Formation Of Hydrocarbon Reservoirs Research Articles

Multiple‐Element Matching Reservoir Formation and Quantitative Prediction of Favorable Areas in Superimposed Basins

Abstract:Superimposed basins in West China have experienced multi‐stage tectonic events and multicycle hydrocarbon reservoir formation, and complex hydrocarbon reservoirs have been discovered widely in basins of this kind. Most of the complex hydrocarbon reservoirs are characterized by relocation, scale re‐construction, component variation and phase state transformation, and their distributions are very difficult to predict. Research shows that regional caprock (C), high‐quality sedimentary facies (Deposits, D), paleohighs (Mountain, M) and source rock (S) are four geologic elements contributing to complex hydrocarbon reservoir formation and distribution of western superimposed basins. Longitudinal sequential combinations of the four elements control the strata of hydrocarbon reservoir formation, and planar superimpositions and combinations control the range of hydrocarbon reservoir and their simultaneous joint effects in geohistory determine the time of hydrocarbon reservoir formation. Multiple‐element matching reservoir formation presents a basic mode of reservoir formation in superimposed basins, and we recommend it is expressed as T‐CDMS. Based on the multiple‐element matching reservoir formation mode, a comprehensive reservoir formation index (Tcdms) is developed in this paper to characterize reservoir formation conditions, and a method is presented to predict reservoir formation range and probability of occurrence in superimposed basins. Through application of new theory, methods and technology, the favorable reservoir formation range and probability of occurrence in the Ordovician target zone in Tarim Basin in four different reservoir formation periods are predicted. Results show that central Tarim, Yinmaili and Lunnan are the three most favorable regions where Ordovician oil and gas fields may have formed. The coincidence of prediction results with currently discovered hydrocarbon reservoirs reaches 97%. This reflects the effectiveness and reliability of the new theory, methods and technology.

Comparison of the Surface and Underground Natural Gas Occurrences in the Tazhong Uplift of the Tarim Basin

Abstract:The oil, gas and water volumes revealed by the productivity of exploratory wells do not reflect the actual underground situations. Under the geologic conditions, a certain amount of dissolved natural gas is stored in oil or water. Based on the production test data of exploratory wells in the Tazhong uplift of the Tarim basin, this paper discusses in detail the differences in occurrence and distribution featrues between the surface and underground natural gases; presents a restoration of the surface gas occurrence to actual underground geologic conditions according to the dissolubility of natural gas under different temperature, pressure and medium conditions; and classifies the natural gas into three states, i.e. the oversaturated, saturated and undersaturated, according to its relative content underground. Through a comparative analysis of the differences in surface and underground occurrences of natural gas, it discusses the hydrocarbon reservoir formation mechanism and distribution rules, thereby providing guidances as new methods and technologies for the prediction of potential natural gas reservoir distribution in the study area.

Turbidity Currents and Their Deposits

The article surveys the current state of our understanding of turbidity currents, with an emphasis on their fluid mechanics. It highlights the significant role these currents play within the global sediment cycle, and their importance in environmental processes and in the formation of hydrocarbon reservoirs. Events and mechanisms governing the initiation of turbidity currents are reviewed, along with experimental observations and findings from field studies regarding their internal velocity and density structure. As turbidity currents propagate over the seafloor, they can trigger the evolution of a host of topographical features through the processes of deposition and erosion, such as channels, levees, and sediment waves. Potential linear instability mechanisms are discussed that may determine the spatial scales of these features. Finally, the hierarchy of available theoretical models for analyzing the dynamics of turbidity currents is outlined, ranging from dimensional analysis and integral models to both depth-averaged and depth-resolving simulation approaches.

Introduction to “Turbidite systems off France and the Lesser Antilles”

Continental margins are a key region for solving future human challenges. They represent important hydrocarbon reservoirs including both oilfields and methane hydrates. This importance has not only an economic aspect. Indeed, 40% of the people in the World live at less than 60 km from the shoreline (http://www.unep.org). As a consequence, the study of continental margins is also of societal importance. For example, geohazards such as sediment slides, which occur frequently on continental margins and may trigger catastrophic tsunamis, can be generated solely by gravity, the most common force on Earth, without any tectonic forces being involved. In addition, continental margins represent an effective hydrocarbon trap. Productivity is high and associated with high sedimentation rates, which plays an important part in the terrestrial carbon dioxide cycle. Within this framework, deep-sea turbidite systems play a fundamental part. They are the locations on the margins where sediment transport and accumulation are highest. As a consequence, these are the sites where organic matter can be rapidly buried and then preserved before decomposition. This both prevents carbon release to the atmosphere and contributes to future hydrocarbon reservoir formation. The understanding of the actual process of carbon trapping is necessary to explore ancient potential reservoirs and to understand how the Earth system can react to the increase of carbon dioxide in the near future. As sediment loading is very important in submarine sedimentary systems, overloading and oversteepening are usually sufficient to generate large-scale instabilities. The instabilities might be tsunamogenic, as for the 16 October 1979 Var event (Habib 1994). The slide and/or the motion of the induced turbidity current generated a 4-m-high tsunami along the shore of Nice, killing 11 people. In the upper part of continental margins, additional processes can substantially increase the failure hazard — hydrodynamic shelf processes (storm waves, surge, and sediment accumulation under the action of shelf currents). During sea-level lowstand, hazard is even enhanced because of the accumulation of sediment close to the steep slopes near the shelf break, the possible presence of a nonbuoyant ice cap, and the destabilisation of methane hydrates due to changes in temperature and pressure conditions. The upward force created by the methane bubbles can lead to giant failures, as it is suspected in parts of the giant Storrega slide off Norway (Bugge 1983; Mienert et al. 1998). In deep-sea turbidite systems, canyons are the most important locations to study sediment transport and slope failures because they are bordered by steep flanks generating frequent sediment slides, and because many canyons are situated along the axes of river mouths where the sediments eroded in the continental drainage basins are concentrated. As a consequence, canyons and the related deep-sea turbidite systems represent a sedimentary record of changes occurring with time at the mouths of rivers, such as flood intensity and frequency, and changes in the nature and volume of sediment loads. These are strongly related to climate changes (cf. precipitation, temperature and related vegetation cover) influencing drainage basins. In that sense, canyons and deep-sea turbidite systems represent important Geo-Mar Lett (2006) 26:305–310 DOI 10.1007/s00367-006-0041-3

Formation of hydrocarbon reservoirs in the deep Earth's crust

Formation of reservoirs in crystalline rocks is associated with the development of rifts, with the periodic axial plunge of the rift floor during the extension of the Earth's crust, and with the elevation of consolidated basement masses during a compression phase.

Linthological architectute, geological processes and energy-field environments are major factors for the formation of hydrocarbon reservoirs

Abstract The formation of hydrocarbon reservoirs is controlled by three major factors: lithological architecture, geological processes and energy-field environments. Among the three major factors, lithological architecture provides the storing medium for hydrocarbon geological processes include hydrocarbon generation, migration, accumulation, preservation; and modification: and energy-field environments refer to the various geothermal and geodynamic forces that affect the lithilogical architecture and drive the geological processes. In this study, we take Kela-2 and Sulige gas reservoirs as two examples to study relationships among the three major factors, and explain how these factors influence the scale and quality of hydrocarbon reservoirs.

Main controlling factors for hydrocarbon reservoir formation and petroleum distribution in Cratonic Area of Tarim Basin

The Cratonic Area of the Tarim Basin is located in the central part of the basin, developing primarily with Cambrian marine source rocks and secondly Middle to Upper Ordovician marine and Carboniferous-Permian transitional facies source rocks. The source rocks were matured in the changeable period and space, forming multiple hydrocarbon generating centers during the periods. The Cratonic Area experienced multiple tectonic orogenies, forming several palaeouplifts. The matching condition between effective hydrocarbon generating centers and the palaeouplifts in various periods is the main control factor for the formation and distribution of hydrocarbon reservoirs. The palaeouplifts have experienced multiple hydrocarbonfilling phases, several periods of modifications and even breakdown. The palaeouplifts and the adjacent slopes around the effective hydrocarbon generating center compose the most favorable places for hydrocarbon accumulation. The hydrocarbon phase is related with the evolution of the hydrocarbon generating center. In the Tarim Basin’s Cratonic Area, reservoirs were mostly formed during late Hercynian. The originally formed hydrocarbon reservoirs which are adjacent to source kitchens and in the good preservation condition are the most favorable prospecting targets. Hydrocarbon is richly accumulated under the regional caprock, surrounding the faulted trends, and over and below the unconformity surfaces. Reservoirs in the Carboniferous sandstone, Ordovician karstic weathered crust and carbonate rock inside the buried hill compose the main intervals for hydrocarbon accumulation. Carboniferous and Silurian sandstone pinchout reservoirs and carbonate lithologic reservoirs with rich fractures and pores are the main targets for further prospecting.

Petrophysical Characteristics, Depositional Systems and Model of Geological Evolution in the Golden Lane Carbonate Sequences

ABSTRACT The Golden Lane area located in the southern Gulf of Mexico is a famous rimmed carbonate platform with significant oil production up to date. Different geological models have been developed to account for the formation of hydrocarbon fields in this area. With accumulation of significant data over the last decades, it came to a time to re-evaluate the mechanisms that controlled the accumulation of reservoir rocks and formation of hydrocarbon fields. In this study we conducted an integrated analysis on the depositional environments, sedimentary facies, sequences variations and geological evolution of the Golden Lane carbonate system in order to provide guidelines for future exploration and field development. We have reviewed a large amount of carbonate cores from various area in the Golden Lane, and compared the core data to petrophysical logs as well as seismic profiles. Our study mainly concerns the Cretaceous interval that contains the major oil producers -- the El Abra and Tamabra Formations. Two major mechanisms have been proposed to explain the geological evolution of the study area. First, the pre-Mesozoic basement experienced a period of stress relaxation, accompanied by post-mountain-building uplift. The Golden area may have started from a shallow marine carbonate bank, and this shallow sea carbonate bank is similar to the Bahama platforms today [Matthews, 1984; Enos, 1983] which rise abruptly out of several hundred meters of water and are constructed by the accumulation of carbonate and evaporite sediments at or near sea level during the continuing subsidence of this area since Cretaceous time. Second, overall sea level was continuously rising during the entire Cretaceous. The magnitude of this sea level rising was in the order of 300 to 400 meters based on a calibration from seismic stratigraphic records (Vail, 1977; Pitman, 1978). Our model differs from previous studies (Coogan, 1972; Minero, 1991) in the major mechanisms controlling the formation and distribution of the thick carbonate sequences, and their relationship to petroleum accumulation. By the end of the Cretaceous, sea-level rise reached its peak. The upper Cretaceous basin facies carbonate covers the entire area. The Tertiary marked another episode of strong tectonic uplift, accompanied by a large-scale sea level falling. A layer of bentonite was deposited on top of the El Abra Formation, marking the end of Mesozoic marine deposit in the area. The area then underwent a period of depositional hiatus, which presumably caused a significant subaerial exposure on top of the Abra Formation. This suggests an important mechanism for the formation of hydrocarbon reservoirs in the study area. Another mechanism for the formation of oil reservoirs is through the development of natural fracture system. Such a general geological model allows us to make certain predictions and compare these predictions to the oil fields over the entire Golden Lane in consecutive studies.

Large-scale flow of geofluids at the Dead Sea Rift

Buoyancy-driven flow associated with salinity variations is proposed as the principal driving force that has caused large-scale migration of brine and hydrocarbons at the Dead Sea Rift. Numerical simulations indicate the coexistence of two basin-scale groundwater flow systems, one atop the other, with opposite flow directions. The first is a density-driven migration of brine through deep aquifers from the rift outward, which has affected hydrocarbon maturation and migration, and the formation of three small gas fields. The second is a topography-driven groundwater flow through relatively shallow aquifers from the surrounding highlands toward the rift valley, which has caused oil biodegradation, forming heavy oils and asphalts. Simulations indicate that flow-field configurations of both groundwater and hydrocarbons have changed during the structural evolution of the rift, illustrating the interrelationships between basin formation, paleohydrology and hydrocarbon reservoir formation.

Palaeohydrology of hydrocarbon maturation, migration and accumulation in the Dead Sea Rift

It is proposed that hydrocarbon maturation, migration and accumulation in the Dead Sea rift, which took place during the last 3‐6 Myr, were significantly affected by density-driven groundwater flow, from the rift westwards through deep aquifers. To test this hypothesis, a quantitative feasibility study was carried out using numerical modelling, which assesses the effects of structural evolution, groundwater flow, heat transport and salinity redistribution on hydrocarbon migration. Results indicate that a significant fraction of hydrocarbons have escaped to the land surface within the graben. Oil that has been forced westward into the rift flanks with the migrating brine is still moving. However, gas that has been forced westward has been trapped and forms the three small commercial gas fields: Zohar, Kidod and Haqanaim. A significant portion of the oil has biodegraded forming heavy oils and asphalts due to subsequent flushing by meteoric water. Simulations indicate that flow-field configurations of both groundwater and hydrocarbons have changed during the structural evolution of the rift, illustrating the interrelationships between basin formation, palaeohydrology and hydrocarbon reservoir formation.