Influence of salinity on the properties of the different HPAM/Al3+ systems

International audienceIn order to achieve oil increment and water cut reduction in the heterogeneous oil reservoirs, a conformance control technology by using HPAM/Al3+ systems has been widely used due to the low price and environmental friendliness. However, the complex structure and state of high-valent metal ions in brine water can directly affect the properties of the different HPAM/Al3+ systems, which may lead to unreasonable applications. Therefore, in order to better utilize the HPAM/Al3+ systems, the characteristics of gelation of HPAM and the three types of aluminum citrate under different salinities are systematically studied. Experimental results show that an important reason for the cross-linking reaction of HPAM/Al3+ being affected by salinity is that the morphology and structure of the aluminum citrate complex is different under the different salinities. Although the change of characteristics of the reaction time and the cross-linking degree of the three HPAM/Al3+ systems are different, the process of the cross-linking reactions of the three HPAM/Al3+ systems are the same. Besides, the thermal stability of the HPAM/Al3+ gels is weakened with the increasing of salinity regardless of the ratio of citrate ligands to Al3+. According to the matching relationship between salinity and HPAM/Al3+ systems, the reaction time can be controlled to achieve the requirements of on-site construction operation for the conformance control of a given heterogeneous oil reservoir

A Method of Quantitative Evaluation of Diagenetic Reservoir Facies of Tight Gas Reservoirs With Logging Multi-Parameters: A Case Study in Sulige Area, Northern Ordos Basin, China

Reservoir and flow characteristics of low, ultra-low permeability tight sandstone reservoir were largely controlled by diagenesis in reservoir assessment. In previous studies, diagenesis were researched only by using core analysis data, and it was difficult that diagenetic reservoir facies of the interval and the well without core analysis data were evaluated. Therefore, it was easy and quick that diagenetic reservoir facies were characterized with logging response characteristics which were extracted effectively. Taking tight gas reservoirs for example in Sulige area, northern Ordos Basin, China, logging response characteristics of different classification were analyzed by multiple samples with core analysis data, and the quantitative evaluation index of diagenetic reservoir facies based on logging multi-parameter was set up. A method of quantitative evaluation of diagenetic reservoir facies of tight gas reservoirs with logging multi-parameters was formed in the method of integration of analysis technology of Grey theory, and the accuracy and availability of the method were evaluated. The results shown that non-digitalized problems of diagenetic reservoir facies evaluation was solved by the digitalization method of logging multi-parameters, and the rate of accuracy, of returned classification using methods of mutual test, reached to 91.2%. The results provided a new and effective evaluation approach of low, ultra-low permeability tight sandstone reservoir

Influence of salinity on the properties of the different HPAM/Al3+ systems

In order to achieve oil increment and water cut reduction in the heterogeneous oil reservoirs, a conformance control technology by using HPAM/Al3+ systems has been widely used due to the low price and environmental friendliness. However, the complex structure and state of high-valent metal ions in brine water can directly affect the properties of the different HPAM/Al3+ systems, which may lead to unreasonable applications. Therefore, in order to better utilize the HPAM/Al3+ systems, the characteristics of gelation of HPAM and the three types of aluminum citrate under different salinities are systematically studied. Experimental results show that an important reason for the cross-linking reaction of HPAM/Al3+ being affected by salinity is that the morphology and structure of the aluminum citrate complex is different under the different salinities. Although the change of characteristics of the reaction time and the cross-linking degree of the three HPAM/Al3+ systems are different, the process of the cross-linking reactions of the three HPAM/Al3+ systems are the same. Besides, the thermal stability of the HPAM/Al3+ gels is weakened with the increasing of salinity regardless of the ratio of citrate ligands to Al3+. According to the matching relationship between salinity and HPAM/Al3+ systems, the reaction time can be controlled to achieve the requirements of on-site construction operation for the conformance control of a given heterogeneous oil reservoir

HuMiTar: A sequence-based method for prediction of human microRNA targets

<p>Abstract</p> <p>Background</p> <p>MicroRNAs (miRs) are small noncoding RNAs that bind to complementary/partially complementary sites in the 3' untranslated regions of target genes to regulate protein production of the target transcript and to induce mRNA degradation or mRNA cleavage. The ability to perform accurate, high-throughput identification of physiologically active miR targets would enable functional characterization of individual miRs. Current target prediction methods include traditional approaches that are based on specific base-pairing rules in the miR's seed region and implementation of cross-species conservation of the target site, and machine learning (ML) methods that explore patterns that contrast true and false miR-mRNA duplexes. However, in the case of the traditional methods research shows that some seed region matches that are conserved are false positives and that some of the experimentally validated target sites are not conserved.</p> <p>Results</p> <p>We present HuMiTar, a computational method for identifying common targets of miRs, which is based on a scoring function that considers base-pairing for both seed and non-seed positions for human miR-mRNA duplexes. Our design shows that certain non-seed miR nucleotides, such as 14, 18, 13, 11, and 17, are characterized by a strong bias towards formation of Watson-Crick pairing. We contrasted HuMiTar with several representative competing methods on two sets of human miR targets and a set of ten glioblastoma oncogenes. Comparison with the two best performing traditional methods, PicTar and TargetScanS, and a representative ML method that considers the non-seed positions, NBmiRTar, shows that HuMiTar predictions include majority of the predictions of the other three methods. At the same time, the proposed method is also capable of finding more true positive targets as a trade-off for an increased number of predictions. Genome-wide predictions show that the proposed method is characterized by 1.99 signal-to-noise ratio and linear, with respect to the length of the mRNA sequence, computational complexity. The ROC analysis shows that HuMiTar obtains results comparable with PicTar, which are characterized by high true positive rates that are coupled with moderate values of false positive rates.</p> <p>Conclusion</p> <p>The proposed HuMiTar method constitutes a step towards providing an efficient model for studying translational gene regulation by miRs.</p

Performance of Air Foam Flooding under Low Frequency Vibration

Foam injection is widely applied in amounts of fields to drilling, production, and formation protection. Sometimes, the application result is disappointing, which is caused by the failure of bubble generation in foam flooding. Therefore, it is necessary to seek ways for improving the performance of foam injection. An increased disturbance to the stratum, like the vibration caused by a seismic oil recovery technique, would be helpful. In the current work, the seepage of air foam in porous media under low frequency (LF) vibration is analyzed with experiments and an investigation of bubble creation/destruction rate change is carried out using mathematical modeling. The resistance factor of foam flooding under indoor vibration increases by 1.5 times and the valid time is obviously extended compared with when no vibration is used. The optimal vibrating acceleration and frequency of 0.7 m/s2 and the natural frequency of the cores-nearby of 18 Hz are achieved in the indoor experiments. Under vibration, the bubble generation rate increases, while bubble break rate by internal expansion or by gas diffusion and transfer decreases. An interesting phenomenon is also observed, which might develop a power level formula between the initially defined dimensionless MRF (maximum foam flooding resistance factor) and dimensionless DMRF (duration of maximum foam flooding resistance factor). The power product and sum of the power exponents of the above formula both equal approximately to 1. With the assistance of LF vibration, the increase of security, adaptability, and efficiency in foam injection may improve the reservoir recovery and extend its application.</span

Plugging Behavior of Polymer Gel in Fractures by Multi-Slug Injection

In order to understand the plugging mechanism, experiments of multi-slug gel plugging in single fracture and multiple fractures system were simulated by indoor visual fracture models. The experiments showed that there were two stages in the process of multi-slug gel plugging in single fracture: gel filling stage and gel compaction stage. When the total injection of gel is consistent, the brine flooding pressure gradient after multi-slug gel injection increased more than 2 times than the pressure gradient after single slug gel continuous injection. While there were three stages in the process of multi-slug gel plugging in multiple fractures system: Gel selectively entrance stage, gel filling stage and gel compaction stage. However, there would be no gel compaction stage, even no gel filling stage in the process of single cycle gel plugging in multiple fractures system.Key words: Fractured reservoir; Multi-slug; Polymer gel; Plugging proces