IPTC 15351_noguchi

AbstractQuantitative evaluation of methane hydrate (MH) bearing turbidite reservoir in the eastern Nankai Trough, offshore Japan is conducted using a combination of 3-D seismic and well data. For constructing 3-D facies model, we have interpreted internal sand body and stacking patterns of the channels to discuss reservoir heterogeneities of the turbidite channels. Geobody using seismic volume rendering shows that the extracted body is distributed toward northeast to southwest directions in good agreement with the direction of the channel-filling sediments according to the seismic sequence stratigraphic analysis. Stacking patterns of channel facies are identified around the ß1 well. The identified channels exhibit low sinuosity channels consisting of various magnitudes of channel widths ranging from tens to several hundred meters. Orientation of these channels typically exhibits north-to-south and north-northeast-to-south-southwest directions, which are consistent with Paleo-flow current directions. Internal property of the stacking patterns of the channel sediments is examined using a seismic acoustic inversion analysis. The distribution patterns of the velocity between the BSR and the top of the MH-bearing sediments show that higher velocities are particularly identified along north-northeast direction, which coincides with the sediment supplies of the turbidite channels. Assuming a simple rock physics model, distribution of hydrate saturation is also correlated well with the facies distributions. This fact suggests that reservoir architecture of the MH-bearing turbidite channels is primary controlled by sedimentary conditions (i.e., depositional systems) of the turbidite channels.IntroductionThe eastern Nankai Trough, which is located offshore of central Japan, is considered an attractive potential resource of methane hydrates (MHs) and a candidate for the exploitation and production of MH test fields (Fujii et al., 2008, 2009; Yamamoto et al., 2009). Previous works conducted various studies of seismic, well logging, and coring operations such as “Nankai Trough” exploratory test well (which was acquired in 1999), a 2-D seismic survey in 2001 (2,802 km), 3-D seismic surveys in 2002 (the total area of three survey fields was 1,960 km 2), and a multiple well-drilling campaign in 2004 by the Ministry of Economy, Trade and Industry (METI). According to the results, MHs are developed in the pore spaces of an unconsolidated sandy sediment within the deep submarine-fan turbidite system (Nakamizu et al., 2004; Takahashi et al., 2004; Tsuji et al., 2004; Uchida et al., 2004). In some locations in the eastern Nankai Trough, MHs are selectively accumulated in the turbidit e formations; such zones are called “MH -concentrated zones”. These MH -concentrated zones are the best targets for recovering MHs for future exploitation and for the commercialization of MHs. Therefore, our primary target is the MH-concentrated zones to characterize reservoir potentials of MHs.In this paper, we focus on the submarine channel types of the MH-bearing sediments (ß MH-concentrated zone, hereafter ß site) in one of the MH-concentrated zones in the eastern Nankai Trough. In particular, we discuss quantitaive evaluation of facies distributiona and internal properties for characterizing the reservoir heterogeneities in the MH-bearing turbidite channels.Background of study around ß siteOur study area is located in the Tokai-Kumano forearc basins along the Nankai Trough, central Japan (Fig. 1). ß site is situated within the 3-D seismic survey area in Daini Atsumi. Depositional system in the eastern Nankai Trough area is submarine-fan turbidites consisting of Pleistocene Kakegawa and Ogasa Formations (Takano et al., 2008, 2009). MH concentrated zone corresponds to a trough-filled channels of turbidite system in Stage 3 (Noguchi et al., 2011). Noguchi et al. (2011) qualitatively interpreted reservoir architectures of the MH-bearing turbidite channels in the ß site by seismic and well IPTC 15351Quantitative characterization of methane hydrate reservoir in the eastern Nankai Trough, Japan Satoshi Noguchi, Toshiko Furukawa, Than Tin Aung, Nobutaka Oikawa, Japan Oil gas and Metals National Corporation, Schlumberger Oil Field Service Copyright 2011, International Petroleum Technology ConferenceThis paper was prepared for presentation at the International Petroleum Technology Conference held in Bangkok, Thailand, 15–17 November 2011. This paper was selected for presentation by an IPTC Programme Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the International Petroleum Technology Conference and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the International Petroleum Technology Conference, its officers, or members. Papers presented at IPTC are subject to publication review by Sponsor Society Committees of IPTC. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of the International Petroleum Technology Conference is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of where and by whom the paper was presented. Write Librarian, IPTC, P.O. Box 833836, Richardson, TX 75083-3836, U.S.A., fax +1-972-952-9435IPTC 15351 Quantitative characterization of methane hydrate reservoir in the eastern Nankai Trough, Japan Satoshi Noguchi, Toshiko Furukawa, Nobutaka Oikawa, Japan Oil gas and Metals National Corporation, Than Tin Aung, Schlumberger K. K. Copyright 2011, International Petroleum Technology Conference This paper was prepared for presentation at the International Petroleum Technology Conference held in Bangkok, Thailand, 15–17 November 2011. This paper was selected for presentation by an IPTC Programme Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the International Petroleum Technology Conference and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the International Petroleum Technology Conference, its officers, or members. Papers presented at IPTC are subject to publication review by Sponsor Society Committees of IPTC. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of the International Petroleum Technology Conference is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of where and by whom the paper was presented. Write Librarian, IPTC, P.O. Box 833836, Richardson, TX 75083-3836, U.S.A., fax +1-972-952-94352 IPTC 15351 data. According to the results, orientation of turbidite channels around ß site is coincident with the direction of sediment supply which was confirmed by seismic sequence stratigraphic analysis. They also suggested that distribution of the channels sediments is roughly correlated with the higher velocity intervals implying that the reservoir architecture of the channels is closely related to sedimentary conditions of the turbidite system.Based on the previous studies, we constructed workflow for characterizing the MH-bearing turbidite reservoirs. Figure 2 depicts workflow for constructing 3-D reservoir model. After constructing 3-D geological frame by geological horizons and faults, internal properties of the geological frame are quantitatively evaluated using both 3-D facies modeling and petrophysical modeling. In this study, we discussed reservoir heterogeneities in the turbidite channels taking into account for an extracting the sand body, an interpretation of the stacked channel patterns, and the internal properties of the channel sediments by using seismic data from around the ß1 well.Results and discussionsFacies distribution of the turbidite channels around ß1 wellOur model area is focused on 2 km x 2 km from a central point of ß1 well. The geological frame consists of several geological horizons. Because there is no strucural falult around ß site, we used simple grid model by five horizons that were identified at sequence boundaries. Internal layers are also classified depending on the thickness of horizons and other technical issues (Aung et al., 2011).Internal sand bodies and connectivity within the MH-bearing sediments are first evaluated by geobody obtained from seismic volume rendering (Fig. 3). Here we examine a seismic sweetness (reflection strength (amplitude envelope)/square root of instantaneous frequency) to identify the channel body of the MH-bearing sediments. Figure 3 shows an interpretation of geobody using the seismic sweetness. Two isolated bodies are identified at below/above the BSR by extracting higher sweetness value (white and green bodies shown in Fig. 3). Green body corresponds to the interval of the MH-bearing sediments. The boundary between the MH-bearing sediments and the sediments without the MHs shows higher impedance contrast which generates higher reflection strength (i.e., high sweetness). Distribution of the extracted green body also coincides with a direction of the channel-filling sediments supplied from northeast according to the seismic facies distribution (Noguchi et al., 2011).On the other hand, northern side of the white body distributes a boundary of the BSR and/or below the BSR. The BSR shows physical boundary between the MH-bearing sediments and gas-bearing sediments below the BSR. Thus, the higher sweetness of the extracted white body is probably due to both high reflection strength and low instantaneous frequency caused by the gas effect. Western side of the white body exhibits a boundary of the gas-water contact implying that the extracted white body represents the gas-bearing sediments. Although distributions of the gas in the sediments may be related to the continuity of the lithofacies (i.e., pathway of gas migration), the extracted white body clearly shows the physical boundary of the gas-bearing sediments, which do not represent sand body of the turbidite channels.Identification of stacked channels and geometriesInterpretation of the several stacking patterns of channel facies is identified within the sequence Og-b around the ß1 well. We first extracted a bottom frame of the stacked channels above the BSR (i.e., the lower generation of the channels) and classified it into several distinct channels (Fig. 4 (a)). One should note that some of the channels of the lower generation below the BSR are difficult to see in the seismic section because of the gas-bearing sediments that disturbed the seismic reflectors. For this reason, we extracted the bottom frame of the stacked channels in this study at the lower stability limit of MH up to the BSR line.The typical bottom frame of the channels exhibits variable widths (from several hundreds of meters), whereas the depth of the channels varies (ranging from several tens to hundreds of meters). The identified bottom frame of the channels mainly descends from the north-northeast to the south-southwest direction (Fig. 4 (a)). The paleo-current direction of the channels is identical to the direction of the sediment supplies (e.g., north-northeast), and this is indicated by the seismic facies distribution of sequence Og-b (Noguchi et al., 2011). Channel orientation and geometries (channel width, depth, and length) are also quantified for each stacked patterns of channel (Fig. 4 (b) and (c)). We account for geometries of various magnitudes of the channels around ß site to construct 3-D facies model. Channel oprientation slightly varies from 0o to 40o depending on the identified channels (BF01–BF04). Similarly, channel width, depth, and length are variable depending on the stacked patterns of the channels. These parameters are set into the facies model by channel object modeling (Fig. 4 (c)).Internal properties of the MH-bearing turbidite channelsThe internal properties of the interpreted channels are evaluated using a seismic impedance inversion analysis. Figure 5 (a) shows the result of acoustic P-impedance between the BSR and the top of the MH-bearing sediments. We used the constant value of the density as 1000 kg/m3in order to evaluate velocity distributions of the MH-bearing sediments. The typical velocities of the MH-bearing sediments around the ß1 well range from 1800 m/s to 2200 m/s. The correlation between the velocity distributions and the bottom frame of the channels shows those higher velocities (e.g., greater than 2,000 m/s) are rarely observed in some locations: at the northern side of the channels above BF01, BF04, BF06, and BF09. The distribution patterns of the higher velocities are oriented toward north-northeast (indicated by arrows) which coincides with the direction of sediment supply of the turbidites.IPTC 15351 3 Distributions of hydrate saturation are also estimated by a simple rock physics model (Lee and Collett, 2001; Inamori et al. 2008) by considering a relationship among seismic velociy (acoustic impedance), hydrate saturation (well), and P-sonic data. Calculated hydrate saturation shows that higher saturation rate is distributed toward north-northeast direction which coincides with the direction of sediment supply of the turbidites (Fig. 5 (b)). Hence, this result satisfactorily explains the relationship between facies distribution and internal property of the channels.Summary and future worksIn this study, we quantitatively discussed the reservoir heterogeneities of the MH-bearing turbidite channels in terms of facies distributions and internal properties by seismic inversion analysis.The interpretation of geobody shows that the extracted body extends to northeast-southwest direction which correlates well with the direction of the channel filled sediments according to the seismic sequence stratigraphic analysis. The stacking patterns of the channels also show that paleo current flow directions of the identified channels are typically oriented along north-to-south and north-northeast-to-south-southwest directions.Internal property of the stacking patterns of the channel sediments is examined using a seismic acoustic inversion analysis. The distribution patterns of the velocity between the BSR and the top of the MH-bearing sediments show that higher velocities are particularly identified along north-northeast direction in coincident with the sediment supplies of the turbidite channels. Estimated hydrate saturation map obtained by inversion data also reveals that there is good relationship between facies distribution and reservoir properties of the channels. This observational fact satisfactorily explains the qualitative evaluation of reservoir architecture of the MH-bearing turbidite channels.AcknowledgementThe 2-D/3-D seismic data and the well-log data of the exploratory test wells “Tokai-oki to Kumanonada” were acquired by METI. We would like to thank METI, Methane Hydrate 21 Research Consortium (MH21 Consortium), and Japan Oil, Gas and Metals National Corporation for providing permission to publish this paper.ReferenceAung, T. T, Noguchi, S., Oikawa, N., Kanno, T., Tamaki, M., Akihisa, K., 2011. Integrated facies modeling workflow for mthane hydrate reservoir along the eastern Nankai Trough, Japan, Proceedings of International Petroleum Technology Conference, Bangkok, Thailand, (IPTC15303).Fujii, T., Saeki, T., Kobayashi, T., Inamori., T, Hayashi, M., Takano, O., Takayama, T., Kawasaki, T., Nagakubo, S., Nakamizu., Yokoi, K., 2008. Resource assessment of methane hydrate in the Eastern Nankai Trough, Japan. Proceedings of 2008 Offshore Technology Conference, Houston, Texas, U.S.A. (OTC19310).Fujii, T., Saeki, T., Kobayashi, T., Inamori., T, Hayashi, M., Takano, O., Takayama, T., Kawasaki, T., Nagakubo, S., Nakamizu., Yokoi, K., 2009, Resource assessment of methane hydrate by applying a probabilistic approach in the Eastern Nankai Trough, Japan. Journal of Geography 118, 814-834 (In Japanese with English abstract).Inamori, T., Fujii, T., Takayama, T., Saeki, T., and Yamamoto, K., 2008. A trial of monitoring of the methane hydrate-production test by sonic well logging data, Abstracts of Japan Geoscience Union Meeting 2008, Makuhari, Japan.Lee, M.W. and Collett, T.S., 2001. Elastic properties of gas hydrate-bearing sediments. Geophysics, 66, 763–771.Nakamizu, M, Namikawa, T., Ochiai, K., Tsuji, Y., 2004. Efforts heading for production of methane from methane hydrate resources–An outline of METI exploratory test well “Nankai Trough” and future research program and development plan. Journ al of the Japanese Association for Petroleum Technology 69, 214-221 (in Japanese with English abstract).Noguchi, S., Shimoda, N., Takano, O., Oikawa, N., Inamori, T., Saeki, T., Fujii, T., 2011. 3-D Internal architecture of methane hydrate- bearing turbidite channels in the eastern Nankai Trough, Japan. Journal of Marine and Petroleum Geology, In Press.Takahashi, H., Yonezawa, T., Takedomi, Y., 2001. Exploration for Natural Hydrate in Nankai-Trough Well Offshore Japan. Proceedings of 2001 Offshore Technology Conference, Houston, Texas, U.S.A. (OTC13040).Takano, O., Nishimura, M., Fujii, T., Saeki, T., 2008. Changes in submarine fan sedimentation processes in response to forearc basin tectonics along the Nankai Trough, Philippine sea plate subduction zone. Abstracts of 6th international Conference on Asia Marine Geology, Kochi, Japan 2008, O-027.Takano, O., Nishimura, M., Fujii, T., Saeki, T., 2009. Sequence stratigraphic distribution analysis of methane-hydrate-bearingsubmarine-fan turbidite sandstones in the Eastern Nankai Trough area: Relationship between turbidite facies distributions and BSR occurrence. Journal of Geography 118, 814-834 (in Japanese with English abstract).Tsuji, Y., Ishida, H., Nakamizu, M., Matsumoto, R., Shimizu, S., 2004. Overview of the METI Nankai Trough Wells: A Milestone in the Evaluation of Methane Hydrate Resources. Resource Geology 54, 3-10.Uchida, T., Lu, H., Tomaru, H., the MITI Nankai Trough Shipboard Scientists., 2004. Subsurface occurrence of natural gas hydrate in the Nankai Trough area: Implication for gas hydrate concentration. Resource Geology 54, 35-44.Yamamoto, K., 2009. Production techniques for methane hydrate resources and field test programs; Journal of Geography, v. 118, no. 5, p. 913–934 (Japanese with English abstract).4 IPTC 15351Figure 1: Location map of the 2-D/3-D seismic surveys and the METI “Tokai-oki toKumano-nada” exploratory test wells.Figure 2: Workflow for constructing 3-D reservoir model.IPTC 15351 5Figure 3: Geobody using seismic volume rendering extracts two isolated bodiesaround ß1 well.Figure 4: (a) A graph depicting the identified bottom frame of the channels around the ß1 well.Arrows indicate the direction of the sediment supplies. (b) Extraction of channel geometries ofvarious magnitudes of channel width, depth, length, and orientations. (c) Constructing faciesmodel by considering geometries within the channel object.6 IPTC 15351Figure 5 (a) Acoustic impedance between the BSR and the top of the MH-bearingsediments.(b) Hydrate saturation map based on the impedance inversion data anda simple rock physics model.。