• Journal of the Korean earth science society
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• v.32 no.6
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• pp.665-673
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• 2011

In order to estimate the hydrocarbon reserves, the porosity of the reservoir must be determined. The porosity of the area without a well is generally calculated by extrapolating the porosity logs measured at wells. However, if not only well logs but also seismic data exist on the same site, the more accurate pseudo porosity log can be obtained through artificial neural network technique by extracting the relations between the seismic data and well logs at the site. In this study, we have developed a module which creates pseudo porosity logs by using the polynomial neural network method. In order to obtain more accurate pseudo porosity logs, we selected the seismic attributes which have high correlation values in the correlation analysis between the seismic attributes and the porosity logs. Through the training procedure between selected seismic attributes and well logs, our module produces the correlation weights which can be used to generate the pseudo porosity log in the well free area. To verify the reliability and the applicability of the developed module, we have applied the module to the field data acquired from F3 Block in the North Sea and compared the results to those from the probabilistic neural network method in a commercial program. We could confirm the reliability of our module because both results showed similar trend. Moreover, since the pseudo porosity logs from polynomial neural network method are closer to the true porosity logs at the wells than those from probabilistic method, we concluded that the polynomial neural network method is effective for the data sets with insufficient wells such as F3 Block in the North Sea.

• Geophysics and Geophysical Exploration
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• v.17 no.4
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• pp.187-201
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• 2014

Compared with the separated inversion of electromagnetic (EM) and seismic data, a joint inversion using both EM and seismic data reduces the uncertainty and gives the opportunity to use the advantage of each data. Seismic fullwaveform inversion allows velocity information with high resolution in complicated subsurface. However, it is an indirect survey which finds the structure containing oil and gas. On the other hand, marine controlled-source EM (mCSEM) inversion can directly indicate the oil and gas using different EM properties of hydrocarbon with marine sediments and cap rocks whereas it has poor resolution than seismic method. In this paper, we have developed a joint EM inversion algorithm using a cross-gradient technique. P-wave velocity structure obtained by full-waveform inversion using plane wave encoding is used as structure constraints to calculate the cross-gradient term in the joint inversion. When the jointinversion algorithm is applied to the synthetic data which are simulated for subsea reservoir exploration, images have been significantly improved over those obtained from separate EM inversion. The results indicate that the developed joint inversion scheme can be applied for detecting reservoir and calculating the accurate oil and gas reserves.

• Geophysics and Geophysical Exploration
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• v.18 no.3
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• pp.125-132
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• 2015

The water saturation ($S_w$), which is very important to estimate hydrocarbon reserves in the reservoir, has been determined from resistivity index (RI) by using the Archie's formula. However, in many cases, it has been reported that n is not constant for a given formation and it could be varied with water saturation. In addition, it frequently happens that the line obtained by linear regression analysis on log-log scale does not pass through the origin. In order to overcome these drawbacks, we suggested a modified Archie's formula, which can handle almost all the RI vs. $S_w$ cross-plots whether the trend is straight or curved and whether it passes through the origin or not. We also demonstrated that how to determine conductivity exponent ${\mu}$, critical water saturation $S_c$, and saturation distribution factor b in the laboratory to use the modified Archie's formula. Since the modified Archie's formula takes into account pore structure, pore water distribution, and wettability of reservoir such as clean sandstone and carbonate rocks, it might improve field applicability.

• Journal of the Geological Society of Korea
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• v.54 no.6
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• pp.641-656
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• 2018

Although an amount of hydrocarbon has been discovered in the West Korea Bay Basin (WKBB), located in the North Korean offshore area, geophysical investigations associated with these hydrocarbon reservoirs are not permitted because of the current geopolitical situation. Interpretation of satellite derived potential field data can be alternatively used to image three-dimensional (3D) density distribution in the sedimentary basin associated with hydrocarbon deposits. We interpreted the TRIDENT satellite-derived gravity field data to provide detailed insights into the spatial distribution of sedimentary density structures in the WKBB. We used 3D forward density modeling for the interpretation that incorporated constraints from existing geological and geophysical information. The gravity data interpretation and 3D forward modeling showed that there are two modeled areas in the central subbasin that are characterized by very low density structures, with a maximum density of about $2,000kg/m^3$, indicating some type of hydrocarbon reservoir. One of the anticipated hydrocarbon reservoirs is located in the southern part of the central subbasin with a volume of about $250km^3$ at a depth of about 3,000 m in the Cretaceous/Jurassic layer. The other hydrocarbon reservoir should exist in the northern part of the central subbasin, with an average volume of about $300km^3$ at a depth of about 2,500 m. A comparison between the TRIDENT derived gravity field and the ship-based gravity field measured in 1980s shows us that our results are highly reliable and there is a very high probability to detect another low-density layer existings in the northwestern part of the central subbasin.

• The Korean Journal of Petroleum Geology
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• v.5 no.1_2 s.6
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• pp.1-8
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• 1997

Seismic stratigraphic analysis of the high resolution profiles obtained from the southeastern shelf of Korea divided the deposits into 4 sequences; 1) sequence D, 2) sequence C, 3) sequence B and 4) sequence A (Holocene sediments). Sequence D was deposited in shallow-water environment at west of the Yangsan Fault as the basin subsided. On the other hand, the eastern part was formed at the slope front. Landward part of the slope-front fill sediments were eroded and redeposited nearby slope due to the syndepositional tilting of the basin. This tilting probably resulted from the continuous closing of the Ulleung Basin. Sequence C is made of stacked successions of the lowstand fluvial sediments, transgressive sediments and marine highstand sediments derived from the paleo-river in the western part of the Yangsan Fault. Sequence C in the eastern part of the Yanshan Fault was formed at the shelf break. Progradation of the lowstand sediments resulted in broadening of the shelf. Sequence C in the eastern part was also tilted but the tilting was weaker than in Sequence D. During the formation of sequence B the tilting stopped and the point source instead of the line source started in both sides of the Yangsan Fault. Sequence B was composed of the highstand systems tract partially preserved around the Yokji island, lowstand systems tract mainly preserved in the Korea Trough and transgressive systems tract. After the stop of the tilting, the force of compression due to the closing of the Ulleung Basin may be released by the strike-slip faults instead of tilting.

• Economic and Environmental Geology
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• v.44 no.1
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• pp.21-35
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• 2011

Inorganic and organic geochemical characteristics of Devonian bitumen carbonates in Alberta were studied using two drilling cores, Saleski 03-34-88-20w4 and Saleski 08-01-88-20w4, taken from the Core Research Center of Canada. The results of elements analyses showed high Total Inorganic Carbon, low Total Nitrogen and Total Sulfur, and Rock-Eval pyrolysis showed double $CO_2$ peaks in the oxidation part. These mean that the Devonian bitumen carbonates are mainly composed of dolomite formed by diagenesis, and its crystal texture is dominantly subhedral to anhedral but often euhedral. Bitumen contents were 3.6~19.0% in Saleski 3-34-88-20w4 and 5.0~16.4% in Saleski 08-01-88-20w4, respectively. As samples color become dark, bitumen and Total Organic Carbon contents are generally increasing in two cores. The results of biomarker analyses showed that the contents of resins and asphaltenes were 5~28% higher than those of saturated hydrocarbon, interring that the bitumen has been heavily biodegradated. According to the results of carbon isotope analyses in each component of bitumen, asphaltenes had highest values and the others had constant values. However, their values were varied in the range of normal crude oil (-18~-30‰).

• 한국석유지질학회:학술대회논문집
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• autumn
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• pp.28-46
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• 2001

Natural gas is a mixture of hydrocarbon gases and impurities such as nitrogen, hydrogen sulfide, and carbon dioxide and a clean energy producing no pollution materials for combustion. Currently, the demand of the natural gas is rapidly increasing due to worldwide environmental problems. According to Hubbert's study in the past, the natural gas was predicted as rapidly depleted resources, and then the results led to high gas price and limitation of usage during 1980s. Afterward, the study of natural gas resources based on geology identified the additional natural gas resources that were not considered in Hubbert's study. They are unconventional gas, additional resources in the existed reservoirs, and natural gas in deep subsurface areas. Such additional resouces made the future of natural gas bright and pormised low and stable gas price in the future. Deep natural gas is defined as the gas existing at or below 15,000ft$(4,752{\cal}m)$ in depth from the surface. According to the study from the U.S. Geological Survey(USGS) in 1995, 1,412 TCF of technically recoverable natural gas was remained to be discovered or developed in the onshore of United States. A significant part of that resource base, 114 TCF, exists at deep sedimentary basins, and it shows wide distribution with various geological environments. In 1995, the deep gas contributed to $6.7\% of total supply amount of natural gas in the United States and is expected to be $18.7\% by 201.5. However, the development of the deep gas is a high risky business due to expensive investment and high portion of dry holes, although it is developed. Thus, for developing the deep gas economically, it is necessary to overcome many technical challenges. In this paper, for increasing success rate of the deep gas, 1) geologic and compositional characteristics, and production cost have been analyzed according to depth, 2) technical problems related to deep gas production have been summarized, and 3) finally future study areas for increasing application of the deep gas have been suggested. For reference, this paper was written based on the study results from USGS and Gas Research Institute(GRI), for the United States is doing the most active R&D in the deep gas area, and thus, has many reliable data.