related to carbonate-type source rock. A side from the influence of source rock facies, the state of maturity of the source material is also of importance. However, much larger variations in composition can cause processes operating in the reservoir. In other words, crude oil alteration processes thermal alteration, deasphalting, biodegradation, and water washing tend to obscure the original character of the oil, and therefore affects crude oil correlation, furthermore influence the quality and economic value of petroleum [ 2 ].

Therefore, the careful studying of the chemical compositions of the rock extracts, seeps, and produced oil can minimize the risk associated with finding petroleum accumulations. The crude oils have high saturated and aromatic fractions and ranging from The high saturated and aromatic fractions with low amount of asphaltene and resin components indicate that these oils are naphthenic oils and have no sign of biodegradation.

The similar bulk property and composition of the analyzed crude oils indicate that only one oil type is present. Biodegradation process may occur in an oil reservoir, and the process dramatically affects the fluid properties of the hydrocarbons, e. The early stages of oil biodegradation are characterized by the loss of n-alkanes or normal alkanes followed by the loss of acyclic isoprenoids e.

Compared with those compound groups, other compound classes e. In this respect, there is no sign of biodegradation among the studied oil samples, where the analyzed oils contain a complete suite of n-alkanes in the low-molecular weight region and acyclic isoprenoids e. The correlation of crude oils with one another and with extracts from their source rocks provide valuable tools for helping the exploration geologist to answer production and exploration trends [ 2 ].

Are there one or more families of oils in a particular rock sequence? Each family of oils represents one element of distinct petroleum system. Oil-source rock correlations are more difficult than oil-oil correlation; this is because many problems are involved in both sampling and interpreting the data. Tissot and Welte [ 2 ] showed that source rock oil is not usually similar in composition to its corresponding reservoir oil for several reasons.

First, there is an evidence for the oil fractionates during the process of leaving the source and migrating to the reservoir accumulation. Second, source rocks do not yield oils of the same composition throughout their generation history. Third, degradation processes can affect the reservoir oil. All these problems require that the correlation be made by parameters e.

These parameters solve most of problems in oil-source correlations, because the differences in the chemical composition of the oil and the organic matters retained in the source rock are a function of migration fractionation and post-migration alteration. Various parameters have been used for oil-source correlation purposes.

These parameters depend mostly on the pre-burial environments of living organisms, the depositional environments of the organic matter, and the diagenetic processes in the source rocks. In this respective study, the applied parameters used for oil-source correlation are the steranes ternary diagrams of oils and source rock extracts by gas chromatographic GC analysis of C 27 , C 28 , and C 29 regular steranes distribution. The distribution of C 27 , C 28 , and C 29 homologous sterols on a ternary diagram was first suggested by Tissot and Welte [ 2 ] as a source indicator.

The objective of this part in this study is to investigate the genetic link between the oils recovered from Sayun-Masilah oilfield and Upper Jurassic source rocks. In an attempt to develop an oil-source rock correlation, we extracted soluble bitumens from four samples of the Madbi shale and analyzed their biomarkers using GC and GC—MS analyses. Overall, the oil data closely match the Upper Jurassic source rock data.

Key factors include biomarker parameters and the similar positions on the cross-plots Figures 14 and 15 [ 51 ]. Ternary diagram of regular steranes C 27 —C 29 showing the relationship between sterane compositions, source organic matter input modified after [ 56 ]. The cap rock is a rock that cannot transmit oil. Examples of cap rock are shale rocks or limestone and sandstone rocks immersed in shale.

An example of a trap is an anticline which looks like a dome of a cap rock over the reservoir rock Fig. Natural gas, which is usually formed together with the oil, is the lightest element, it will be at the top of the dome unless it completely dissolves in the oil. Then there is a deposition of oil. Deep underground salty water, called brine, is the densest, it is at the bottom below the oil Figs. Most evidence supports an organic rather than an inorganic origin of oil. Second, the oil has optical rotary power, i.

Third, many crude oils contain porphyrins, which may come either from chlorophyll in plants or from red cells in blood. Forth, most crude oils contain nitrogen, which is an essential element in amino acids. Fifth, the oil is found in sedimentary rocks spanning many geological times from Precambrian more than million years ago to Pleistocene about a million years ago , which is an indication that oil forms continuously in the sedimentary rocks.

Sixth, the sedimentary rocks contain enough organic material to form the oil. The chemical composition of the petroleum is similar to the composition of the organic material, although there is more carbon and hydrogen and less oxygen and nitrogen in the oil compared to the organic material.

The knowledge about oil generation, migration and accumulation can be used to search for oil fields and to estimate the remaining oil reserves. Oil is formed and trapped in sedimentary rather than igneous rocks. Regions where the ancient precambrian igneous rocks are exposed at the surface of the Earth are called shields.

As one can see from Fig. These forces create basins: areas of deep sedimentary rocks which are necessary to produce the oil. The forces also deform the sedimentary rocks which leads to creation of traps necessary for oil and gas accumulation.

One can also see in Fig. Since all the orogens and basins on the Earth are known, one can estimate the amount of undiscovered oil assuming that the current theory of oil formation is correct. 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.

Like sandstone, carbonates are sedimentary rocks commonly found in conjunction with shale. Carbonates, however, are formed largely from remains of marine life, particularly shells and bones, combined with other minerals. Because of this, they are full of calcium and other compounds that lead to their classification: limestones, which contain calcium carbonate, and dolomites, which contain calcium magnesium carbonate.

The spaces between their fused fragments are where oil and gas may be found.