石油实验地质

2015, 37(4): .

Abstract(651) PDF-CN(1074)

Abstract:

Shale gas preservation conditions in the Lower Paleozoic, Yangtze block

Xu Zhengyu, Yao Genshun, Liang Xing, Xiong Shaoyun, He Yong, Zhang Jiehui, Wang Gaocheng, Liao Yong, Shi Yuanhui

2015, 37(4): 407-417. doi: 10.11781/sysydz201504407

Abstract(1286) PDF-CN(1386)

Abstract:
Two sets of organic-rich shale developed in the Yangtze block during the Early Paleozoic. The first set was in the Lower Cambrian Niutitang Formation, while the second set was in the Upper Ordovician Wufeng Formation and the Lower Silurian Longmaxi Formation. The shales experienced four stages of orogenic events, including the Guangxi, Indosinian, Yanshanian and Himalayan. Shales are well-preserved in the Upper Yangtze region and to the west of the middle Yangtze region, where only two or three phases of deformation took place. The shale gas content is high, showing a good potential for exploration. In the east of the middle Yangtze region and the west of the lower Yangtze region, shale gas preservation conditions are poorer due to three or four phases of deformation. As a result, the shale gas content is lower as is the exploration potential. In the east of the lower Yangtze region and in the periphery orogenic front of the Yangtze block, four phases of deformation took place, which led to the poorest preservation conditions for shale gas. As to the whole Yangtze block, the residual synclines are most favorable for shale gas preservation.

Source of gas reservoirs in the fourth member of the Middle Triassic Leikoupo Formation in Western Sichuan Depression

Xie Gangping

2015, 37(4): 418-422. doi: 10.11781/sysydz201504418

Abstract(1069) PDF-CN(1209)

Abstract:
A set of thick charcoal grey dolomicrite and micrite source rocks developed in the Middle Triassic Leikoupo Formation in the Western Sichuan Depression, in addition to four sets of marine source rocks in the Permian and its underlying strata. The gas generation intensity of the source rocks is about (1-4)×10⁹ m³/km², showing a good potential for medium or giant gas fields. According to the gas composition, carbon and hydrogen isotopes, reservoir bitumen and migration conditions, the major sources for the gas reservoirs of the fourth member of the Leikoupo Formation vary in different tectonic zones in the Western Sichuan Depression. The gas from well PZ1 in the Longmenshan piedmont tectonic zone displays high H₂S content, high δ¹³C₂ value (-26.4‰), positive alkane carbon isotopic series and light δD₁ value (-140‰), consistent with characteristics of mixed gas. The thermal evolution degree reflected by natural gas compositions and carbon isotopes falls between those of Permian and Leikoupo source rocks, which indicates that the gas was sourced from both of them, and the deep faults in front of the Longmenshan Mountains provide favorable conditions for gas migration and accumulation from the source rocks. Meanwhile, the gases from well CK1 in the Xinchang tectonic zone display trace to moderate H₂S content, low δ¹³C₂ value (-33.2‰), partial reversal of alkane carbon isotopic series and a light δD₁ value (-147‰), consistent with oil-type gas. The thermal evolution degree reflected by natural gas compositions and carbon isotopes is similar to that of Leikoupo source rocks, which indicates that the gases were mainly from the interior source rocks of the Leikoupo Formation.

Influence of reservoir wettability changes on oil-bearing features during tight oil accumulation: A case study of Jurassic tight oils in Sichuan Basin

Gong Yanjie, Liu Shaobo, Liu Keyu, Jiang Lin, Yuan Xuanjun, Tao Shizhen

2015, 37(4): 423-429. doi: 10.11781/sysydz201504423

Abstract(1438) PDF-CN(1115)

Abstract:
A physical simulation of tight oil microcosmic filling was carried out with core samples from the Jurassic tight oil reservoirs in the central Sichuan Basin. A sandstone thin section model (2.5 cm×2.5 cm×0.6 mm) was adopted. Oil for the experiment was filled through a chute, and the pressure gradually increased until oil instead of water flowed out of each outlet end. Percolation characteristics were observed and oil saturation was calculated. Experiment results showed that the sum of irreducible water saturation before filling plus oil saturation after filling was more than 100%. Reservoir wettability changed from water wet to oil wet after filling, so the final oil saturation degree is higher than the displaced moveable water saturation according to magnetic resonance analyses. The change of reservoir wettability during tight oil migration and accumulation counteracted the inhibition function of irreducible water saturation of a tight oil reservoir on the saturation of tight oil, and was favorable for tight oil migration and accumulation, which explained the high oil saturation of tight oil reservoirs.

Tectonic effects and hydrocarbon preservation conditions in Upper Paleozoic, lower Yangtze region

Peng Jinning, Zhang Min, Liu Guangxiang, Lü Junxiang

2015, 37(4): 430-438. doi: 10.11781/sysydz201504430

Abstract(962) PDF-CN(1074)

Abstract:
The tectonic deformations during the Mesozoic and Cenozoic influenced the marine strata and the overlying formations in the lower Yangtze region. The tectonic evolution history, uplift and denudation, fault activity, magmatic activity, hydrogeological condition and cap rock effectiveness of the study area were studied to evaluate the basin scale preservation conditions for oil and gas in the Upper Paleozoic. (1) The preservation conditions for oil and gas in the Upper Paleozoic vary in the lower Yangtze region, generally featured by "belts from north to south, and blocks from east to west". (2) The hydrocarbon preservation conditions were categorized to three types. Jurong-Huangqiao and the central and northern Haian Sag are most favorable for hydrocarbon preservation, judged as class Ⅰ. The North Jiangsu Basin (including Dongtai-Dafeng, Sheyang, Baoying-southern Jinhu, Jiangyan-Haian) and the southern Jiangsu and Anhui region (including Wuwei, Wangjiang-Qianshan, Jurong-Changzhou) are also favorable for hydrocarbon preservation, judged as class Ⅱ. The other areas in the lower Yangtze region have poor preservation conditions, and are judged as class Ⅲ.

Inorganic carbon dioxide gas reservoir formation in Changling Fault Depression, Songliao Basin

Li Kuang, Wang Guoshou, Zhou Zhuoming

2015, 37(4): 439-444. doi: 10.11781/sysydz201504439

Abstract(1275) PDF-CN(1058)

Abstract:
With the development of deep gas exploration, some huge, enriched zones of CO₂ have been found in the Changling Fault Depression of the Songliao Basin. The origin of the CO₂ was analyzed for carbon isotope values of and the ³He/⁴He ratio was determined. The CO₂ gas in the Changshen2, 4, 6 well blocks and the Songnan gas field is mainly inorganic gas sourced from the mantle, while that in the Dongling gas field is organic gas. The type was controlled by the distribution of deep fractures in the fault depression. The low-speed and high-conductivity magma chambers resulted from crustal thinning during mantle uplift, the "mesh structure" tectonic detachment belt in the deep Changling Fault Depression and the deep and extensive faults on the basement are the advantageous conditions for the formation of inorganic CO₂ reservoirs.

Characteristics of clastic rock reservoirs in Jiufotang Formation, Zhangwu Depression, Songliao Basin

Hong Xue, Zhou Zhuoming, Liu Fuchun

2015, 37(4): 445-451. doi: 10.11781/sysydz201504445

Abstract(1025) PDF-CN(1242)

Abstract:
The diagenetic effect, porosity and its influence on physical properties of clastic reservoirs in the Jiufotang Formation in the Zhangwu Depression were analyzed by means of core observation, ordinary and casting thin section microscopic identification, SEM and X-ray diffraction. Compaction, cementation and erosion effects are common in the Jiufotang Formation, and are mainly in stage A of the middle diagenetic phase. The diagenetic process of clay minerals was described as clay rim, compaction, early dissolution, chlorite, illite, secondary quartz overgrowth, micro quartz, sodium feldspar, calcite and late dissolution. Both primary and secondary pores were found. The secondary pores include intergranular dissolution pores, giant pores, intragranular dissolution pores, mold pores and fracture pores. A set of fan delta front sediments provided reservoirs. Rock type, clay content, diagenetic effect and sedimentary micro-facies influenced the distribution of high-quality reservoirs.

Identification and prediction of source rocks in Carboniferous volcanic systems in Malang Sag, Santanghu Basin

Liu Bo, Jia Mengcheng, Huang Zhilong, Chen Xuan, Shen Ying, Wu Hongzhu

2015, 37(4): 452-459. doi: 10.11781/sysydz201504452

Abstract(1086) PDF-CN(961)

Abstract:
The formation of volcanic reservoirs in the Malang Sag, the Santanghu Basin is obviously controlled by the distribution of hydrocarbon source rocks. As a result, the identification and prediction of source rocks in the volcanic systems are significant for petroleum exploration. Some core samples have been collected from the study area to calibrate the logging response of source rocks. The distribution of source rocks in different formations of Carboniferous is predicted through mathematical modeling based on the comparison between geologic background and actual logging data, and combined with the symbiotic relationship between source rocks and volcanic rocks. The occurrence of source rocks in the volcanic systems can be categorized into two types, and volcanic rocks coexist with source rocks in four ways, showed by distinctive logging-seismic responses. The contact relationships between source rocks and volcanic rocks in the Haerjiawu and Kalagang formations are quite different, referring to two occurrence types which should be studied with different mathematical models. The Kalagang source rocks are separate and limited in space formed in the normal sedimentation not belonging to the onshore volcanic system. The Haerjiawu source rocks are widespread, forming multiple thickness centers between volcanic vents.

Reservoir characteristics and influencing factors of Weizhou Formation in eastern Maichen Sag, Beibuwan Basin: A case study of reservoir XW6

Chen Ping, Ma Yingjun, Shi Yan, Cheng Wei

2015, 37(4): 460-465. doi: 10.11781/sysydz201504460

Abstract(1099) PDF-CN(1129)

Abstract:
The lithologic characteristics, physical properties, pore structure and their controlling factors of the XW6 reservoir in the Weizhou Formation in the eastern Maichen Sag were studied based on thin section observations, scanning electron microscopy and X-ray diffraction analysis. The physical propertiesof the Weizhou Formation aregenerally poor with the second member featuring fine grain size, medium-poor sorting, medium porosity, medium-low permeability and medium-narrow throat diameters. The third member has coarse grain size, poor sorting, ultra-low porosity, super-low permeability and microthroat diameters, indicating less favorable physical properties.The controlling factors for physical propertieswere summarized as follows. Compaction made the physical propertiesof the reservoir become worse. Hydrocarbon filling was beneficial for the generation of dissolved pores and the preservation of porosity and permeability. Sedimentary micro-facies and rock type played a very important role in reservoir physical properties.

Genesis and sources of natural gas in eastern Qiongdongnan Basin, South China Sea

Zhang Yingzhao, Fan Caiwei, Xu Xinde, Yuan Bing

2015, 37(4): 466-472. doi: 10.11781/sysydz201504466

Abstract(1471) PDF-CN(1247)

Abstract:
The genesis and sources of natural gas in the Songdong and Baodao sags in the eastern Qiongdongnan Basin were analyzed through gas geochemistry and pool-forming research methods based on sample tests and seismic data. The natural gas in the study area is mainly the oil type. In the BF13 and SF24 regions on the northern slope of the Songdong Sag, mature natural gas of the oil type was found in the Miocene. In the BF19-2-3 region in the fault belt no.2 in the northern Baodao Sag, high-maturity and over-mature natural gas of the oil type (sometimes mixed with coal gas) was found in the Upper Oligocene Lingshui Formation. The findings differed from former reports about the coal-type gas in the Yinggehai and Qiongdongnan basins. The discovered oil type natural gas mainly was sourced from lacustrine deposits in the Eocene, and partially from the coal formations in the Yacheng Formation. It was deduced that there was another set of important gas source rocks besides the coal formations in the Yacheng Formation. The northwestern slope of the Songdong Sag and the fault belt no. 2 in the northern Baodao Sag are important exploration targets for natural gas.

Distribution features and exploration potential of oil and gas in a deepwater area of the Gulf of Mexico Basin

Han Yu, Huang Juan, Zhao Wen

2015, 37(4): 473-478. doi: 10.11781/sysydz201504473

Abstract(1426) PDF-CN(1482)

Abstract:
The hydrocarbon exploration conditions and geologic features of the Gulf of Mexico Basin were studied, and the formation, evolution and distribution of salt deposits which were closely related to the reservoirs were analyzed. From the Oxfordian Stage of the Upper Jurassic to the Pleistocene Series of the Quaternary, four sets of excellent hydrocarbon source rocks and various favorable reservoirs developed. Effective sealing formations were widespread in the Cenozoic. Faults provided pathways for hydrocarbon migration. Structural and stratigraphic traps were common. All these contributed to the generation and preservation of hydrocarbon. Thick salt deposits were widespread in the Middle Jurassic of the basin, which had a close relationship with giant oil and gas pools. Major discoveries have been made in both pre-salt and post-salt formations. As petroleum exploration theory and technique advanced, the pre-salt formations in the deepwater area of the basin attracted more attention and showed good potential.

Geological characteristics and exploration potential of Karoo clastic play, Ogaden Basin, Ethiopia

Wang Jianjun, Li Haowu, Wang Qing, Hu Xiangyu, Zhou Chao, Zhao Xu

2015, 37(4): 479-486. doi: 10.11781/sysydz201504479

Abstract(1424) PDF-CN(1361)

Abstract:
The Karoo clastic play is the most important gas play in the Ogaden Basin. The Bokh mudstones and the Calub and Adigrat sandstones worked as source rocks and reservoirs. Various traps developed in the Karoo clastic play, including faulted blocks, low-amplitude anticlines, lithologic pinchouts, channel sands and lens-shaped sand bodies. The distribution of regional paleo highs controlled the planar accumulation of hydrocarbon while trap formation timing determined the effectiveness of hydrocarbon charging. The traps which formed before the Late Cretaceous should be most efficient, for the Bokh source rocks had entered the gas window at that time. But in the following history, uplift took place in most parts of the Ogaden Basin, and the maturity of source rocks changed little. The Adigrat Formation has coarse sandstones in the northern basin and fine sandstones in the Bodle deep. The lower Adigrat Formation has better physical properties than the upper section. Structural traps are dominant in the lower part, while lithologic traps develop in the upper part. For the Bokh source rocks lay above the Calub reservoir, lateral migration was important for hydrocarbon accumulation. Intra-sag paleo highs are the most favorable, and the pinch outs in the basin slope also have a good potential. The Calub paleo high is a realistic exploration target since it is surrounded by the Bokh source rocks, where the Calub and Adigrat reservoirs were well developed. A widespread fracture system and various structural orientations also contribute to hydrocarbon migration and accumulation.

Oil generation abilities of chemically bound organic matter in different types of organic clay complexes

Yang Yan, Lei Tianzhu, Xing Lantian, Cai Jingong, Wu Yingqin, Si Guicai

2015, 37(4): 487-493. doi: 10.11781/sysydz201504487

Abstract(1413) PDF-CN(993)

Abstract:
A series of high temperature and high pressure thermal simulation experiments were carried out to compare the oil generation ability of chemically bound organic matter in montmorillonite organic clay and illite organic clay. Both types of c chemically bound organic matter had the same ability to translate into crude oil, and it was the amount of organic matter that controlled the amount of crude oil. Chemically bound organic matter in organic clay would contribute to immature oil; however, most organic matter contributed to mature crude oil. The chemically bound organic matter in montmorillonite organic clay had a greater ability to sustain oil generation than that in illite organic clay. Both types of chemically bound organic matter easily generated non-hydrocarbons which contained heteroatoms such as nitrogen, oxygen and sulfur. The chemically bound organic matter in montmoril-lonite organic clay generated non-hydrocarbon more easily. Therefore, the importance of organic matter quantity rather than mineral types should be emphasized when secondary hydrocarbon generation ability of argillaceous source rock is assessed. At the same time, it appears that crude oil quality would become poor.

Thermal and hydrocarbon generation history of Wufeng and Longmaxi shales in Pengshui area, eastern Sichuan Basin: A well PY1 case study

Xu Ershe, Li Zhiming, Yang Zhenheng

2015, 37(4): 494-499. doi: 10.11781/sysydz201504494

Abstract(1274) PDF-CN(1070)

Abstract:
The erosion thickness and paleogeothermal gradient of the Pengshui area in the eastern Sichuan Basin during various tectonic movements were established by means of vitrinite reflectance forward modeling and basin modeling software (BasinMod 1-D). Since the Late Paleozoic, the paleo heat flow and paleogeothermal gradient in the study area first increased and then decreased. The average paleogeothermal gradients from Silurian to the Middle Permian, from the Middle Permian to the Early Cretaceous, and from the end of the Early Cretaceous until now were 25–30 °C/km, 30–35 °C/km, and 20–25 °C/km, respectively. In the Caledonian and Indosinian periods, the erosion thickness of the study area was less than 500 m; while in the Yanshanian and Himalayan periods, it reached 4 300 m. The Wufeng and Longmaxi shales entered the threshold of oil generation in the Early Devonian, and reached peak generation from the Late Permian to the Late Triassic. Gas generation started in the Early Jurassic, and over-mature dry gas was generated in the Middle Jurassic. In the following Yanshan and Himalayan movements, the study area was uplifted and eroded, which raised challenges for the preservation of shale gas.

Geochemical characteristics and origin of natural gas from the Silurian in Jiannan gas field

Li Airong, Li Jinghong, Zhang Jingong, Song Lijun

2015, 37(4): 500-505. doi: 10.11781/sysydz201504500

Abstract(1069) PDF-CN(1061)

Abstract:
The geochemical characteristics and origin of the gas are studied according to gas composition and carbon isotope data from the Jiannan and adjacent areas and combined with regional hydrocarbon source rock data. Results show that the Silurian natural gas in the Jiannan gas field is dry. The content of non-hydrocarbon gas is low, and no H₂S exists. The carbon isotopes of n-alkanes are lower than -40‰, indicating a petroliferous gas origin from sapropel kerogens. The correlation between ln(C₁/C₂) and ln(C₂/C₃) shows that the present day Silurian gas mainly comes from the secondary cracking of crude oil. The analyses of geologic features indicate that the Silurian gas in the Jiannan gas field source from the carbonate shale in the Longmaxi Formation. The local reversal of alkane carbon isotopes can be explained by the mixing of late stage crude oil cracking gas and early stage kerogen degradation gas. The Longmaxi shale is mature and widespread in the middle and upper Yangtze region, indicating it is a good prospect for natural gas exploration in Silurian and Carboniferous.

Vitrinite reflectance correction of residues in organic matter pyrolysis simulation experiments

Que Yongquan, Zheng Lunju, Cheng Qiuquan, Qin Jianzhong, Qiu Nansheng

2015, 37(4): 506-511. doi: 10.11781/sysydz201504506

Abstract(932) PDF-CN(1141)

Abstract:
The relationship between the vitrinite reflectance of residual matter and hydrocarbon yield rate was established through pyrolysis experiments that simulated maturation of organic matter. R_o values calculated through pyrolysis simulation indicative of different maturities were compared to natural evolution profiles. Using these data, an Easy%R_omodel and the relationship between H/C ratio and R_o of kerogen were applied based on the multi-stage evolution of vitrinite reflectance. We put forward an Easy%R_o correction chart, a multi-stage H/C correction approach and the formula for the pyrolysis simulation experiment. The hydrocarbon generation model rebuilt using the corrected vitrinite reflectance was much closer to the natural evolution model.

Application of calcium-XANES technique in solid bitumen simulation experiments under temperature and pressure

Wei Zhihong, Luo Houyong, Liu Wenhui, Tenger, Wang Wangchun, Liang Mingliang, Su Long, Zhao Yidong

2015, 37(4): 512-517. doi: 10.11781/sysydz201504512

Abstract(996) PDF-CN(1111)

Abstract:
The Lower Cambrian solid bitumen, with high organic content, high hydrogen index and low asphaltene maturity, was collected from the Kuangshanliang area in the northwestern Sichuan Basin to study the evolution of calcium speciation during TSR and pyrolysis of solid bitumen.. The generation and expulsion simulation experiments were carried out in a high temperature and pressure simulator, and the calcium speciation was determined using a direct, non-destructive synchrotron-based calcium K-edge X-ray Absorption Near Edge Structure (XANES). Calcium carbonate was the major calcium compound in the asphalt pyrolysis simulation experiments (series 1). However, in the asphalt TSR simulation experiment (series 2), with the increases of temperature and pressure, the yield of H₂S and sulfate increased, indicating that both oxidation and reduction reactions occurred. The generation and enrichment of calcium sulfate in the simulation experiments of series 2 indicated that the acidic fluid from the TSR process could produce significant dissolution in dolomite reservoirs.

Causes and countermeasures for low liquid production in low-permeability reservoirs in Shengli region

Zhang Shoupeng, Teng Jianbin, Yin Yumei, Han Yiyun

2015, 37(4): 518-524. doi: 10.11781/sysydz201504518

Abstract(945) PDF-CN(1147)

Abstract:
Majordiscoveries have been made in the tight sandstone and strongly-cemented carbonate reservoirs in the deep formations of the Shengli region in the recent years. However, provenreserves have failed to increasesince the productionratefor liquids is low in a singe well. Oil-bearing core samples were collected from the wells with low permeability and low productionrate, and were tested to find out the causes for that low liquid productionrate. The complicated lithologic characteristics of reservoirs, crude oil properties and technical supporting measures were correlated with liquid shortage. Some internal and external factors for low liquid productionrate were identified. Low flow amountsresultingfrom the tight rock structure, an unclear oil/water relationship resultingfrom rock heterogeneity, various sensitivityresultingfrom clay variety, discontinuous output of crude oil resulting from low oil saturation, and oil flow deviationresultingfrom heavy oil were regarded as the internal causes. Clay particles in pore throats during fracturing and deposits from the reaction between acid frac-fluid and the reservoir made permeability become worse, which were regarded as the external causes. For different problems, the improvement measures for some single well layerswere formulated and producedgood results.

Shale preparation using Ar-ion milling

Wang Liang, Zhang Xiongdong, Cao Haihong

2015, 37(4): 525-529. doi: 10.11781/sysydz201504525

Abstract(1256) PDF-CN(918)

Abstract:
There are many micropores in shale, and the micropore structures can be exposed by Ar-ion milling technology. An Ar-ion beam was applied to treat a cross-section of shale with variable acceleration voltage, milling time, incidence angle and rotation speed of the sample holder. The milling effects were observed with a scanning electron microscope (SEM). The results show that appropriately lower voltage makes a smoother milling surface, and there is an optimal milling time. Meanwhile, a higher incidence angle and lower rotation speed of the holder can improve the milling effects.

Parameter definition in resource calculation of a trap: A fault block example

Yang Shuang, Yan Xiangbin, Cai Lixue, Liu Zhipeng, Huang Xiaoxuan

2015, 37(4): 530-534. doi: 10.11781/sysydz201504530

Abstract(1337) PDF-CN(1307)

Abstract:
In the early period of petroleum exploration, high value parameters were usually applied in resource calculation due to the limitation of data or knowledge. As a result, trapped resources were overestimated, which impacted exploration strategy. The key factors influencing the main parameters for resource calculation were analyzed in this paper to make estimation more realistic. Central limit theorem, probability distribution function and some other related theories were applied. Parameters were combined and multiplied under different situations to obtain multiple sets of parameters. A straight line regression of the least squares derived on a log-log plot finally determined rational parameters for calculating resources.

Fan Ming, Yu Lingjie

2015, 37(4): 535-535.

Abstract(540) PDF-CN(1042)

Abstract:

2015 Vol. 37, No. 4

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