Thermal Cracking Of Crude Oils Research Articles

Effects of effluent pressure on the thermal cracking of crude oil: insights from thermal simulation experiments and phase analysis

This study discusses the anhydrous glass tube isothermal pyrolysis simulation for a crude oil, in order to explore the effects of effluent pressure on crude oil cracking. The results of gas chromatograph indicate that effluent pressure promotes the cracking of crude oil, increasing yields of C1–C5 saturates but inhibiting the generation of olefins. According to the calibration result of Soave–Redlich–Kwong equation of state, fluid phase transitions occur at very high effluent pressures, resulting in constant effluent pressure with no further increase in cracking efficiency and with invariant yields of pyrolysates. This study suggests that fluid phase transitions should be considered in petroleum exploration, which can help us to precisely determine the type of petroleum resources.

Characteristics and significance of the solid bitumen in the second member of Dengying Formation of Sinian system in the north of central Sichuan Basin, China

With ongoing advancements in natural gas exploration, the second member of the Sinian Dengying Formation (Deng 2 Member) has emerged as a crucial region for providing natural gas reserves in the north of the central Sichuan Basin. The Deng 2 Member has a significant volume of reservoir solid bitumen. Geochemical characteristics and development mechanism of the solid bitumen were determined through measurements and analyses of the Deng 2 Member samples collected from primary exploration wells by using optical microscopy, SEM, gas chromatograph-mass spectrometer, and laser Raman spectrometer. The results show that the Deng 2 Member has a generally high content of solid bitumen, ranging from 2.96% to 5.13% on average in single wells. The solid bitumen mainly occurs as the fillings of dissolved pores (caves) and fractures, followed by intergranular pores, in the shape of spots, balls, plates, and veins dominantly. Diasteranes content and laser Raman spectrograms indicate that the solid bitumen is in the high maturity stage. The bitumen reflectance calculated by laser Raman spectroscopy is distributed between 2.49% and 4.09%, indicating the major source of the thermal cracking of crude oil. Solid bitumen in the Deng 2 Member has different contents of 21α(H)–C29 norhopane, C35 hopane, and C34 hopane, and Ts/Tm values from the Deng 4 Member in the Gaoshiti Moxi area. It is inferred that some solid bitumen is from the source rocks of the Lower Cambrian Maidiping Formation and the Sinian Doushantuo Formation. Two stages of bitumen were developed in the Deng 2 Member, indicating possible two stages of oil filling and thermochemical sulfate reduction (TSR) in the geologic history.

Origin and Genesis of Solid Bitumen from the Sinian Dengying Reservoir in the Deyang–Anyue Rift within the Sichuan Basin (SW China): Evidence from Biomarkers and Microscopic Features

Deep-carbonate gas reservoirs are a significant field for conventional gas exploration in the Sichuan Basin, and industrial-grade gas reservoirs have recently been discovered in the second member of the Dengying Formation in the Deyang–Anyue rift. Drilling results have indicated that the large amount of solid bitumen that is commonly found in pores and fractures in the reservoir of the second member of the Dengying Formation. However, systematic studies have not yet been conducted on the solid bitumen of the second member of the Dengying Formation and its genesis and parent source remain unclear. This study is based on the systematic analysis of solid bitumen samples collected from new exploratory wells, with the aid of optical microscopy, scanning electron microscopy, and gas chromatography–mass spectrometry to clarify the genesis, thermal maturity, and parent source deposition environment of the solid bitumen. Electron microscopy and biomarker results indicate that bitumen is in a high-maturity stage and is a product of the thermal cracking of crude oil. Energy dispersive spectrometer results and the continuous distribution of n-alkanes indicate that the bitumen is not subjected to strong thermochemical sulfate reduction and biodegradation. Isoprenoids and terpenes suggest that the palaeoreserves associated with the bitumen of the second member of the Dengying Formation originate in reductive marine carbonate sediments. The combination of regional stratigraphic contact relationships, lithology, and biomarker characteristics implies that the Maidiping Formation muddy dolomite and the Dengying Formation algal dolomite are the potential parent sources of solid bitumen in the second member of the Dengying Formation.

Biomarkers and Re–Os geochronology of solid bitumen in the Beiba Dome, northern Sichuan Basin, China: Implications for solid bitumen origin and petroleum system evolution

Solid bitumen is ubiquitous in the Sinian Dengying Formation dolomite, a crucial gas reservoir in the Sichuan Basin. We use biomarkers and Re–Os geochronology, coupled with burial-thermal evolution history to trace the source and formation timing of the solid bitumen, and to reconstruct the petroleum system evolution in the Dengying Formation of the Beiba Dome, northern Sichuan Basin. The bitumen reflectance (Rb) values of solid bitumen range from 1.92 to 3.95%, with the solid bitumen showing no fluorescence, indicating that the solid bitumen in the Dengying Formation dolomite has a high thermal maturity, which consequently belongs to pyrobitumen formed by thermal cracking of crude oil. The isoprenoids and terpanes indicate that the solid bitumen was sourced from a marine shale deposited under a reducing environment. The C27–C29 regular sterane distribution of the solid bitumen is consistent with the Lower Cambrian Guojiaba Formation (Є1g) organic-rich shale, indicating that the solid bitumen was derived from the Є1g shale, rather than dolomite or shale within the Dengying Formation. The burial-thermal evolution history indicates that initial oil generation began in the Late Cambrian to the Early Silurian. Since the Early Permian, the Є1g organic-rich shale re-entered the oil generation window, and formed a giant paleo-oil accumulation during the Late Triassic. Thermal cracking of crude oil occurred from the Late Triassic to the Early Cretaceous forming the extensive solid bitumen. The Re–Os isotopes of solid bitumen yield two similar isochron ages of 128.1 ± 7.3 Ma and 126.2 ± 8.0 Ma, which represents the timing of thermal cracking termination, i.e. the final timing of dry gas generation. This work highlights that the Re–Os geochronology has great potential to constrain the absolute timing of evolution of the petroleum system.

Origin and accumulation of high-maturity oil and gas in deep parts of the Baxian Depression, Bohai Bay Basin, China

Great quantities of light oil and gas are produced from deep buried hill reservoirs at depths of 5,641 m to 6,027 m and 190 °C to 201 °C in the Niudong-1 Well, representing the deepest and hottest commercial hydrocarbons discovered in the Bohai Bay Basin in eastern China. This discovery suggests favorable exploration prospects for the deep parts of the basin. However, the discovery raises questions regarding the genesis and accumulation of hydrocarbons in deep reservoirs. Based on the geochemical features of the hydrocarbons and characteristics of the source rocks as well as thermal simulation experiments of hydrocarbon generation, we conclude that the oil and gas were generated from the highly mature Sha-4 Member (Es4) source rocks instead of thermal cracking of crude oils in earlier accumulations. The source kitchen with abnormal pressures and karsted carbonate reservoirs control the formation of high-maturity hydrocarbon accumulations in the buried hills (i.e., Niudong-1) in conjunction with several structural-lithologic traps in the Es4 reservoirs since the deposition of the upper Minghuazhen Formation. This means the oil and gas exploration potential in the deep parts of the Baxian Depression is probably high.

Geochemistry of Palaeozoic marine petroleum from the Tarim Basin, NW China: Part 3. Thermal cracking of liquid hydrocarbons and gas washing as the major mechanisms for deep gas condensate accumulations

The Lunnan Lower Uplift in the Tarim Basin, NW China contains a composite petroleum system with mainly biodegraded heavy oil in the west, normal oil in the center and gas condensate in the east. Twenty-three gas samples and 37 oil samples taken from three major hydrocarbon bearing intervals in the Lunnan lower bulge were analyzed for their stable carbon isotopes and molecular biomarkers. On the basis of their isotopic compositions, biomarkers, especially diamondoids, and integrating the physical properties of the hydrocarbons including densities, GOR and PVT relationships, it has been concluded that the recently discovered deep (6500 m) eastern Lungu giant Ordovician gas condensate pool with an estimated reserve of 723 million bbl oil equivalent is a secondary hydrocarbon accumulation derived from the mixing of an early formed oil and a late formed gas. The extremely dry gases with a gas dryness of >0.98 were derived from thermal cracking of crude oils and charged to an existing oil reservoir causing extensive gas washing and secondary alteration. Compared with most of the hydrocarbons in the Lunnan area, the gas from the eastern Lungu gas condensate pool has a heavier carbon isotopic composition, higher dryness and a higher maturity level. The unique physical, chemical and isotopic compositions of the gas condensate are believed to be a direct result of gas flushing of an early formed eastern Lungu oil pool by a late formed dry gas from oil cracking. The eastern Lungu gas condensate pool is presently characterized by containing “dry gas, heavy oil, abundant aromatics and high wax”.

Evidence for multiple stages of oil cracking and thermochemical sulfate reduction in the Puguang gas field, Sichuan Basin, China

The Puguang gas field is the largest gas field found in marine carbonates in China. Marine carbonate reservoirs in this field were buried to a depth of about 7000 m (22,966 ft) and experienced maximum temperature up to 220C before uplift to the present-day depth of 5000–5500 m (16,404–18,045 ft), with present-day thermal maturity between 2.0 and 3.0% equivalent vitrinite reflectance (Ro). Sulfur-rich pyrobitumens with reflectance up to 3.5% are widespread in the reservoirs and resulted from thermal cracking of crude oils most likely generated from Upper Permian source rocks and thermochemical sulfate reduction (TSR). Natural gases in the Puguang gas field have wide variations in nonhydrocarbon gas contents, with H2S contents between 5.1 and 58.3% and CO2 contents between 7.9 and 18.0%. The hydrocarbon gases originated mainly from thermal cracking of accumulated oil but were altered by TSR. Thermochemical sulfate reduction in the study area exerted different effects on the isotope compositions of different hydrocarbon gas components at different TSR stages. The differential increase of 13C values for different gas components reflects transformation from a heavy-hydrocarbon-gas–dominated TSR stage to a methane-dominated TSR stage. This caused a decrease of 13Cmethane13Cethane values and a corresponding conversion from reversed to normal isotope distributions. Thermochemical sulfate reduction in the study area appears to have been limited by sulfate concentrations in the reservoirs. A successive, three-stage TSR series, namely, liquid-hydrocarbon–involved TSR, heavy-hydrocarbon-gas–dominated TSR, and methane-dominated TSR, occurred in reservoirs with sufficient sulfate concentration. Methane can be the dominant organic reactant for TSR, but only at elevated temperature and after most C2+ hydrocarbons are exhausted.

A Simple Kinetic Model for Coke Combustion During an In-Situ Combustion (ISC) Process

Abstract Although coke combustion studies have long been conducted, the literature is still lacking an accurate understanding of reaction kinetics. To this end, the thermo-oxidative behaviours of Neilburg oil and its asphaltene fraction were examined in the presence of core sand. Thermo gravimetric analysis (TGA) was performed in a flowing atmosphere at the heating rate of 10 °C/min up to 750 °C. Both nitrogen and air were used at a flow rate of 45 ml/min in the experiments. As earlier researchers have observed, at least two main regions of reactions were identified by the thermo gravimetric (TG) and derivative thermo gravimetric (DTG) thermo grams. Various effects, including distillation, low-temperature oxidation (LTO), thermal cracking, middle-temperature oxidation (MTO), high-temperature oxidation (HTO) or combustion, and even mineral decomposition, were observed. In this study, Neilburg oil and asphaltenes were completely cracked in a nitrogen atmosphere at 425 ° C to produce coke. Subsequently, the fresh coke was subjected to isothermal combustion at several temperatures from 374 °C to 519 °C. A two-step oxidation reaction model was applied to describe this combustion process. The chemical reactions were simplified into two oxidations occurring in series. In the first reaction, coke was partially oxidized to form an intermediate product, which was then burned in the second reaction. Based on the TGA data, kinetic parameters were estimated with the aid of custom written software. For comparison, the one-step oxidation reaction model was also employed to predict the combustion process. The two-step oxidation reaction model gave a better fit to the experimental data. It was also confirmed that the coke derived from the Neilburg asphaltenes is reasonably representative of the coke derived from the whole oil. Introduction It has long been recognized that in situ combustion (ISC) might be a potentially effective enhanced oil recovery (EOR) technique, particularly suitable for medium and heavy crude oil-bearing reservoirs, as well as for steam depleted reservoirs. However, the fact that the fundamental reaction mechanisms of the ISC process have not been completely understood makes its field performance prediction unreliable. It is generally believed that there are three major reactions during an ISC process: thermal cracking, low temperature oxidation (LTO) and high temperature oxidation (HTO). Thermal cracking of crude oil, including visbreaking and coking, produces a solid residue on the surface of the reservoir sand grains. The solid residue, or so-called coke, is consumed as the fuel for combustion. LTO reactions, which are typically heterogeneous reactions between the gas and condensed phases, involve the formation of oxygenated hydrocarbons. During an ISC process, LTO is possible if oxygen is present ahead of the combustion front, either due to the oxygen flux being relatively high or due to bypassing of the front by some of the injected oxygen(1). HTO is the heterogeneous (gas-solid) reactions that consume the coke deposited by thermal cracking to produce carbon oxides and water. Some efforts to investigate the oxidation reaction mechanisms during ISC can be found in the literature. An early extensive study was carried out by Dart et al.(2) who tested the combustion rate for oxidation of carbonaceous residues on clay catalyst pellets.

Geochemical and carbon isotopic studies of crude oil destruction, bitumen precipitation, and sulfate reduction in the deep Smackover Formation

Crude oil generated by the Lower Smackover source facies migrated to Upper Smackover reservoirs where slow thermal cracking of crude oil resulted in the formation of gas-condensate and late solid bitumen. Ultimately, only pyrobitumen, methane, and nonhydrocarbon gases including hydrogen sulfide persist in the deepest Smackover reservoirs. The carbon isotopic compositions of crude oils became heavier during crude oil destruction. The carbon isotopic compositions of asphaltenes, NSO-compounds, and saturated hydrocarbons in late solid bitumen and the Lower Smackover source facies became isotopically lighter during crude oil destruction. It is suggested that some isotopically-light components from crude oils were incorporated in late solid bitumen by reactions involving thermochemical sulfate reduction. Thermochemical sulfate reduction and crude oil destruction occurred over a long span of geologic time at temperatures in the 120–150°C range.

New Kinetic Models for Thermal Cracking of Crude Oils in In-Situ Combustion Processes

Summary This paper presents two kinetic models for representing the thermal cracking of crude oils, which incorporate the cracking rate parameters and stoichiometric coefficients to correlate experimental data. The models presented show that the first-order kinetics generally accepted for pure components are unsatisfactory for multicomponent systems characterized by pseudocomponents. We conclude that three corrections to the existing first-order model are needed for modeling thermal cracking of mixtures. First, the apparent reaction order is always greater than one. Second, the reaction order is a decreasing function of temperature. Third, coke may also be formed from intermediate products. These corrections are incorporated into the models. In the first model, crude oil is split into two pseudocomponents, while in the second model, crude oil is represented by three pseudocomponents. The models can be easily extended to any number of pseudocomponents. The models successfully correlated experimental data of four systems available in the literature. Furthermore, it was confirmed that coke is not always the sole source of the fuel burned in an in-situ combustion process.

Geochemical Studies of Crude Oil Generation, Migration, and Destruction in Mississippi Salt Basin: ABSTRACT

ABSTRACT The main source for crude oil in the Mississippi Salt Basin is the laminated lime mudstone facies of the Lower Smackover. Crude oil generation and migration commenced at a level of thermal maturity equivalent to about 0.55% vitrinite reflectance. Short-range lateral migration of crude oil was focused to Upper Smackover and Norphlet reservoirs, but vertical migration also charged some overlying Cotton Valley, Rodessa, Lower Tuscaloosa, and Eutaw reservoirs. Following migration from the Lower Smackover, thermal maturity history of reservoir rocks controls the preservation of crude oil, gas-condensate, and methane. Slow thermal cracking of crude oil occurred in deep Upper Smackover reservoirs, resulting in formation of gas-condensate and precipitation of solid bitumen. The maximum thermal maturity for preservation of condensate is equivalent to about 1.3% vitrinite reflectance. Only methane, pyrobitumen, and nonhydrocarbon gases including hydrogen sulfide persist at higher levels of thermal maturity. Early destruction of methane in deep Upper Smackover reservoirs near the Wiggins Arch is driven by thermochemical sulfate reduction. Lesser availability of sulfate in Norphlet reservoirs in Lower Mobile Bay could account for methane preservation at higher levels of thermal maturity. One basic geochemical strategy for further exploration of the Mississippi Salt Basin is to focus exploration effort on traps with reservoirs in the thermal maturity window for hydrocarbon preservation. Another strategy is to avoid drilling traps with overmature reservoir rocks.

Thermal Cracking of Crude Oil in Circulation System of Fluidized Beds

Thermal Cracking of Crude Oil in Circulation System of Fluidized Beds

Thermal Cracking of Crude Oil in Fluidixed Bed with Annular Section

Thermal Cracking of Crude Oil in Fluidixed Bed with Annular Section

Voids in the Carbon Fiber Produced by Kureha Process

One of carbon fibers commercially available in Japan is produced by Kureha Chemicals Co. from the pitch which is a by-product of a thermal cracking of crude oil. This fiber was heat-treated at 1300°C, 1500°C, and 2000°C for an hour and voids existing in the original fiber and heat-treated ones were investigated by X-ray small angle scattering. And the following results were obtained;1) There was almost no void in the commercially available original fiber with the nominal heat-treatment temperature of 1000°C.2) With increase of heat-treatment temperature of this original fiber, increased voids or the region intensity of carbon atoms of which was so small that these parts could be regarded substantially as voids.3) Radius of gyration of the sample heat-treated at 2000°C was calculated as 13Å along equator and 11-18Å along meridian.4) Even helium gas could substantially not penetrate into these voids.