Petroleum Migration Pathways Research Articles

Migration and occurrence of high wax oils in the Damintun Depression, Northeast, China: Implication for primary controls of petroleum migration pathways in heterogeneous carrier beds

This paper discusses migration styles and primary controls of petroleum migration pathways in heterogeneous carrier beds in the Damintun Depression, Bohai Bay Basin. There are two types of crude oils in the Damintun Depression: a high wax oil (wax hydrocarbon content between 8 and 60%) and a normal oil (wax hydrocarbon content lower than 8%). The high wax oil and normal oil are distinctly different both in biomarker compositions and in distribution patterns of carbon isotopic ratios for individual alkanes, and were confirmed to have been generated from different source rocks. Modeling of secondary migration pathways of both the high wax oil and the normal oil was conducted using a simple three-dimensional model, which assumes that the positions of petroleum migration pathways are controlled by the morphology of the sealing surfaces without taking into consideration the influence of permeability heterogeneity (the morphology-controlled migration model). The modeling results have reasonably well predicted the occurrences of both the high wax oil and the normal oil. All commercial petroleum accumulations are along the predicted preferential petroleum migration pathways (PPMP) formed by focusing of numerous “small petroleum streams” close to the kitchens. The focusing of oils originating from a large area of the generative kitchens is essential for the formation of large oilfields. The strong porosity and permeability heterogeneities of the carrier beds, and the relatively high prediction accuracy of the modeling, suggest that the preferential petroleum migration pathways, although influenced by permeability contrast at local scales, can be effectively predicted at a basin or depression scale under certain circumstances using a model that does not take into consideration the effect of heterogeneity. Most dry holes are not on the predicted petroleum migration pathways, suggesting that the three-dimensional migration pathway modeling may provide a useful tool to reduce exploration risk.

Accumulation Mechanisms and Evolution History of the Giant Puguang Gas Field, Sichuan Basin, China

Abstract:Solid bitumens were found throughout the carbonate reservoirs in the Puguang gas field, the largest gas field so far found in marine carbonates in China, confirming that the Puguang gas field evolved from a paleo‐oil reservoir. The fluid conduit system at the time of intensive oil accumulation in the field was reconstructed, and petroleum migration pathways were modeled using a 3‐D model and traced by geochemical parameters. The forward modeling and inversion tracing coincided with each other and both indicated that oils accumulated in the Puguang‐Dongyuezhai structure originated from a generative kitchen to the northwest of the Puguang gas field. The deposition of organic‐rich Upper Permian source rocks dominated by sapropelic organic matter in the Northeast Sichuan Basin, the development of fluid conduit system that was vertically near‐source rock and laterally near‐generative kitchen, and the focusing of oils originated from a large area of the generative kitchen, were the three requirements for the formation of the giant paleo‐oil reservoir from which the giant Puguang gas field evolved. The Puguang gas field had experienced a three‐stage evolution. The post‐accumulation processes, especially the organic‐inorganic interaction in the hydrocarbon‐water‐rock system, had not only profoundly altered the composition and characteristics of the petroleum fluids, but also obviously changed the physicochemical conditions in the reservoir and resulted in complicated precipitation and solution of carbonate minerals.

Petroleum migration and accumulation in the Bozhong sub-basin, Bohai Bay basin, China: Significance of preferential petroleum migration pathways (PPMP) for the formation of large oilfields in lacustrine fault basins

This paper discusses migration styles and primary controls of petroleum migration pathways in heterogeneous carrier beds in Bozhong sub-basin, Bohai Bay basin. Modeling of secondary petroleum migration pathways has been conducted using a simple three-dimensional model, which assumes that the positions of petroleum migration pathways are controlled by the morphology of the sealing surfaces. The modeling results have accurately predicted the petroleum occurrences, and have been supported by petroleum geochemical studies. Most commercial petroleum accumulations are on the predicted preferential petroleum migration pathways (PPMP) formed by focusing of numerous “small petroleum streams” close to the kitchens, and most large fields (petroleum reserves greater than 1×10 8 ton) have more than one preferential petroleum migration pathway to convey petroleum to the traps. The focusing of petroleum originated from a large area of the generative kitchens into restricted channels is essential for the formation of large oilfields. The strong porosity and permeability heterogeneities of the carrier beds, and the relatively high prediction accuracy by a model that does not take into consideration of the effect of heterogeneity, suggest that the positions of petroleum migration pathways in heterogeneous carrier beds in the lacustrine fault basins are determined primarily by the morphology of the sealing surfaces at regional scales.

Pleistocene recharge and flow reversal in the Williston basin, central North America

Low δ18O values of formation waters, collapse structures related to salt dissolution, hydrodynamic blowout structures, and biodegradation of oils, all suggest a significant influx of fresh water into the Williston Basin along the outcrop belt in southern and central Manitoba during Pleistocene glaciation. The thickness of the continental ice sheet over Manitoba would have provided sufficient hydrologic head to reverse the regional-scale flow system of the Williston Basin. The dynamic nature of the flow system suggests that modern day pressure distributions may not be good proxies for ancient petroleum migration pathways as is commonly assumed.

Reversal of the regional-scale flow system of the Williston basin in response to Pleistocene glaciation

Low δ18O values of formation waters, collapse structures related to salt dissolution, hydrodynamic blowout structures, and biodegradation of oils all suggest a significant influx of fresh water into the Williston basin along the outcrop belt in southern and central Manitoba during Pleistocene glaciation. The thickness of the continental ice sheet over Manitoba would have provided sufficient potentiometric drive to reverse the regional-scale flow system of the Williston basin. The dynamic nature of the flow system suggests that modern-day pressure distributions may not be good proxies for ancient petroleum migration pathways as is commonly assumed.

Petroleum Migration Pathways and Charge Concentration: A Three-Dimensional Model: Discussion

Petroleum Migration Pathways and Charge Concentration: A Three-Dimensional Model: Discussion

Geochemical constraints on models for secondary petroleum migration along the Upper Devonian Rimbey-Meadowbrook reef trend in central Alberta, Canada

The Upper Devonian Rimbey-Meadowbrook reef trend of central Alberta, Canada, is one of the classical examples that was originally used to support Gussow's model of differential hydrocarbon entrapment. However, the clear discrepancies existing between the ideal hydrocarbon distribution predicted by this model and the one actually observed led to several alternative geological models, most of which have not been constrained by organic geochemical data. The present study uses a wide range of bulk and molecular parameters to determine the oil source characteristics and thermal maturity along the reef trend. The concentrations and isomeric distributions of alkylcarbazoles and non-alkylated benzocarbazoles in oils are employed to study petroleum migration pathways and to constrain the existing secondary petroleum migration models. The data indicates that Gussow's principle is generally applicable, as the oils in the up-dip direction generally have longer implied migration distances although this is not always the case. Other factors not recognized previously, such as the presence of two subfamilies of the Duvernay Formation sourced oils, may also have contributed significantly to the discrepancies in the oil and gas distributions between the model predictions and the actual observational data.

The Effect of Allochthonous Salt on the Petroleum Systems of Northern Green Canyon and Ewing Bank (Offshore Louisiana), Northern Gulf of Mexico

The northern Green Canyon/Ewing Bank region, northern Gulf of Mexico basin, contains the Oxfordian-Neogene (.), Tithonian-Neogene (.), Albian-Neogene (.), Turonian-Neogene (.), and Eocene-Neogene (.) petroleum systems. The systems encompass 42 fields or discoveries in the study area and include four subsalt discoveries. Essential elements of the systems include source shales of Oxfordian, Tithonian, Albian, Turonian, and Eocene age; Neogene siliciclastic turbidite reservoirs; allochthonous salt; and overburden strata ranging in age from Jurassic to Quaternary. The petroleum systems of the area are significantly affected by the evolution of allochthonous salt. The high thermal conductivity of salt retards the thermal maturation of subsalt petroleum source rocks and causes late generation and migration from them. Most traps were formed during the Pliocene-Pleistocene, and the generation-migration-accumulation of petroleum ranges from early Miocene to the Holocene. The critical moment of peak oil generation for each source varies spatially and temporally as a function of the overlying sediments and allochthonous salt evolution. The impermeability of salt prevents vertical petroleum migration and causes migration pathways to be deflected laterally up the dip of base salt. Where salt welds form, petroleum migration is unimpeded and continues vertically. By integrating predictions of potential source rocks, structural restorations, thermal maturation modeling, regional salt maps, and petroleum systems logic, we can determine petroleum migration pathways and zones of concentration. All 42 fields or discoveries within the study area are associated with predicted zones of paleosubsalt petroleum concentration. Present-day salt geometries do not delineate many of these zones because of salt weld formation during the Pleistocene. This generation, migration, and accumulation technique enables geoscientists to focus their exploration efforts toward areas with a greater probability of success.

97/01739 Recovery of highly viscous products from open or closed storage areas such as tanks and sumps

The mudstones in the third member of the Shahejie Formation (Es3) are the primary source rocks in the Banqiao Depression of Bohai Bay Basin. They are rich in organic matter with Total Organic Carbon (TOC) content up to 3.5%. The sandstones in the Es3 member are the deepest proven hydrocarbon reservoir rocks with measured porosity and permeability values ranging from 3.6% to 32.4% and from 0.01 md to 3283.7 md, respectively. One, two and three-dimensional basin modelling studies were performed to analyse the petroleum generation and migration history of the Es3 member in the Banqiao Depression based on the reconstruction of the burial, thermal and maturity history in order to evaluate the remaining potential of this petroleum province. The modelling results are calibrated with measured vitrinite reflectance (Ro), borehole temperatures and some drilling results of 63 wells in the study area. Calibration of the model with thermal maturity and borehole temperature data indicates that the present-day heat flow in the Banqiao Depression varies from 59.8 mW/m2 to 61.7 mW/m2 and the paleo-heat flow increased from 65 Ma to 50.4 Ma, reached a peak heat-flow values of approximately 75 mW/m2 at 50.4 Ma and then decreased exponentially from 50.4 Ma to present-day. The source rocks of the Es3 member are presently in a stage of oil and condensate generation with maturity from 0.5% to 1.8% Ro and had maturity from 0.5% to 1.25% Ro at the end of the Dongying Formation (Ed) deposition (26 Ma). Oil generation (0.5% Ro) in the Es3 member began from about 37 Ma to 34 Ma and the peak hydrocarbon generation (1.0% Ro) occurred approximately from 30 Ma to 15 Ma. The modelled hydrocarbon expulsion evolution suggested that the timing of hydrocarbon expulsion from the Es3 member source rocks began from 31 Ma to 10 Ma with the peak hydrocarbon expulsion shortly after 26 Ma. Secondary petroleum migration pathways in the Es3 member of the Banqiao Depression are modelled based on the structure surfaces at 26 Ma and present-day, respectively. The migration history modelling results have accurately predicted the petroleum occurrences within the Es3 member of the Banqiao Depression based on the calibration with drilling results of 10 oil-producing wells, one well with oil shows and 52 dry holes. Six favorable zones of oil accumulations in the Es3 member of the Banqiao Depression are identified especially oil accumulation zones I and II due to their proximity to the generative kitchens, short oil migration distances and the presence of a powerful drive force.

Petroleum Migration Pathways and Charge Concentration: A Three-Dimensional Model

Petroleum migration pathways through a basin are determined by the three-dimensional distribution of discontinuous sealing surfaces, which are usually parallel to bedding. The petroleum migrates below the sealing surface, taking the structurally most advantageous route. The three-dimensional distribution of migration pathways within the petroleum system can be modeled on a personal computer using a program based on the parameters discussed in this paper. Application of the model to the Paris and Williston basins demonstrates that a good correlation between predicted pathways and discovered accumulations can be made using simple models. Pathways form a dense network overlying generating areas in the central parts of basins. Toward the basin margins these routes commonly become increasingly focused into discrete pathways by the sealing-surface morphologies. Eventually, these pathways may reach the surface as seepages. It is important to integrate surface outcrops of migration routes (surface seepages) into migration modeling. Deflection of the pathways from the structurally most advantageous route below the sealing surface may be caused by lateral sealing barriers due to facies variation in the carrier rock below the seal, fault juxtaposition, or cross-formational seals such as salt intrusions. Deflection of pathways also occurs where there are hydrodynamic conditions in response to topography-driven groundwater flow. Zones of vertical migration are associated with facies changes along the horizon of the sealing surface into a nonsealing facies, or juxtaposition to nonsealing strata by faults. Vertical migration from either normally or abnormally pressured strata is most likely to occur into normally or lesser pressured strata at intrabasinal highs where hydrocarbons can be stored and transferred at times of temporary seal rupture. Reverse modeling of individual pathways from fields and seepages to potential sources is a powerful exploration tool. It assists in predicting the boundaries of the leaking accumulations or areas of petroleum expulsion.

SEISMIC DELINEATION OF STRUCTURE-CONTROLLED CARBONATE CEMENT AND POTENTIAL ECONOMIC IMPLICATIONS, ANGEL FIELD, NORTH WEST SHELF

Major carbonate-cemented zones occur in Late Jurassic Angel Formation sandstones of marine mass flow origin that contain large hydrocarbon reserves in the Angel Field, Dampier Sub-basin. Preliminary results suggest that poikilotopic dolomite cement is dominant. The carbonate-cemented zones are identifiable from wireline log response and 3D seismic data, and occur in discrete intervals with a cumulative thickness of approximately 165m at Angel-2. These intervals produce a zone of high amplitude reflections of about 100 ms two-way time. Field-wide seismic mapping indicates that these carbonate-cemented zones sharply abut the northern margin of a major east-west trending strike-slip fault system that traverses this field. The carbonate-cemented zones extend in a wedge-like shape towards the northeast and concentrate along the crest of the main structural trend.The results underscore the importance of 3D seismic data for a better estimation of reservoir risk and reserves in variably carbonate-cemented sandstones.The carbonate-cemented zones may represent a 'plume' related to migration of petroleum and/or carbon dioxide. Therefore delineation of major carbonate-cemented zones using seismic data may aid in the identification of petroleum migration pathways and pools in the North West Shelf. Alternatively, carbonate cements dissolved south of the major fault zone and possibly in downdip locations in which case dissolution pores may exist in these areas. Further research is required to evaluate these hypotheses.

CALCITE-CEMENTED ZONES IN THE EROMANGA BASIN: CLUES TO PETROLEUM MIGRATION AND ENTRAPMENT?

The occurrence of calcite cementation zones in oil- bearing sequences of the Jurassic-Cretaceous Eromanga Basin is of importance to petroleum exploration. The erratic distribution and thickness of these calcite-cemented intervals is problematic for both prediction of subsurface reservoir quality and structural interpretation of seismic data due to velocity anomalies.Carbon isotope signatures suggest the carbonate cements may form by dissipation of carbon dioxide upward from the Cooper Basin into the calcium-bearing J-aquifers of the Great Artesian Basin of which the Eromanga Basin forms a part. The model is feasible if the pH of the Eromanga Basin aquifer waters is buffered externally, by generation of organic acid anions during kerogen maturation or aluminosilicate reactions.Hydrocarbons are likely to have migrated up-dip along the same conduits as the carbon dioxide. Consequently, delineation of massive calcite-cemented zones in the Eromanga Basin reservoirs using well log and seismic data may aid in the identification of petroleum migration pathways, and sites of hydrocarbon entrapment.