Showing papers on "Petroleum reservoir published in 2006"

Phase Behavior of Petroleum Reservoir Fluids

Abstract: Developed in conjunction with several oil companies using experimental data for real reservoir fluids, Phase Behavior of Petroleum Reservoir Fluids introduces industry standard methods for modeling the phase behavior of petroleum reservoir fluids at different stages in the process. Keeping mathematics to a minimum, this book discusses sampling, cha

Sequence stratigraphically controlled diagenesis governs reservoir quality in the carbonate Dehluran Field, southwest Iran

Abstract: The Sarvak Formation (late Albian–early Turonian) is one of the major oil and gas reservoir units in southwestern Iran and was deposited in a wide carbonate ramp marine setting. Three major transgressive–regressive sequences are interpreted in the upper part of the Sarvak Formation in the Dehluran Field. Sequence boundaries are recognized from facies shifts and diagenetic effects related to sea-level fall, whereas maximum flooding episodes are indicated by deep-water facies characterized by abundant bioturbation and high gamma-ray log responses. Diagenesis is the main controlling factor on reservoir quality and plays both a constructive and a destructive role. Permeability is decreased by cementation, which fills primary porosity and disconnects pore throats, while compaction decreases porosity by establishing tighter intergrain contacts. Conversely, the dissolution of unstable minerals (mainly aragonite) is the major process that improves porosity and then permeability by enlarging pores and pore throats. Dolomitization, when associated with dissolution, creates the best reservoir intervals in the Sarvak Formation, although this is not a widespread phenomenon. These diagenetic processes are controlled by sea-level fluctuations, and thus the sequence stratigraphic development. Dissolution, early cementation and exposure-related dolomitization took place during falling sea-levels, mainly in the uppermost, regressive parts of the major sequences. Dolomitization is recognized in the transgressive and in the regressive systems tracts. Stylolitization and fracturing are independent of sea-level fluctuations and are most likely to have formed through a combination of compaction and tectonic events.

Geological and Geochemical Signatures of Hydrothermal Activity and Their Influence on Carbonate Reservoir Beds in the Tarim Basin

Abstract: Intensive igneous activities took place in the Tarim Basin in the Permian. Hydrothermal fluids were derived from igneous activities, migrated along faults and fractures and reacted with carbonate host rocks. When carbonates are dissolved by hydrothermal fluids, some mineral assemblages, typical of hydrothermal genesis, would precipitate from the hydrothermal fluids. The mineral assemblages include (1) fluorite-quartz, (2) sphalerite-chlorite-calcite and (3) barite-quartz-pyrite-siderite assemblages. The carbonates are relatively enriched in Fe, Mn and Si, where the carbonates were partially dissolved by hydrothermal fluids. Under the influence of hydrothermal fluids, numerous dissolution pores of few millimeter were created, and consequently the porosity and permeability of carbonate reservoir beds were significantly enhanced. The enhancement in porosity and permeability is very important for carbonates to be efficient oil and gas reservoir beds, particularly for those that have not experienced subaerial karst.

Methods of using a laser to perforate composite structures of steel casing, cement and rocks

Abstract: Apparatus and methods of using lasers are provided for the perforation of oil and gas well casings and rock formations. A rock removal process called laser spallation is provided that utilizes a combination of laser-induced thermal stress and laser induced superheated steam explosions just below the surface of the laser/rock interaction to spall or fracture the rock into small fragments that can then be easily removed from the rock formation. The use of high power laser beams of kilowatt level is provided to rapidly cut the steel casings and perforate into the formation. Techniques of the invention increase permeability and reduce hole tapering while perforating a deep hole in reservoir rock formations.

Gas-assisted gravity drainage (GAGD) process for improved oil recovery

Abstract: A rapid and inexpensive process for increasing the amount of hydrocarbons (e.g., oil) produced and the rate of production from subterranean hydrocarbon-bearing reservoirs by displacing oil downwards within the oil reservoir and into an oil recovery apparatus is disclosed. The process is referred to as “gas-assisted gravity drainage” and comprises the steps of placing one or more horizontal producer wells near the bottom of a payzone (i.e., rock in which oil and gas are found in exploitable quantities) of a subterranean hydrocarbon-bearing reservoir and injecting a fluid displacer (e.g., CO 2 ) through one or more vertical wells or horizontal wells. Pre-existing vertical wells may be used to inject the fluid displacer into the reservoir. As the fluid displacer is injected into the top portion of the reservoir, it forms a gas zone, which displaces oil and water downward towards the horizontal producer well(s).

Anomalous Acid Reaction Rates in Carbonate Reservoir Rocks

Abstract: It is generally assumed that the reaction of acid with limestone reservoir rock is much more rapid than acid reaction with dolomite reservoir rock. This work is the first to show this assumption to be false in some cases, because of mineral impurities commonly found in these rocks. Trace amounts of clay impurities in limestone reservoir rocks were found to reduce the acid dissolution rate by up to a factor of 25, to make the acid reactivity of these rocks similar to that of fully dolomitized rock. A rotating disk instrument was used to measure dissolution rates of reservoir rock from a deep, dolomitic gas reservoir in Saudi Arabia (275°F, 7,500 psi). More than 60 experiments were made at temperatures of 23 and 85°C and HCl concentration of 1.0 M (3.6 wt%). Eight distinctly different rock types that varied in composition from 0 to 100% dolomite were used in this study. In addition, the mineralogy of each rock disk was examined before and after each rotating disk experiment with an environmental scanning electron microscope (ESEM) using secondary and backscattered electron imaging and energy dispersive X-ray (EDS) spectroscopy. Acid reactivity was correlated with the detailed mineralogy of the reservoir rock. It was also shown that bulk anhydrite in the rock samples was converted to anhydrite fines by the acid at 85°C, a potential source of formation damage.

Extrusive sandstones (extrudites): a new class of stratigraphic trap?

Abstract: Abstract Extrusive sandstone bodies are identified as entirely stratigraphic traps associated with sand injectites. They may be difficult to recognize but have four-way dip closure and are invariably connected through underlying lower permeability strata to parent sandbodies by sandstone dykes or transgressive sills that belong to sand injectite complexes. Extrusive sandstones (extrudites) constitute an immature exploration target, which is largely untested by deliberate exploration wells. Using seismic data alone, the distinction between extrudites and intrusive sills, and between extrudites and depositional sands, may be problematic. Sedimentological criteria may make differentiation possible when core is available. Extrudites are likely to have been drilled and misinterpreted as conventional deep-water turbidites within deep-water systems affected by sand injection.

Late Visean to Bashkirian Platform Cyclicity in the Central Tengiz Buildup, Precaspian Basin, Kazakhstan: Depositional Evolution and Reservoir Development

Abstract: The Tengiz buildup, an intensely cored and studied isolated carbonate platform in the Precaspian Basin, contains a succession of shallow-water deposits ranging from Famennian to Bashkirian in age. From a reservoir perspective, Tengiz can be subdivided into platform (central and outer) and rim-slope (flank) regions. The upper Visean, Serpukhovian, and Bashkirian form the main hydrocarbon-bearing interval in the platform. Depositional cycles (high-frequency sequences) in this interval are several to tens of meters thick for the Visean and Serpukhovian, and decimeter to meter scale for the Bashkirian. Cycles are made up of a succession of lithofacies overlying a sharp base that locally shows erosion, calcretes, meteoric diagenesis, and other evidence for subaerial exposure. At the base of the succession, tight peloidal mudstone and ash beds are associated with sequence boundaries and are thought to reflect low-energy conditions developed in deeper platform areas at lowstand and during initial flooding. Above this, beds with in-situ articulated brachiopods signal initial open-marine but still low-energy conditions. Succeeding crinoid-dominated intervals represent maximum marine flooding and overlying skeletal-peloidal grainstones highstand shoaling phases. Visean and Serpukhovian cycles are generally easy to correlate from well to well over several kilometers distance. Volcanic ash beds are identified by gamma-ray spikes, and flooding intervals show as low-porosity zones. In contrast, Bashkirian cycles are thinner and incomplete, dominated by thin, peloidal mudstone intervals alternating with high-energy coated-grain and ooid grainstone, and are more difficult to correlate. High-frequency icehouse sea level fluctuations exposed the platform during each fall of sea level, and rapid flooding resulted in incomplete cycles and complex lateral facies changes that may explain relatively poor lateral continuity of log character. The distribution of reservoir rock types in the central platform is determined by burial diagenetic modification of an earlier reservoir system that includes meteoric alteration and porosity enhancement below major sequence boundaries and reduced dissolution along higher order sequence boundaries associated with the presence of volcanic ash. The lateral continuity of tight layers at sequence boundaries probably greatly affected later fluid flow as well as the ultimate distribution of cements, dissolution, and bitumen in the central platform reservoir. The burial diagenetic overprint included two major phases of reservoir modification. First, a corrosion and cementation phase significantly enhanced existing matrix porosity in the interior central platform while reducing porosity in the exterior central and outer platform by pore-filling equant calcite cement. This was followed by bitumen emplacement and associated corrosion. These processes not only exerted an overall porosity-reducing effect prior to and associated with bitumen invasion toward the exterior central platform, but also dampened or flattened the initial cyclic porosity variations and obscured relationships between pore types and permeability. The bitumen overprint is nearly absent in the innermost platform wells; bitumen concentrations are highest near the bases of the cycles, which may imply that the first fill of hydrocarbons migrated through the flanks laterally into the platform cycles.

Relationship between deformation bands and petroleum migration in an exhumed reservoir rock, Los Angeles Basin, California, USA

Abstract: An oil-bearing sandstone unit within the Monterey Formation is exposed in the Los Angeles Basin along the Newport-Inglewood fault zone in southern California. The unit preserves structures, some original fluids, and cements that record the local history of deformation, fluid flow, and cementation. The structures include two types of deformation bands, which are cut by later bitumen veins and sandstone dikes. The bands formed by dilation and by shear. Both types strike on average parallel to the Newport-Inglewood fault zone (317°–332°) and show variable dip angles and directions. Generally the older deformation bands are shallow, and the younger bands are steep. The earlier set includes a type of deformation band not previously described in other field examples. These are thin, planar zones of oil 1–2 mm thick sandwiched between parallel, carbonate-cemented, positively weathering ribs. All other deformation bands appear to be oil-free. The undeformed sandstone matrix also contains some hydrocarbons. The oil-cored bands formed largely in opening mode, similar to dilation bands. The oil-cored bands differ from previously described dilation bands in the degree of carbonate cementation (up to 36% by volume) and in that some exhibit evidence for plane-parallel shear during formation. Given the mostly oil-free bands and oil-rich matrix, deformation bands must have formed largely before the bulk of petroleum migration and acted as semi-permeable baffles. Oil-cored bands provide field evidence for early migration of oil into a potential reservoir rock. We infer a hydrofracture mechanism, probably from petroleum leaking out of a stratigraphically lower overpressured reservoir. The deformation bands described here provide a potential field example of a mechanism inferred for petroleum migration in modern systems such as in the Gulf of Mexico.

Fluid Pressure Variation in a Sedimentary Geothermal Reservoir in the North German Basin: Case Study Groß Schönebeck

Abstract: The Rotliegend of the North German basin is the target reservoir of an interdisciplinary investigation program to develop a technology for the generation of geothermal electricity from low-enthalpy reservoirs. An in situ downhole laboratory was established in the 4.3 km deep well Gros Schonebeck with the purpose of developing appropriate stimulation methods to increase permeability of deep aquifers by enhancing or creating secondary porosity and flow paths. The goal is to learn how to enhance the inflow performance of a well from a variety of rock type in low permeable geothermal reservoirs. A change in effective stress due to fluid pressure was observed to be one of the key parameters influencing flow properties both downhole, and in laboratory experiments on reservoir rocks. Fluid pressure variation was induced using proppant-gel-frac techniques as well as waterfrac techniques in several different new experiments in the borehole. A pressure step test indicates generation and extension of multiple fractures with closure pressures between 6 and 8.4 MPa above formation pressure. In a 24-hour production test 859 m3 water was produced from depth indicating an increase of productivity in comparison with former tests. Different depth sections and transmissibility values were observed in the borehole depending on fluid pressure. In addition, laboratory experiments were performed on core samples from the sandstone reservoir under uniaxial strain conditions, i.e., no lateral strain, constant axial load. The experiments on the borehole and the laboratory scale were realized on the same rock types under comparable stress conditions with similar pore pressure variations. Nevertheless, stress dependences of permeability are not easy to compare from scale to scale. Laboratory investigations reflect permeability variations due to microstructural heterogeneities and the behavior in the borehole is dominated by the generation of connections to large-scale structural patterns.

Effect of Operational Parameters on Carbon Dioxide Storage Capacity in a Heterogeneous Oil Reservoir: A Case Study

Abstract: Underground storage of carbon dioxide (CO2) is attracting considerable interest worldwide as a means of avoiding continued release of CO2 from anthropogenic sources. Here, a heterogeneous oil reservoir in Alberta, Canada, was chosen for evaluating the potential use of this site for storage of a mixture of 90% CO2 + 10% H2S produced from a nearby gas plant. This reservoir produces 34° API light oil from a pinnacle reef, which is a carbonate reservoir with a depth of 4800 ft (1441 m). A fully compositional, three-dimensional (3-D) reservoir simulation model, CMG-GEM, was used to simulate various operational conditions, study the reservoir and fluid characteristics, and investigate the amount of CO2 stored and oil recovered. The results of this study show that a combination of two vertical injectors and one horizontal producer optimizes the incremental oil recovered and amount of CO2 stored. The procedure developed in this study, and the findings of this study, can be used as guidelines for designing and imp...

Hydrocarbon Resources of the Polish Carpathian Foredeep: Reservoirs, Traps, and Selected Hydrocarbon Fields

Abstract: The intention of this chapter is to present a short description of the reservoir rocks, recognized types of the hydrocarbons traps, and a few chosen oil and gas fields in the basement and in the Miocene cover of the Carpathian Foredeep. Most of the oil produced from the Carpathian Foredeep basin has come from Oxfordian carbonates and Cenomanian sandstones, two of the most oil-productive reservoir rocks. The Devonian, Carboniferous, and Cretaceous carbonates are the secondary basement reservoirs. However, from the commercial point of view, the overlying Miocene clastic deposits cover has the prominent status. It consists of excellent source and reservoir rocks that have produced large amounts of gas. The primary reservoirs are sandstones of different depositional elements of submarine fans, sandstones of deltaic environments (large mouth bar, distributary channels, and others), the shallow-marine clastic deposits of estuaries, and sandy barriers. Sporadically, the gas accumulations are located in the secondary porous anhydrites. The most common basement oil and gas trap is the combination structural-stratigraphic type with varying systems of sealing. Traps are related mainly to the sub-Miocene and less to the sub-Cretaceous unconformity. The pinching-out stratigraphic traps are known from the Cenomanian sandstones. The stratigraphic traps in the carbonate buildups (reefs) have still-undiscovered potential. The traps for gas accumulations in the Miocene (Badenian and Sarmatian) deposits of the Carpathian Foredeep are related, first of all, to the paleomorphology of the pre-Miocene basement formed by the erosion supported by the faulting processes. This type of trap is classified as the compactional trap. The second, very productive structural traps were recognized beneath the Carpathian sole thrust, at the front of the Carpathians. The fault-related trapping mechanism is also known from several gas fields. The pinching-out trap types caused by the horizontal and the vertical facies changes are sparse and occur most commonly in the topmost part of the Miocene succession because of the more favorable facies and less compactional deformation of the strata. During last 50 yr of exploration, more than 120 gas and oil fields were discovered in the Carpathian Foredeep. The bulk of the produced hydrocarbons (97%, mainly gas) were contained in the Miocene deposits, with a further 3% in the Miocene basement. The Miocene contains only gas fields, whereas both oil and gas were found in the basement rocks. The Miocene gas fields are typically multihorizontal and saturated by gas with a very high methane content, normally from 95 to 99%. About 90 billion m3 (3.2 tcf) of this kind of gas has already been produced. The Przemysl gas fields group is the largest in Poland with gas initially in place (GIIP) of nearly 71 billion m3 (2.5 tcf), and the cumulative field production, as of December 31, 2002, amounted to 55 billion m3 (1.9 tcf). The Grobla and Plawowice are the biggest oil fields accumulated in the Oxfordian carbonates and Cenomanian sandstones of the Carpathian Foredeep basement. A few important gas fields, like Tarnow and Lubaczow, were also founded in the Oxfordian carbonates. According to the results of the latest deep wells, the basement of the Carpathian Foredeep is still highly prospective for hydrocarbons, especially the Devonian and Carboniferous carbonates in the central part of the foredeep and the Oxfordian buildups in the more western part. The deep wells like Hermanowa proved to be a very high source potential of the lower Paleozoic rocks, which allows for the prediction of new significant oil and gas discoveries in the nearest future. The improvement of methods, particularly the direct hydrocarbon indicators method, opened a new stage of exploration for gas accumulations in the Miocene deposits. In only the last 8 yr, nearly 20 new gas fields were discovered on the basis of such interpretation results.

Digital core laboratory: rock and flow properties derived from computer generated rocks

Abstract: We use a geologically based reconstruction technique to generate virtual rocks of complex sandstone lithofacies in a North Sea oil reservoir. Effective properties of the computer generated rocks, such as fluid permeability, electrical resistivity, and elastic moduli, are compared with those determined from microtomographic images of the actual rocks. The comparison largely shows an excellent agreement. Using network modeling techniques, we compute waterflood relative permeabilities for the computer generated rocks and compare them with experimental data. The experimental core samples exhibited large differences in wettability with measured Amott indices ranging from 0.3 to 0.7. The physical origin for this variation is not known. However, our results demonstrate clearly that for a fixed pore level distribution of wettability, both the residual oil saturation and the Amott index increases with increasing initial water saturation. This is caused primarily by reduced oil film stability in mixed wet pores. The present study demonstrates the potential and feasibility of combining computer generated rocks with numerical calculations to derive important rock and flow properties for reservoir rocks.

sequestration field test in the West Pearl Queen reservoir, New Mexico

Abstract: Carbon dioxide (CO2) sequestration in geological formations is the most direct carbon management strategy for reducing anthropogenic CO2 emissions into the atmosphere and will likely be needed forcontinuationoftheglobalfossil-fuel–basedeconomy.Storageof CO2 into depleted oil reservoirs may prove to be both cost effective and environmentally safe. However, injection of CO2 into oil reservoirs is a complex issue, spanning a wide range of scientific, technological, economic, safety, and regulatory issues. Detailed studies about the long-term impact of CO2 on the host reservoir are necessary before this technology can be deployed. This article provides an overview of a U.S. Department of Energy–sponsored project that examines CO2sequestration in a depleted oil reservoir. The main objectives of the project are (1) to characterize the oil reservoir and its sequestration capacity; (2) to better understand CO2 sequestration-related processes; and (3) to predict and monitor the migration and ultimate fate of CO2 after injection into a depleted sandstone oil reservoir. The project is focused around a field test that involved the injection of approximately 2090 tons (2.09 million kg) of CO2 into a depleted sandstone reservoir at the West Pearl Queen field in southeastern New Mexico. Geophysical monitoring surveys, laboratory experiments, and numerical simulations were performed in support of the field experiment. Results show that the response of the West Pearl Queen reservoir during the field experiment was significantly different than predicted response based on the preinjection characterization data. Furthermore, results from a 19-month bench-scale experiments of CO2 interaction with the Queen sand were not able to be fully

Multi-parameter dimension-reducing oil-gas-water-layer identifying method

Abstract: A multi parameter dimension reducing oil gas water layer identifying method, which contains 1, investigating oil reservoir geologic condition, collecting the data of test oil and test production of oil reservoir, 2, determining object reservoir layer of well according to electrical logging comprehensive explanation and logging oil gas display result, 3, selecting reservoir parameter of electrical logging and logging, 4, compiling computer program by statistical mathematics-factor analysis method, combining the liquid producing data of object reservoir, making linear combination and dimension reducing to two main factors, 5, using the established oil, gas and water figure board in step 4 to judge oil, gas and water in oil reservoir and other object reservoir.

Method for optimizing area well net of enhancing lowest permeable reservoir oil extracting amount

Abstract: The invention discloses special low permeating reservoir petroleum reservoir engineering calculation and area well pattern optimization method based on the calculation. Formula is set up to know output and reserves by analyzing the parameter of the well spacing and pouring-exploiting differential pressure, and confirm the relationship between starting pressure gradient and permeability. The method can apply in low permeating container rock petroleum reservoir engineering valuation, and special low permeating container rock area well pattern optimization design.

Discrete Element Modeling of Stress and Strain Evolution Within and Outside a Depleting Reservoir

Abstract: Stress changes within and around a depleting petroleum reservoir can lead to reservoir compaction and surface subsidence, affect drilling and productivity of oil wells, and influence seismic waves used for monitoring of reservoir performance. Currently modeling efforts are split into more or less coupled geomechanical (normally linearly elastic), fluid flow, and geophysical simulations. There is evidence (from e.g. induced seismicity) that faults may be triggered or generated as a result of reservoir depletion. The numerical technique that most adequately incorporates fracture formation is the DEM (Discrete Element Method). This paper demonstrates the feasibility of the DEM (here PFC; Particle Flow Code) to handle this problem. Using an element size of 20 m, 2-D and 3-D simulations have been performed of stress and strain evolution within and around a depleting reservoir. Within limits of elasticity, the simulations largely reproduce analytical predictions; the accuracy is however limited by the element size. When the elastic limit is exceeded, faulting is predicted, particularly near the edge of the reservoir. Simulations have also been performed to study the activation of a pre-existing fault near a depleting reservoir.

Overview of a CO2 sequestration field test in the West Pearl Queen reservoir, New Mexico

Abstract: Carbon dioxide (CO2) sequestration in geological formations is the most direct carbon management strategy for reducing anthropogenic CO2 emissions into the atmosphere and will likely be needed for continuation of the global fossil-fuel–based economy. Storage of CO2 into depleted oil reservoirs may prove to be both cost effective and environmentally safe. However, injection of CO2 into oil reservoirs is a complex issue, spanning a wide range of scientific, technological, economic, safety, and regulatory issues. Detailed studies about the long-term impact of CO2 on the host reservoir are necessary before this technology can be deployed. This article provides an overview of a U.S. Department of Energy–sponsored project that examines CO2 sequestration in a depleted oil reservoir. The main objectives of the project are (1) to characterize the oil reservoir and its sequestration capacity; (2) to better understand CO2 sequestration-related processes; and (3) to predict and monitor the migration and ultimate fate of CO2 after injection into a depleted sandstone oil reservoir. The project is focused around a field test that involved the injection of approximately 2090 tons (2.09 million kg) of CO2 into a depleted sandstone reservoir at the West Pearl Queen field in southeastern New Mexico. Geophysical monitoring surveys, laboratory experiments, and numerical simulations were performed in support of the field experiment. Results show that the response of the West Pearl Queen reservoir during the field experiment was significantly different than predicted response based on the preinjection characterization data. Furthermore, results from a 19-month bench-scale experiments of CO2 interaction with the Queen sand were not able to be fully reproduced using the latest numerical modeling algorithms, suggesting that the current models are not capturing important geochemical interactions.

The Analysis of Microseisms Spectrum at Prospecting of Oil Reservoir on Republic Tatarstan

Abstract: Are represented the results of the analysis of a microseisms spectrum, which is received at prospecting of small oil reservoirs on territory of Republic Tatarstan. For this analysis it is used the method based on revealing of peak abnormal high amplitude in a range of 1-10 Hz. Are discussed two alternatives hypothesis about nature of this peak over oil reservoirs. Based on experimental data it is shown, that the hypothesis of resonant amplification of microseisms in the resonator between daylight surface and oil reservoir is more adequate. It is shown, that it is can observe oil reservoirs, the border a sedimentary cover - the crystal and of other geological structures, such as active fault, as a peak on microseism spectrum.

Contribution to Oil Exploration and Development - A Successful Inductive Multi-Frequency EM Survey On-Shore Brazil

Abstract: In this work we discuss the results of an experimental study performed using a multi-frequency electromagnetic method over a mature oil field in Reconcavo basin, Bahia-Brazil. Five 1.8 km transects, 200 m apart, were surveyed over a selected oil reservoir block. The processed EM data are represented as cross-sections and maps of apparent resistivity and induced polarization parameter, using a consistent plotting procedure. All the sections, controlled by well logging data, allow to recognize the following geological features: (i) the oil sandstone horizons and their trapping shales; (ii) the oil-water interface and some zones of water invasion; and (iii) lateral electric contrasts representing fault zones. These results suggest the real possibility of the use of the spectral EM method in the direct detection of hydrocarbons, as well as for monitoring the efficiency of the artificial fluid injection used for secondary recovery. Also, this experiment brings about a further development in the inductive measurement of IP and introduces, for the first time, the use of this property in oil reservoir exploration and characterization.

Geochemistry and Genesis of Bitumen in Paleo-oil Reservoir in the Nanpanjiang Basin,China

Abstract: Reef paleo-oil reservoirs in the Nanpanjiang Basin were mainly distributed in Permian and Devonian strata. Reservoir of paleo-oil is mainly bioherm limestone. Bitumen mainly occurs in cavities and fractures, and also in matrix pores and biological coelomata. The maturity of the bitumen is very high, and the atomic ratio of hydrogen to carbon of the bitumen is less than 0. 4. So, the bitumen is mainly composed of carbon residue, which is the reason that there is no extract in the bitumen by non-polarity or polarity extracting. Based on the geochemistry of paleo-oil reservoir, it is concluded that the bitumen in paleo-oil reservoir is mainly from Devonian source rock and secondly from Permian source rock in the Nanpanjiang Basin. The bitumen of the paleo-oil reservoirs in the Nanpanjiang Basin is pyrobitumen formed of oil cracking under high temperature and pressure in depth, much different from biodegradation bitumen and asphaltene bitumen.