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In view of the geological characteristics of high pressure in salt-gypsum formation of deep wells in Tarim Piedmont structure, high-density oil-based drilling fluids are widely used, which makes it difficult for subsequent cementing work. In order to solve the technical difficulties of cementing high-density oil-based drilling fluid and salt-gypsum formation in KS well, which is a key exploration well in this area, through analysis of cementing technical problems, combined with salt-gypsum formation cementing and deep well ultra-deep well cementing technology, targeted measures before casing running, optimization of flushing aggravated isolating fluid and aggravating agent are carried out. In addition, relevant technical measures are put forward based on the optimization of cement slurry additives, the design of slurry formulation pipe string structure and the optimization of cementing technology. A set of flushing aggravating isolating fluid was prepared by introducing small particle size, concentrated superfine aggravating agent and hematite powder with relatively large particle size, and a set of high-density cement slurry with good comprehensive performance was obtained by optimizing cement slurry additives and introducing super high-density aggravating agent GM-1. In order to ensure the safety of cementing, the adaptability test of cement slurry formula was carried out, focusing on the adaptability test of cement slurry temperature and density: when the temperature changes + 5 °C the density increases + 0.03 g/cm3, the thickening time of the system changes less than 44 min, the system has good stability, and the anti-channeling performance of cement slurry SPN is less than 3, which has good anti-channeling function and meets the construction requirements, At the same time, the compatibility experiments of different proportions and different media and the simulated intermittent cementing experiments are added to meet the requirements. Field application of KS well shows that the technology can meet the cementing requirement of oil-based drilling fluid in Piedmont area.

During cementing operation with oil-based drilling fluids, the casing and well wall are in the "oil wet" environment, and the cement slurry cannot achieve good cementation with the second interface, which seriously affects the cementation quality of the cementing interface. Therefore, it is very important to select a flushing fluid with good performance and high flushing efficiency for cementing operation with an oil-based drilling fluid. An integrated measurement system of interface parameters and a rotating liquid interface tension tester is selected in the room. A set of evaluation methods of wetting reversal is developed to evaluate the wetting reversal ability of type A and type-B flushing fluids on site to optimize the reasonable type and concentration of the flushing fluid. The experimental results show that under the same concentration, the surface tension and interfacial tension of type A flushing solution are lower than those of type-B; that is, the hydrophilic effect of type A flushing solution is better than that of type-B. The wettability reduction of type A is better than that of type-B. The wetting reversal ability of type A flushing solution with a surfactant concentration of 30% is better than that of type-B. The evaluation methods include surface tension, interface tension, dewetting ability, and oil washing ability of the flushing fluid, and the evaluation of the wetting reversal ability is carried out on the basis of the sandstone, sheet metal (steel for three open casings on site), and slide glass (as a reference). Then, according to the optimal concentration of the flushing fluid, a mixing experiment of the two kinds of flushing fluids is carried out to evaluate the ability of wetting reversal, and compared with the experimental results of A and B, the reasonable flushing fluid formula is finally selected. A proper analysis of the adaptability of the evaluation method of the flushing fluid is conducive to the reliable evaluation of the performance of the flushing fluid and the enhancement of the operator's ability to grasp the cementing quality. To guide the field practice has a very important practical significance, but it also has a guiding role for the development of new pre-liquid products.

The annulus has a wide and narrow clearance due to casing eccentricity in the cementing process and due to the eccentricity of casing in the process of cementing. Because the flow resistance of the drilling fluid in the wide gap is less than that in the narrow gap, the phenomena of a delayed flow or even an overall nonflow occurs in the narrow gap. Based on the existing displacement efficiency calculation model, this paper establishes the cementing displacement efficiency model under the condition of oil-based drilling fluid, explores the residual layer thickness of drilling fluid on the casing side and the sidewall side, and then links the annular displacement efficiency to the injection displacement in combination with the circulating mode resistance pressure drop formula so as to explore the change in the cementing displacement efficiency under different displacements. Considering the change in the physical parameters of annulus fluid, the change in annulus displacement efficiency is obtained. On this basis, the relationship between the wellhead cement injection flow and the annulus retention layer is studied; then, the displacement is calculated. The reasonable cementing displacement is calculated by combining the displacement with annulus displacement efficiency. The results show that the thickness of the annular detention layer increases with the increase in the casing eccentricity in the same well depth, and the growth rate of the detention layer on the wellbore side is greater than that on the casing side at the same circumferential angle. The greater the displacement, the greater the annular circulation pressure drop and circulation equivalent density, thus increasing the cementing risk. The displacement is reasonably designed. The research results in this paper have a certain guiding significance for improving the displacement rate of isolation fluid under oil-based drilling fluid conditions.

The LH11-1 FPSO is an 80,000 t cylindrical structure that is responsible for the processing, storage, and offloading of process oil from existing and newly developed oilfields. In this paper, a full probabilistic analysis was developed based on very detailed CFD simulation results to evaluate ventilation, gas dispersion, explosion, and fire scenarios. A detailed fire and explosion risk analysis of LH11-1 FPSO was performed based on NORSOK Z-013 and FABIG Technical Note 11. The risk-based calculations were performed applying FLACS, KFX, and DNV GLEXPRESS Fire. Finally, the oil and gas dispersion, fire, and explosion consequence risks were calculated under the credible combination of leak frequency and leak location. By this probabilistic risk analysis, it was found that the west wind could generate optimal ventilation conditions for the topside process area of FPSO compared to other wind directions, while the hull region was poorly ventilated for all wind directions. The explosion risk analysis showed that the FPSO system would take no action in terms of explosion risk according to the acceptance criteria of 10−4 occ/year. Meanwhile, the fire risk analysis demonstrated that the PR1 first and second deck, PR2 first and second deck, process deck, offloading on starboard, and the base of the flare tower would have different impacts from the fire, and the PR1 first deck and PR2 first deck at the topside deck would be severely impacted regions.

In this paper, the three-dimensional (3-D) non-linear dynamics of inclined supported pipes conveying fluid with motion constraints are investigated. The motion constraints are modeled by an array of four and an array of two cubic non-linear springs. The spring forces are incorporated into the equations of motion via the method of virtual work. The equations of motion, obtained from Hamilton's principle, are discretized into 18 coupled non-linear ordinary differential equations using Galerkin's method, and solved numerically via Houbolts's method and Newton-Raphson iterative technique. Bifurcation diagram and oscillation trajectories are plotted to show the characteristics of some typical motions. The effect of system parameters, such as the inclination angel and spring stiffness, on the system dynamics is investigated.

In the exploration and development of deep reservoir resources, well kick often occurs during drilling. The occurrence of well kick can change the flowing state and the various properties of the drilling fluid, which can have a very important impact on the wellbore temperature distribution. Based on the actual situation in the drilling process, the wellbore and formation heat transfer model in the case of normal circulation and in the case of well kick in the open-hole formation was established. The model was discretized by using the finite volume method and solved with under-relaxation iterative method. By comparing with previous research results, the validity of the model was established. Compared with the condition of normal circulation, the occurrence of well kick significantly changes the wellbore temperature distribution and has an important influence on the temperature difference profile and formation radial temperature distribution. Sensitivity factors that affected the wellbore temperature distribution were analyzed. Based on the difference in wellbore temperature distribution under normal circulation conditions and well kick conditions, this paper proposes a new method to detect the occurrence of well kick by monitoring the annulus temperature change. The new method can provide guidance for the well control operations and drilling operations.

Methane hydrate is the vast potential resources of natural gas in the permafrost and marine areas. Due to the occurrence of phase transition, the gas hydrate is dissociated into gas and water and absorbs lots of heat. The incomprehensive knowledge of endothermic reaction in permafrost sediments still restricted the production efficiency of hydrate commercial development. This endothermic reaction leads to a complex thermal diffusion in permafrost, which directly influences the phase transition in turn. In this research, the heat during the exploitation is transferred in two forms (specific heat and latent heat). Besides, the melting point is not constant but depends on the pore size of the reservoir rock. According to these features, a thermal diffusion model with phase transition is established. To calculate the governing equation, the pore size distribution is obtained by using the nuclear magnetic resonance (NMR) method. The heating tests are conducted and simulated to calibrate the coefficient (i.e., transverse surface relaxivity) of NMR. Then, the temperature field evolution of the hydrate reservoir during the exploitation is simulated by using the calibrated values. The results show that the temperature curves have a typical plateau related to the pore size distribution, which is effective to obtain the surface relaxivity. The heat transfer is remarkably limited by the endothermic effect of the phase transition. The hydrate recovery efficiency may depend largely on the heating capacity of the engineering operation and the rate of gas production. Compared to the conventional petroleum industry, it is significant to control the maximum temperature and temperature distribution in engineering operations during hydrate development. This research on the temperature behavior during onshore permafrost hydrate production could provide the theoretical support to control heat behavior of offshore hydrate production.

In is paper, the hydrate decomposition behaviours in the sediments were captured by the Cryo-SEM method, and the microcosmic characteristics of sand production during the decomposition process were analyzed. (1) The gas hydrate decomposition increases pore space and reduces reservoir strength: The expansion action of decomposition water & gas, softening action of decomposition water and compression action by overlying stress (crustal stress) promoted sand production, deformation and subsidence of NGH reservoirs in the mining process. (2) Decomposition of NGH has a greater impact on sediments with smaller particle size. (3) The particle size of NGH may be larger than the particle size of mud in the reservoirs, and acting as "gravel" plays a certain role in sand control. Therefore, the particle size of NGH cannot be ignored in the design of sand control. (4) It has been revealed and verified that sputtering (splashing) is a unique process for sand production caused by NGH decomposition. In other words, the rapid expansion of the volume by decomposed gas and water from NGH leads to eruption and sputtering of hydrate particles, providing the driving force for sand migration, which is the different way of sand production in conventional oil and gas.

Polymeric surfactant flooding is an effective method to improve oil recovery, and the stability of the emulsion is closely related to the effect of surfactant flooding. The preparation method for a surfactant-stabilized emulsion is relatively simple, and the emulsion produced by the existing device cannot simulate the real formation conditions. To better simulate the emulsification of polymeric surfactant during formation and to study the influencing factors of emulsion stability, a new sieve plate rotary emulsification device was used to prepare emulsions instead of the traditional high-speed shear emulsifier, and the stability of emulsions prepared by different methods was compared. The parameters of the device were optimized by determining the water content, particle size, and Turbiscan Stability Index TSI (stability parameter) of the emulsion. The factors affecting the stability of the emulsion were studied by using the optimized experimental device. The results showed that the optimized parameters of the sieve plate rotary emulsification device were 5 sieve plates, diameter of 1 mm, and emulsification time of 60 min. The stability of the emulsion prepared by the new device was better than that of the emulsion prepared by the traditional high-speed stirrer, which can be attributed to the more abundant contact and mix of oil and surfactant solution. Meanwhile, as the polymeric surfactant concentration, salinity, and water–oil ratio increased, the stability of the polymeric surfactant emulsion increased. The results of this study provide a theoretical basis and guidance for better simulation of polymeric surfactant migration and emulsification during formation.

In the exploration and development of deep reservoir resources, the occurrence of well kick will have a very important impact on wellbore temperature distribution during circulation. This study aims to investigate the wellbore temperature distribution during circulation when well kick occurs in a continuous formation from the bottom-hole. A transient temperature model was established by the first law of thermodynamics. The finite volume method was used to discretize the model and the under-relaxation iterative method was used for numerical calculation. The validity of the model has been verified by the previous typical models and actual measured temperatures. The calculation results showed that the highest temperature of annulus fluid was at the bottom-hole and annulus fluid temperature increased as the formation high-temperature fluid continuously enters the annulus when well kick occurred. The occurrence of well kick led to a significant increase in outlet fluid temperature and bottom-hole fluid temperature. The occurrence of well kick changed the formation radial temperature distribution and the temperature difference distribution between the annulus fluid and the drilling fluid inside the drill string. The flow rate of the well kick and the location of the well kick occurred also had an important impact on wellbore temperature distribution.

In this paper, the coupled axial and transverse non-linear vibrations of a simply supported pipe, subjected to motion-limiting constraints, conveying pulsating fluid are investigated. The equations of motion are discretized into a set of coupled ordinary differential equations via Galerkin's method, which are then solved using Houbolt's method combined with Newton-Raphson iterative technique. The bifurcation diagrams are constructed to present the global dynamics of the system. Phase-plane portraits, Poincare maps and power spectrum diagrams are plotted to show the characteristics of some typical motions, such as quasi-periodic and chaotic motions. Finally, the influence of axial motion on the system dynamics is investigated.

Purpose Chitosan is an easily accessible and biocompatible natural molecule which facilitate the immune system. In recent studies, chitosan is being applied to the drug nanosphere to deliver drugs. However, whether chitosan could promote health under exercising condition remains yet to be elucidated. Hence, we designed to investigate the effect of chitosan on swimming rats. Methods Sprague-Dawley (SD) rats were divided into four groups, exercise with chitosan, exercise with water, sedentary with chitosan, and sedentary with water. After four weeks of exercise and chitosan/water gavage, the blood was collected, and its biochemical index, complete blood count, and related parameters, and cytokines were detected and analyzed. Results The level of blood urea nitrogen (p = 0.0380), total cholesterol (p = 0.048), and low-density lipoprotein (p = 0.0338) were decreased, while the number of red blood cells (p = 0.001), hematocrit (p = 0.01), and mean corpuscular volume (p = 0.039) were increased in chitosan group. Furthermore, the combination of chitosan and swimming decreased the red blood cells distribution width. Conclusions Our study support that chitosan could facilitate the health during exercise.

In this work, we investigate immiscible displacement in porous media with the displaced fluid being shear-thinning. We focus on the influence the heterogeneous viscosity field in the shear-thinning fluid brings on viscous fingering, which has received little attention in the existing researches. Lattice Boltzmann simulations of immiscible displacement with a power law model implementation in the displaced fluid are conducted. The lattice Boltzmann algorithm is validated against Newtonian and non-Newtonian flows in a channel. The effects of the shear-thinning property and the viscosity heterogeneity on viscous fingering are considered in the simulations. The results show that with stronger shear-thinning property (lower power law exponent n), there is stronger viscosity heterogeneity in the displaced fluid, and the viscous fingering shows weaker instability. The influence of a heterogeneous viscosity field on viscous fingering is dominated by the viscosity in the low-viscosity regions, while the high-viscosity regions show little influence. The influence of the local viscosity on viscous fingering is dependent upon the local shear rate. A concept of ‘effective field viscosity’ is introduced to quantitatively characterize a heterogeneous viscosity field. A shear rate weighted averaging algorithm is proposed to calculate the effective field viscosity from a heterogeneous viscosity field. The algorithm is tested in several cases and shows good performance to represent the influence of the heterogeneous viscosity field.

We investigated immiscible displacement in a channel considering regular surface roughness at walls. A color-fluid LBM code is developed and validated against the Hagen–Poiseuille flow before it is employed for simulating the displacement process. The dimensionless roughness height and roughness spacing ratio are defined to characterize the surface roughness. The simulation results show that the presence of surface roughness obviously impels a finger formation in a channel. The impelling effect is more significant at larger roughness heights and medium roughness spacing ratios. The critical capillary number and viscosity ratio of a finger formation is reduced with increasing roughness height. The obvious effect of wettability on the finger development in a smooth channel is attenuated in rough channels. The attenuation magnitude increases with increasing roughness height.

Natural gas hydrate (NGH) is one of the potential clean energy resources in the 21st century. The gas and water permeability of hydrate-bearing sediments (HBS) is a significant factor that can be used to evaluate the productivity of NGH. China's marine NGH mostly exists in silty-clay sediments which has a high risk of sand production. Thus, it is difficult to discuss the dynamic permeability of the HBS during exploitation with sand production. It restricts the sustainable and economical production of the HBS. This study put new insights into sand production experiments during depressurization production in hydrate silty-clay sediments. The results show that the NGH particle size (saturation) plays a role in retaining mud/sand during exploitation and it influences the abnormal permeability. From the relationship between particle size of gravel pack and permeability, a new relationship between the hydrate saturation (particle size) and permeability is proposed. The permeability of the HBS during exploitation presented increase-decrease-increase trends with a decrease in the NGH saturation.

An experimental investigation was conducted on a flexible riser with and without various helical strake coverages, with the aim of further improving the understanding of the response performance of the vortex-induced vibration (VIV) of a riser with helical strakes. Two current profiles, including uniform and linearly sheared currents, were simulated. The VIV displacements, VIV strains and hydrodynamic forces were directly measured from the test. Based on the fatigue damage method, the fatigue damage was obtained from the measured strain. Strakes with different coverages were analysed, and response parameters such as the displacement response and fatigue damage were studied. The results of the straked model test indicate that the response characteristics of a bare riser model can be quite distinct from those of a riser with helical strakes, and the response performance closely depends on the coverage of the helical strakes. The results also show that the flexible riser with 75% and 50% strake cover...

The effects of different helical strake coverage on the vortex-induced vibration (VIV) of a model flexible riser were studied experimentally, with the aim of further improving the understanding of VIV responses. Uniform and linearly sheared currents were simulated to study response parameters such as non-dimensional displacement, fatigue damage, suppression efficiency, and the comprehensive evaluation is further studied. Test results of the bare model for a uniform current showed that the behavior of both the standing wave and traveling wave dominated VIV displacement. However, for a linearly sheared current, traveling wave behavior dominated VIV displacement in the high-velocity range. The results of the straked model tests indicated that the response was strongly dependent upon the amount of coverage of helical strakes. The flexible riser with 75% strake coverage gave the best comprehensive evaluation in a uniform current, and 50% strake coverage gave the best comprehensive evaluation in a linearly sheared current.

During the drilling process, the variations of the thermophysical properties of drilling fluid have an important effect on the wellbore temperature distribution. As the wellbore temperature changes, the thermophysical properties of drilling fluid change. In this work, the effect of the variations of density, thermal conductivity, specific heat capacity, and viscosity of drilling fluid with temperature on wellbore temperature calcilation during drilling was studied using water as drilling fluid, and the extent to which each thermophysical property affected the calculation of the wellbore temperature distribution was compared. The calculation results show that the variations of density and thermal conductivity of drilling fluid with temperature have a little effect on wellbore temperature calcilation, and the variation of specific heat capacity of drilling fluid with temperature has negligible effect on wellbore temperature calcilation, while the variation of viscosity of drilling fluid with temperature has significant effect on wellbore temperature calcilation. Therefore, whether to consider the variations of thermophysical properties of drilling fluid with temperature can have a certain effect on the calculation of wellbore temperature distribution during drilling. The thermophysical property of the drilling fluid that is very sensitive to temperature variation should be fully considered during the wellbore temperature distribution calculation.

Chitosan oligosaccharide (COS) degraded by chitosan, is an easily accessible and biocompatible natural molecule, which can facilitate the immune system. Running is one of the most effective forms of exercise. Persistence in running can effectively improve the body's resistance against pathogens. However, whether the combination of COS and running could benefit immune status still remains to be elucidated. We used Sprague-Dawley (SD) rats to explore the combinatory effect of COS and running. The organs and blood of the rats were collected after four weeks and the organ body mass index, biochemical and blood routine examination, cytokines, and T cells in the spleen and blood were detected and analyzed. In the group intragastric administration of COS only, the level of blood lactate dehydrogenase was increased, while the blood creatinine, red blood cells, lymphocytes, and serum TNF were decreased. Furthermore, COS combined with running promoted the development of spleen and lung, the level of lymphocytes, T cell and CD8+ T cell ratio in the blood, and serum TNF level. At the same time, the level of lactate dehydrogenase, serum IL-2, and T cell ratio in spleen were decreased. Therefore, our study indicated that COS combined with running could improve the immune status of rats.

During the drilling process, the temperature distributions of the borehole and the formation under the condition of drilling fluid loss have a very significant effect on the borehole pressure prediction, the rheological design of drilling fluid and the borehole stability. Aiming at the complex downhole situations as drilling fluid loss occurs during drilling, a new two-dimensional model is proposed to study the temperature distributions of the borehole and the surrounding formation in the presence of the lost circulation. The law of the borehole temperature distribution when drilling fluid loss took place in the two-dimensional area at the bottom of the well was obtained. Comparing with the scenario of no drilling fluid loss, the borehole temperature is reduced at the same well depth in the case of drilling fluid loss. The occurrence of drilling fluid loss greatly disturbs the temperature distribution of drilling fluid in the annulus in the drilling fluid loss area. The location of drilling fluid loss has a conspicuous effect on the borehole temperature distributions. The occurrence of drilling fluid loss renders a more prominent effect of casings on the temperature profile of the medium around the borehole. As the drilling fluid loss rate increases, the borehole temperature at the same well depth decreases.

Horizontal well drilling technology is widely used in the exploitation of petroleum and natural gas, shale gas, and geothermal resources. The temperature distribution of wellbore and surrounding formation has a significant influence on safe and fast drilling. This study aims to investigate the temperature distribution of horizontal wellbores during circulation by using transient temperature model. The transient temperature prediction model was established by the energy conservation law and solved by the relaxation iterative method. The validity of the model has been verified by the field data from the Tarim Oilfield. The calculation results showed that the highest temperature of the drilling fluid inside the drill string was at the bottomhole and the highest temperature of annulus drilling fluid was at some depth away from the bottomhole. Sensitivity analysis of various factors that affect the temperature distribution of annulus drilling fluid were carried out, including the circulation time, the flow rate, the density of drilling fluid, the inlet temperature, the vertical depth, the horizontal section length, and the geothermal gradient. It can be found that the vertical depth and the geothermal gradient have a significant influence on the bottomhole temperature, and inlet temperature plays a decisive influence on the outlet temperature. These findings can supply theoretical bases for the horizontal wellbore temperature distribution during drilling.

Laboratory tests were conducted on a flexible cylinder to improve the understanding of the response performance of vortex-induced vibration (VIV). The experiment was performed in a towing tank and the relative current was simulated by towing the flexible cylinder in one direction. Based on modal superposition, VIV displacements were obtained from the measured strain. VIV responses from different current cases were analysed, and the response performances, such as the motion trajectory, strain response, and fatigue damage, were studied. The motion trajectory for the flexible cylinder at low velocity displays the typical type-eight figure, very similar to that for a rigid cylinder. However, with increased velocity, the motion trajectory becomes chaotic, induced by the multi-mode VIV responses. Simplified fatigue damage based on the typical steady motion trajectory is usually a little larger than the measured fatigue damage based on the chaotic motion trajectory, but of the same order.

There is no united method to evaluate developed low-grade reservoir. Cash flow economic evaluation method is widely used in China and other countries. Cash flow method contains three different economic evaluation methods, they are VP, IRR and investment recovery period methods. In this paper, we evaluate a developed low-permeability sandstone reservoir and a developed middle-high permeability complex fault block sandstone reservoir with the cash flow economic evaluation method. We get the evaluation standard charts of the developed low grade big reservior, developed fault block reservior with middle-high permeability, developed fault block reservior with low permeability and heavy oil thermal recovery reservior. This new cash flow method lays theoretical foundations for evaluation of developed low-grade reservoir and other kinds of reservoirs.

Continental strata in Northeast Sichuan presents poor drillability due to high formation pressure, which leads to low ROP, wellbore inclination and lost-circulation with mud drilling technique. Gas drilling not only dramatically improves ROP and well quality, but also decreases construction cycle. However, this method was apt to trigger downhole explosion through payzones drilling, which would result in downhole tool broken, drilling failure and even well abandonment. During the exploitation of gas reservoirs in Northeast Sichuan, downhole explosion has happened in P104-1, P303-1, Y2 and Y3 wells, and these severe accidents provide an important incentive for developing a downhole explosion monitoring system for gas drilling to decrease downhole explosion risk. This paper will focus on the development of this system based on MIC-2718-a high-gain, high-performance multifunction DAS card-and other high-precision chemical sensors, which can monitor the concentration changes of CO2, CO, O2, H2S and CH4 in real-time. Visual C++ was employed to develop the real-time data acquisition and display interface, which are useful to display and save or playback curves of real-time data, what's more, intelligent alarm function is also available. This system features simple installation, convenient wire routing and great system stability. Furthermore, the usage of new developed downhole explosion monitoring system provides a safe downhole environment for gas drilling.