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. 

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.

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. 

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. 

ROP optimization is an important technical approach to reducing drilling costs. It has been found that the water-based drilling fluid composition have a significant impact on ROP in field applications for many years, but the underlying mechanisms are not yet clear. In this study, targeting the difficult-to-drill formations of the Shaximiao Formation in the central Sichuan region, the interaction mechanisms between drilling fluids and rocks, as well as their effects on rock mechanics and drillability, were experimentally explored by altering the composition of the drilling fluids with the aim of enhancing the infiltration capability of fluid. The research indicates that among water-based drilling fluids formulated with bentonite, sepiolite, palygorskite, and nanoclay, the nanoclay-based fluid exhibits the highest rapid infiltration capability into the tight sandstone of the Shaximiao Formation, followed by sepiolite, palygorskite, and bentonite. Nanoclay, due to its low clay platelet content, has a slow filter cake formation rate and a higher instantaneous filtration loss, resulting in a stronger rapid infiltration capability for the configured drilling fluid. The stronger the rapid infiltration capability of the drilling fluid, the more deteriorated the mechanical properties and drillability of rock, and the lower drillability index value, leading to higher rock fragmentation efficiency. The underlying mechanism lies in the promotion of hydration reactions in the Y/ M layer by rapid infiltration, which disrupts the original cementation state within the rock and reduces its resistance to fracturing under external forces. Field tests have shown that after optimizing the drilling fluid, the mechanical drilling speed increased from an average of 1.25 m/h in the upper wellbore section to 2.29 m/h, indicating that improving the rapid infiltration capability of the drilling fluid has good adaptability for ROP optimization in the tight sandstone formations of the Shaximiao Formation and is worthy of further promotion and application. 

The serious and even fatal water lock damage cannot be avoided or eliminated at tightsand reservoirs in China by using the technology system of drilling, completion and fracturing are all with water-based fluids. This leads to low production and low efficiency, and even development failure. Even the popular horizontal well segmented fracturing technology also cost lot with low benefit due to water lock damage. Currently, gas drilling is the only way to completely eliminate water lock damage. By analyzing the geological characteristics of tight gas and the reservoir damage during exploration and development, this paper points out the advantages of gas drilling technology in tight gas exploration and development, and advocates the use of gas drilling technology in tight gas exploration and development to improve the discovery and development of reservoirs. Taking the well of Tarim DX1 as an example, the gas drilling technology for tight gas exploration is demonstrated. Taking Sichuan Basin gas drilling vertical wells, inclined wells, and horizontal wells as examples, the gas drilling technology used for shallow tight gas development is demonstrated.Taking Tarim DB104 well as an example, gas drilling technology for deep tight gas development is demonstrated. Finally, it is pointed out that gas drilling is a new technology for exploration and development of tight gas, and there are still many technical problems to be solved, especially the matching technology of gas drilling in horizontal wells. However, these technologies should be solvable at the current level of science and technology and industry, and what is needed is attention, input and persistence.

The conventional logging while drilling system is far away from the bit and has a large blind area,which makes it impossible to judge the dip angle and formation lithology in time accurately, therefore, a downhole near-bit measurement while drilling system with independent intellectual property rights is designed to solve these problems. The tool can measure the azimuth gamma and dynamic well inclination within 1 meter of the bit,and the measured data can be transmitted across the screw to the logging while drilling system by using electromagnetic wave short-transmission technology, which can realize the precise control of the drill bit in the reservoir. The field application shows that the instrument with the characteristics of stable data transmission and long continuous working time, which can effectively improve the drilling ratio and rate of penetration in the horizontal section exploitation of coalbed methane wells, shale gas wells and thin oil wells and has a good prospect for promotion and application in horizontal well applications.

Abstract: Compared with fishing operations, the large-borehole fishing success rate has been low. The main reason is that the hole size is too large compared with the fish size, and the fish drilling tool is tilted to the side, and the fishing tool can not effectively trap the fish head and guide the fish head into the fishing tool. In this paper, according to the relationship between fishing tools, fish head and borehole size, the relevant parameters and key points affecting the success rate of fishing are obtained by establishing the geometric and force state model, which provides theoretical support for the scientific design of fishing tools. Meanwhile, in the standardization of manufacturing fishing tools, the purpose of standardization and rapid use is realized by integrating fishing tool components, so as to improve tool reliability and save preparation time. Through field tests, the optimized and improved large-borehole integrated fishing tool have significantly improved the success rate of fishing, and has promotion and guiding significance for the treatment of similar accidents in the future.

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. 

Toe fracturing sliding sleeve technology has become the key technology developed in recent years, which is especially suitable for creating the channel of first frac stage in deep shale gas wells with long horizontal sections. This technology does not require the perforation of coiled tubing, and is not limited by well depth and horizontal section length. The sliding sleeve can be opened only by applying pressure to the wellhead, and the channel for first frac stage / pumping can be created, which effectively solves the problem faced by first stage stimulation in deep shale gas wells with long horizontal sections in China. The development of Shale gas in North America has been commercialized, and a series of reservoir stimulation technologies and supporting tools for shale gas long horizontal wells have been formed. China has also made great progress in the development of shale gas related processes and independent tools. By conducting research on deep and long horizontal well toe end fracturing sliding sleeve technologies such as immediate opening, delayed opening, and depressurization opening, this paper focuses on the structural composition, working principle and technical characteristics of different types of toe fracturing sliding sleeve tools, and comparatively analyses the technical level and application status of toe fracturing sliding sleeve tools at home and abroad. Combined with the development needs of domestic shale gas reservoirs, it is indicated that the future researches shall focus on the research of delayed opening toe fracturing sliding sleeve, the popularization and application of depressurization opening toe end fracturing sliding sleeve and the pilot research of wireless intelligent toe fracturing sliding sleeve.

In order to improve the efficiency of oil and gas exploration and production, more and more oil fields need to achieve both borehole imaging and forward-looking imaging during the exploration and development process. However, there are still some blind spots in the current downhole imaging system while drilling, which affects the imaging effect. Moreover, it requires multiple trips to achieve borehole imaging and forward-looking imaging, which affects efficiency. Therefore, this paper investigates the current research status of acoustic borehole imaging and forward-looking imaging while drilling, and explores the downhole panoramic imaging technology that integrates while drilling acoustic borehole imaging and forward-looking imaging. On this basis, the challenges from the current development of acoustic borehole imaging and forward-looking imaging while drilling are analyzed, and then four perspectives, including breakthrough in measurement blind spots, the combination acoustic signal and electric signal, the fusion of borehole imaging and forward-looking imaging, and digital twin visualization are proposed, to achieve the upgrade of downhole acoustic panoramic imaging technology while drilling, which will provide reference for effectively promoting the visualization and intelligentization of downhole imaging systems while drilling. 

Heavy oil resources are very rich in the world and stearm injection thermal recovery is the main development method. In this paper the current situation of thermal recovery technology for heavy oil at home and abroad was summarized, including the basic mechanisms and application conditions of steam huff and puff, steam flooding, steam assisted gravity drainage (SAGD), in-situ combustion, etc. A variety of steam assisted gravity drainage (SAGD) technologies have been developed by changing well pattern, adding solvent or flue gas for heterogeneous ultra-heavy oil reservoirs with interlayers and poor permeability. Aiming at thin or deep or ultra-heavy oil reservoirs, the multicomponent thermal compound flooding technologies of different reservoirs are formed by using composite chemical agents and gases, and utilizing the synergistic effects of steam, chemical agents and gases. At the end of steam injection, the in-situ combustion models of different reservoirs have been developed, and the enhanced oil recovery was 25% -30% compared with steam huff and puff in field tests. Heavy oil in situ was modified through mass and heat transfer and deasphaltene reaction with thermal solvent recovery, 75% carbon emission less than that of SAGD. By heavy oil in-situ upgrading, the heavy components such as gum and asphaltene was changed into light oil though underground thermal cracking or catalytic modification, so as to realize the effective development of heavy oil. The next development direction of heavy oil thermal recovery technology  is multi-disciplinary integration, energy saving and consumption reduction in the whole development process, shifting toward low-carbon, clean and efficient development.