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4 CH of CH gas transfer from ground to atmosphere were studied at four representative sectors in the Yakela FRQGHQVHGJDV7¿HOGLQWKH DULPIDXOW7KHVHD%DVLQ;LQMLDQJ&KLQDUH WKHRLO±JDVLQWHUIDFHVHFWRU sector, 3) oil–water interface sector, 4) an external area. Variation in CH LQVRLOJDVSUR¿OHVVKRZHGWKDW CH microseepage resulted from the migration of subsurface hydrocarbon from deep-buried reservoirs to the earth’s surface. It was found that CH from deep-buried reservoirs could migrate upwards to the surface through faults, fissures and permeable rocks, during which some CH was oxidized and the unoxidized methane remained in the soil or was emitted into the atmosphere. The lowest level of CH at WKHVRLOJDVSUR¿OHZDVIRXQGDWWKH&+ gas-phase equilibrium point at which the CH migration upwards 4 4 from deep-buried reservoirs and the CH GLIIXVLRQGRZQZDUGVIURPWKHDWPRVSKHUHPHW7KHį C 4 CH and ethane, propane in soil gas exhibited thermogenic characteristics, suggesting the occurrence of CH microseepage from deep-buried reservoirs. A linear correlation analysis between CH concentrations in soil gas and temperature, moisture, pH, Eh, Ec and particle size of soil indicated that both soil Eh and soil temperature could affect CH FRQFHQWUDWLRQLQVRLOJDVZKLOHVRLOS+FRXOGLQGLUHFWO\LQÀXHQFHVRLO methanotrophic oxidation via impacting soil Eh. Soil gas, CH concentration, carbon isotope, microseepage, oil reservoir Key words: source for CH emissions after wetlands, while geological 1 Introduction seepage has been recognized as a new category in the During the past two decades, geologic CH emission has 4 81(&((0(3DVN7)RUFH(PLVVLRQ,QYHQWRU\*XLGHERRN always been considered as a negligible contributor to CH 4 (WLRSH(WLRSHHWDO(WLRSHDQG&LFFLROL concentration in the atmosphere. According to the Second Etiope and Klusman, 2010). and Third IPCC Assessment Report (Lelieveld et al, 1998), During the 1920s and 1930s, studies suggested that a methane hydrate was found to be a minor source of natural close correlation existed between concentration anomalies geologic methane, only accounting for about 0.9% of the total of hydrocarbon gases near the surface of the earth and deep- atmospheric methane budget. However, recent studies have buried oil and gas reservoirs. Soil gas methane has been an shown that natural geologic emissions of CH could play an 4 important indicator of deep-buried reservoirs (Laubmeyer, important role in the atmospheric methane budget, mainly .OXVPDQ+XQW$EUDPV ,WZDV due to CH emissions from petroleum seepage through faults, 4 not until recently that numerous field surveys have been ¿VVXUHVDQGSHUPHDEOHURFNVPXGYROFDQLVPPDULQHVHHSV conducted on CH ÀX[IURPSHWUROHXPEHDULQJVHGLPHQWDU\ DQGJHRWKHUPDOPDQLIHVWDWLRQV0HDQZKLOHWKHVHJHRORJLF basins by researchers in the USA, Europe (Italy, Germany, CH emissions may represent an important component of the 4 *UHHFH DQG$VLD$]HUEDLMDQ&KLQD .OXVPDQDQG-DNHO ‘missing’ source of fossil CH (radiocarbon-free), as recently 4 7KLHOHPDQQHWDO(WLRSH(WLRSH recognized in the atmospheric budget (Etiope et al, 2008). DQGDQJ0LONRYHW<DODQJ7HWDO In the Fourth Assessment Report of IPCC, geological CH 4 (WLRSHDQG&LFFLROL(WLRSHDQG.OXVPDQ sources have been considered as the second highest natural 2010). Now, it has become an international research focus that microseepage of hydrocarbon gas throughout the area related to petroleum-bearing sedimentary basins is an *Corresponding author. email: Tang_jhjh@163.com important source of atmospheric CH 0LFURVHHSDJHFDSDFLW\ Received October 12, 2012 RIK\GURFDUERQJDVIURPGHHSEXULHGUHVHUYRLUVLVLQÀXHQFHG 184 Pet.Sci.(2013)10:183-189 by the complexity of geological conditions, instability and relation to the subsurface geo-structural features and gas-oil regionality of hydrocarbon gas distribution, difference in setting. The CH ÀX[LVKLJKHUDWIDXOWVDQGDUHDVDVVRFLDWHG concentration and pressure of hydrocarbon gas in reservoirs, with gas-oil interfaces, and lower over oil-water interfaces which is more obvious at faults or broken caprocks. The (where the gas pressure is lower) and outside the petroleum leakages can lead to particular traces underground and in the DQJHWDO ¿HOGERXQGDU\7 surface, such as anomalies of hydrocarbon concentration of As a follow-up work of our previous CH flux surveys soil gas or adsorbed gas in the surface. CH which failed to conducted in the Yakela condensed gas field (Fig. 1), this be oxidized or decomposed may eventually be released into study aims to further identify the “extra-soil” CH sources the atmosphere (Klusman, 1993). Our previous CH flux and the potentials of CH gas transfer from ground to the 4 4 surveys, conducted at different geologic sectors in the Yakela atmosphere by analyzing soil CH FRQFHQWUDWLRQDQGį C at 4 CH condensed gas field in the Tarim Basin, Northwest China, VRLOJDVSUR¿OHVDQGE\FRPSDULQJVRLO&+ in soil gas with have shown a spatial variability of microseepage flux in our previous CH ÀX[HVVXUYH\GDWD Yishen 4 Wen1 Yishen2 Misibulake Yishen6 Yangxia coal mine Yinan4 Tuzi1 Yixi1 Kezi1 Yinan2 Kela3 Dian1 Yangxia Sag Kela201 Kela2 Dian2 Kela202 Yangxia zone Southern anticlinal zone Tiergen Luntai Kuche Dayoudusi Yakela Xinhe Donghetang Hongqi Santamu forest farm Yingmaili Halahatang Shaya Caohu pasture Tarim River China 1 2 3 4 5 6 8 9 10 11 Fig. 1 Sketch geological map showing distribution of the Kuche Depression and main exploratory wells and RLO¿HOGV/LDQJHWDO 5LYHU.XFKH'HSUHVVLRQERUGHUUDS7VWUXFWXUH%RXQGDU\RIRQVKRUH (continental) and marine facies areas, 5. Oil/gas well, 6. Oil sand outcrop, 7. Exploratory well, 8. Place name, 9. Study area, 10. Background area, 11. Second-order tectonic units The Yakela condensed gas field is a large high pressure 2 Geologic setting FRQGHQVHG¿HOGZKLFKLVORFDWHGWHFWRQLFDOO\LQWKH/XQWDL DNHODFRQGHQVHG7KH<JDV¿HOG)LJ OLHVLQWKH.XFKH Yakela faulted uplift zone of the eastern part of the Shaya Depression, northern Tarim Basin in the arid northwest of Upwarping in the northern Tarim Basin (Fig. 1). The zone China which is a distinctive oil accumulation area (Song et is a faulted block lying between the southern Luntai Fault al, 1998). This area is characterized by arid climate, high and the northern Yaha Fault. There are three types of buried evaporation and infiltration, strong salt-base reaction and KLOOFRQGHQVDWHUHVHUYRLUVLQWKH¿HOGQDPHO\ FRQGHQVDWH low land productivity, thereby resulting in limited biogenetic reservoirs trapped in an anticline structure in the Cretaceous production of CH near the earth surface. Therefore, the Kabushaliang Group, 2) lithological-structural composite Yakela condensed gas field is an ideal site for investigating FRQGHQVDWHUHVHUYRLUVLQWKHPLGGOHWRORZHU-XUDVVLF geologic CH emission behaviors. and 3) buried-hill type condensate reservoirs in the upper Northern anticlinal zone Qiulitake anticlinal zone Baicheng Sag Pet.Sci.(2013)10:183-189 185 -6 -6 -6 Proterozoic, upper Cambrian and lower Ordovician. All gas of 2.04×10 CH , 1.01×10 C H and 1.05×10 C H , 4 2 6 3 8 these oil/gas traps were formed from carbonate and clastic mixed with 99.999% pure He were used for making external rock types. The caprocks are mainly of mudstone lithology standard curves. The working condition was set as: stainless (mudstone, shaly siltstone, etc) formed in low sedimentation, VWHHOFROXPQPP±P ¿OOHGZLWKD;PROHFXODUVLHYH with evaporites. There are multi-set caprocks from Palaeozoic of 60/80 meshes, N (99.999%) as load gas with a flow of WR0HVR&DLQR]RLFZKLFKDUHGRPLQDWHGE\WKH-LGLNH 30 mL/min, at column temperature of 55 °C, FID detector )RUPDWLRQ.DSXVKDOLDQJ*URXSDQGORZHU-XUDVVLF&KHQ temperature of 200 °C, and CH measure error of 0.11%– et al, 2012). Based on the geologic and petroleum reservoir 0.25%. To ensure the comparability of data, all concentrations features, soil gas borehole drilling was undertaken during were converted to standard temperature and pressure a dry spring season in the following four areas: 1) oil-gas conditions (STP: 0 °C, 101.325 kPa). sector, 2) fault sector in correspondence with Luntai fault- The stable carbon isotope atmospheric CH were measured OLQNHGFURVVLQJWKHGHHSUHVHUYRLUV'HQJHWDO=KXHW by using an on-line CH extraction system as described al, 2012), 3) oil-water sector, 4) an external area, i.e., outside in detail by Tang et al (2006). The system was interfaced WKHQRUWKHUQJDVILHOGERXQGDULHV0HDQZKLOHLQRUGHUWR with a Thermo Quest GC/TC (Thermo Finnigan, Bremen, make a comparative study, an area was selected near the Germany) and an isotope ratio mass spectrometer (Thermo Taklamakan Desert for a control study. It is located about 110 4XHVW'HOWDSOXV7KHUPR;3)LQQLJDQ%UHPHQ*HUPDQ\ DNHODFRQGHQVHGJDV¿HOG<NLORPHWHUVVRXWKHDVWRIWKH The GC–pyrolysis interface (Precon) contains a combustion furnace and is connected to isotope-ratio mass spectrometer 3 Methodology ,506 ,VRWRSHYDOXHVDUHJLYHQLQWKHGQRWDWLRQUHODWLYHWR the internationally adopted VPDB standard. The minimum detectable concentration of CH ZDVQPRO/7KHį C 3.1 Field methods 4 values were determined with a precision of 0.4‰ (n=10). A portable copper probe with an interior diameter of 0.08 m was used for collecting soil gas. At each site, soil gas at 4 Results and discussion depths of 0.3, 0.6, 0.9, 1.2 and 1.5 m were collected for two continuous days at 8:30–12:30 a.m., 1:30–5:30 p.m., 6:30– 4.1 Variation characteristics of CH concentrations 10:30 p.m. and 0:00–4:00 a.m., respectively. However, at the in soil gas faults, soil gas samples were only collected during the former three time periods. Two samples of soil gas were collected In the Yakela condensed gas field, thick sand strata are DWHDFKGHSWKGXULQJWKHVDPHPHDQWLPHSHULRG0HDQZKLOH widely distributed, predominantly consisting of light loam two air samples were also taken as soil gas samples (0 m at and sandy loam, while only a slight change in soil textures, the ground surface). which is mainly consisted of light brown fine sandy loam The detailed sampling procedure was as follows. The to light loam changing with depth into brown light loam or lower end of the probe was closed with a steel ball of sandy clay loam. There is only a little difference in thickness diameter 0.08 m in order to avoid the probe being blocked of soil layers among the four sites. Therefore, to a certain by soil when it was inserted into the ground. The probe was degree, the CH VRXUFHVFDQEHHDVLO\LGHQWL¿HGE\H[DPLQLQJ inserted into the ground with a sliding hammer and pulled the variation characteristics of CH concentrations at soil gas again upwards about 0.10 m to the required depth, so that SUR¿OHVDPRQJWKHIRXUVLWHV the steel ball seal opened letting the soil gas diffuse into Fig. 2 shows the variation in CH concentrations in the probe. The top end of the copper probe was closed with soil gas for different time periods at the four sites in the Shimadzu rubber mats. In order for the probe to be fully Yakela condensed gas field. It can be seen overall that CH sealed, tape was used to seal the junction between the copper concentrations increased significantly with an increase of probe and the rubber mat. Soil gas was extracted by inserting GHSWKLQVRLOJDVSUR¿OHVIRUHDFKWLPHSHULRGDWDOOWKHIRXU a syringe. Before the soil gas was collected, the air inside sites, similar to the results reported by Klusman et al (2000) the probe was purged to avoid contamination and after about in four semiarid sedimentary basins in the American state of 4-hour’s equilibration the soil gas was collected by extracting Colorado. The phenomena might suggest that there was CH it with a syringe. microseepage from deep-buried reservoirs. At 30 cm to 60 0HDQZKLOHDLUWHPSHUDWXUHDQGEDURPHWULFSUHVVXUHZDV cm depth, CH concentrations at soil gas profiles dropped monitored in order to check potential ‘false anomalies’ due slowly with increasing depth and reduced to a value less to atmospheric pumping. Soil properties such as temperature, than the atmospheric concentration in the afternoon at all the moisture, porosity, pH, Eh and salinity were also monitored in four sites. Similar phenomena were also observed at some concentration 4 other sites studied. The phenomenon above might indicate in soil gas. WKDWWKHVRLOKDVVXI¿FLHQWSHUPHDELOLW\DQGSRURVLW\WRDOORZ CH from the atmosphere to diffuse downward into the soil 3.2 Laboratory measurement gas. A part of the CH which had diffused downwards was Concentrations of CH , C H and C H in soil gases oxidized by free oxygen or methanotrophic bacteria in soil. 4 2 6 3 8 were analyzed by using an HP-5890 gas chromatograph Then CH concentrations of soil gas increased progressively equipped with a flame ionization detector (FID). Standard to concentrations above atmospheric concentration with an RUGHUWRDGGUHVVWKHLUSRWHQWLDOLQÀXHQFHRQ&+ 186 Pet.Sci.(2013)10:183-189 increase of depth at the 90 cm and deeper at all the four sites. from the atmosphere (Fig. 2). These increasing gradients were higher than sampling and In addition, Fig. 3 indicated that the CH concentration analytical error (0.11%–0.25%), especially at the faults. Thus at the same depth in the soil gas profile was obviously it can be seen that the lowest point of CH concentration at higher at the fault than that at the other three sites while the depth of 30 cm or 60 cm was just the CH equilibrium CH concentrations at the other three sites showed little 4 4 point of gas-phase formed by the gas migrating upwards from difference. CH concentrations at 90 cm depth were slightly the deep-buried reservoirs and the gas diffusing downwards higher than or close to those measured at 120 cm depth at the 8:30-12:30 13:30-17:30 3 3 CH concentration, mg/m CH concentration, mg/m 4 4 01 2 3 4 5 01 2 3 4 5 18:30-22:30 00:00-04:00 3 3 CH concentration, mg/m CH concentration, mg/m 4 4 01 2 3 4 5 0 123 45 Oil-gas sector Oil-water sector Fault sector External area Fig. 2 Variation of CH concentrations in soil gas in representative areas of the Yakela FRQGHQVHGJDV¿HOG1RWHV&+ concentration of atmosphere at 0 cm) fault, presumably due to CH microseepage arising from the FRQGHQVHGJDV¿HOGWKHH[LVWHQFHRIDD,,,VXEIDXOWQDPHG< existence of a 10-20 cm fine sandy layer at the fault. Thus would be able to result in a small amount of CH seepage to it can be concluded that light hydrocarbon gases, i.e. CH the surface from deep oil/gas traps. The phenomenon above DNHODFRQGHQVHGJDV¿HOGIURPGHHSEXULHGUHVHUYRLUV<LQWKH is consistent with those observed in our previous study (Tang could relatively easily migrate upwards to the earth’s surface et al, 2010), in which CH fluxes at the fault sector were along the fault. found to be higher than those at the other three sites in the concentrations at the depth of 90- DNHOD<FRQGHQVHGJDV¿HOGVXJJHVWLQJWKDW&+ from deep- 150 cm at the oil-gas sector were only slightly higher than buried reservoirs could migrate upwards to surface through those found at the oil-water sector and the external area. permeable rocks, fissures and faults, of which part was Although the external area is located outside the Yakela oxidized or decomposed during the migrating process. Depth, cm Depth, cm Depth, cm Depth, cm &+0RUHRYHUDYHUDJH Pet.Sci.(2013)10:183-189 187 In contrast, CH concentrations decreased gradually with C isotope ratio of methane in soil gas DQLQFUHDVHRIGHSWKLQWKHVRLOJDVSUR¿OHDWWKHFRQWUROVWXG\ -50 -45 -40 -35 -30 -25 -20 -15 -10 -5 0 area, indicating the possible methanotrophic oxidation of atmospheric CH diffusing downwards (Fig. 3). CH average concentration, mg/m 01 2 3 4 5 0 80 30 100 Oil-gas sector Oil-water sector Fault sector External area 150 13 DULDWLRQFKDUDFWHULVWLFVRI9į C in soil gas in representative areas Fig. 4 CH DNHODFRQGHQVHGJDV¿HOG1RWHVį<RIWKH C of atmosphere at 0 cm) CH Oil-gas sector Oil-water sector Fault sector Background area External area Fig. 3 Variation characteristics of CH average concentrations in soil an increase in depth, which was accompanied by a decrease gas in representative areas of the Yakela condensed gas field (Notes: CH of CH concentrations in soil gas to a value less than the concentration of atmosphere at 0 cm) atmospheric concentration (Fig. 3). The case above shows that CH from atmosphere diffused downwards into soil gas, 4.2 Variation of carbon isotope of CH in soil gas where the microbial processes of methanotrophic bacteria in With the development of isotope measurement techniques, soil preferentially consumes the lighter isotope while leaving 13 12 C and H isotope systematics ( C/ C, D/H) and radioactive the residual CH į0RUHRYHULVRWRSLFDOO\KHDYLHU C at the 4 CH carbon isotope ( C) have been widely applied for tracing depth from 90 cm to 150 cm became gradually heavier with the sinks/sources of atmospheric CH , for estimating 4 the increase of depth and fell into the range characterized as global or regional CH budgets and source strength, and 4 thermogenic CH , in concert with our previous petroleum for interpreting environmental mechanisms of production, JHRORJLFDO¿QGLQJVLQDNHODWKH<FRQGHQVHGJDV¿HOGDQJ7 transport and release of CH 5XVW6WHYHQVDQG 4 DQG/LX 0HDQZKLOHWKHSURFHVVHVDERYHZHUH (QJHONHPHLUDKOHQ:HWDO+LONHUWHWDO accompanied by an increase of CH concentrations in soil gas Rice et al, 2001). The origin of CH can be divided into two 4 to a value more than the atmospheric concentration. All these major categories, namely “bacterial” and “thermogenic” CH . 4 VXJJHVWHGWKDWWKHUHZDVDWKHUPRJHQLFVRXUFH6SHFL¿FDOO\ Thermogenic CH is generally, but not exclusively enriched 4 occurrence of C H and C H in soil gas further proved that 2 6 3 8 13 13 in C compared with bacterial CH DQGKDVDUDQJHRIį C 4 there was hydrocarbon microseepage from deep-buried extending roughly from -50‰ to -20‰. The term “bacterial DNHODFRQGHQVHGJDVUHVHUYRLUV¿HOGLQ <:KLWLFDUWKH CH ” is preferred over “biogenic” because the carbon in both 4 especially at the fault, while there were no C H and C H 2 6 3 8 bacterial and thermogenic natural gases was originally from detected at the background area studied (Table 1). biological material. Bacterial CH KDVDZLGHUDQJHRIį C, ,QÀXHQFLQJIDFWRUVRQ&+ concentrations in soil varying from -110‰ to -50‰. Petroleum geological studies gas in the Yakela condensed gas field have demonstrated that į C in deep natural gases is typical of pyrogenic gases, CH concentrations in soil gas have been reported to be CH ranging from -42‰ to -31‰ (Tang and Liu, 2002). greatly affected by temperature, moisture, particle size of soil DULDWLRQ9FKDUDFWHULVWLFVRIį C in soil gas at the four and seasonal changes, etc. A linear correlation analysis (Table CH VLWHVDUHVKRZHGLQ)LJ,WFDQEHVHHQWKDWWKHį C of 2) indicated that CH concentration of soil gas was negatively CH the soil gases taken from air at the surface (0 cm) ranged correlated with soil temperature and soil Eh at a significant from -44.2‰ to -45.8‰, which is close to the global OHYHORIĮ DWPRVSKHULFį C level (-47.3‰ to -46.2‰) (Stevens, Soil Eh is a measure of the oxidation-reduction status in CH \OHU7 ,WLVREYLRXVWKDWį C in soil gas VRLO0HWKDQRWURSKLFEDFWHULDDUHREOLJDWHDHURELFEDFWHULXP CH became gradually heavier with increasing depth (Fig. 4). The Higher soil Eh is helpful for the activities of methanotrophic increasing gradients were higher relative to sampling and bacteria. Therefore, CH migrating upwards from deep- 13 13 DQDO\WLFDOSUHFLVLRQWKHSUHFLVLRQRIį C LVÅ į C buried reservoirs is easily oxidized when soil Eh is high, CH CH 4 4 at the depth from 30 cm to 60 cm in the Yakela condensed leading to lower CH concentration in soil gas. Conversely, gas field, except at the fault became slightly heavier with when activity of methanotrophic bacteria is subdued, this Depth, cm Depth, cm 188 Pet.Sci.(2013)10:183-189 Table 1+\GURFDUERQFRPSRVLWLRQVLQVRLOJDVSUR¿OHVLQUHSUHVHQWDWLYH leads to higher CH concentration in the soil gas. The Eh of DNODFRQGHQVHGJDV¿HOG<VLWHVRIWKH soil in the Yakela condensed gas field ranged from 97.3 to 190.7, showing weakly reducing conditions, which favored Site Depth, cm CH C H C H C H C H nC H iC H 4 2 4 2 6 3 6 3 8 4 10 4 10 the preservation of CH migrating upwards from deep- 0 2.01 0.04 nd nd nd nd nd buried reservoirs. Relatively speaking, Eh (97.3–123.7) at 30 2.01 0.05 nd nd nd nd nd the fault sector was lower than that at the other three sectors (Eh: 126.5–160.3 at the oil-gas sector, 123–180 at the oil- 60 2.05 0.03 nd nd nd nd nd Oil-gas water sector, 135.9–190.7 at the external area, respectively), sector 90 2.28 0.1 0.03 nd nd 0.01 nd resulting in a higher CH concentration at the fault than at the 120 2.50 0.03 0.04 nd 0.02 nd nd other three sectors, which also verified that the fault was a 150 2.61 0.09 0.11 nd 0.07 0.03 nd good conduit for light hydrocarbons to migrate upwards from 0 1.86 nd nd nd nd nd nd deep-buried reservoirs. 30 1.90 nd nd nd nd nd nd Similarly, oxidizing activities of methanotrophic bacteria in soil are also affected by soil temperature. Higher 60 1.97 0.03 nd nd nd nd nd Oil-water temperature is advantageous for methanotrophic oxidation sector 90 2.16 nd nd nd nd nd nd in soil. Thereby a part of CH , migrating from the oil/gas 120 2.23 0.03 0.06 nd 0.01 nd nd reservoirs to the surface, was absorbed and oxidized by soil. 150 2.36 0.07 0.09 nd 0.06 0.02 nd ,QDGGLWLRQDEOH7VKRZVWKDWVRLOS+ZDVVLJQL¿FDQWO\ 0 2.11 0.07 nd nd nd nd nd DQGQHJDWLYHO\FRUUHODWHGWRVRLO(KĮ VXJJHVWLQJ that soil pH could indirectly influence soil methanotrophic 30 2.14 0.05 nd nd nd nd nd oxidation by affecting soil Eh. However, no obvious 60 2.62 0.11 0.03 nd nd nd nd Fault correlation was found between soil CH concentration and 90 3.25 0.1 0.05 nd 0.03 0.06 nd other soil factors such as moisture, salinity and porosity. 120 3.16 0.08 0.11 0.03 0.09 0.08 nd 150 3.91 0.17 0.19 0.03 0.11 0.07 nd 5 Conclusions 0 2.01 0.03 nd nd nd nd nd Variation in CH in soil-gas profiles showed that CH 4 4 30 1.97 nd nd nd nd nd nd microseepage was a quite common phenomenon in the 60 2.06 0.03 nd nd nd nd nd External DNHOD<FRQGHQVHGJDV¿HOG+\GURFDUERQJDVHVPHWKDQHLQ area 90 2.08 0.05 0.02 nd nd nd nd particular, were liable to migrate upwards by microseepage from the deep-buried reservoirs to the earth’s surface 120 2.24 nd nd nd nd nd nd through faults, fissures, micro-fracture networks and rock 150 2.33 0.06 0.03 nd 0.01 nd nd pore networks, during which some unoxidized CH was 0 1.82 nd nd nd nd nd nd preserved in soil gas or emitted into the atmosphere. Results 30 1.71 nd nd nd nd nd nd showed that CH microseepage was relatively easily emitted 60 1.64 nd nd nd nd nd nd DORQJWKHIDXOWDQGWKHį C , ethane and propane in CH Background 90 1.67 0.02 nd nd nd nd nd VRLOJDVH[KLELWHGWKHUPRJHQLFFKDUDFWHULVWLFV0RUHRYHU higher soil temperature and Eh could enhance the activities 120 1.59 0.03 nd nd nd nd nd of methanotrophic bacteria, while soil pH, via impacting 150 1.56 nd nd nd nd nd nd soil Eh, could indirectly influence soil methanotrophic oxidation, thereby resulting in a reduction in soil gas CH Notes: Concentrations are as ppmv, ‘nd’ indicates ‘not detected’ concentration. Correlation between CHDNHODFRQGHQVHGJDV¿HOGĮ < Table 2 CH concentration Temperature 0RLVWXUH pH Eh Ec Porosity CH concentration 1.000 Temperature -0.215* 1.000 0RLVWXUH -0.092 0.027 1.000 pH 0.207 -0.199 -0.604* 1.000 Eh -0.549* 0.239* 0.053 -0.443* 1.000 Ec -0.168 0.045 0.782* -0.512* 0.100 1.000 Porosity -0.062 -0.050 -0.334* 0.048 -0.131 -0.152 1.000 Number of samples N=88 6LJQL¿FDQWFRUUHODWLRQDWWKHOHYHORIĮ FRQFHQWUDWLRQLQVRLOJDVDQGHQYLURQPHQWDOIDFWRUVRIVRLOLQWKH Pet.Sci.(2013)10:183-189 189 QJ'/LD &KHQ-=KDQJ%HWDO7KH+\GURFDUERQ*HQHUDWLRQRI Acknowledgements Terrestrial Facies in the Kuche Depression, Tarim Basin. Petroleum Industry Press. 2004. 52 (in Chinese) This work was supported by the National Natural Science Ric e A L, Gotoh A A, Ajie H O, et al. High-precision continuous- Foundation of China (Grant No. 40973076 and 41072099). IORZPHDVXUHPHQWRIį &DQGį'RIDWPRVSKHULF&+ . 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Petroleum Science – Springer Journals
Published: May 18, 2013
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