Due to strong heterogeneity between horizontal well sections or encounter faults, large natural fracture zones during drilling, casing deformation of shale gas wells in Sichuan Basin often occurs, which will result in conventional mechanical segmentation tools cannot pass through the casing deformation section, posing a huge challenge to the efficient stimulation of shale gas horizontal wells. To this end, a non-sequential fracturing process suitable for unconventional oil and gas reservoir horizontal wells is proposed. This process is different from the traditional sequential fracturing from target B in the horizontal section to target A, but instead achieves cluster perforation and fracturing at any position of the horizontal segmented reconstruction well section, and the entire well section can be temporarily sealed after each fracturing. For well sections that may be at risk, it is recommended to avoid them and fracturing the normal well section first, and then fracturing the risky well section. For horizontal sections affected by faults or casing wells, highly targeted solutions are provided. Taking the A1 well of shale gas in southern Sichuan as an example, on-site experiments verified the feasibility of non-sequential fracturing technology for horizontal wells, and to some extent, the negative impact of large fracture zones on the volume of stimulation was reduced, effectively avoiding repeated coverage of the stimulation area. In addition, the minimum outer diameter of the tool string used in this process is only 79 mm, which is also adaptable and targeted for the casing transformation well section. It can be a beneficial supplement to the plug segmentation process and has broad promotion and application value. 

Narrow density window, simultaneous leakage and influx, high temperature and high pressure have become the difficult problems faced by and to be solved urgently for realizing safe and efficient drilling in deep water drilling. The managed pressure drilling technology has achieved good application effect on land and shallow sea in China, but the research on this technology and equipment system has not been systematically carried out in the domestic deep-water field. Based on the investigation and analysis of the drilling engineering needs of a work area in the South China Sea, this paper proposes the deep-water managed pressure drilling technology below the tension ring, and describes the deep-water managed pressure drilling riser pipe system and managed pressure drilling platform manifold system from the aspects of system composition and function; the comparison and analysis are made between the jack-up platform and the floating platform in terms of the working state of the platform, the deployment sequence of the riser system of the managed pressure drilling, and the characteristics of the drilling fluid circulation; taking the bottom hole pressure as the research objective, the simulation calculation of the influence of rig heave, large displacement drilling, booster injection / throttling parameters and other factors on it were carried out. On this basis, it is pointed out that China′s deep-water managed pressure drilling should carry out key research from the aspects of technology, bottom hole pressure fluctuation mechanism and control methods, and real-time hydraulic calculation software development to enrich China′s deep-water drilling technology, meet the needs of deepwater drilling projects, and help efficient exploration and development of deep-water oil and gas resources. 

Nitrogen drilling and completion of reservoirs is one of the revolutionary technologies for effectively utilizing reserves and releasing production capacity in low-permeability gas reservoirs such as tight sandstones. During the nitrogen drilling and completion operation of the reservoir, the wellhead is in an open state during the tripping and completion of the well string. At this time, it is necessary to use the wellhead nitrogen suction technology to control the flow of natural gas produced by the formation to the outlet of the sand discharge pipeline for treatment. Therefore, based on numerical simulation methods, the article systematically studied the gas flow law during nitrogen suction operation under open well conditions, considered the diffusion phenomenon of natural gas, established a gas flow model, and quantitatively analyzed the main factors affecting the nitrogen suction effect. Research has shown that the effectiveness of nitrogen suction is mainly influenced by injection method, nitrogen suction volume, installation position of suction device, length of sand discharge pipeline, and natural gas production. The concentric injection method has better suction effect compared to the oblique insertion injection method; under low suction volume, the larger the nitrogen injection volume, the higher the suction rate. As the suction volume continues to increase, the suction rate reaches its peak and then decreases; the closer the suction device is to the outlet of the sand discharge pipeline, the shorter the sand discharge pipeline, and the lower the gas production of the formation, the better the suction effect, and the lower the critical suction volume required to achieve complete suction. The research results provide theoretical support for optimizing the design of nitrogen suction process and ensuring safe operation under open well conditions for nitrogen drilling and completion in reservoirs. They have been applied on-site in Sichuan Datachang Gas Field, achieving 100% suction of natural gas produced in the formation under open well conditions for nitrogen drilling and completion in reservoirs, ensuring operational safety. 

The gravel layer of Kuqa Piedstone in Tarim Basin is developed, with high gravel content, large particle size, high compressive strength and poor drillability in Bozi block, which are the key factors resulting in low drilling efficiency and complex drilling accidents. In this paper, the formation lithology characteristics, drilling characteristics and failure mode analysis of the large gravel layer in the fore-salt section are carried out, and on the basis of this, the special-shaped cutter structure design of the PDC bit, the optimization of cutters layout and rock breaking efficiency are studied, and the design scheme of the special-shaped tooth PDC bit with strong impact resistance and aggression is formed. The design scheme not only improves the anti-impact but also improves anti-eddy performance and the rock breaking efficiency of PDC special cutter bit, which effectively expands the application range of PDC special-cutter bit in gravel layer. This bit has been tested in the high gravel layer of Kuqa Piedstone and achieved excellent application results. The single bit footage reaches 545 m, the average ROP is 4. 72 m/ h, compared with the PDC bit used for this formation in the same adjacent well, the single bit footage increased by 35% , the average ROP by 55% , it successfully solved the problems of low ROP and short footage of single bit in Kuqa formation and other formations. 

Due to the strong reservoir heterogeneity in Sichuan-Chongqing area,in order to increase the means of handling downhole complexities in deep and ultra-deep well sections,a stand-by casing is often used during well design to block out potentially complexities,of which handling is more difficult. If the drilling operation is relatively smooth and the stand-by casing is not utilized,the drilling and completion method for deep slimhole well with ultra-large annulus will be implemented. If the drilling mud density window of target formation is narrow, easily causing leak and collapse,and it′s difficult to deal with,therefore,stuck pipe is likely to occur. To ensure the safe drilling of this kind of well,taking well DB-1 in Penglai gas area as an example,in this paper the difficulties of slimhole drilling for well with ultra-large annulus were analyzed,which includes poor well cleaning,difficulty in loss prevention and treatment and easy stuck pipe,and the technical solutions of this technology has been researched. The safe slimhole drilling technology for deep well with large annulus suitable for DB-1 well is formed through optimization of drilling parameters,drilling fluid properties and study of slimhole drilling supporting technologies. Through field application,it is proved that safe slimhole drilling and completion has been realized in well DB-1,and the drilling task of this well has been successfully completed,which has a good guiding significance for the safe drilling of similar Wells.

According to the problems of deep buried reservoirs in Sichuan Basin, developed fractures and caves, lost-circulation intervals, pipe stuck in faults and fracture zones, highly compacted formation and high temperature, poor drillabiility, frequent failure of downhole tools and etc. , a series of unique drilling technologies have been explored through multiple approaches in recent years. Combining the interaction mechanism of oil-based drilling fluid and shale, multi-stage micro-nano sealing agents and emulsifiers have been developed, the strong plugging technology of oil-based drilling fluid has been formed to cope with the complications of loss, wellbore wall instability and sticking in the drilling process; focusing on the drillability and abrasiveness of the formation, the customized bit was designed to achieve efficient rock breaking in the difficult-to-drill formation; by introducing oscillating screw and enhanced torque impactor, the vibration classification control technology has been formed to improve the stability of downhole tools; the self-developed cooling device is applied to high temperature resistant rotary guide tools, reducing the failure rate of downhole tool; with reference to the mature technology of pressure control and density reduction in the " Three high" well, precise pressure control and density reduction have been implemented to release power for speed increase. These series of technologies have strongly supported the exploration and development of deep shale gas in Sichuan Province and met the needs of sustainable exploration and development of deep shale gas.

Hollow light particles are prone to crush under high temperature and high pressure at the bottom of the hole, resulting the deterioration of rheological properties of low-density cement slurry, which leads to increase of friction resistance, density and cement loss risk. To deal with the phenomenon, a high-activity low-density cement slurry system (HALDCP) with constant density and secondary hydration characteristics was developed, using high active composite solid materials and supporting activators. Isothermal microcalorimeter, x-ray diffractometer, thermal gravimetric analyzer, scanning electron microscope were applied to analyze the development rule of early hydration, chemical structure of hydration products, microstructure and compressive strength. The results indicated that HALDCP had constant density and rheology. In HALDCP, alkaline hydration products and hydration heat generated by Portland cement activated composite lighting materials, which made the hydration process of the slurry had secondary hydration and formed “Double exothermic peaks”. At the meanwhile, it increased hydration heat and the content of hydration products. Ca(OH)2 was depleted by the hydration of HALDCP to form lots of calciumite and C-(A)-S-H, increasing hydration products of the cement, solid volume fraction, microstructural density. In contrast with enameled perlite cement with low density, the compressive strength of HALDCP hydrating for 28 days enhanced 16. 7% , and had good durability. 

Improving drilling efficiency is an important part in the process of oil drilling. The optimization of drilling operation is mainly achieved by adjusting drilling parameters, reducing mechanical specific energy and increasing ROP. The specific mechanical energy(MSE) is one of the main indexes to evaluate drilling performance. However, complex drilling operations cause the limitations of most evaluation models in the application process, and formation uncertainty will lead to the problems such as reducing generalization ability of ROP prediction model and non-production time. In this study, multiple prediction models are established for different formations of the target well, the best performance model is selected by evaluation. Firstly, the controllable parameters affecting ROP are analyzed based on the theory of MSE and mutual information method. Secondly, the historical mean value is used as the ROP-increase threshold to convert the regression prediction into the classification prediction, and the prediction performance of classification algorithm models such as K nearest neighbor (KNN), multilayer perceptron (MLP), na?ve Bayes (NB), and logistic regression(LR) is evaluated. Finally, the KNN model suitable for each formation of the target well is optimized, and applied to adjacent well in the same area. The actual verification results show that the prediction accuracy in the four formations of the adjacent well is 0. 94, 0. 94, 0. 92, 0. 96, respectively, and the AUC value is 0. 98, 0. 97, 0. 96, 0. 98, respectively. The model performs well and can help scientific decision-making of drilling construction. 

Weiyuan shale gas well has the characteristics of high production and rapid decline in the initial stage of production. According to the production characteristics, it can be divided into three production stages:flowback after fracturing stage, rapid decline stage, low pressure and low production stage. There are obvious differences in production characteristics in different stages. At low pressure and low production stage, gas well production is low, pressure is low, decline rate is slow, production period is long, and production contribution reaches 60% . The production is easily affected by many factors, such as liquid loading of gas well, frac hit water flooding, system export pressure fluctuation, wellbore plugging and so on. It is the main stage for the implementation of stable production technology. In view of the factors affecting the production and different types of problem wells, technical countermeasures for stabilizing production of old wells with pressurization, foam drainage, plunger, gas lift,shaft cleaning and their combination has been innovatively formed. For instance, priority should be given to pressurization and foam drainage measures for wells with slight fluid accumulation, foam drainage or plunger technology is preferred for intermittent effusion wells, gas lift measures such as opening or closing wells are preferred for wells with serious fluid accumulation, wellbore cleaning or coiled tubing flushing shall be adopted for blocked wells, for water flooded wells with fracturing and channeling, priority should be given to synchronous depressurization gas lift, coiled tubing gas lift and displaced flow. Through the practice of stable production technology at low production stage, a special technical template is formed to effectively solve various production problems of gas Wells, maximize the production of gas Wells, improve the sustainable and stable production capacity of old Wells, and realize the efficient development of shale gas.