Abstract:The shape memory polymer sand control system has been successfully applied in the second phase of natural gas hydrate production in Japan. However， the effects of the shape memory on the pore-permeability characteristics and sand control performance of polymers is rarely researched. Therefore， in this paper， a shape memory polymer sand control material taking the polyurethane as the matrix is developed. The polymer’s shape memory characteristics as well as the changes in pore-permeability and mechanical strength before and after the shape memory process are investigated and the sand control performance is also evaluated. The results revealed that the developed porous polyurethane shows excellent shape memory characteristics and pore-permeability properties： the shape fixed rate exceeded 98%， the shape recovery rate reached 100%， the shape memory temperature was 59.8°C， the permeability remained at approximately 10D before and after the shape memory process， and the compressive strength was maintained at around 1MPa. The mercury injection tests indicated that the shape memory process is a compression-rebound process for the polyurethane material with large pores， which will lead to some changes in the internal structure of the material， resulting in a slight decrease in compressive strength and a small increase in permeability after complete shape recovery. The sand control performance tests indicated that a small amount of sand production occurred only in the initial test， and the presence of sand particles caused some damage to the permeability of the polyurethane material， however， the permeability could still be maintained at around 10 D for the fully recovered polyurethane. According to the comprehensive performance analysis of the above materials， the developed shape memory polyurethane material can be used in conjunction with a mechanical sand control screen pipe， which could meet the requirements of sand control in hydrate production wells.

Abstract:To address the issue of wellbore instability resulted from hydrate decomposition during offshore drilling for natural gas hydrate， this paper developed a dual-purpose additive which possess both hydrate decomposition inhibition and filtration reduction properties. It was synthesized using 2-acrylamido-2-methylpropane sulfonic acid， dimethyldiallyl ammonium chloride and dimethoxy methylvinylsilane-modified cellulose as the starting materials （named as “CAD”）. The molecular structure was characterized through infrared spectroscopy. Thermal analysis revealed that the product decomposition initiated at around 290°C， demonstrating commendable thermal stability. The hydrate decomposition evaluation experiments indicated that the presence of 1% of the dual-function additive extended the total decomposition time of hydrates by approximately 1-fold and reduced the hydrate decomposition rate by 19.8%， which highlights the outstanding performance of hydrate decomposition inhibition. Filtration in freshwater-based slurry and 5 wt% NaCl saline-based slurry measured to be 6.8 and 8 mL respectively， signifying effective filtration reduction capabilities for hydrate reservoirs. The filtration for the freshwater-based slurry amounted to 6.5 mL at low temperatures， indicating the dual-function additive has favorable performance of low-temperature rheology. All these research offers substantial support for the advancement of high-performance drilling fluids designed for natural gas hydrates.

Abstract:The exploration and exploitation of natural gas hydrate need to obtain the pressurized core from the formation for physicochemical property testing， reserve evaluation and mining technology research. However， in the process of drilling， gas hydrate is easily decomposed with the change of temperature and pressure， which brings great difficulties to the core drilling of hydrate. In order to solve the pressure maintaining reliability problem of gas hydrate pressure maintaining coring drill， the project team developed a new type of gear and rack closed ball valve for gas hydrate pressure maintaining coring drill. The ball valve was driven by lifting force of rope fishing. The structure and working principle of the pressure maintaining core drill are introduced in detail. The specific pressure of working seal of ball valve and lifting force required for fishing inner pipe are calculated. The indoor test and sea test of the pressure maintaining core drill are introduced. The research shows that the hydrate pressure retaining coring drill has the advantages of simple coring process， good reversing and sealing performance of ball valve， high success rate of coring， and all functions and performance indexes meet the design requirements.

Abstract:The depressurization method is a common approach for the exploitation of natural gas hydrate reservoirs in marine areas. This method can induce complex multi-physical coupling responses in the near-wellbore reservoir， leading to pressure changes， temperature variations， hydrate decomposition， deterioration of reservoir mechanical properties， and formation subsidence. This study utilizes a fully-coupled hydro-thermo-mechanical numerical model to analyze the mechanical property deterioration and subsidence characteristics of marine natural gas hydrate reservoirs caused by depressurization in horizontal wellbores， characterizing the multi-field coupling response laws of the horizontal wellbore and surrounding reservoir， and identifying the influencing factors of reservoir mechanical property deterioration and subsidence. The simulation results indicate that the affected area of reservoir pressure and temperature changes is much larger than the decomposition front of hydrates， and the distribution of effective normal stress varies significantly in different directions. The deterioration area of cohesion induced by depressurization is highly correlated with the plastic zone and hydrate decomposition zone. The subsidence characteristics in the shallow and deep areas relative to the horizontal wellbore exhibites distinct features. The simulation results provide a reference for the stability analysis of marine natural gas hydrate reservoirs during depressurization exploitation through horizontal wellbores.

Abstract:The riserless mud recovery system can realize the recovery and recycling of mud under open drilling conditions， which has the advantages of safety and environmental protection， simplified wellbore structure and drilling risk reduction. This technology has been developed abroad for many years and successfully promoted in the industrial application， however， China is still in the stage of tracking research. This paper introduces the design and development process of first 400m riserless mud recovery system in China， and verifies the functions and indicators of the system through sea trial tests. The results show that the prototype of the developed equipment is equipped on the “Marine Geology-10” ship， the equipment loading is reasonably adapted， the maximum sea test depth is 384.7m， the functions of the equipment meet the design requirements， the identification and automatic control function of mud level are successfully realized， and the feasibility of riserless mud recovery and circulation drilling technology is verified in the whole process.

Abstract:The wellhead suction module is one of the key equipment of riserless mud recovery drilling （RMR） system，and the status when working on the seabed has a certain impact on the drilling work. In this paper， an open wellhead suction module is designed， a three-dimensional model is established， morison equation is used to calculate the internal wave current load， the P-y curve method is used to simulate the spring equivalent of the soil conditions， and the wellhead suction module is analyzed statically and modally. The research shows that the displacement of wellhead equipment is greatly reduced compared with that of the normal deep-water drilling， and the stress and strain of suction module and its connecting parts are smaller when using RMR drilling technology. The intrinsic frequency of wellhead suction module is obtained from the modal analysis of wellhead suction module， which provides referencial value for the size optimization of wellhead suction module and the application of the RMR technology， and provides technical support for drilling to deep ocean.

Abstract:During drilling， when circulating drilling fluid flows axially in the wellbore ring， the circumferential motion occurs due to the rotation of drilling tools， and spiral flow is formed in the whole annulus. This may have a potential impact on the friction pressure drop in the annulus， especially the narrow gap. In this paper， the laminar flow under the rotation of concentric narrow gap ring drilling tools is calculated and analyzed by numerical simulation software. Among them， the drilling tool is ideal as drill pipe or cylinder， and the drilling fluid is composed of three kinds of Bingham fluid with different rheological parameters. The drilling fluid is the current numerical simulation results show that the PLR （pressure-loss ratio） is almost constant at different drilling tool/rod speeds； this indicates that the friction pressure drop in the annulus does not change significantly during the drilling tool/rod rotation； However， a comparison of some empirical formulas reveals that， with the exception of Ooms （1999） formula， which matches the current calculations， none of the other formulas can reflect the phenomenon. Moreover， by observing the radial variation of annulus pressure， the results show that the pressure is almost constant along the radial direction in the current 180rad/min range， and even when the rotational speed increases to 600 rad/min， the radial variation is very limited， accounting for about 2×10^-5 order of magnitude. therefore， in the current engineering application range （drilling tool speed within 180rad/min）， drilling tool rotation will neither cause an increase in axial friction pressure drop nor cause significant changes in pressure along the radial direction. The results of this paper provide some references for the estimation of friction pressure drop caused by rotating drilling tools in the actual drilling process， which can help to optimize the drilling process and equipment design， and improve the drilling efficiency and safety.

Abstract:Predicting the drill ability level of rocks can provide effective assistance for the development of drilling engineering projects， and selecting reasonable processes， methods， and technologies based on the drillability level of rocks can provide technical support and assistance for the project. In this paper， considering the impact of complex environmental factors on rocks in underground space， five factors affecting rock drill ability grade are selected from geophysical exploration data， mechanical properties and physical properties of rocks. Principal component analysis （PCA） is used to explain the correlation and contribution rate between each influencing factor， and the correlation between the five factors is eliminated. Three principal components with low correlation were selected to replace the data samples for prediction evaluation. The LM-BP algorithm was compiled， reasonably set the parameter values of the prediction model， and based on the data samples after principal component analysis， establish a rock drill ability level prediction model. Analyze and compare the prediction results with the measured results of indoor experimental methods. It was found through analysis that the PCA-LM-BP prediction model has the characteristics of high prediction accuracy and short prediction time in rock drill ability level prediction， it can be applied to rock drill ability analysis in drilling engineering.

Abstract:At present， the resource exploitation in Jinchuan mining area is gradually going to the deep part， and laying medium-deep boreholes in the mining roadways is the main exploration method. Complex geological conditions such as borehole collapse， slurry making， water inrush and strata breaking often occur， which greatly affect the exploration efficiency. In order to find the reasons why the complex strata in the mining area affect the stability of borehole walls， physical and chemical analysis， micro and mechenical analysis of the rock samples taken from the mining area are made. The results show that the strata encountered with strong water-sensitive， highly fractured， strong water inrush and high geostress during drilling is the main reason which affect the borehole wall destabilization in Jinchuan mining area. Through the stability evaluation of borehole wall in the mine area， drilling countermeasures for complex strata were made from the perspectives of flushing fluid technology and engineering technology， which provides technical support for drilling work of the mine area.

Abstract:Geological drilling is a high-risk industry. The construction site is not fixed， the working environment is harsh， the employee mobility is high， the technical requirements are low， and the construction involves many machinery and equipment. There has been always complex and changeable influencing factors， the risk of hidden dangers of safety production problems. This paper introduces 4M1E analysis method （Man Machine Material Method Environment analysis method）， discusses the significance of safety management and control in each process stage by analyzing the characteristics of geological drilling safety work， focuses on the application of 4M1E analysis method to identify the main risk factors in each work link in the drilling implementation stage， and then puts forward corresponding management and control measures from five aspects， such as human， machine， material， method and environment， to show the systematic advantages of 4M1E in safety management. In order to promote the practitioners to understand and master 4M1E analysis method， and promote its application in safety management.

Abstract:Compared with traditional vertical drilling， horizontal directional wire-line core drilling has higher investigation efficiency due to its technological characteristics in the investigation of tunnels and underground engineering in the difficult mountainous areas in western China. However， due to the complex geological conditions and fragile ecological environment in this area， hole collapse， leakage and other accidents are easy to occur in the drilling process， which requires that the flushing fluid used should have strong inhibition， non-toxic and harmless characteristics while ensuring rheological properties. In view of the performance problems of horizontal directional drilling fluid in wire-line coring， polymer polyols， which are environmentally friendly and easy to degrade and have strong inhibition， are selected as the main research object， and environmentally friendly cellulose and nano-SiO₂ are selected to improve their rheological properties. The developed polyalcohol anti-collapsing flushing fluid system： 2% PVA+0.5‰ MC-9+0.5‰ LE-5+0.1% SiO₂+0.3‰ DD-1+0.2% DS-957+0.8% KCl， composed of environmentally friendly materials， has good rheological property， anti-collapse inhibition ability can also meet the requirements of directional core drilling engineering. It provides a new idea to solve the technical problem of flushing fluid in horizontal wire-line coring directional drilling and has reference significance and value for similar projects.

Abstract:The No.15 coal bed of Taiyuan Formation in Qinshui Basin is generally feathured with low-pressure， low-permeability and low-saturation. The coal reservoir is relatively thin with complex geological conditions， and the coal bed methane （CBM） production is commonly low. Taken the Zhengzhuang Block in Qinshui Basin as the example， the key technology of CBM drilling and completion technology， marker formation determination， and well trajectory control in low pressure and low permeability coal reservoir are discussed comprehensively based on the successful experience of the LDP-22H multi-branch horizontal well in No.15 coal bed.The results show that the integrated geosteering technology of drilling and logging can effectively fix the target coal bed and modify the bit track in real time， which can improve the average drilling rate to above 97% and greatly improve the effective footage. The 865-day drainage and production practice shows that the daily gas production of the LDP-22H multi branch horizontal well has exceeded 150，000 m³， the current daily gas production is stable at about 80，000 m³， and the total cumulative gas production is 20915469.3 m³， achieving ultra-high and stable production， which marks good applicability of the multi branch horizontal well in the efficient development of CBM in low-pressure and low-permeability coal reservoirs. Moreover， it is necessary to optimize the well position， strengthen the drainage and production capacity at the bottom of the horizontal well， stabilize the pressure drop rate， reduce the sensitivity damage to the permeability of the coal reservoir， improve the continuity of drainage and production， reduce pump downtime and the frequency of maintenance operations， and ensure the continuity of production capacity.

Abstract:By analyzing the data obtained from groundwater stratification tests， it was realized that the pressure of different reservoirs varies due to the influence of mud content， porosity， permeability and other factors， indicating the phenomenon of cross layer recharge between different aquifers in the same geothermal well. This paper analyzed the impact of factors such as cross layer supply， well flushing process， and drilling fluid invasion into the reservoir on reinjection， and proposed suggestions for implementing layered pumping reinjection， geothermal well drilling and completion， and fine technology on well formation.

Abstract:In order to investigate the lithology and stratigraphy of the Cretaceous-Permian strata in the Wangjiang Depression of the Lower Yangtze Area， verify the geophysical information， and evaluate the petroleum potential， the Wanwangdi 4 well was deployed by the China Geological Survey， which is a large-caliber shale gas geological survey well， and the total depth of which is 2503.9m. To deal with the complex drilling situation of variable formations， soft and hard interlayers， and large sections of multi-layered mudstone layers， drilling technologies such as bit adaptability optimization， inclination correction and reliable drilling fluid system were implemented to achieve anti-deviation and fast penetration， ensure core recovery rate， and achieve the drilling goals. The drilling technology used in this well can provide useful experience for oil and gas drilling in surrounding areas.

Abstract:Shengli Jiyang shale oil block is the key development block of Sinopec and the third national shale oil development pilot zone of China， where the geological conditions are complex. Problems exist in the second spud such as shot bit life， less drilling footage， high “supporting pressure” of sliding drilling in the deviated section in the upper gravel layer， and prominent conflict exists between bit aggressivity and tool face stability. In view of the above problems， research was carried out on the optimization of drilling process in sections， optimization of well trajectory， development of efficient bit and matching of speed-raising tools， etc.， and a high-efficiency drilling technology for ?311.1mm large hole of Shengli shale oil was formed. The technology was applied in 20 wells of Niuzhuang depression， which achieves significant results in speed-raising and efficiency improvement. The mechanical penetration rate was increased by 40.8%， the average drilling footage was increased by 46.35% higher than that in the early stage of the same block， and the average drilling cycle of the second spud is shorter by 55.55% compared to that of early stage in the same block， which effectively guarantees the smooth progress of the construction in the national shale oil demonstration area of Shengli Oilfield.

Abstract:The Well Ke-20 is a gas storage well located in the Kekeya condensate gas field. The cementing quality of the well section above the top boundary of the gas reservoir does not meet the requirements， and it needs to be resealed after casing forging and milling. Due to the deep forging and milling point， the high steel grade of the forging and milling casing， the insufficient construction displacement and pump pressure of the on-site equipment， the forging and milling tools cannot completely forge and mill the casing coupling， and the milling cutter tension is not enough， it brings about many difficulties for the forging and milling operation. After optimizing the forging milling tool sellection， designing the forging and milling construction parameters and drilling fluid system， increasing the displacement of the pump truck with the mud pump， polishing the forging and milling tool inhibiting device， and adjusting the viscosity of the drilling fluid funnel in stages， the forging and milling footage in a single drilling trip is 19.33m， the forging and milling speed is 0.48m/h， the cutting return rate is 71%， and the milling tool utilization rate is 90%. Compared with the previous drilling trips， the indicators mentioned above are increased by 55.5%， 26.3%， 9.2% and 26.3% respectively， and the forging and milling efficiency is improved effectively. Which provides an important experience reference for the efficient construction of other similar casing forging and milling wells.

Abstract:Technical problems exists in slim-hole drilling of North Ordos Gas Field such as drilling and cementing high pump pressure， low rate of penetration and imperfect drilling technology. Well bore structure， track profile， drilling pipe， dynamical drilling tools， PDC bits， slurry density， number and setting position of the casing centralizers were optimized， and thereby formed the fast drilling and completion technology for slim-holes with low cost. 200 wells were tested using this technology， as a result， the rate of drilling cycle was reduced by more than 12%， the mechanical drilling rate increased to over 18m/h， the drilling waste and slurry for cementation decreased by 27% and 41% on average， about 500 thousand RMB on average was decreased for single well drilling cost ， the goals of cost reduction， efficiency improvement and environment protection were achieved which find out the direction for low cost and high efficient development in North Ordos Gas Field.

Abstract:Normative system design of ?76mm steel tooth tricone bit was carried out， aiming at the small diameter non-coring drill. The paper designed the value of the structure parameters and checked the calculated diameter of ?76mm steel tooth tricone bit， referring to the value of structure design parameters of domestic petroleum tricone bits. The drawing method of crushing-diagram at the drilling-hole bottom and gear ring meshing-diagram， as well as the optimization method for the tooth ring arrangement of milling tooth cone are introduced systematically. Using steel ball to lock cone， with the unsealed sliding bearing structure. And the ball bearings are designed and calculated， to determine the number of balls， rolling track size， and clearance. The parameters of wedge teeth are calculated accurately， to determine the angles and installation angles of the milling cutters. The part details and processing technology of small diameter steel tooth tricone bit are described. The problems of the traditional heavy manual calculation and cumbersome 2D projection manual drawing have been solved， by utilizing Excel functions and 3D parameterized solid simulation software， improving the design efficiency and accuracy， to provide a reference for the design of similar roller cone bit.

Abstract:Aiming at the problems of complex structure and high failure rate of traditional top drive rigs， a new top drive system suitable for 4000m drilling rigs was developed. The new top drive uses a permanent magnet synchronous motor to drive spindle rotary drilling directly， and the water cooling technology is used for motor cooling. Compared with the traditional top drive， the new top drive lays out the hydraulic station on the ground， while eliminating the gearbox， lubrication pump station， cooling fan and other components at the same time， so that the number of parts reduced by more than 45% The lifting ring is directly connected with the motor housing， and the main bearing is placed inside the motor rotor， which reduces the size of the top drive and reduces the number of main loaders.The guide rail structure has been optimized to improve the convenience of operation. The new top drive has the advantages of simple structure and low failure rate. It has been applied in more than 20 wells in the field， which has verified its reliability and increased the operation efficiency. The new top drive can be widely used in oil and gas drilling and workover， geological exploration， shale gas and coal seam exploration and other fields， and has a good market application prospect.

Abstract:Discussed the situation of the paper in Volume 50.