Analysis of Multiple Annular Pressure in Gas Storage Well and High-Pressure Gas Well

In gas storage or high-pressure gas wells,annular pressure is an unavoidable threat to safe,long-term resource production.The more complex situation,however,is multiple annular pressure,which means annular pressure happens in not only one annulus but two or more.Such a situation brings serious challenges to the identification of well integrity.However,few researches analyze the phenomenon of multiple annular pressure.Therefore,this paper studies the mechanism of multi-annular pressure to provide a foundation for its prevention and diagnosis.Firstly,the multi-annular pressure is classified according to the mechanism and field data.Then the failure mechanism and function of the wellbore safety barriers in the process of passage formation are analyzed.Finally,some suggestions are put forward for identifying and controlling multi-annular pressure.The results show that gas storage wells and high-pressure gas wells have the conditions to generate pressure channels,which leads to the expansion of annular pressure from a single annulus to multiple annuli.The pressure channel is composed of the tubing string,casing string,and a cement mantle,and the failures among the three have causal and hierarchical relationships.According to the channel direction,it can be divided into two types:tubing-casing annulus to casing annulus and casing annulus to the tubing-casing annulus,of which the former is more harmful.Some measures can be considered to prevent pressure channeling,including improvement of cementing quality,revision of maximum allowable annular pressure,and suitable frequency of pressure relief.

Effect of polymer and fiber additives on pressure drop in a rectangular channel

The influence of minute amounts of additives on pressure drop is an interesting fundamental phenomenon, potentially with important practical applications. Change of the pressure drop in a quasi-two-dimensional channel flow using various additives is experimentally investigated. Tests were conducted for a wide range of concentrations（100 ppm-500 ppm） and Reynolds numbers（16 000-36 000） with two polymers and four rigid fibers used as additive. Maximum drag reduction of 22% was observed for xanthan gum. However, xanthan gum loses its drag-reducing property rapidly. It was also seen that drag reduction percentage of xanthan gum remains almost constant for different Reynolds numbers. Guar flour demonstrated good drag reduction property at high Reynolds numbers. Drag reduction of 17.5% at Re= 33 200 using 300 ppm solution was observed. However, at low Reynolds numbers guar flour will cause an increase in pressure drop. Fiber fillers（aspect ratio=21） have been tested as well. In contrast to polymers, they increased the drag for the range of examined concentrations and Reynolds numbers. Polyacrylonitrile fiber with three different aspect ratios（106, 200, 400） was also used, which showed an increase in pressure drop at low aspect ratios. Polyacrylonitrile fibers of larger lengths（6 mm） demonstrated minor drag-reducing effects（up to 3%）.

MECHANISM OF WALL PRESSURE FLUCTUATIONS BENEATH THE OPEN CHANNEL FLOW

Based on the measured results that wall pressure fluctuations are mainly de- cided by coherent structures of turbulence, the relationship between root-mean- square wall pressure and wall shear stress in turbulent shear flow and that between the intensities of pressure and fluctuating velocity in homogeneous and isotropic turbulence are established in this paper. These relationships are consistent with former works, and have good agreement with experimental data. The paper also dis- cusses the concept of 'apparent pressure' on the wall in mean flow.

Benidipine has effects similar to losartan on the central blood pressure and arterial stiffness in mild to moderate essential hypertension

Background Central blood pressure （BP） is pathophysiologically more important than peripheral BP for the pathogenesis of cardiovascular disease. Arterial stiffness is also a good predictor of cardiovascular morbidity and mortality. The effects of benidipine, a unique dual L-IT-type calcium channel blocker, on central BP have not been reported. This study aimed to compare the effect of benidipine and Iosartan on the central BP and arterial stiffness in mild to moderate essential hypertensives. Methods This 24 weeks, multi-center, open label, randomized, active drug comparative, parallel group study was designed as a non-inferiority study. The eligible patients （n=200） were randomly assigned to receive benidipine （n=101） or Iosartan （n=99）. Radial artery applanation tonometry and pulse wave analysis were used to measure the central BP, pulse wave velocity （PWV） and augmentation index （AIx）. We also measured the metabolic and inflammatory markers. Results After 24 weeks, the central BP decreased significantly from baseline by （16.8±14.0/10.5±9.2） mmHg （1 mmHg =0.133 kPa） （systolic/diastolic BP; P 〈0.001） in benidipine group and （18.9±14.7/12.1±10.2） mmHg （P 〈0.001） in Iosartan group respectively. Both benidipine and Iosartan groups significantly lowered peripheral BP （P 〈0.001） and AIx （P 〈0.05）, but there were no significant differences between the two groups. The mean aortic, brachial and femoral PWV did not change in both groups after 24-week treatment. There were no significant changes of the blood metabolic and inflammatory biomarkers in each group. Conclusion Benidipine is as effective as Iosartan in lowering the central and peripheral BP, and improving arterial stiffness.