Study of vibrating drag reduction mechanism during horizontal drilling in slim borehole

Resource reserves can be effectively controlled through slim borehole horizontal drilling, which can significantly reduce costs and enhance efficiency. Therefore, it has been widely used in petroleum, geothermal, shale gas and water resources exploration. But the large friction between the drilling string and borehole can cause downhole accidents. In this paper, a new method of vibrating drag reduction is proposed, with using turbine to drive the rotary valve to control flow. Axial vibration excitation produced by high-pressure water can greatly reduce the friction. Firstly, a rotary valve mathematical model with flow hydraulic oscillation and vibration is established, whose work characteristics are simulated using numerical methods. And then lab experiments are conducted to verify the design

Experimental Study on Sonic Vibration Grouting in Fine Silty Sand Layer

Fine silty sand layer is one of the common weak strata. It is easy to deform suddenly and induce accidents under the external load due to its loose structure and poor self-stability. To improve the stability of the strata in engineering construction, the grouting is usually used for antiseepage reinforcement in the fine silty sand layer. This paper presents the basic principle of the sonic vibration grouting, develops the experimental device and the simulated stratum condition, mixes the acidic water glass for engineering application, and carries out the experimental study on the sonic vibration grouting. The results show that the effect of the exciting force on the sonic vibration grouting is not obvious, and the vibration duration has a greater influence on it. With the increase of the vibration duration, the grouting diffusion distance is enlarging gradually and stabilizes eventually at a certain value. The vibration frequency has the greatest impact on the grouting. The grouting effect is the best when the vibration frequency is close to the natural frequency of the fine silty sand. The grouting diffusion distance is getting smaller, which means the grouting effect is becoming worse, when the vibration frequency is far away from the natural frequency of the stratum. The grouting effect in the fine silty sand layer can be improved effectively by vibration technology using the sonic vibration grouting which has excellent effect in engineering application. This paper lays a foundation for the further study on mechanism and engineering application of the sonic vibration grouting

Design and Output Performance Model of Turbodrill Blade Used in a Slim Borehole

Small-diameter turbodrills have great potential for use in slim boreholes because of their lower cost and higher efficiency when used in geothermal energy and other underground resource applications. Multistage hydraulic components consisting of stators and rotors are key aspects of turbodrills. This study aimed to develop a suitable blade that can be used under high temperature in granite formations. First, prediction models for single- and multi-stage blades were established based on Bernoulli’s Equation. The design requirement of the blade for high-temperature geothermal drilling in granite was proposed. A Φ89 blade was developed based on the dimensionless parameter method and Bezier curve; the parameters of the blade, including its radial size, symotric parameters, and blade profiles, were input into ANASYS and CFX to establish a calculation model of the single-stage blade. The optimization of the blade structure of the small-diameter turbodrill enabled a multistage turbodrill model to be established and the turbodrill’s overall output performance to be predicted. The results demonstrate that the design can meet the turbodrill’s performance requirements and that the multistage model can effectively improve the accuracy of the prediction

Coupling Effect of Creep Deformation and Prestress Loss of Anchored Jointed Rock

To explore the variation behaviour of anchor jointed rock subject to high in situ stress states, a coupling effect calculation model based on stress equality was established based on the original rheological model of rock by combining element combination theory and experiment, and the model was verified. The coupling effect between rock mass creep and bolt prestress loss is established by setting the deterioration function of bolt prestress loss. The uniaxial creep test is performed on specimens with different joint angles, and the results show that the prestress loss time in anchor rods decreases linearly with increasing stress level. With increasing stress level, the time of prestress loss decreases linearly with the increase in stress level. With increasing axial load, the deformation caused by the transverse expansion stress of the specimen can offset the compression deformation of the prestressed anchor rod. The relationship between prestress loss in anchors and creep of rock is solved theoretically, and the stability criterion for anchor jointed rock is proposed. The results of this study provide a scientific reference for anchor design of deep jointed rock mass

Sharp injuries: a cross-sectional study among health care workers in a provincial teaching hospital in China

Abstract Background The objectives of this study are to investigate the incidence and reporting behavior of sharp injuries among healthcare workers (HCWs) and identify the risk factors associated with these injuries. Methods A cross-sectional survey was conducted in February 2017 in a provincial teaching hospital in China. Data were collected from 901 HCWs using a self-administered questionnaire which included demographic information, experience, and reporting behavior of sharp injuries. Stepwise logistical regression was used to analyze the risk factors. Results HCWs (248 [27.5%]) had sustained a sharp injury in the previous year. Factors including seniority, job category, title, education, department, and training programs were associated with the occurrence of sharp injuries. According to the stepwise logistical regression, seniority, and training programs were the risk factors associated with the occurrence of sharp injuries. Of 248 sharp injuries, 130 HCWs were exposed to blood. Only 44 (33.9%) HCWs reported their injuries to the concerned body. The main reasons for not reporting the sharp injuries were as follows: perception that the extent of the injury was light (30.2%), having antibodies (27.9%), and unaware of injury (16.3%). Conclusions Sharp injuries in the studied hospital were common and were likely to be underreported. Therefore, an effective reporting system and sufficient education on occupational safety should be implemented by the relevant institutions. Moreover, it is important to take effective measures to manage sharp injuries in HCWs and provide guidance for their prevention

Equivalent Circulation Density Analysis of Geothermal Well by Coupling Temperature

The accurate control of the wellbore pressure not only prevents lost circulation/blowout and fracturing formation by managing the density of the drilling fluid, but also improves productivity by mitigating reservoir damage. Calculating the geothermal pressure of a geothermal well by constant parameters would easily bring big errors, as the changes of physical, rheological and thermal properties of drilling fluids with temperature are neglected. This paper researched the wellbore pressure coupling by calculating the temperature distribution with the existing model, fitting the rule of density of the drilling fluid with the temperature and establishing mathematical models to simulate the wellbore pressures, which are expressed as the variation of Equivalent Circulating Density (ECD) under different conditions. With this method, the temperature and ECDs in the wellbore of the first medium-deep geothermal well, ZK212 Yangyi Geothermal Field in Tibet, were determined, and the sensitivity analysis was simulated by assumed parameters, i.e., the circulating time, flow rate, geothermal gradient, diameters of the wellbore, rheological models and regimes. The results indicated that the geothermal gradient and flow rate were the most influential parameters on the temperature and ECD distribution, and additives added in the drilling fluid should be added carefully as they change the properties of the drilling fluid and induce the redistribution of temperature. To ensure the safe drilling and velocity of pipes tripping into the hole, the depth and diameter of the wellbore are considered to control the surge pressure