New Development of Air and Gas Drilling Technology

Gas drilling technology has been widely promoted and applied in recent years. Known for being capable of discovering and protecting reservoirs, improving the penetration rate and avoiding loss circulation, two key issues of gas drilling still need to be addressed. First, a more accurate way of determining the gas injection rate is needful. In this text, we present a modified mathematical model for predicting the optimum range of gas injection rate required to balance the borehole cleaning and well-integrity issues. The optimum gas injection rate should be sought between the minimum value required for hole cleaning and the maximum permissible value to avoid hole erosion. Good consistency between the model prediction and field problem-free nitrogen gas injection rate indicates the reliability of the proposed model. Second, the problem of environmental pollution and wasting of resources caused by direct discharging or combustion of the returned gas is to be solved. To address the latter issue, we introduce a new technology of gas recycling system (GRS). Our research group has carried out a comprehensive investigation, including integration design, technological process, cuttings transport analysis, separation and filter equipment selection, and control system design. The feasibility of GRS has been verified through an open-loop pilot test

Nitroxoline inhibits bladder cancer progression by reversing EMT process and enhancing anti-tumor immunity

Nitroxoline is considered to be an effective treatment for the urinary tract infections. Recently, it has been found to be effective against several cancers. However, few studies have examined the anti-tumor activity of nitroxoline in bladder cancer. The purpose of the study was to reveal the possible mechanisms how nitroxoline inhibited bladder cancer progression. In vitro assay, we demonstrated that nitroxoline inhibited bladder cancer cell growth and migration in a concentration-related manner. Western blot analysis demonstrated that nitroxoline downregulated the expressions of epithelial mesenchymal transition (EMT)-related proteins. Furthermore, treatment with nitroxoline in the C3H/He mice bladder cancer subcutaneous model resulted in significant inhibition of tumor growth. Moreover, the percentage of myeloid-derived suppressor cells (MDSC) in peripheral blood cells significantly decreased after treatment of nitroxoline. Taken together, our results suggested that nitroxoline may be used as a potential drug for bladder cancer

New Method to Analyse the Cement Sheath Integrity During the Volume Fracturing of Shale Gas

Accurate prediction of the hoop stress distribution of the cement sheath and its variation regularities during volume hydraulic fracturing in shale formations is of great significance for maintaining the wellbore integrity of shale gas horizontal wells. A finite element model of casing-cement sheath-formation system (CCFS) coupling between stresses and temperature was established through a staged finite element method based on the elastic anisotropy of shale. With this new model, the effects of operation parameters and formation mechanical property changes on the cement sheath hoop stress during the multi-stage hydraulic fracturing process were analyzed, and the results were compared with the conventional model. The results revealed that the increase of the temperature of the fracturing fluid could reduce the hoop stress of the cement sheath, which decreased gradually with the decreasing elastic modulus of the cement sheath, and eventually changed to compressive stress from tensile stress. The hoop tensile stress of the cement sheath increases first and then tends to decrease with the increasing internal casing pressure, the larger the local formation stress, the smaller the pore pressure and the smaller the hoop tensile stress of the cement sheath it preforms. The findings of this paper are of great guiding significance to the research of the cement sheath stress variations during volume fracturing in shale formations and to the optimization of fracturing design

New Analytical Method to Evaluate Casing Integrity during Hydraulic Fracturing of Shale Gas Wells

An accurate analysis of casing stress distribution and its variation regularities present several challenges during hydraulic fracturing of shale gas wells. In this paper, a new analytical mechanical-thermal coupling method was provided to evaluate casing stress. For this new method, the casing, cement sheath, and formation (CCF) system was divided into three parts such as initial stress field, wellbore disturbance field, and thermal stress field to simulate the processes of drilling, casing, cementing, and fracturing. The analytical results reached a good agreement with a numerical approach and were in-line with the actual boundary condition of shale gas wells. Based on this new model, the parametric sensitivity analyses of casing stress such as mechanical and geometry properties, operation parameters, and geostress were conducted during multifracturing. Conclusions were drawn from the comparison between new and existing models. The results indicated that the existing model underestimated casing stress under the conditions of the geostress heterogeneity index at the range of 0.5–2.25, the fracturing pressure larger than 25 MPa, and a formation with large elastic modulus or small Poisson’s ratio. The casing stress increased dramatically with the increase of in situ stress nonuniformity degree. The stress decreased first and then increased with the increase of fracturing pressure. Thicker casing, higher fluid temperature, and cement sheath with small modulus, large Poisson’s ratio, and thinner wall were effective to decrease the casing stress. This new method was able to accurately predict casing stress, which can become an alternative approach of casing integrity evaluation for shale gas wells

Mechanical Properties and Acoustic Emission Properties of Rocks with Different Transverse Scales

Since the stability of engineering rock masses has important practical significance to projects like mining, tunneling, and petroleum engineering, it is necessary to study mechanical properties and stability prediction methods for rocks, cementing materials that are composed of minerals in all shapes and sizes. Rocks will generate acoustic emission during damage failure processes, which is deemed as an effective means of monitoring the stability of coal rocks. In the meantime, actual mining and roadway surrounding rocks tend to have transverse effects; namely, the transverse scale is larger than the length scale. Therefore, it is important to explore mechanical properties and acoustic emission properties of rocks under transverse size effects. Considering the transverse scale effects of rocks, this paper employs the microparticle flow software PFC2D to explore the influence of different aspect ratios on damage mechanics and acoustic emission properties of rocks. The results show that (1) the transverse scale affects uniaxial compression strength of rocks. As the aspect ratio increases, uniaxial compression strength of rocks decreases initially and later increases, showing a V-shape structure and (2) although it affects the maximum hit rate and the strain range of acoustic emission, it has little influence on the period of occurrence. As the transverse scale increases, both damage degree and damage rate of rocks decrease initially and later increase

Stick–Slip Characteristics of Drill Strings and the Related Drilling Parameters Optimization

To eliminate or reduce stick–slip vibration in torsional vibration of the drilling string and improve the rate of penetration (ROP), a stick–slip vibration model of the drilling string considering the ROP was established based on the multidimensional torsional vibration model of the drilling string. The model was verified by simulation analysis. The characteristics of the drilling string stick–slip vibration in the three stages of stationary, slip, and stick were analyzed. This paper investigated the influence of rotary torque, rotary speed, and weight on bit (WOB) on stick–slip vibrations in the drill string. Based on this, the relationship between the drilling parameters and ROP was established. Drilling parameter optimization was completed for soft, medium-hard, and hard formations. Results showed that appropriately increasing torque and decreasing WOB can reduce or even eliminate stick–slip vibrations in the drill string and increase the ROP. The parameter optimization increased the ROP by 11.5% for the soft formation, 13.7% for the medium-hard formation, and 14.3% for the hard formation. The established drill string stick–slip vibration model provides theoretical guidance for optimizing drilling parameters in different formations