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The Xihu Depression is the largest hydrocarbon-bearing depression of the East China Sea Shelf Basin (also referred to as the ECSSB). However, the depositional systems and reservoir distribution of the Oligocene Huagang Formation in the Xihu Depression are still controversial. Under the guidance of sedimentology and stratigraphy, this study documented a marine-terrestrial transitional environment in the restricted bay setting of the Oligocene Huagang Formation through core description, well logging, and seismic data analysis. This study also revealed that the Oligocene Huagang Formation is dominated by tidal delta, estuary, and gravity flow deposits in the central anticline zone of the Xihu Depression. The new understanding of the sedimentary systems and the discovery of the transgressive gap in the eastern Diaoyu Islands uplift explain the origin of fine-grained sediments and the EW-trending sand bodies in the central depression and the sand bodies parallel to shoreline in the west slope belt, which cannot be explained by previous study results, such as southern transgression or fluvial deltas and even lacustrine deposition. Moreover, the tidal channels, tidal sand flats, and gravity flow sand bodies formed by the transgressive tides are high-quality reservoirs. The study will provide a basis for well placement and serve as guidance for the selection of favorable hydrocarbon exploration areas in the Xihu Depression. [ABSTRACT FROM AUTHOR]

The Ordovician reservoirs in the Tahe oilfield are dominated by fractured-vuggy carbonate reservoirs, of which fault-karst reservoirs are a hot topic in recent years. Fault-karst reservoirs feature high production, large burial depth, and strong heterogeneity under the control of faulting and karstification. Based on geological, logging, and seismic data, this study classified the Ordovician fault-karst reservoirs in the Yuejin block of the Tahe oilfield into three types, namely karst-cave, dissolved-vug, and fractured types, and established the integrated identification criteria of the three types of reservoirs. This study characterized karst caves, dissolved vugs, and multi-scale faults through seismic wave impedance inversion and frequency-domain detection of multi-scale faults. 3D geological models of different types of reservoirs were built using the combined deterministic and stochastic methods and characterized the spatial distribution of multi-scale faults, karst caves, dissolved vugs, and physical property parameters of reservoir. This study established the method for the geological modeling of fault-karst reservoirs, achieved the quantitative characterization and revealed the heterogeneity of fault-karst reservoirs. The karst-cave and dissolved-vug types are high in porosity and act as reservoirs, while the fractured type is high in permeability and act as flow pathway. This study lays the foundation for the development index prediction, well emplacement, and efficient development of the fault-karst carbonate reservoirs. [ABSTRACT FROM AUTHOR]

Sand consisting of round quartz grains is widely used as a proppant during hydraulic fracturing to produce natural gas from tight shale formations. This paper presents results from sand characterization and crushing tests on Jordan Formation frac sand. It includes an assessment of grain-size reduction, changes in particle shape, and reduction in void ratio. It also examines the implications for permeability reduction through a sand pack caused by the closure stress on a hydraulic fracture. The sand from two size ranges (0.6 to 0.71mmand 0.5 to 0.6 mm) was tested dry under applied compressive stresses of up to 40 MPa in a crushing cup. The overall sand pack stress-strain response becomes softer as grains are crushed. The particle shape shifts from nearly spherical grains to diametrically split grains and then to small elongated and angular fragments for the smaller particle sizes. The permeability of the sand pack reduces by more than 40% at a 20 MPa stress, which is mainly caused by a decrease in void ratio due to compaction. The permeability reduces by over 70% at a 40 MPa stress, which is primarily caused by void ratio decrease, reduction in particle size, and a shift away from spherical particle shapes. Compared to the ISO 13503-2 standard where only the sand crushing percentage after crushing tests is measured, this paper demonstrates that more information can be extracted from sand crushing tests and that sand pack permeability can be assessed to optimize frac sand selection. A sand with a larger size range has a higher crushing percentage, but is more permeable compared to a sand with a smaller size range. This further indicates that frac sand selection based only on sand crushing percentage is not sufficient to achieve better sand pack permeability. [ABSTRACT FROM AUTHOR]

Current dominant methods for slope stability analysis are the limit equilibrium method and the strength reduction method. Both methods are based on the limit equilibrium conditions. However, the limit equilibrium methods are limited to the rigid body assumption, while the strength reduction method is computationally expensive and has convergence issues due to the non-linear iterative computations. In this paper, we propose a current stress-based search algorithm to directly obtain the critical slip surface and the safety factor. The numerical manifold method, which unifies the continuum and discontinuum analysis problems, is used for stress analysis to obtain the stress distribution of soil slopes or rock slopes cut by joints. Based on the stress results obtained, a graph theory is used to convert the solution of the critical slip surface to a shortest path problem, which can be directly solved by the Bellman-Ford algorithm. The proposed method couples the numerical manifold method and the graph theory allowing for stability analyses of both rock and soil slopes within the same framework. The method completely removes the computational effort needed for iterations in the strength reduction method as well as eliminating the rigid body assumptions in the limit equilibrium method. [ABSTRACT FROM AUTHOR]

At present, the architecture modeling method of fluvial reservoirs are still developing. Traditional methods usually use grids to characterize architecture interbeds within the reservoir. Due to the thin thickness of this type of the interlayers, the number of the model grids must be greatly expanded. The number of grids in the tens of millions often makes an expensive computation; however, upscaling the model will generate a misleading model. The above confusion is the major reason that restricts the largescale industrialization of fluvial reservoir architecture models in oilfield development and production. Therefore, this paper explores an intelligent architecture modeling method for multilevel fluvial reservoirs based on architecture interface and element. Based on the superpositional relationship of different architectural elements within the fluvial reservoir, this method uses a combination of multilevel interface constraints and non-uniform grid techniques to build a high-resolution 3D geological model for reservoir architecture. Through the grid upscaling technology of heterogeneous architecture elements, different upscaling densities are given to the lateral-accretion bedding and lateral-accretion bodies to simplify the model gridding. This new method greatly reduces the number of model grids while ensuring the accuracy of lateral-accretion bedding models, laying a foundation for large-scale numerical simulation of the subsequent industrialization of the architecture model. This method has been validated in A layer of X oilfield with meandering fluvial channel sands as reservoirs and B layer of Y oilfield with braided river sands as reservoirs. The simulation results show that it has a higher accuracy of production history matching and remaining oil distribution forecast of the targeted sand body. The numerical simulation results show that in the actual development process of oilfield, the injected water will not displace oil in a uniform diffusive manner as traditionally assumed, but in a more complex pattern with oil in upper part of sand body being left behind as residual oil due to the influences of different levels of architecture interfaces. This investigation is important to guiding reservoir evaluation, remaining oil analysis, profile control and potential tapping and well pattern adjustment. [ABSTRACT FROM AUTHOR]

Background The aim of the present study was to evaluate whether the level of expression of tissue or plasma miR-106b can be used to predict clinical outcomes in breast cancer patients. Methods Both tissue and plasma samples were collected and analyzed from 173 patients with primary breast cancer and a set of 50 women with fibroadenoma. The relative expression levels of miR-106b were determined using real-time quantitative reverse transcription polymerase chain reaction and in situ hybridization. Results The levels of miR-106b were upregulated in both tissue and plasma samples from breast cancer patients. The expression levels showed a linear correlation (rs = 0.748, P < 0.001) and were significantly correlated with tumor size, Ki67 expression, and lymph node metastasis (all P < 0.05). Patients with high miR-106b expression levels tended to have shorter disease-free survival times and overall survival times (P < 0.001). In a Cox regression model, high-level tissue and plasma miR-106b expression were unfavorable prognostic factors, and receiver-operating characteristic analysis revealed that the tissue and plasma miR-106b levels provided considerable diagnostic accuracy, yielding an area under the ROC curve of 0.785 and 0.856, respectively. Conclusions MiR-106b was found to be associated with a high risk of recurrence of breast cancer, and miR-106b is a putative plasma marker for risk assessment in patients with breast cancer. [ABSTRACT FROM AUTHOR]