Pub Date : 2015-03-01DOI: 10.2113/GSCPGBULL.63.1.66
Ningxi Li, Zi-hui Feng, Haiping Huang, Xue Wang, Z. Dong
Abstract Organically rich immature source rocks occur commonly at shallow burial depths in Songliao Basin, NE China. This has led to the general assumption that there must be a large biogenic gas resource in these organic rich, shallow strata. However, except for a few small gas fields that are generally associated with biodegraded oil, only a small amount of biogenic gas has been discovered. In order to determine the geological factors controlling biogenic gas generation and accumulation, a suite of potential source rock shale samples from burial depth less than 1600 m was analyzed for organic composition, grain size distribution and permeability. The results show that selected samples are organic rich and thermally immature. The grain size analysis shows a mixed distribution of silt and clay with D10 generally below 1.6 μm. The measured permeability values are generally below 1 μd under in situ stress conditions with pore throats that are most likely smaller than that of methanogenic bacteria. Very low permeability and very small pores resulting from compaction and diagenesis restrict bacteria movement and activity, limit nutrient transport, diminish space availability, and lead to a reduced biodiversity. Currently, no microbes can survive in these Cretaceous shales even though the shales never reached geopasturization temperatures and there is sufficient substrate. Biogenic gas generation is inferred to be restricted to near surface strata while elsewhere in this succession methanogenesis has ceased, which significantly reduces the exploration potential for biogenic gas.
{"title":"Lithological and diagenetic restrictions on biogenic gas generation in Songliao Basin inferred from grain size distribution and permeability measurement","authors":"Ningxi Li, Zi-hui Feng, Haiping Huang, Xue Wang, Z. Dong","doi":"10.2113/GSCPGBULL.63.1.66","DOIUrl":"https://doi.org/10.2113/GSCPGBULL.63.1.66","url":null,"abstract":"Abstract Organically rich immature source rocks occur commonly at shallow burial depths in Songliao Basin, NE China. This has led to the general assumption that there must be a large biogenic gas resource in these organic rich, shallow strata. However, except for a few small gas fields that are generally associated with biodegraded oil, only a small amount of biogenic gas has been discovered. In order to determine the geological factors controlling biogenic gas generation and accumulation, a suite of potential source rock shale samples from burial depth less than 1600 m was analyzed for organic composition, grain size distribution and permeability. The results show that selected samples are organic rich and thermally immature. The grain size analysis shows a mixed distribution of silt and clay with D10 generally below 1.6 μm. The measured permeability values are generally below 1 μd under in situ stress conditions with pore throats that are most likely smaller than that of methanogenic bacteria. Very low permeability and very small pores resulting from compaction and diagenesis restrict bacteria movement and activity, limit nutrient transport, diminish space availability, and lead to a reduced biodiversity. Currently, no microbes can survive in these Cretaceous shales even though the shales never reached geopasturization temperatures and there is sufficient substrate. Biogenic gas generation is inferred to be restricted to near surface strata while elsewhere in this succession methanogenesis has ceased, which significantly reduces the exploration potential for biogenic gas.","PeriodicalId":56325,"journal":{"name":"Bullentin of Canadian Petroleum Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2113/GSCPGBULL.63.1.66","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68207084","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-03-01DOI: 10.2113/GSCPGBULL.63.1.1
Zhuoheng Chen, Shuichang Zhang, S. Grasby, Y. Shuai
Generation of biogenic gas occurs under environmental conditions different from those of thermogenic gas (Rice and Claypool, 1981; Whiticar et al. 1986; Shurr et al., 2003). Microbial activity takes place at shallow depth in a semi-open system where sediments are not fully compacted, seal integrity is not well developed, and accumulation and leakage of microbial gas are competing processes. Thus the formation of a commercial biogenic gas field needs both sufficient microbial activity to maintain gas supply and an efficient entrapment mechanism to minimize gas leakage. This depends on not only the temperature and other microbial growth conditions, but also on the characteristics and internal architecture of both source and reservoir strata. A better understanding of the essential controls and optimal conditions for critical microbial activity, and for the efficient entrapment of gas generated, is important to successful exploration for biogenic resources. This Special Issue of the Bulletin of Canadian Petroleum Geology contains nine thematic research articles on microbial gas resources and their characteristics in the Western Canada Sedimentary Basin and selected Chinese basins. The nine articles are based on the results and findings from a comparative study of shallow biogenic gas resources in Canadian and Chinese basins conducted under a collaborative research agreement between PetroChina and the Geological Survey of Canada during 2010–2013. The agreement provided a unique opportunity to study shallow biogenic gas fields with different origins and characteristics in the two countries. The primary objective of the project is to better understand the critical geological controls on biogenically derived natural gas resources in shallow strata and their resource potential. The characteristics of the biogenic gas fields and available data for describing and quantifying the biogenic gas fields in the two countries are complimentary. The long production history and large amount of public data make the …
生物气的生成是在不同于热成因气的环境条件下发生的(Rice and Claypool, 1981;Whiticar et al. 1986;Shurr et al.， 2003)。微生物活动主要发生在半开放体系的浅层，在这种体系中，沉积物没有完全压实，密封完整性不完善，微生物气体的聚集和泄漏是相互竞争的过程。因此，商业生物气田的形成既需要足够的微生物活性来维持天然气供应，也需要有效的圈闭机制来减少天然气泄漏。这不仅取决于温度和其他微生物生长条件，还取决于烃源层和储层的特征和内部结构。更好地了解关键微生物活动的基本控制和最佳条件，以及有效圈闭所产生的气体，对于成功勘探生物资源至关重要。本期《加拿大石油地质公报》特刊收录了9篇关于加拿大西部沉积盆地和中国部分盆地微生物气资源及其特征的专题研究文章。根据中石油与加拿大地质调查局2010-2013年的合作研究协议，这九篇文章基于加拿大和中国盆地浅层生物气资源对比研究的结果和发现。该协议为研究两国不同来源和特征的浅层生物气田提供了独特的机会。该项目的主要目的是更好地了解浅层生物源天然气资源的关键地质控制因素及其资源潜力。两国生物气田的特征和现有的生物气田描述和量化资料是互补的。悠久的生产历史和大量的公共数据使得…
{"title":"Biogenic gas accumulations in Canada and China: geological characteristics and new insights","authors":"Zhuoheng Chen, Shuichang Zhang, S. Grasby, Y. Shuai","doi":"10.2113/GSCPGBULL.63.1.1","DOIUrl":"https://doi.org/10.2113/GSCPGBULL.63.1.1","url":null,"abstract":"Generation of biogenic gas occurs under environmental conditions different from those of thermogenic gas (Rice and Claypool, 1981; Whiticar et al. 1986; Shurr et al., 2003). Microbial activity takes place at shallow depth in a semi-open system where sediments are not fully compacted, seal integrity is not well developed, and accumulation and leakage of microbial gas are competing processes. Thus the formation of a commercial biogenic gas field needs both sufficient microbial activity to maintain gas supply and an efficient entrapment mechanism to minimize gas leakage. This depends on not only the temperature and other microbial growth conditions, but also on the characteristics and internal architecture of both source and reservoir strata. A better understanding of the essential controls and optimal conditions for critical microbial activity, and for the efficient entrapment of gas generated, is important to successful exploration for biogenic resources.\u0000\u0000This Special Issue of the Bulletin of Canadian Petroleum Geology contains nine thematic research articles on microbial gas resources and their characteristics in the Western Canada Sedimentary Basin and selected Chinese basins. The nine articles are based on the results and findings from a comparative study of shallow biogenic gas resources in Canadian and Chinese basins conducted under a collaborative research agreement between PetroChina and the Geological Survey of Canada during 2010–2013. The agreement provided a unique opportunity to study shallow biogenic gas fields with different origins and characteristics in the two countries. The primary objective of the project is to better understand the critical geological controls on biogenically derived natural gas resources in shallow strata and their resource potential. The characteristics of the biogenic gas fields and available data for describing and quantifying the biogenic gas fields in the two countries are complimentary. The long production history and large amount of public data make the …","PeriodicalId":56325,"journal":{"name":"Bullentin of Canadian Petroleum Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2113/GSCPGBULL.63.1.1","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68206800","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-03-01DOI: 10.2113/GSCPGBULL.63.1.53
Shuichang Zhang, Y. Shuai
Of twenty-nine known biogenic gas fields in China, three with reserves of nearly 100 × 109 m3 are located in Qaidam Basin, western China, and two with reserves of 50 × 109 m3 are located in Yinggehai Basin, southern China. The other fields, concentrated in eastern and south-eastern China, have smaller reserves. The gas geochemical characteristics, including data from more than 300 gas samples, over 200 isotopic analyses and 12 inert gas analyses, reveals the following. Gases are predominated by methane (CH4) (95%), followed by nitrogen (N2; 0–15%) and carbon dioxide (CO2; <3% but commonly <1%). Methane δ13C1 values are very light, usually <−55‰. The ethane δ13C2 values range widely from −60‰ to −20‰ and the δ13CCO2 values are between −39‰ and 5‰. Hydrogen isotope values of CH4 range from −260‰ to −190‰, which indicate that the gases are formed by CO2 reduction. 3He/4He ratios are between n × 10−8 and n × 10−7. 40Ar/36Ar ratios are between 231 and 439 and R/Ra ratios are 0.03. These biogenic gases exhibit geochemical characteristics and occur in geological settings that indicate two major biogenic gas types in China: early, or primary, biogenic gas and secondary biogenic gas that formed through crude oil biodegradation. Primary biogenic gas reserves are large while secondary biogenic gas reserves are smaller but widely distributed. The geological settings of the two types differ significantly. The primary biogenic gases are concentrated in Cenozoic successions characterized by rapid sedimentation, high organic matter content and syndepositional entrapment. Most secondary biogenic gases are associated with biodegraded heavy oil occurrences and these are not confined to any specific sedimentary strata or epoch.
{"title":"Geochemistry and distribution of biogenic gas in China","authors":"Shuichang Zhang, Y. Shuai","doi":"10.2113/GSCPGBULL.63.1.53","DOIUrl":"https://doi.org/10.2113/GSCPGBULL.63.1.53","url":null,"abstract":"Of twenty-nine known biogenic gas fields in China, three with reserves of nearly 100 × 109 m3 are located in Qaidam Basin, western China, and two with reserves of 50 × 109 m3 are located in Yinggehai Basin, southern China. The other fields, concentrated in eastern and south-eastern China, have smaller reserves. The gas geochemical characteristics, including data from more than 300 gas samples, over 200 isotopic analyses and 12 inert gas analyses, reveals the following. Gases are predominated by methane (CH4) (95%), followed by nitrogen (N2; 0–15%) and carbon dioxide (CO2; <3% but commonly <1%). Methane δ13C1 values are very light, usually <−55‰. The ethane δ13C2 values range widely from −60‰ to −20‰ and the δ13CCO2 values are between −39‰ and 5‰. Hydrogen isotope values of CH4 range from −260‰ to −190‰, which indicate that the gases are formed by CO2 reduction. 3He/4He ratios are between n × 10−8 and n × 10−7. 40Ar/36Ar ratios are between 231 and 439 and R/Ra ratios are 0.03. These biogenic gases exhibit geochemical characteristics and occur in geological settings that indicate two major biogenic gas types in China: early, or primary, biogenic gas and secondary biogenic gas that formed through crude oil biodegradation. Primary biogenic gas reserves are large while secondary biogenic gas reserves are smaller but widely distributed. The geological settings of the two types differ significantly. The primary biogenic gases are concentrated in Cenozoic successions characterized by rapid sedimentation, high organic matter content and syndepositional entrapment. Most secondary biogenic gases are associated with biodegraded heavy oil occurrences and these are not confined to any specific sedimentary strata or epoch.","PeriodicalId":56325,"journal":{"name":"Bullentin of Canadian Petroleum Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2113/GSCPGBULL.63.1.53","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68207065","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-03-01DOI: 10.2113/GSCPGBULL.63.1.84
Y. Shuai, P. Peng, Y. Zou, Shuichang Zhang, Ling Huang
Abstract Many small and medium-sized Paleogene pull-apart basins in southern China contain an abundance of biogenic gas shows. Such shallow gas with biogenic characteristics has been thoroughly investigated only in Baise Basin. Hence, the research results from Baise Basin could serve as a model for the origin and characteristics of shallow gases in similar basins and areas in Southern China. There are ten gas fields with a total of proven reserves of 20 billion cubic meters discovered in Baise Basin. Three gas fields are located on the western and southern flank of the basin, and they are gas caps to heavy oil pools from depths between 600 m and 850 m. These accumulations contain dry biogenic gases, with C1/C1-5 exceeding 0.99, light δ13C1 (–76 to −54‰), and heavy δD1 (−218‰). Trace heavy gaseous hydrocarbons are strongly biodegraded (iC4/nC4>3). The other seven gas fields are located in the northern fault zone and the central Nakun uplift of the basin at depths between 300 m and 700 m. Gases are mainly unassociated and condensed gases. The condensed gases are depleted in 13C (δ13C1: −67 to −53.7‰, δ13C2: −52.3 to −36.1‰, δ13C3: −43.3 to −33.4‰), but wet with C1/C2+3 mostly less than 20, suggesting a mainly thermal origin at low maturity. The unassociated gases are dominated by methane, with C1/C2+3 ratio above 100, variable N2 (0 to 5.4%), and traces of CO2. The δ13C value of methane in the unassociated gases is between −76 to −60‰, and δD1 values from −248 to −213.7‰. These gases also contain isotopically light ethane with δ13C2 values of −64.5 to −42‰, which we infer to have originated from deeper horizons as a result of migration or diffusion from low-maturity thermal gases with light stable carbon isotopic compositions (C1/C2+3 <20, δ13C2 from −60‰ to −58‰). A similar thermal origin is inferred for the other heavy gaseous hydrocarbons. Formation water with the shallow gases of this basin is mainly NaHCO3-type with low TDS ranging from 1000 to 4500 ppm. The (HCO3+CO3)/Cl ratios range from 1.5 to 100, indicating a relative open hydrodynamic condition and the possible intrusion of meteoric water. These data indicate that early biogenic gas generated syndepositionally was probably not preserved, and that the current biogenic gas accumulation formed mainly as a result post-depositional of crude oil biodegradation in the western basin and coal biodegradation in the northern fault zone. Shallow gases in Baise Basin are mainly secondary biogenic gases, with an admixture of low maturity thermogenic gases from deeper horizons.
{"title":"Geochemistry and origin of shallow gas in the Baise Basin, southern China","authors":"Y. Shuai, P. Peng, Y. Zou, Shuichang Zhang, Ling Huang","doi":"10.2113/GSCPGBULL.63.1.84","DOIUrl":"https://doi.org/10.2113/GSCPGBULL.63.1.84","url":null,"abstract":"Abstract Many small and medium-sized Paleogene pull-apart basins in southern China contain an abundance of biogenic gas shows. Such shallow gas with biogenic characteristics has been thoroughly investigated only in Baise Basin. Hence, the research results from Baise Basin could serve as a model for the origin and characteristics of shallow gases in similar basins and areas in Southern China. There are ten gas fields with a total of proven reserves of 20 billion cubic meters discovered in Baise Basin. Three gas fields are located on the western and southern flank of the basin, and they are gas caps to heavy oil pools from depths between 600 m and 850 m. These accumulations contain dry biogenic gases, with C1/C1-5 exceeding 0.99, light δ13C1 (–76 to −54‰), and heavy δD1 (−218‰). Trace heavy gaseous hydrocarbons are strongly biodegraded (iC4/nC4>3). The other seven gas fields are located in the northern fault zone and the central Nakun uplift of the basin at depths between 300 m and 700 m. Gases are mainly unassociated and condensed gases. The condensed gases are depleted in 13C (δ13C1: −67 to −53.7‰, δ13C2: −52.3 to −36.1‰, δ13C3: −43.3 to −33.4‰), but wet with C1/C2+3 mostly less than 20, suggesting a mainly thermal origin at low maturity. The unassociated gases are dominated by methane, with C1/C2+3 ratio above 100, variable N2 (0 to 5.4%), and traces of CO2. The δ13C value of methane in the unassociated gases is between −76 to −60‰, and δD1 values from −248 to −213.7‰. These gases also contain isotopically light ethane with δ13C2 values of −64.5 to −42‰, which we infer to have originated from deeper horizons as a result of migration or diffusion from low-maturity thermal gases with light stable carbon isotopic compositions (C1/C2+3 <20, δ13C2 from −60‰ to −58‰). A similar thermal origin is inferred for the other heavy gaseous hydrocarbons. Formation water with the shallow gases of this basin is mainly NaHCO3-type with low TDS ranging from 1000 to 4500 ppm. The (HCO3+CO3)/Cl ratios range from 1.5 to 100, indicating a relative open hydrodynamic condition and the possible intrusion of meteoric water. These data indicate that early biogenic gas generated syndepositionally was probably not preserved, and that the current biogenic gas accumulation formed mainly as a result post-depositional of crude oil biodegradation in the western basin and coal biodegradation in the northern fault zone. Shallow gases in Baise Basin are mainly secondary biogenic gases, with an admixture of low maturity thermogenic gases from deeper horizons.","PeriodicalId":56325,"journal":{"name":"Bullentin of Canadian Petroleum Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2113/GSCPGBULL.63.1.84","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68207426","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-03-01DOI: 10.2113/GSCPGBULL.63.1.96
G. Hu, Jin Li, Song-Mei Hu
Abstract The Eastern Depression of Qaidam Basin in China is the largest Quaternary gas producing area in the world. The chemical compositions, C1–C2 carbon and hydrogen isotopic compositions, low molecular weight hydrocarbons (C6–C7LMWHs) in 10 natural gas samples from three large gas fields (Tainan, Sebei 1 and Sebei 2) in Eastern Depression of Qaidam Basin were analyzed. The carbon and hydrogen isotopic composition of methane in the three gas fields is relatively enriched in 12C and 1H with δ13C1 values ranging from −69.6 ‰ to −65.5 ‰ (average −67.4 ‰) and δ1H from −251 ‰ to −231 ‰ (average −244 ‰). The data shows that the gases are defined as microbial in origin and generated primarily by bacterial CO2 reduction. The composition distribution of C6–C7LMWHs differs between the fields. LMWHs associated with the gas in the Sebei 1 gas field are different from those in the Tainan and Sebei 2 gas fields. The relative content of cycloalkane among C6–C7LMWHs in the Tainan and Sebei 2 gas fields is very high, ranging from 37.02% to 43.36% and 33.99% to 43.71% respectively. However, in the Sebei 1 gas field, of the total C6–C7LMWHs, the relative content of isoalkane is the highest, ranging from 37.17% to 45.92% with an average of 42.48. These traits indicate that the origins of C6–C7LMWHs are probably different from the bacterial action that is predominant in the Sebei 1 gas field. We infer that catalytic reaction affects the C6–C7LMWHs compositions in the Tainan and Sebei 2 gas fields.
{"title":"The origin of low molecular weight hydrocarbons associated with biogenic gas from the Eastern Depression in Qaidam Basin, China","authors":"G. Hu, Jin Li, Song-Mei Hu","doi":"10.2113/GSCPGBULL.63.1.96","DOIUrl":"https://doi.org/10.2113/GSCPGBULL.63.1.96","url":null,"abstract":"Abstract The Eastern Depression of Qaidam Basin in China is the largest Quaternary gas producing area in the world. The chemical compositions, C1–C2 carbon and hydrogen isotopic compositions, low molecular weight hydrocarbons (C6–C7LMWHs) in 10 natural gas samples from three large gas fields (Tainan, Sebei 1 and Sebei 2) in Eastern Depression of Qaidam Basin were analyzed. The carbon and hydrogen isotopic composition of methane in the three gas fields is relatively enriched in 12C and 1H with δ13C1 values ranging from −69.6 ‰ to −65.5 ‰ (average −67.4 ‰) and δ1H from −251 ‰ to −231 ‰ (average −244 ‰). The data shows that the gases are defined as microbial in origin and generated primarily by bacterial CO2 reduction. The composition distribution of C6–C7LMWHs differs between the fields. LMWHs associated with the gas in the Sebei 1 gas field are different from those in the Tainan and Sebei 2 gas fields. The relative content of cycloalkane among C6–C7LMWHs in the Tainan and Sebei 2 gas fields is very high, ranging from 37.02% to 43.36% and 33.99% to 43.71% respectively. However, in the Sebei 1 gas field, of the total C6–C7LMWHs, the relative content of isoalkane is the highest, ranging from 37.17% to 45.92% with an average of 42.48. These traits indicate that the origins of C6–C7LMWHs are probably different from the bacterial action that is predominant in the Sebei 1 gas field. We infer that catalytic reaction affects the C6–C7LMWHs compositions in the Tainan and Sebei 2 gas fields.","PeriodicalId":56325,"journal":{"name":"Bullentin of Canadian Petroleum Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2113/GSCPGBULL.63.1.96","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68207590","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-03-01DOI: 10.2113/GSCPGBULL.63.1.33
Zhuoheng Chen, Y. Shuai, K. Osadetz, T. Hamblin, S. Grasby
Abstract Compared to conventional thermogenic petroleum, the exploration for large biogenic gas accumulations is more challenging because the gas occurs commonly at shallow depths in a petroleum system with weak top and lateral seals. In addition to fundamental environmental requirements, such as temperature and formation water composition, microbial gas generation and retention require adequate petroleum system elements in order to form economic accumulations. The geological characteristics of Southeast Alberta Gas Field (SAGF), a giant biogenic gas accumulation located in southeastern Alberta and southwestern Saskatchewan within the Western Canada Sedimentary Basin (WCSB), are compared to those of Sanhu Sag, Qaidam Basin in northwestern China, to provide insight into the critical geological controls for economic biogenic gas accumulations. It was found that multilayered reservoirs, consisting of multiple layers of thin porous units and interbedded with source rocks, provide a most efficient storage mechanism. Low relief structural and stratigraphic traps with lateral permeability seals, commonly of stratigraphic or diagenetic origin, are the most effective trapping mechanisms. The recognition of these common constraints provides insight for future exploration of other biogenic gas fields and prospects in the basins studied elsewhere.
{"title":"Comparison of biogenic gas fields in the Western Canada Sedimentary Basin and Qaidam Basin: implications for essential geological controls on large microbial gas accumulations","authors":"Zhuoheng Chen, Y. Shuai, K. Osadetz, T. Hamblin, S. Grasby","doi":"10.2113/GSCPGBULL.63.1.33","DOIUrl":"https://doi.org/10.2113/GSCPGBULL.63.1.33","url":null,"abstract":"Abstract Compared to conventional thermogenic petroleum, the exploration for large biogenic gas accumulations is more challenging because the gas occurs commonly at shallow depths in a petroleum system with weak top and lateral seals. In addition to fundamental environmental requirements, such as temperature and formation water composition, microbial gas generation and retention require adequate petroleum system elements in order to form economic accumulations. The geological characteristics of Southeast Alberta Gas Field (SAGF), a giant biogenic gas accumulation located in southeastern Alberta and southwestern Saskatchewan within the Western Canada Sedimentary Basin (WCSB), are compared to those of Sanhu Sag, Qaidam Basin in northwestern China, to provide insight into the critical geological controls for economic biogenic gas accumulations. It was found that multilayered reservoirs, consisting of multiple layers of thin porous units and interbedded with source rocks, provide a most efficient storage mechanism. Low relief structural and stratigraphic traps with lateral permeability seals, commonly of stratigraphic or diagenetic origin, are the most effective trapping mechanisms. The recognition of these common constraints provides insight for future exploration of other biogenic gas fields and prospects in the basins studied elsewhere.","PeriodicalId":56325,"journal":{"name":"Bullentin of Canadian Petroleum Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2113/GSCPGBULL.63.1.33","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68206786","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-03-01DOI: 10.2113/GSCPGBULL.63.1.75
Y. Shuai, Shuichang Zhang, Dade Ma, Liquan Wang, G. Jiang, Ziyuan Xu, Ling Huang, Yirui Xu
Abstract The Quaternary Qigequan Formation, a continental clastic sedimentation system in Sanhu Depression of eastern Qaidam Basin, west-central China, contains abundant biogenic gas resources. Favorable characteristics of the Sanhu Depression’s geological history and framework responsible for biogenic gas production include rapid sedimentation, shallow burial depth, organic-rich sediments, high porosity/permeability, and a saline depositional environment. Gases are dominated by methane (>99%), with trace ethane/propane (C2+3<0.5%) and minor non-hydrocarbon gases (CO2 <0.5%; N2 <3%). Methane has δ13C1 values of −70 to −62‰ and δD1 values of −240 to −220‰, suggesting generation following a CO2 reduction pathway. Ethane is very light with δ13C2 values of −50 to −44‰; propane δ13C3 values range from −34 to −32‰. Ethane and propane are inferred to have the same thermocatalytic origin under low organic maturity levels and are unrelated to the biogenic origin of methane. Biogenic methane is equilibrated with the saline formation waters. The formation water geochemistry data, including stable isotope values (δD and δ18O) and 36Cl age, suggest recent dilution by meteoric waters. Methanogenesis is currently active, as indicated by the presence of both abundant hydrogen and microbes. The recent and ongoing biogenic gas generation model proposed explains why biogenic gas accumulations are so abundant in a shallow geological setting where the conditions for accumulation and preservation are otherwise considered relatively poor.
{"title":"Quaternary biogenic gases in the Qaidam Basin, Western China","authors":"Y. Shuai, Shuichang Zhang, Dade Ma, Liquan Wang, G. Jiang, Ziyuan Xu, Ling Huang, Yirui Xu","doi":"10.2113/GSCPGBULL.63.1.75","DOIUrl":"https://doi.org/10.2113/GSCPGBULL.63.1.75","url":null,"abstract":"Abstract The Quaternary Qigequan Formation, a continental clastic sedimentation system in Sanhu Depression of eastern Qaidam Basin, west-central China, contains abundant biogenic gas resources. Favorable characteristics of the Sanhu Depression’s geological history and framework responsible for biogenic gas production include rapid sedimentation, shallow burial depth, organic-rich sediments, high porosity/permeability, and a saline depositional environment. Gases are dominated by methane (>99%), with trace ethane/propane (C2+3<0.5%) and minor non-hydrocarbon gases (CO2 <0.5%; N2 <3%). Methane has δ13C1 values of −70 to −62‰ and δD1 values of −240 to −220‰, suggesting generation following a CO2 reduction pathway. Ethane is very light with δ13C2 values of −50 to −44‰; propane δ13C3 values range from −34 to −32‰. Ethane and propane are inferred to have the same thermocatalytic origin under low organic maturity levels and are unrelated to the biogenic origin of methane. Biogenic methane is equilibrated with the saline formation waters. The formation water geochemistry data, including stable isotope values (δD and δ18O) and 36Cl age, suggest recent dilution by meteoric waters. Methanogenesis is currently active, as indicated by the presence of both abundant hydrogen and microbes. The recent and ongoing biogenic gas generation model proposed explains why biogenic gas accumulations are so abundant in a shallow geological setting where the conditions for accumulation and preservation are otherwise considered relatively poor.","PeriodicalId":56325,"journal":{"name":"Bullentin of Canadian Petroleum Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2113/GSCPGBULL.63.1.75","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68207200","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-03-01DOI: 10.2113/GSCPGBULL.63.1.20
Haiping Huang
Abstract Western Canada Sedimentary Basin oil sand deposits are derived from light oils generated in southwestern Alberta, which migrated to the north and east for more than 100 km. Biodegradation is the primary process that transformed the original light crude oil into heavy oil and bitumen, although other alteration mechanisms were present. Biodegradation levels increase from the southwest (non-biodegraded) to the northeast (extremely biodegraded) and are associated with decreasing reservoir paleo-temperature that plays the primary role in controlling the biodegradation regime. Compositional gradients and variable biodegradation within a single reservoir column indicate that water-leg size is a critical local control on vertical variations of biodegradation degree and oil physical properties. Secondary biogenic gas is a by-product of the formation of heavy oils and bitumens by anaerobic biodegradation, and “gas over bitumen” is a common feature of the bitumen accumulations. Observed 13C-depleted methane and 13C-enriched CO2 provides direct evidence for methanogenic biodegradation and biogenic methane generation. Supplemental evidence for anaerobic biodegradation is found in the geochemistry of associated formation water. The gases associated with anaerobic biodegradation are easily differentiated from primary biogenic gases using the isotopic signature of C2+ alkane components. Based on the observed crude oil biodegradation levels, the stoichiometry of methanogenic alkane biodegradation, and assuming a conversion rate of carbon dioxide to methane, approximately 141.3 × 1012 m3 (4991 Tcf) of secondary biogenic methane was generated accompanying the biodegradation of these petroleum accumulations. However, assessing how much secondary biogenic gas is preserved currently in the subsurface is difficult. Gas resource assessments performed prior to and independent of biodegradation studies suggests that McMurray Formation is expected to contain approximately 58.7 × 109 m3 natural gas in place and that all Mannville Group reservoirs associated with the oil sand regions (Athabasca and Lloydminster) are expected to contain approximately 608.5 × 109 m3 of raw gas in place. Even if the estimates of retained gas are conservative, it is apparent that the vast majority of the secondary biogenic methane generated during biodegradation is leaked into the overburden, dissolved in formation water, or escaped into the atmosphere.
{"title":"Recognition and sources of secondary biogenic gases in the oil sand areas, Western Canada Sedimentary Basin","authors":"Haiping Huang","doi":"10.2113/GSCPGBULL.63.1.20","DOIUrl":"https://doi.org/10.2113/GSCPGBULL.63.1.20","url":null,"abstract":"Abstract Western Canada Sedimentary Basin oil sand deposits are derived from light oils generated in southwestern Alberta, which migrated to the north and east for more than 100 km. Biodegradation is the primary process that transformed the original light crude oil into heavy oil and bitumen, although other alteration mechanisms were present. Biodegradation levels increase from the southwest (non-biodegraded) to the northeast (extremely biodegraded) and are associated with decreasing reservoir paleo-temperature that plays the primary role in controlling the biodegradation regime. Compositional gradients and variable biodegradation within a single reservoir column indicate that water-leg size is a critical local control on vertical variations of biodegradation degree and oil physical properties. Secondary biogenic gas is a by-product of the formation of heavy oils and bitumens by anaerobic biodegradation, and “gas over bitumen” is a common feature of the bitumen accumulations. Observed 13C-depleted methane and 13C-enriched CO2 provides direct evidence for methanogenic biodegradation and biogenic methane generation. Supplemental evidence for anaerobic biodegradation is found in the geochemistry of associated formation water. The gases associated with anaerobic biodegradation are easily differentiated from primary biogenic gases using the isotopic signature of C2+ alkane components. Based on the observed crude oil biodegradation levels, the stoichiometry of methanogenic alkane biodegradation, and assuming a conversion rate of carbon dioxide to methane, approximately 141.3 × 1012 m3 (4991 Tcf) of secondary biogenic methane was generated accompanying the biodegradation of these petroleum accumulations. However, assessing how much secondary biogenic gas is preserved currently in the subsurface is difficult. Gas resource assessments performed prior to and independent of biodegradation studies suggests that McMurray Formation is expected to contain approximately 58.7 × 109 m3 natural gas in place and that all Mannville Group reservoirs associated with the oil sand regions (Athabasca and Lloydminster) are expected to contain approximately 608.5 × 109 m3 of raw gas in place. Even if the estimates of retained gas are conservative, it is apparent that the vast majority of the secondary biogenic methane generated during biodegradation is leaked into the overburden, dissolved in formation water, or escaped into the atmosphere.","PeriodicalId":56325,"journal":{"name":"Bullentin of Canadian Petroleum Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2113/GSCPGBULL.63.1.20","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68207210","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2014-12-01DOI: 10.2113/GSCPGBULL.62.4.289
B. Maclean, G. Williams, Shunxin Zhang
Abstract Cretaceous rocks underlie most of the northeast Baffin shelf, are present in Cumberland Sound, and may underlie the southeast Baffin shelf. New palynological, Rock Eval, and vitrinite reflectance analyses of bedrock samples, obtained from the Baffin shelf and Hudson Strait during a shallow core-hole drilling programme undertaken in the 1970s and 1980s, provide a better understanding of the stratigraphy and petroleum potential of the region. The samples from the Buchan Gulf, Scott Inlet, and Home Bay areas on the northeast Baffin shelf, which were originally considered to be of primarily Campanian age, are now considered to be Coniacian to early Campanian. Non-marine Aptian-Albian rocks occur in the Padloping area, farther south along the northeast Baffin shelf, and in Cumberland Sound. Based on Rock Eval and vitrinite reflectance data, the Cretaceous rocks sampled on the Baffin shelf contain gas-prone Type III kerogen and are immature to marginally mature. However, the presence of an oil seep off Scott Inlet indicates that more mature source rocks capable of generating oil exist in the region. Additional shallow cores would further define the biostratigraphic and geochemical aspects of strata on the Baffin shelf.
{"title":"New insights into the stratigraphy and petroleum potential of the Baffin shelf's Cretaceous rocks","authors":"B. Maclean, G. Williams, Shunxin Zhang","doi":"10.2113/GSCPGBULL.62.4.289","DOIUrl":"https://doi.org/10.2113/GSCPGBULL.62.4.289","url":null,"abstract":"Abstract Cretaceous rocks underlie most of the northeast Baffin shelf, are present in Cumberland Sound, and may underlie the southeast Baffin shelf. New palynological, Rock Eval, and vitrinite reflectance analyses of bedrock samples, obtained from the Baffin shelf and Hudson Strait during a shallow core-hole drilling programme undertaken in the 1970s and 1980s, provide a better understanding of the stratigraphy and petroleum potential of the region. The samples from the Buchan Gulf, Scott Inlet, and Home Bay areas on the northeast Baffin shelf, which were originally considered to be of primarily Campanian age, are now considered to be Coniacian to early Campanian. Non-marine Aptian-Albian rocks occur in the Padloping area, farther south along the northeast Baffin shelf, and in Cumberland Sound. Based on Rock Eval and vitrinite reflectance data, the Cretaceous rocks sampled on the Baffin shelf contain gas-prone Type III kerogen and are immature to marginally mature. However, the presence of an oil seep off Scott Inlet indicates that more mature source rocks capable of generating oil exist in the region. Additional shallow cores would further define the biostratigraphic and geochemical aspects of strata on the Baffin shelf.","PeriodicalId":56325,"journal":{"name":"Bullentin of Canadian Petroleum Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2014-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2113/GSCPGBULL.62.4.289","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68206634","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2014-12-01DOI: 10.2113/GSCPGBULL.62.4.232
C. Jauer, G. Oakey, G. Williams, J. Wielens
Abstract Saglek Basin is the more northerly of the two major sedimentary basins along the Labrador margin of the Canadian east coast in which exploration drilling was undertaken in the 1970s-early 1980s. Saglek Basin has an area of over 100,000 km2, and contains a clastic-dominated succession of late Cretaceous to Pleistocene age. Nine wells were drilled in Saglek Basin, with only one significant discovery. The Hekja O-71 well, drilled in the northern half of the basin just east of Frobisher Bay, flowed natural gas with condensates and has reserves estimated at approximately 6.51 × 1011 m3 (2.3 Tcf). A new interpretation of seismic and marine Bouguer gravity data shows the very strong influence of reactivated basement structures on the overlying section. Earthquake activity along the Labrador Sea seismic zone is proposed as a possible cause for episodic venting of thermogenic natural gas through pre-existing fracture networks. This may account for the observations of persistent oil slick features on the sea surface observed in satellite radar data. The presence of these oil seep indicators in the southern part of the basin implies the existence of a second petroleum system that is more oil prone. Source rock analysis indicates that three formations in the post-rift succession of the basin have petroleum source potential. Previous studies have raised the issue of inadequate thermal maturation of these rocks in downgrading the petroleum potential of the basin. An integrated 4-D basin modelling study, that shows significant natural gas generation, estimated that volumes of 2.83 × 109 m3 (100 Tcf) could occur, along with a minor oil component, in self-sourced petroleum kitchens in some reservoirs and from sites deeper in the basin. Three separate prospect fairways are interpreted along the western side of the basin. Collectively, these observations suggest the petroleum potential of the Saglek Basin may be significantly higher than estimated previously.
{"title":"Saglek Basin in the Labrador Sea, east coast Canada; stratigraphy, structure and petroleum systems","authors":"C. Jauer, G. Oakey, G. Williams, J. Wielens","doi":"10.2113/GSCPGBULL.62.4.232","DOIUrl":"https://doi.org/10.2113/GSCPGBULL.62.4.232","url":null,"abstract":"Abstract Saglek Basin is the more northerly of the two major sedimentary basins along the Labrador margin of the Canadian east coast in which exploration drilling was undertaken in the 1970s-early 1980s. Saglek Basin has an area of over 100,000 km2, and contains a clastic-dominated succession of late Cretaceous to Pleistocene age. Nine wells were drilled in Saglek Basin, with only one significant discovery. The Hekja O-71 well, drilled in the northern half of the basin just east of Frobisher Bay, flowed natural gas with condensates and has reserves estimated at approximately 6.51 × 1011 m3 (2.3 Tcf). A new interpretation of seismic and marine Bouguer gravity data shows the very strong influence of reactivated basement structures on the overlying section. Earthquake activity along the Labrador Sea seismic zone is proposed as a possible cause for episodic venting of thermogenic natural gas through pre-existing fracture networks. This may account for the observations of persistent oil slick features on the sea surface observed in satellite radar data. The presence of these oil seep indicators in the southern part of the basin implies the existence of a second petroleum system that is more oil prone. Source rock analysis indicates that three formations in the post-rift succession of the basin have petroleum source potential. Previous studies have raised the issue of inadequate thermal maturation of these rocks in downgrading the petroleum potential of the basin. An integrated 4-D basin modelling study, that shows significant natural gas generation, estimated that volumes of 2.83 × 109 m3 (100 Tcf) could occur, along with a minor oil component, in self-sourced petroleum kitchens in some reservoirs and from sites deeper in the basin. Three separate prospect fairways are interpreted along the western side of the basin. Collectively, these observations suggest the petroleum potential of the Saglek Basin may be significantly higher than estimated previously.","PeriodicalId":56325,"journal":{"name":"Bullentin of Canadian Petroleum Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2014-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2113/GSCPGBULL.62.4.232","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68206237","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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