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Intensively faulted zones and their controlling on the hydrocarbon migration and accumulation: a case study of the Wangfu depression, Songliao basin
Abstract
In order to understand the controlling of intensively faulted zones on the hydrocarbon migration and accumulation, the Wangfu depression was selected as a case study. Based on the lateral and vertical characteristics of intensively faulted zones, the intensively faulted zones were classified into four types in the Fuyang oil layer of Wangfu depression, including graben-antithetic fault terrace, graben-antithetic-consequent fault terrace, graben-horst-antithetic fault terrace and graben-horst-consequent fault terrace. Through analyzing evidences of Fuyang oil layer in intensively faulted zones, the effect of intensively faulted zones on hydrocarbon migration and accumulation were discussed. The results show that the intensively faulted zones have transverse sealing and lateral fluid conduction function in secondary migration, and influence oil-gas accumulation. While the strike of the intensively faulted zone nearly parallels the dip direction of formation, the horst and antithetic on both sides of it are favorable part to collect oil. While the strike of the intensively faulted zone nearly plumbs the dip direction of formation, the horst and antithetic on the side that is near the depression center are propitious to catch oil. The crossovers of the intensively faulted zones are avail for oil accumulation.
... The fracture dense belt consist of a series of faults, which have genetic connection and are strip-shaped [4] . There are 648 faults that are recognized, 1.06 faults being in one square kilometer. ...
Xingnan ABSTRACT: Through the analysis of the Putaohua oil layer of Xingnan area's geological information, sums up the fault form in section and the main form in the plane. Analyze the influence of different fracture dense belt for oil and gas migration and enrichment of sand body ,and controlling action on hydrocarbon accumulation. It's found that the Xingnan Putaohua oil layer have mainly developed 4 fracture dense belts,which are divided into horst-graben type belt and stepwise fracture belt. Two kinds of dense belt with A - SGR values are more than 30%, showing that both have a certain sealing property, and the stepwise fracture dense belt sealing is stronger than that of the horst-graben type fracture, but it is weak in ability of channel. The horst-graben type fracture dense belt of sand-controll ing ability is stronger than that of the stepwise fracture dense belt, and it's favorite for the formation of oil and gas reservoirs.
Combining various aspects such as tectonic character, effective source rock zone, intensively faulted zone, fault-sand-stratum matching and overpressure, the hydrocarbon enrichment laws of Fuyu Formation in Wangfu Depression was analyzed. The results show that the tectonic character of Fuyu Formation in Wangfu Depression controls the fluid potential, and also controls the migration direction and the distribution regions of hydrocarbon. The effective source rock area controls the distribution range of hydrocarbon. Intensively faulted zone has transverse sealing and lateral fluid conduction function in hydrocarbon migration. The combination of fault, sand body and stratum, which has different trends, tendencies and distributions, controls the formation of traps. The overpressure of source rock in Qingshankou Formation affects the downward migration distance of hydrocarbon. While the buried depth of source rocks in Wangfu Depression is more than 1 200 m, the residual hydrocarbon is saturated and hydrocarbon starts expelling from source rocks. The source rocks buried more than 1 200 m are effective hydrocarbon source rocks. The region from the line of Shuang 51, Shuang 35 and Shuang 50 wells to the center of depression is favorable exploration areas of fault-lithological reservoir in Fuyu Formation of Wangfu Depression.
To investigate the ancient sealing performance of fault and its sealing effectiveness, this study considers the quantitative research on the present displacement pressure controlled by two factors of normal stress and diagenesis time, using the recovery method of ancient displacement pressure, and examines the displacement pressure evolution and sealing effectiveness of fault rock of B29 fault in K1d2 mudstone caprock on Huhenoure structural zone in Beier depression of Hailaer basin. The result shows that the sealing ability of fault rock of B29 fault in K1d2 mudstone caprock was formed in the late K1y2+3 sedimentary period. This period was earlier than the first period when large quantities of hydrocarbon was expelled from K1n sourcerock, but it was not effective to seal oil and gas expelled from K1n sourcerock. At the same time, with the second period that large quantities of hydrocarbon discharged from K1n sourcerock, it was effective to seal oil and be expelled secondarily from K1n sourcerock. This application indicates that the method is practical to recover the ancient displacement pressure of fault rock.
In order to improve the oil-gas exploration efficiency of eastern Linqing depression, this paper, on the basis of theories of tectonic analysis and petroleum system, analyzed the fault characteristics and developing evolution in the use of quantitative and qualitative methods, and studied the influence of oil-gas accumulation elements and conditions on the coal-derived gas accumulation of Upper Palaeozoic. The results show that: according to the strike, the faults can be divided into two groups, namely strike NE (or NNE) and NW (or EW); there are two kinds of fault, namely normal faults and reverse faults; normal faults develop in the place from basement to cap rock, while reverse faults only develop in the stratum under the Jurassic, and have the characteristics of basement involved; active faults become the migrating pathway of oil-gas, and played an important role in controlling oil-gas migration and adjustment in the vertical direction. Because of strong tectonic movements in the history, many tectonic traps related to the faults had been formed. The time of trap formation matched well with the hydrocarbon generation stage. By the comprehensive analysis of accumulation conditions, four coal-derived gas accumulation models have been presented in eastern Lingqing depression. The faults are characterized by multi-phase development, and control the accumulation of Upper Palaeozoic coal-derived gas in eastern Linqing depression. The exploration of coal-derived gas should focus on the Cenozoic fault depression, and regard the late period accumulation as the main exploration reservoir type.
To analyse the accumulation characteristics of heavy oil in low permeability sandstone, this paper studied the reservoir characteristics and origins of crude oil of Pingdiquan formation in Huobei aera based on the analysis of reservoir petrology, reservoir physical property, reservoir pore type, carbon isotope of crude oil and saturated hydrocarbon chromatogram. This study concluded that reservoir property plays an important control role in hydrocarbon accumulation in terms of tight reservoir. Reservoir with good porosity-permeability are benefical to fluid exchange in pores, and hydrocarbon accumulation with high maturity can still be formed during the late stage after the products of source rock with low maturity was accumulated. It results in the low maturity of crude oil in poor physical property, while maturity of crude oil in good physical property is high. The results show that: the rock type in this area are mainly ultrafine dolomitic sandstone with poor pores; the porosity is mainly less than 5%; the permeability is generally less than 0.1 mD; and the pore throat radius ranges from 0.037 μm to 0.148 μm which belongs to category of nano-pore. The Pr/Ph ratio of crude oil in this area ranges from 1.34 to 1.36, and carbon isotope ranges from -30.21‰ to -30. 01‰. The saturated hydrocarbon chromatograph has odd-even predominance, and parameter of sterane maturityC29ββ/(αα+ββ) ranges from 0.24 to 0.27, which show that it belongs to the product of Permian Pingdiquan formation generated at lower evolutionary stages. The crude oil mainly accumulates near source rocks, and it is difficult for crude oil to migrate laterally because the reservoir is tight, so the mature oil of Permian Pingdiquan formation in deep depression fails to accumulate in Huobei area. The distribution area of source rock with low maturity should be taken seriously for the exploration of low permeability reservoir.
By using the results about fine structure interpretation, reservoir prediction and sublayer sedimentary microfacies, development characteristics of faults and their control to the deposition of Fuyu oil layer in Zhaoyuannan region were discussed, and then control effect of fault condensed belts in hydrocarbon accumulation was researched with the distribution of oil and water in Zhaoyuannan region. The results show that faults of Fuyu oil layer are made up of middle and long-term faults, and there are eight condensed belts in the plane by the control of basement faults. When hydrocarbons in source rocks are generated and then expelled, the NNW-trending faults were reactivated in eastern fault condensed belts, while only boundary faults were reactivated in the western. By the control of basement and long-term growth faults, there are two spatial combinations between western fault condensed belts and distributary channel: high-angle intersection or distributary channel's long-distance extension along fault condensed belts in the upside of boundary faults, while the spatial combinations between eastern fault condensed belts and distributary channel is low-angle intersection. The oil in Fuyang layers, Sanzhao Depression migrates laterally to Zhaoyuannan region along the fault condensed belts connected by sand bodies with the buoyancy force and then accumulated in fault block, and fault-lithologic traps besides fault condenses belts. Hydrocarbon migration and accumulation in fault condensed belts is controlled by fault activity and spatial combinations between fault condensed belts and distributary channel: In eastern "transporting fault-sand" system is formed by reactive faults and distributary channel, and fault block within, fault-lithologic traps besides fault condensed belts are both accumulated by oil; In western "boundary fault-sand" transporting ridge is formed in the upside of boundary faults of condensed belts, and the oiliness becomes gradually poor from fault-lithologic traps besides to fault block within fault condensed belts.
Based on the analysis of the reservoir distribution characteristics of Chepaizi and its surrounding areas, which combines the basic geologic information and test data, modern hydrocarbon migration theory and geochemical tracer techniques are adopted to investigate the oil-source, migration paths and direction of hydrocarbon in this study area. The features and model of the hydrocarbon migration system in each formation are certified. The burial depth of the strata above Carboniferous is shallower in the northwest and deeper in the southeast, and there is a hydrocarbon supply from the deep sag in the southeast. The results indicate that the light oil in the Neogene Shawan formation is sourced from coal source rock of the Jurassic Badaowan formation, which may be mixed with some oils from lacustrine source rocks. Oil that accumulated in the Cretaceous Qinshuihe formation and Jurassic Badaowan formation are sourced from the source rock of Permian Wuerhe formation. The average thickness ratio of sand layer over total strata in the Shawan, Qinshuihe and Badaowan formations are 0.50, 0.25 and 0.40, respectively. Their sand bodies can be considered to be the preferred paths for hydrocarbon migration in the lateral direction. The wells with oil shows within unconformities at the bottom of Cretaceous and Jurassic are located in the area with porosity higher than 10%, indicating that the unconformities are suitable paths for hydrocarbon migration in the lateral direction. The geochemical tracer parameters show that the hydrocarbon migration direction points to the sand bodies with higher thickness ratio and unconformities with higher porosity. The deep and large thrust faults formed in the Carboniferous-Jurassic connect the hydrocarbon generation center with the accumulation areas. The normal faults subsequently developed exhibit a satisfactory adjustment and reforming effect to the hydrocarbon reservoirs. Hydrocarbon migrates from deep to shallow and from sag to uplift and subsequently accumulates in the higher positions of structures. The hydrocarbon pathway system becomes more complex in the shallow layers than in the deep layers. ©, 2014, China University of Mining and Technology. All right reserved.
By combining seismic with geology, we processing a detailed stratigraphic classification in the Wangfu depressed areas. In this way, targeting the geologic horizons and seismic horizons in the wells according to the synthetic seismic logs. We may gain an Corresponding Relation between seismic with geology. Then compare the stratigraphic division . From the point of evolutionary history of regional structure, geological information generated by tectonic movement was recorded, for example, plane of unconformity, sedimentary cycle, lithology, lithofacies, and their responds in the seismic profile.
A group of oil and gas pools have been found in the Changchunling anticline, southeastern Songliao Basin. Predecessors thought that gas from deep formation occupied upper zone of the structure, and oil from upper source rock only filled the down-zone of the structure. Through researching the reservoir formation, the paper indicates that oil and gas from the K1 qn1 section source rock migrated downward with abnormal pressure and passed through fault to the structure. When the basin evolution was in the extruding-shrivel period, the Changchunling anticline had taken shape. Gas in deep formation passed through fault, migrated upward and accumulated in the structure. Then oil was expelled to the down-zone of the structure, the oil displayed a 'gas-washing' character. Because the gas in deep formation was abundant and several destruction of the reservoir caused original gas reservoir to be substituted by the gas in deep formation, the mixed gas was with little associated gas. It is such a process that leads to gas reservoir locating at the upper of the structure and oil ring appearing in the down of the structure.