Research on the Water Ridge and Slamming Characteristics of a Semisubmersible Platform under Towing Conditions

During the towing of semisubmersible platforms, waves impact and superpose in front of the platform to form a ridge shaped “water ridge”, which protrudes near the platform and produces a large slamming pressure. The water ridges occur frequently in the towing conditions of semisubmersible platforms. The wave–slamming on the braces and columns of platform is aggravated due to the water ridges, particularly in rough sea conditions. The effect of water ridges is usually ignored in slamming pressure analysis, which is used to check the structural strengths of the braces and columns. In this paper, the characteristics of the water ridge at the braces of a semisubmersible platform are studied by experimental tests and numerical simulations. In addition, the sensitivity of the water ridge to the wave height and period is studied. The numerical simulations are conducted by a Computational Fluid Dynamics (CFD) method, and their accuracy is validated based on experimental tests. The characteristics of the water ridge and slamming pressure on the braces and columns are studied in different wave conditions based on the validated numerical model. It is found that the wave extrusion is the main reason of water ridge. The wave–slamming pressure caused by the water ridge has an approximately linear increase with the wave height and is sensitive to the wave period. With the increase of the wave period, the wave–slamming pressure on the brace and column of the platform increases first and then decreases. The maximum wave–slamming pressure is found when the wave period is 10 s and the slamming pressure reduces rapidly with an increase of wave period.

Analysis of the mechanical behavior of adobe walls without reinforcement through computational modelling

The construction of civil structures on land has played an important role for centuries, however, due to the seismic requirements and the minimum safety standards that are currently required for any structure, this type of construction has been lagged, it is denoted that the related regulations they are widely dispersed and in most cases. In developed countries, numerous technical and legal problems arise to carry out construction with these materials. In relation to this work, a set of models of raw earth type walls are presented, through the SAP 2000 software, having as a supply of the mechanical properties of this material the Peruvian regulation E.080. For the analysis of these models, a static linear analysis for finite elements and a stress analysis of the service limit state concept were studied. Finally, the models with their respective stress studies, management and design recommendations are presented under the criteria of the analyses carried out, leaving open the possibility of both carrying out an experimental phase to develop the analogy with the postulates and proposed results, as well as such as the option to perform a static pressure analysis by finite elements in order to achieve greater precision and calibration of the model with respect to what can be evidenced in laboratory tests.

Integration of Borehole Acoustic Reflectivity Survey and Fracture Pressure Analysis to Determine Properties of Far-Field Heterogeneities During Stimulation in Tight Reservoirs

The presence of conductive and extended heterogeneous features not connected to the wellbore and located beyond the investigation depths of standard characterization tools can be the reason for unexpected loss of net pressure during stimulation treatments due to the hydraulic fracture breakthrough into these heterogeneous areas. In current field practice, if such breakthrough occurs, it is considered as bad luck without the possibility of the quantitative analysis. This mindset can be changed in favor of the stimulation and reservoir management success using an approach that ties the thorough fracture pressure analysis with the output of the specific acoustic reflectivity survey capable of identifying position, shape, and orientation of far-field heterogeneous features. The approach consists of four steps and is applicable to cases when the hydraulic fracture experiences breakthrough into the heterogeneity. First, before the stimulation treatments, at the reservoir characterization stage, a borehole acoustic reflectivity survey is run. Gathered data are interpreted and visualized according to a specific workflow that yields the image of the heterogeneous areas located around the wellbore in the radius of several tens of meters. Second, the hydraulic fracturing treatment is performed, and fracture pressure analysis is performed, which identifies the pressure drops typical for the breakthrough. Third, after the breakthrough into the heterogeneity is confirmed, the distance to this heterogeneity is used as a marker for calibration of the fracture properties and geometry. Finally, the post-stimulation pressure and production data are used to define the properties of the heterogeneous features, such as conductivity and approximate dimensions. The comprehensive field application example of the suggested approach confirmed its effectiveness. For the tight carbonate formations, the heterogeneity in a form of fracture corridor was revealed by the acoustic reflectivity survey at least 20 m away from the wellbore. The breakthrough into this heterogeneity was observed during the acid fracturing treatment. The distance to the heterogeneity and observed pumping time to breakthrough were used as markers characterizing fracture propagation; reservoir and rock properties were adjusted using a fracturing simulator to obtain this fracture propagation. Finally, the post-stimulation production data were analyzed to determine infinite conductivity of the fracture corridor and quantify its extent downward. Data gathered during reservoir and hydraulic fracture properties calibration allowed for optimization of stimulation strategy of the target layer throughout the field; the information about the heterogeneity’s properties allowed for optimization of the completion and reservoir development strategy.

Identification of Geo – Hazard Using Pore Pressure Analysis in ‘MAC’ Field, Niger Delta

Identification of geo-hazard zones using pore pressure analysis in ‘MAC’ field was carried out in this research. Suite of wireline logs from four wells and RFT pressure data from two wells were utilized. Lithologic identification was done using gamma ray log. Resistivity log was used to delineate hydrocarbon and non-hydrocarbon formations. Well log correlation helps to see the lateral continuity of the sands. Pore pressure prediction was done using integrated approaches. The general lithology identified is alternation of sand and shale units. The stratigraphy is typical of Agbada Formation. Three reservoirs delineated were laterally correlated. Crossplot of Vp against density (Rho) colour coded with depth revealed that disequilibrium compaction is the main overpressure generating mechanism in the field. Prediction of overpressure by normal compaction trend was generated and plot of interval transit time against depth show that there is normal compaction from 250m to about 1700 m on MAC-01, but at a depth of about 1800m, there was abnormal pressure build up that shows the onset of overpressure. A relatively normal compaction was observed on MAC-02 until a depth of about 2100m where overpressure was suspected. The prediction of formation pore pressure using Eaton’s and Bower’s method to determine the better of the two methods to adopt for pore pressure prediction shows that the pore pressure prediction using Eaton’s method gave a better result similar to the acquired pressure in the field. Hence Eaton’s method appears to be better suited for formation pore pressure estimation in ‘MAC’ field. The validation of the pore pressure analysis results with available acquired pressure data affirmed the confidence in the interpreted results for this study.

Emergence And Circulation of Dengue Virus Serotype 2 In Guangzhou Over A Period of 20 Years

Objectives The dengue epidemic in Guangzhou has imposed a rising burden on society and health infrastructure. Here we present the genotype data for dengue virus serotype 2 (DENV-2) to improve the understanding of dengue epidemic. Methods We sequenced the envelope gene of DENV-2 obtained from patient serum sample, and subsequently performed the maximum-likelihood phylogenetic analysis using PhyMLv3.1, the maximum clade credibility analysis using BEAST v.1.10.4 and selection pressure analysis using Datamonkey 2.0 . Results The DENV-2 prevalent in Guangzhou region related to the strains of Southeast Asian countries.Our results suggest that the Malaysia/Indian subcontinent genotype is prevalent in Guangzhou and no genotype shift has occurred during the last 20 years. Episodic positive selection was detected at one site. Conclusions Prevention and monitoring imported cases are important for local control. The shift between the lineages of the Malaysia/Indian subcontinent genotype, which originated at different time points, may be the underlying cause of rising DENV-2 cases in Guangzhou.The low rate of dengue haemorrhagic fever in Guangzhou may be explained by the dominance of the less virulent Malaysia/Indian subcontinent genotype.

Machine Learning Applications in Modelling and Analysis of Base Pressure in Suddenly Expanded Flows

Base pressure becomes a decisive factor in governing the base drag of aerodynamic vehicles. While several experimental and numerical methods have already been used for base pressure analysis in suddenly expanded flows, their implementation is quite time-consuming. Therefore, we must develop a progressive approach to determine base pressure (β). Furthermore, a direct consideration of the influence of flow and geometric parameters cannot be studied by using these methods. This study develops a platform for data-driven analysis of base pressure (β) prediction in suddenly expanded flows, in which the influence of flow and geometric parameters including Mach number (M), nozzle pressure ratio (η), area ratio (α), and length to diameter ratio (φ) have been studied. Three different machine learning (ML) models, namely, artificial neural networks (ANN), support vector machine (SVM), and random forest (RF), have been trained using a large amount of data developed from response equations. The response equations for base pressure (β) were created using the response surface methodology (RSM) approach. The predicted results are compared with the experimental results to validate the proposed platform. The results obtained from this work can be applied in the right way to maximize base pressure in rockets and missiles to minimize base drag.

Unconventional Well Test Analysis for Assessing Individual Fracture Stages through Post-Treatment Pressure Falloffs: Case Study

Researchers and operators have recently become interested in the individual stage optimization of unconventional reservoir hydraulic fracture. These professionals aim to maximize well performance during an unconventional well’s early-stage and potential Enhanced Oil Recovery (EOR) lifespan. Although there have been advances in hydraulic fracturing technology that allow for the creation of large stimulated reservoir volumes (SRVs), it may not be optimal to use the same treatment design for all stages of a well or many wells in an area. We present a comprehensive review of the main approaches used to discuss applicability, pros and cons, and a detailed comparison between different methodologies. Our research outlines a combination of the Diagnostic Fracture Injection Test (DFIT) and falloff pressure analysis, which can help to design intelligent production and improve well performance. Our field study presents an unconventional well to explain the objective optimization workflow. The analysis indicates that most of the fracturing fluid was leaked off through natural fracture surface area and resulted in the estimation of larger values compared to the hydraulic fracture calculated area. These phenomena might represent a secondary fracture set with a high fracture closure stress activated in neighbor stages that was not well-developed in other sections. The falloff pressure analysis provides significant and vital information, assisting operators in fully understanding models for fracture network characterization.