The Seismic Acquisition Technology for Double Complex Areas in the Southern Margin of the Junggar Basin
Due to the complex surface seismic geological conditions and complex deep seismic wave field and structural characteristics，the overall seismic data signal-to-noise ratio in the southern margin of the Junggar Basin is low，making it difficult to accurately analyze the structure，which has seriously affected the oil and gas exploration process. With the significant breakthrough of the GT1 well in the lower combination，the overall deployment of the area has implemented wide azimuth，wide bandwidth and high density seismic exploration project covering more than 3 800 km2 in steps over the past five years. In the seismic data acquisition phase of these exploration projects，a series of targeted technologies have been applied，including surface conglomerate survey techniques，laser radar aerial information—assisted shot points pre-design，and well-seismic mixed source efficient acquisition techniques. These technologies have enabled the annual increase in shot density within the affordable cost range. After several years of integrated technical breakthroughs，the imaging effect of seismic data in this area has been greatly improved，and the well-seismic error has been significantly reduced. The seismic acquisition technology in the dual complex area on the southern margin of the Junggar Basin is of great reference significance for similar seismic acquisition projects in exploration areas.
The existing formation testing and fluid drainage operation methods are found with problems such as the long operation duration，complex operations，and likely damage to equipment，which seriously restrict the improvement of oil and gas field development efficiency and the reduction of development costs. Given these，this paper conducts a summary and analysis of the current state of technology regarding non-metallic composite coiled tubing materials and their associated running and pulling equipment used in the oil and gas field development sector. The technical parameters and field operation cases of different types of tubing and equipment are listed. Comparative analysis shows that in terms of tubing materials，the non-metallic composite coiled tubing available in China still cannot meet the operation requirements for wells with depths over 2 000 m，due to factors such as material strength and temperature resistance. It is necessary to further optimize material performance and develop and apply composite coiled tubing materials with higher strength and temperature resistance；in terms of equipment selection，skid-mounted operation equipment，combined tubing operation equipment，composite coiled tubing operation vehicles，etc.，can all meet the basic needs of current on-site operations of non-metallic composite coiled tubing in China. Comprehensive comparison of various operating equipment in terms of equipment costs，technical parameters，and operation efficiency suggests the combined use of non-metallic composite coiled tubing and conventional lightweight workover rigs is the most suitable application configuration for the current formation testing and fluid drainage operation using non-metallic composite coiled tubing.
As the exploration and development of Tuha Oilfield gradually advances toward deeper and more complex areas，the well site deployment is approaching environmentally sensitive farmland and forest. In order to ensure the safe drilling of deep wells，higher technical requirements are proposed on environment protection，high temperature resistance and handling capacity of downhole complex issues and anomalies of drilling fluids. Considering factors such as wellbore stability，wellbore cleanup，and reduction of friction and resistance，researches were conducted in terms of the drilling fluid performance of inhibition，plugging，lubrication and environment protection. Through the laboratory experiments to optimize the desulfonation degradable high temperature resistant treatment agent and system composition，a high temperature environmentally friendly drilling fluid system was derived from the composite salt drilling fluid formula. As shown in laboratory testing，the drilling fluid has stable performance at 160 °C，with the EC50 of 5.1×104，and is non-toxic with the heavy metal content complying with the national ecological environment discharge criteria. The HTHP fluid loss is less than 10 mL，the mud cake drag coefficient is 0.043 7-0.052 4，the yield point is greater than 12 Pa，and the shale rolling recovery rate is 95.36%. The high temperature environmentally friendly drilling fluid system has been successfully applied in Well Jixin-6. The drilling of the whole well is smooth with no complex issue，creating a new record of the deepest vertical depth of the Jixin-1 Block and sufficiently proving that the drilling fluid system has good performances of inhibition，plugging，cutting-carrying and lubrication.
Cuttings Transport Mechanisms in Slimhole Horizontal Wells Considering Drill String Eccentricity
The narrow annulus in slimhole horizontal wells leads to significant differences in Cuttings transport，compared to conventional horizontal wells. To investigate the cutting transport mechanisms in slimhole horizontal wells，a CFD-based numerical model accounting for drill string eccentricity was developed for solid-liquid two-phase flow in the annulus. This study analyzed the effects of key factors，including flow rates，drill pipe rotation speeds，well inclination angles，and drilling fluid properties，on cutting transport in slimhole horizontal wells. The results showed that increasing the drill pipe rotation speed enhances the tangential and axial velocities of the annular fluid and expands the "viscous coupling" region. This facilitates the upward movement of cuttings from the lower side to the upper side of the annulus，thereby improving transport efficiency. Critical thresholds for "rotation speeds" and "flow rates" were identified in highly inclined sections，where cutting transport becomes the most challenging with the two parameters both below the thresholds，and in horizontal sections，where transport becomes more difficult with the two parameters both exceeding the thresholds. Increasing the drilling fluid density enhances the buoyancy acting on cuttings and reduces deposition. The effects of drilling fluid rheological parameters on wellbore cleanup exhibit non-linear trends，with an optimal range existing under different flow rates and rotation speeds. The findings of this research provide theoretical support for optimizing hydraulic parameters in slimhole horizontal wells and preventing issues like drill string sticking.
Research Methods and Main Control Factors of Proppant Migration and Placement Characteristics within Fractures
Proppant transport is a critical process that determines the conductivity of hydraulic fractures and thus，is of great significance for the efficient development of unconventional oil and gas reservoirs. This paper systematically reviews the progress in research on proppant transport，summarizes the advantages and limitations of three types of research methods，namely theoretical models，physical experiments，and numerical simulations，and reveals the multi-factor coupling effects of proppant characteristics，fracture morphology，operational parameters and reservoir environment are revealed. It is indicated that micronized proppants can enhance the filling rate of secondary fractures，but need to be combined with composite proppant injection processes to compensate for insufficient near-end support. In complex fractures，proppant distribution is considerably influenced by the flow splitting and rough fracture surface，requiring optimization through temporary plugging diversion and high-viscosity fracturing fluids. The integration of numerical simulations and machine learning techniques has significantly improved the prediction accuracy of complex fracture networks. Future research shall more focus on dynamic characterization of multi-scale fracture networks，long-term conductivity evaluation under high temperature and pressure，and the industrial application of intelligent fracturing technologies to facilitate controllable proppant placement and long-term conductivity and provide theoretical support for the efficient development of unconventional oil and gas resources.
Experimental Research on the Microscopic Imbibition Mechanism of Tight Sandstone Oil Reservoirs
Imbibition，as one of the main methods to improve the degree of crude oil production in tight sandstone reservoirs，has attracted much attention. Measurement errors of produced oil in imbibition tests lead to wrong evaluation of imbibition performance. Taking the Chang 7 Member of the Yanchang Formation of the Luohe Oilfield in the Ordos Basin as the research object，the effects of imbibition time，interfacial tension，wettability，rock physical properties and imbibition pressure on the imbibition efficiency were studied at the microscopic pore scale through experimental methods such as high-pressure mercury injection and nuclear magnetic resonance. The results show that：（1） The pore structure of the Chang 7 Member core is dominated by small pores，and the capillary force is the main driver for imbibition. With 96 hours of imbibition，the imbibition efficiency of cores reaches a plateau，and the imbibition efficiency of small pores controls the imbibition efficiency of the core. （2） Due to the large seepage resistance of small pores，the imbibition efficiency of small pores is affected by both the driving force and resistance of dialysis. With the decrease in core permeability and interfacial tension，the imbibition efficiency shows a fluctuating trend，and with the increase in the wetting angle，it decreases significantly. （3） When the permeability is lower than 1 mD，the imbibition resistance controls the imbibition efficiency. As the permeability increases，the influence of the imbibition driving force is strengthened. The Chang 7 Member core presents the best imbibition efficiency in the case of an interfacial tension of 3.08 mN/m，a wetting angle of 20°，and an imbibition pressure coefficient of 1.45. The findings of this research provide references for improving the interfacial tension，wettability and imbibition pressure of imbibition treatment media.
Prediction of Sand Production in Underground Gas Storage Rebuilt from a Sandstone Reservoir under Multi-Cycle Alternating Injection-Production
Most of the underground gas storage （UGS） facilities built in China are rebuilt from sandstone gas reservoirs. They are subjected to increased risks of sand production due to the cumulative alternating damage to the reservoir rock structure after multi-cycle alternating injection and production. In order to effectively predict sand production risks，an alternating mechanics experiment considering multi-parameter sensitivity was designed by combining the stress field of the borehole wall of the injection-production well and the shear failure criterion of rocks. Based on the alternating mechanics experiment，the degree of rock strength damage was calculated，and a sand production critical drawdown pressure model based on rock damage degree was proposed. Research showed that the stress field of the reservoir dynamically changes with the production of the gas storage，resulting in a change in the difference between the circumferential and radial stresses of the surrounding rock of the borehole wall of the injection-production well. At the same time，the stress difference also changes along the wellbore circumference. Under the alternating loads，the cumulative damage of rocks grows with the increasing water saturation （for the same particle sizes of rocks） and larger particle sizes of rocks （for the same water saturations of rocks）. The sand production critical drawdown pressure predicted using the proposed method is 11.41 MPa in the early stage of gas production and 3.97 MPa in the late stage. This study provides a new method for determining experimental parameters in alternating mechanics，as well as a new method for judging sand production in alternating injection and production for UGS facilities to guide the UGS production planning and control.
Numerical Simulation Study on Thermal Stimulation Testing Method for Production Profile of Horizontal Wells with Low Fluid Production
Given the technical problems such as noise interference and low testing accuracy existing in production logging of horizontal wells with low fluid production，a production logging method based on active thermal stimulation is proposed. Specifically，a "temperature tracer particle" heat source area with a controlled direction is formed in the wellbore，and the water content and the fluid velocity in the horizontal well are precisely measured at the same time，by monitoring the temperature rise and the movement pattern of the temperature tracer particle through the optical fiber. The results of theoretical model calculation and analysis show that for fluids with different water content，the temperatures of temperature tracer particles formed with the same heating power and heating time are considerably differentiated. The temperature rise of temperature tracer particles is higher in the case of lower water content，and vice versa. Moreover，the fluid velocity in the horizontal well can be effectively captured by measuring the velocity of the released temperature tracer particle with the optical fiber. The temperature tracer particle based on active thermal stimulation are a double tracer of both thermodynamics and kinetics—the temperature evolution directly shows the water content of fluids，and the movement velocity is an accurate measure to invert the fluid flow status. The integration of the two features provides a new technical route for the measurement of parameters of horizontal wells with low fluid production，and reliable and quantitative references for production profile logging of horizontal wells with complex wellbore conditions.
Research Progress of Carbon Based Photothermal Phase Change Composite Materials
Carbon based materials have a wide absorption range for sunlight，high photothermal conversion efficiency，and excellent thermal conductivity and can be used for photothermal conversion of solar power. They are key materials for achieving green utilization of renewable solar energy. However，solar radiation is intermittent，which is unfavorable for the large-scale utilization of solar energy. Therefore，by combining carbon based photothermal materials with phase change materials，the solar energy absorbed by the photothermal materials can be stored in the phase change materials for nighttime use. This research summarized and classified carbon based photothermal conversion materials，reviewed the composite encapsulation strategies of carbon based photothermal conversionand phase change materials，summarized the effects of different combination methods on photothermal conversion efficiency and thermal storage performance，and briefly introduced the applications of photothermal phase change composites in solar water heaters，building energy conservation，and human-body thermal management. Finally，the future development direction of carbon based photothermal phase change composites wasanalyzed，providing references for the preparation of new photothermal phase change composites with high conversion efficiency.
Intelligent Design Methodology of Large Scale Photovoltaic Power Stations in Desert Areas Based on Particle Swarm Optimization
The 2 640 MW large scale centralized grid-connected photovoltaic power station in Karamay，Xinjiang，is taken as an example in this paper，and an intelligent design method for photovoltaic power stations is proposed，based on the Particle Swarm Optimization （PSO） algorithm. This method uses photovoltaic module type selection，installation angle，array spacing and other design parameters as optimization variables，with annual power generation maximization as the objective function and investment costs as constraints，to construct a multi-objective optimization model. Power generation simulation is performed using the PVsyst software combined with MATLAB programming to implement PSO algorithm optimization. Simulation results show that compared with traditional design methods，the intelligent optimization method proposed in this paper can increase the annual power generation of the 2 640 MWphotovoltaic power stations by 3.2% to 41.26×108 kW·h，and shorten the investment payback period by 0.5 years. After completion，the project can reduce CO2 emissions by approximately 7.176×107 t per year，with significant economic and social benefits. The proposed method provides new ideas for intelligent design of large scale photovoltaic power stations.
Technical and Economic Analysis of Solid Particle Thermal Energy Storage Technology in Heavy Oil Thermal Recovery
Review of the current status of molten salt thermal energy storage，concrete and magnesia brick thermal energy storage，and fluidized solid particle thermal energy storage revealed that molten salt thermal energy storage has defects such as low energy density and high pipeline corrosion rates，while concrete and magnesia brick thermal storage suffers from low contact surface heat transfer efficiency. The basic situation of thermal storage was analyzed for an oil field，and a new technical route based on solid particle electric thermal storage was proposed，given the bottlenecks of frequently-used molten salt thermal storage such as high solidification risks，severe corrosion，and high costs. In this technical proposal，sand proppants for fracturing with particle sizes of 0.3~0.7 mm were used as the thermal storage media，and the co-production of steam through efficient electric heating and gravity flow heat exchange was experimentally investigated，which determined a suitable electric thermal conversion efficiency of 85% at an unloading frequency of 2 Hz. Compared with molten salt systems，this technology breaks through the upper temperature limit，avoids the risk of phase transformation （solidification） and reduces the corrosion rate to almost zero. Calculation showed that the payback period of a double-tank flowing solid particle steam production system with a steam output of 100 t/h is about 11.61 years，and the levelized steam costs over a 30-year life cycle is about 172.36 CNY/ton.
