Water saturation is one of the most important parameters in petroleum exploration and development. However, its calculation has been limited by the insufficient logging data required by a new technique that further influences the calculation of the free gas content. The accuracy of water saturation estimates is also a critical issue because it controls whether or not we can obtain an accurate gas saturation estimate. Organic matter plays an important role in shale-gas reservoirs, and the total organic carbon (TOC) indirectly controls the gas content and gas saturation. Hence, water saturation is influenced by inorganic and organic components. After analyzing the relationship among TOC, core water saturation, and conventional gas saturation, considering the influence of TOC on gas saturation in organic-rich shale reservoirs, we developed two new methods to improve the accuracy of water saturation estimates: the revised water saturation-TOC method and the water saturation separation method, in which Archie water saturation, modified total shale water saturation, and TOC are integrated. According to case studies of Longmaxi-Wufeng shale, southeastern Sichuan Basin, China, the water saturation results from these two methods in shale reservoirs with different lithologies are consistent with those from core analysis. We concluded that these two methods can be evaluated quickly and they effectively evaluate the water saturation of shale reservoirs.
Identifying fractures and evaluating the parameters of tight reservoirs are important problems. Developing methods to accurately interpret logging data for tight sandstone and shale reservoirs is of great significance, especially when only conventional logging data can be obtained. Identifying natural fractures with limited available data is challenging. Comparing and analyzing the log response characteristics of the natural fracture zone of a tight reservoir indicate that acoustic (AC) and density (DEN) data are highly sensitive to fractures in tight reservoirs. First, we have obtained the characteristics and differences of the log response of natural fractures. Second, we established a model that is based on these sensitive log-response characteristics (AC and DEN) to identify fractures (correlation coefficient method with window lengths), and we analyzed the cut-off of the correlation coefficient. Then, we established a model (the revised Wyllie difference method) to characterize the fracture porosity based on the difference in the sensitive log responses of the fracture (the difference in the AC and DEN curves). Finally, we applied this methodology to a case study of a tight reservoir in the Sichuan Basin, China, and the AC-DEN correlation coefficient and fracture porosity are calculated. The AC-DEN correlation coefficient adequately identifies fractures, and the calculated fracture porosity is consistent with the fracture porosity from full borehole microresistivity imaging. Thus, this method is applicable to evaluating fractures in tight-fracture reservoirs.
Stratigraphic sequence interpretation and correlation are part of basic geologic research, but present frequent problems such as subjective and accurate division and correlation of sequence cycles, and a multiplicity of solutions to highfrequency sequences. We developed a novel method, termed frequency trend attribute analysis (FTAA), to solve these problems and improve the accuracy of division. The method was based on maximum entropy spectrum analysis data, built on theoretical foundations, and tested on geologic models as well as empirical data. We developed examples of how FTAA can improve stratigraphic division and correlation. We extracted frequency trend lines from well logging data (using all or a selected part of a facies-sensitive log such as the natural gamma-ray log) whereby the FTAA outcome reflected the overlay series and cycle structures. The resulting frequency trend lines also indirectly reflected changes to the sedimentary environment and base level, and the precise stratigraphic division and isochronous comparisons were automatically deduced from the frequency trend lines. According to the practical comparison with wells in the field, the frequency trend lines were found to be more accurate than using outcrop data, and the method proved to be effective and convenient in use. The FTAA significantly improved the precision and accuracy of automatic division and correlation of sequence cycles.
Quantitative estimation of total organic carbon (TOC) content using well logs is very important for shale-gas reservoir evaluation especially when core data is limited.Even though many techniques have been developed to calculate TOC from well logs, they all have their limitations and accurate assessment of TOC in organic-rich tight shales is still challenging. This paper presents an improved log-overlay method for evaluating TOC content in organic-rich tight shale reservoirs by overlying the properly scaled GR, DT, DEN curves on top of the CNL curve based on the same concept to the original ∆logR technique. These logging curves are overlapped with the CNL in non-source intervals and are separated in organic-rich shale reservoirs. The separation magnitude increase along with the increase of TOC content of the shale and this relationship is transformed to calculate TOC. This method was tested and verified by doing a case study using well-log data from the Jiaoshiba tight shale-gas play in the Sichuan Basin. The results show that the new TOC evaluation method is more practical and effective compared with existing TOC evaluation methods.
The objectives of this study were to show the effect of miR-222 expression on angiogenesis and the mechanism of angiogenesis differentiation of bone microvascular endothelial cells. For the study, the concentration of VEGF release was detected by ELISA, and cell activity was shown using a CCK-8 (Cell Counting Kit-8). We used western blotting to detect VEGFR, TGF-β, and bFGF expression. The results showed that miR-222 expression by day 14 was significantly lower compared to the expression results for days 3 and 7. Additionally, miR-222 expression on day 7 was significantly lower than on day 3. MiR-222 expression in the control group and PELA group decreased gradually over time. On day 14, miR-222 expression in the VEGF microcapsule scaffold group was at its lowest level. Our conclusions were that the regulation of the angiogenesis of bone microvascular endothelial cells appears to be related to (1) the effect of miR-222 on VEGFR and TGF-β, and (2) how bFGF expression is regulated.
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