The important breakthroughs in marine petroleum exploration recently show that the enormous exploration potential and new progress of theoretical research on oil and gas geology, including the theory on hydrocarbon generation: multiformity of type of hydrocarbon source and conversion in marine strata, indicate that manifold hydrocarbon sources coexist in mutual conversion, and in continuous or superposed hydrocarbon generation despite different phases or ages, present the mechanism of "multi-source complex and multi-stage continuity" on formation and evolution of natural gases; preliminary trace index system are proposed; experimental geology and experimental methods & analytical techniques are developing quickly; the biodegradation of modern algae and the simulating experiments of modern algae thermal evolution, catalytic hydropyrolysis from the higher evolved organic sediment, and the compositions of noble gases and their isotopic quantitative analysis are presenting a good research platform and experimental techniques for the in-depth studies on the theory of hydrocarbon generation and perfect the trace index system. Whereas, the marine petroleum exploration is still faced with many challenges, which include many unresolved questions relating to the mechanism, index, and technique for effective revealing of main hydrocarbon source, so the theory of hydrocarbon generation is up for perfection, and the composite application of multiple index and development of new index is still an important way.
Low yield gas was discovered in the subsalt Mawu 7 reservoir at Longtan 1 well in the east of Ordos basin. As revealed by the test data, the gas contains 96.871% of methane, only 2.396% of C2+ heavy hydrocarbon characteristic of dry gas of high maturity, and very low contents of non-hydrocarbon components, indicating that the gas is a normal type in a typical reservoir. The carbon isotope of methane is light type, with δ13C1 being -39.26‰, indicating that the gas is of primitive oilfield type at overmature stage in the Ordovician. The hydrocarbon specific carbon isotope of C2+ heavy hydrocarbon components is obviously heavy type, withδ13C1varying between -19.27‰ and -23.78‰, suggesting that the gas is similar to coal-generated gas of high maturity. Based on the spatial distribution of the gas reservoir, coal-generated gas in upper Paleozoic is less likely to be involved in the formation of the salt gas, as a result, secondary reactions like TSR reaction could be the dominating affecting element for formation of the salt gas. When Mawu 7 gas from Longtan 1 well is taken as an end member of oilfield type gas and the carbon isotope of methane as a major index, the major source for the Ordovician gas in the Jingbian gasfield can be identified, and a conclusion can be drawn that the major source for natural gas in the Ordovician weathering crust in Jingbian gasfield is the Upper Paleozoic coal measure.
Based on the data of the 28 continental oils in Pearl River Mouth Basin, the three-ring preference (3RP) is greater than 5RP and 6RP in LHs from fresh water lacustrine facies source rocks. The three-ring preference (3RP) is less than 5RP and 6RP in LHs from coal-measures source rocks. The transition metals and their structures of the surrounding ligands in fresh water lacustrine facies source rocks are favor to k3(velocity constant).Kerogen Ⅰand Ⅱ1 are favorable to forming the 3RP, higher content of C7-isoalkanes exist in the LHs. The transition metals and their structures of the surrounding ligands in coal-measures source rock are favor to k5 and k6,kerogenⅡ2 and III are likely to form 5RP and 6RP,LHs contain high amount of C7-cycloalkanes and toluene.
Based on the hydrocarbon yields and carbon isotopes of methane from the three end-member macerals (vitrinite, exinite, inertinite) under closed system pyrolysis, isothermal temperature conditions, a mathematic model of oil generation and efficient expulsion from coal as a hydrocarbon-sourcing rock was done when the efficient expulsion of hydrocarbons from coal is experientially assumed to be 30 mg/gTOC.According to the simulated results, the hydrogen enriched maceral is prone to the oil generation, where the relative proportion of exinite component in coal as an active oil source is at least 5.0% whereas vitrinite is at most 95.0%. If the exinite content is more than 22.9% of coal components, the oil is generated and efficiently expelled from coal whatever the contents of two other macerals (vitrinite and inertinite). Meanwhile, the carbon isotope fractionation of methane from the maceral components at thermal stages was matched according to the simulated model. These mathematically calculated observations imply that coals with the different end\|member macerals would generate natural gas with changed δ13CCH4 values, where the maximum δ13CCH4 value is 2.3‰. Thus, the δ13CCH4 value is constrained by not only thermal maturity of source rock, but also maceral components.
It is observed that the natural gas is from the saline lacustrine source rock in the Minfeng area, Dongying Sag. In order to study the origin of the natural gas, this paper conducts a series of thermal simulation, finds that carbonate sulfate and chlorate can increase the hydrocarbon gas yield. The increases of hydrocarbon are 35%, 77% and 46% , respectively, at 550℃ when the three evaporates are mixed with the source rock. By comparison with the composition and parameter of the light hydrocarbon, it is concluded that evaporates could change the generating ways of chemical compounds and promote the evolution of organic matter. Furthermore, the composition of gaseous hydrocarbons generated from the source rock with evaporates are more similar to those of natural gases found in the Minfeng area. In view of above, the conclusion of the thermal simulation has an important effect on the recognition of the saline lacustrine hydrocarbon generation and the natural gas origin in the Minfeng area.
The crude oil samples of Sha 4 Member in early maturity stage (enclosing the mixture of oil, water and sand in proportion) were heated continuously in an autoclave in Thermal simulation experiments. According to the yields of hydrocarbon cracking gas in 11 simulation temperature points, the accumulative yield of cracking gas is at 650 to 660 cubic meters per ton oil. The yield of cracking gas has two obvious peaks when RO was 1.3% to 1.5% and 2.3% to 2.7%. The amount of methane and the ratio of C2/C3 in cracking gas increase with the simulation temperature, but the ratio of C1/C2 changes little. Carbon isotopes in the cracking gas are relatively light in the mature stage, but become weight in high to over mature stage. At the same time, the differences of carbon isotope between ethane and methane as well as ethane and propane have a growing trend.
Qintong depression are divided by three structure belts, the faulted belt, the deep sag belt and the slope belt, controlling the banded distribution of oil fields. Beihanzhuang oil field is in the exterior slope belt. According to the analysis of biomarker parameters and concentration in extracts of source rock and oil, combined with the routine geological and geochemical methods, the process of migration and accumulation of Beihanzhuang oil field is studied systematically. The results indicate that two types oil could be identified. The first type is Es1 and Ef3 member oil, which is derived from Ef2 member source rock of deep sag. The second type is Ef1 member oil which is derived from Ef1 member source rock of deep sag. Integrated with the analysis of pyrrolic nitrogen compounds and its parameters, Beihanzhuang Ef3,/Ef1 and Es1 member oil migrated from deep sag to Beihanzhuang structure belt apparently. Also, in accordance with of the generation and discharging history of hydrocarbon, the faulted sealing capacity and the formation stage of accumulation, Ef2 member source rock generated and expulsed hydrocarbon during the Dainan formation period and reached the generated hydrocarbon peak during the Eogene period, which is matched with the Ef3 member the formation stage of accumulation. After Sanduo movement, the vertical sealing capacity of Beihanzhuang faults was competent so that the Ef3, Ef1, Es1 member oil was generated from Ef2 and Ef1 source rock and migrated by Ef3 and Ef1 member sand body from deep sag to slope belt forming the lithologic structrual oil reservoirs dominantly.
By means of detailed study about the lithology, pore type, physical property and diagenesis of Paleogene Low Ganchaigou Formation reservoir in the north edge of Qaidam Basin, this paper confirms that Low-Ganchaigou Formation reservoir sandstones consist of arkose, lithic arkose and arkose rock fragment sandstone, and the cement is carbonates. The reservoir sandstones have low compositional maturity and medium textural maturity. The development extent of pore and the accumulation property have apparent deviation in different tectonic belts. Both the development extent of pore and the accumulation property in Mahai-Nanbaxiang area are best, and produced mainly primary intergranular pores. The reservoir has high porosity and middle permeability. The development extent of pore is very good to good and the accumulation property is good in Lenghu tectonic belt, and produced mainly primary intergranular pores. The reservoir has mid-low porosity and mid\|ow permeability. Reservoir porosity and accumulation property are relatively very poor in Eboliang tectonic belt, and merely has a few relict intergranular pores and secondary solution pores, and the reservoir has extremely low porosity and extremely low permeability. The rock component of sandstone reservoir and diagenesis are the main factors which control the reservoir property of Paleogene in the north edge of Qaidam Basin. The diagenesis mainly contains compaction and cementation. Carbonate cementation and clay encrustation have constructive and devastating effects to reservoir property.
Turpan-Hami (Tuha) basin is a typical Jurrassic coal measure basin located in northwest of China, Middle or large scale gas fields are not only undiscoveried in recent years, but also the quanlities and the reserves of discoveried gas fields are much less than those of oil fields, which is different from other coal measure basins that are usually prone to generate and accumulate natural gas. This paper analyzed natural gas petroleum geological conditions and natural gas accumulation controlled factors of known gas fields. The results indicate that the low maturity of the coal measures source and low gas generation rates are the major reasons for poor gas discoveries; Maturity of the coal measures source and preservation of oil gas pools are the key control factors for the formation and accumulation of middle or large scale gas fields; The areas surrounding Shenbei, Qiudong and Xiaocaohu are the potential domains for further natural gas exploration.
Weathering crust reservoir of C2k volcanic rock was the significant target of oil and gas exploration in recent years in the Santanghu Basin of Tuha Oilfield. According to its petrology and the natural characteristics revealed by drilling and logging data, this crust of weathering can be divided in vertical into weathered clay layer (sedimentary cover), highly weathered detritus, (the upper belt of weathering crust), weakly weathered block layer (the bottom belt of weathering crust) and nonweathering rock (dense volcanic belt). Effective reservoir space is developed in highly weathered detritus and weakly weathered block layer. According to the pore origin of the volcanic rock reservoir and the relations of the hydrocarbon source rock and the volcanic rock, the pattern of the volcanic rock crust of weathering is that the group hydrocarbon source rock for the volcanic rock is in C2h, the upper of which is nonhydrocarbon source rock, reservoirs are dissolved pores and fissures, and the upper part of the rocks is caprock, which constitute a good source reservoir cap association. The recognition of the volcanic rock crust of weathering is significant for seeking volcanic rock crust of weathering reservoir in the Santanghu Basin.
Panlongdong organic reefs is the most typical Permian reefs of Changxing Formation in northeastern Sichuan, and its paleo-reservoir is the typical representation of this kind of reservoirs. By analyzing the lithofacies features, reservoir space, sulfur-containing asphalts characteristics and diagenesis, this paper indicates that the reef paleo-reservoir has good reservoir space and is filled with massive higher evolution-degree asphalt, mainly carbonaceous and asphaltene asphalts. The thermochemical sulfate reduction (TSR) occurred in this reservoir, and the asphalt with high sulfur was the result of TSR reaction and provided acidic material such as H2S for dissolution at late. The replacement process of dolomitization was an equal volume replacement. Dolomitization made the dispersed small pores of Panlongdong reefs reservoir become bigger and connect, enhanced the petrosal transmission capacity and established the material base for large-scale dissolution at later time. The two stages of the dissolution had different action effects for reef reservoirs. The dissolution of parasyngenetic stage was prone to become the selective denudation pore. The advanced dissolution mainly dissolved and reformed the dolomitic reservoirs, and the dolomites whose crystal form was developed half baked would be corrosed at first.
The quantitative research on the lithofacies palaeogeography of T1j15 of Jialingjiang Formation in Chishui area is based on the firsthand quantitative information of the major measured section, and uses the method of single factor analysis and multifactor comprehensive mapping. In combination with the study of sedimentary facies, this paper discusses the development and distribution of favorable reservoirs. Two kinds of facies belts for favorable reservoirs are developed in the layer of T1j15 and the major microfacies is the dolomitic flat of restricted platform and the secondary is the platform shoal of open platform.
TZ12 structure, an inherited paleo uplift during geologic epoch, is located in the central part of TZ10 structure. The show of oil and gas including fluorescence, oil slick, oil trace, asphalt and crude oil is quite active in many Silurian and Ordovician intervals. In addition, the industrial oil has been got in Silurian. The analysis reveals that the show of oil and gas, oil trace and fluorescence in Carboniferous may come from the underneath strata through fault leakage. The multiple oil/gas reservoiring process for Silurian and Upper Ordovician of TZ12 structure is discussed by analyzing fault seal, pyrrole nitrogen compound, source rock correlation as well as other scholars′ research on inclusion composition and homogenization temperature, which will help better understand the oil and gas distribution of Tazhong area. Moreover, the hydrocarbon pooling conditions of Lower Ordovician indicates that it′s quite likely to get industrial gas flow.
Dina gas field is a large gas reservoir with the proved reserves in 2006 of more than one hundred billion cubic meters in Kuche depression, and its gas bearing layers are Suweiyi Formation and Kumugeliemu Group of Palaeogene age. It is believed that Dina 2 gas field is a long E-W-trending axis anticline controlled by the north and south thrust faults. The reservoir rocks are mainly silt stone and fine sand stone, and the types of pore are mainly primary intergranular pores, to a lesser extent, primary solution pores, microfissures and micropores. In general, the reservoir is of low porosity and low permeability or extra low permeability with strong heterogeneity. The reservoir is mainly controlled by sedimentary facies, and its diagenetic stage is in the period of middle diagenesis subage A. Compaction, cementation and solution are the main influence factors of reservoir property. With intense solution, secondary pores are developed, and the reservoir gets better.
Aiming at the present situation that Sulige gas-field, Ordos basin, has the characteristics of "low permeability, low pressure, low product" and needs urgent development, this paper, from geological, seismic and modeling angles, evaluates the advantaged development blocks of the He-8 reservoir, the main reservoir in Sulige gas-field. On the basis of the final research result, this paper selects six development blocks as targets. These blocks provide basis for the project of one billion of oil and the planning of three billion of oil, and for the development of the gasfield economically and efficiently.
Kendong area is located close to the west branch fault of Tan-Lu fault zone and strike-slip motion behaves intensely there. The south segment of Kendong fault with its NE extension part and the shallow strike-slip zone between the Kendong buried hill and the east slope are the two important strike-slip zones in the study area. Based on the carefully interpreted seismic sections and time slices across the strike-slip zones, the strike-slip structural feature is further discussed. According to the different geometrical shapes in the horizontal and vertical sections, the strike-slip structure in the study area is divided into two styles: matured strike-slip zone and buried strike-slip zone. Based on the research result of the strike-slip feature in the study area, in combination with the oil and gas distribution and accumulation characteristics, this paper discussed the influence of the strike-slip motion on the reservoir resource, hydrocarbon migration, accumulation and protection at different epochs.
Nanpu sag in Bohaiwan basin is a Tertiary halfgraben-type fault sag, and is also one of the subtectonic units of Huanghua depression. The Paleozoic hydrocarbon pool was studied. The source rock in the peripheral areas of Nanpu sag isn't the carbonates but the Lower Tertiary strata. Fault and unconformity are the main long-distance migration pathways, and oil accumulates at the high position of structure, which forms the reservoir of young source and old reservoir type. It is characterized by the lower matrix porosity for carbonates, and the primary pore hasn't the reservoir capacity. The late-|formed unfilled tectonic fracture is the dominant reservoir space for oil migration and accumulation. The paleokarst zone can'tbe explicitly divided in vertical, and corroded cavity is isolated, with worse connectivity. In this zone, the reservoir types mainly consist of unconformity reservoir and structural reservoir.
The Shahejie Formation of the 5th structure in Napu sag is buried deeply. Its stratigraphic skeleton is composed of volcanic and sedimentary rocks. It is hard to recognize the distribution of volcanic lithology owing to its complexity and the lack of core data, thin slice data and elements logging data. This paper firstly uses core data, thin slice and reliable logging data for the research of volcanic lithologic types, used cross plots to separate sedimentary rocks from volcanic rocks, then used the MN cross plot to separate the same type of volcanic lithologic rocks apart which are with different architecture and structure. The results of core data, slices, cross plots and MN cross plots were used as training samples, and equations of 10 parameters, 9 parameters, 8 parameters and 6 parameters were established. The coincidence rate attains over 80%, which shows that the dentification method is feasible in the study area.
As an important hydrocarbon reservoir, reefs and carbonates have great potential in oil exploration. The South China Sea is the biggest marginal sea in the West Pacific and its evolutionary process supply proper growing environment to the reef and carbonate. The south deepwater sag of Qiongdongnan Basin away from the provenance developed many structural highs on which reef and carbonate platforms were greatly developed. With the seismic profile and the comparison between the eustatic sea level change and sequence, the authors find that there developed different scales of reef and carbonate platforms in the sag. These reef and carbonate platforms have many developing stages which can be correlated with the eustatic sea level change and evolutionary stages, besides, they all have preferable hydrocarbon potential.
Baiyun Sag is the largest sedimentary basin depression in the Pearl River Mouth Basin northern South China Sea, located at the center of subsidence and deposition of Tertiary in the basin, and the maximum thickness of sediment is more than 12 km in Cenozoic era, in which there are a huge reservoir sediment filling system and basic geological conditions for the migration and accumulation of oil and gas. Based on the component of natural gas and light hydrocarbon, as well as the characteristics of carbon isotope and hydrogen isotopes, acquired from adjacent exploration wells and LW3-1-1 well in deep water region, this article analyzed the origin of nature gas and the type of gas composition in this area, and also analyzed and discussed its resources potential and exploration prospects in combination with its oil and gas reservoir geological conditions.
The complexity of carbonate reservoirs formation and the difference of seismic data cause obvious characteristics difference of seismic response in the northern slope zone of Tazhong area. The well seismic calibration is used to predict the carbonate reservoir response characteristics on the basis of analyzing the main control factors of reservoirs. The distribution rules of different grade karst reservoirs are identified using the spectral decomposition, instantaneous frequency, correlation length, well-seismic calibration inversion technology and the geology-seismic comprehensive technology, and the accuracy of reservoir prediction is improved. It is successfully applied in the study area.
Ordovician carbonate rock is the main reservoir in the Tazhong area of Tarim basin. Geophysical characteristics of Ordovician carbonate rock were studied using drilling data. Impedance is affected mostly by material properties and reservoirs types, to a negligibly extent by lithology and flow. Compact layers and minor fracture reservoirs of Ordovician carbonate rock have characteristics of high density, high velocity and high impedance, and the prediction of minor fractures reservoir is difficult by the general seismic ways. Big fractures and fractured vuggy and vuggy and cavity reservoirs of Ordovician carbonate rock have characteristics of minor density and low velocity and low impedance in central Tarim basin, which obviously different from the surrounding rock and produce obvious characteristics in seismic data, so reservoirs can be predicted by applying general seismic data. The conclusion provides guidance for predicting carbonate reservoirs and reducing exploration risk.
Fault Sealing is very important for both hydrocarbon accumulation and injection production well arrangement. The diagnostic method of fault sealing for the complex block flauted oil field in Dagang is presented in this paper. Two methods are used in this example. First, In order to calculate the pressure on either side of the fault, its interval velocity is extracted based on the model inversion from seismic data, and the fault sealing is determined according to the pressure continuance in that formation. Second, numerical simulation is applied to analyze the fault sealing. On the controlled conditions (Fault Sealing), WWCT is simulated, and then to fit with WWCTH in the producction well. The degree of fitting is used to determine fault sealing.
Fractal theory is applied in the provenance analysis, namely, the fractal dimension of natural gamma logging curve is used in the provenance analysis. The method gets the same conclusions as the heavy minerals analysis in the application in Lower Ganchaigou Formation of the Qigequan-Shibei area, Qaidam basin. It can be used as a new method of provenance analysis.
Coal-bed Methane is a special type of unconventional natural gas resources. Its basic theories and methodology, such as selecting of the blocks, benefit evaluation, development and etc., are still at a relatively immature stage compared with the conventional natural gas. In this paper, aimed at selecting of the coal-bed methane blocks, we come up with three key technical indicators. Also, considering the actual situation of domestic and abroad coal-bed methane exploration and development, we conclude 10 specific indicators so as to provide effective help for coal-bed methane project blocks. Due to the complexity of coal-bed methane project evaluation, some factors which impact the benefits of coal-bed methane projects are analyzed systematically, for offering some approaches to economic analysis and evaluation of coal-bed methane projects. Coal-bed methane project evaluation is based on the economic recoverable reserves. In the paper, two ways to assess economic coal-bed methane reserves is presented, that is, the cash flow method and the economic limit method.
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