Design of Shaped Cutter PDC Bit for Deep Hard Plastic Mudstone
With oil and gas exploration and development approaching the deep-burial，deep-water and unconventional fields，the encountered formations become increasingly complex. Deep mudstone formations exhibit strong hard plastic characteristics during drilling，resulting in difficulties in penetrating of cutters into formations and low rates of penetration （ROP）. Given the challenge of improving ROP in hard plastic mudstone，rock-breaking simulation tests of PDC （Polycrystalline Diamond Compact） cutters were conducted for hard plastic formations，and the rock-breaking effects of various shaped cutters were analyzed. The results indicated that the 3D-shaped cutter exhibits the best rock-breaking efficiency and certain durability: it delivers a maximum ROP improvement of 116.4% in the hard plastic mudstone in Shengli Luojia Oilfield. Furthermore，a staggered cutter arrangement design，combining axe-shaped and 3D-shaped cutters，was proposed for drilling deep and complex formations，like sand-mudstone interbedding formations，which delivers the highest ROP increment of 215.7% in Yongjin Oilfield in Junggar Basin. Additionally，potential measures for enhancing ROP in hard plastic mudstone were discussed. The design principles of "sharp breakthrough，plane advancing and intensive scraping with small-diameter cutters" are recommended to improve the drilling efficiency. The research findings provide valuable insights for optimizing the design of PDC bits for hard plastic mudstone.
Analysis of the Effects for Reamer Size under Different Operation Conditions：a Case Study of Well H101 in the Southern Margin of Junggar Basin
The determination of the reamer size（the desirable reamed borehole size） is a global challenge for research on reaming in drilling. To ensure smooth drilling and cementing of reamed borehole sections，an in-depth case study of Well H101 drilled in the southern margin of Junggar Basin was performed to identify the affecting patterns of the reamed borehole size on drilling，tripping and cementing operations. The requirements for the reamer size were analyzed from perspectives of the drilling tool bending deformation，pump rate optimization，BHA vibration，swab and surge pressure during tripping and fluid density window，surge pressure of running liners，equivalent circulating density（ECD） during cementing，and wellbore integrity incorporating wellbore curvature，and the impacts of changes in casing sizes on cementing of the reamed borehole section were investigated. Finally，the above analyses were combined with a mathematical statistical approach to comprehensively determine the reamer size. The determined reamer size was applied to Well H101 and analogous wells in the southern margin of Junggar Basin，which were all found with smooth drilling operations after reaming，and moreover，Well H101 delivered a daily penetration of 101 m for the reamed borehole section. The presented method and strategy for the reamer size optimization incorporate more factors and are more reliable. They provide important references for determining the reamer size of to-be-reamed wells.
In order to solve the troublesome tubing and casing annulus pressure caused by sealing failure of the gas injection packer during high-pressure gas injection，a new insert-type high-temperature high-pressure gas injection packer was developed by optimizing the packer structure and sealing mechanism and elements. The integral insert sealing tubing is designed to reduce the connection parts and therefore，leakage risks. The sealing rings are integrated into the insert tubing body via the in-situ vulcanization to avoid damage to sealing rings due to string creep and improve the sealing effect and service life of the insert tubing. The gas-sealing rubber cylinder is adopted and equipped with split-open rigid support protectionto avoid damage to the rubber cylinder，improve the gas injection sealing performance and prolong the service life of the packer.The invented packer reduces the risks of casing annulus pressure，solves the potential safety hazards in high-pressure gas injection，and provides technical support for gas flooding in Jidong Oilfield.
Tangdong Block of Dagang Oilfield has complex geology. The main target layers are the third member of Dongying Formation and Shahejie Formation. The target layers are deeply buried and rather thick, and the damage mechanisms between the reservoirs are very different. The applications of fine calcium carbonate and plugging agents for drilling fluids in reservoir damage prevention present insufficient performance for exploration and appraisal wells in this block, due to the low technical adaptiveness to the reservoirs and inferior practice management. The core permeability recovery rate for the reservoirs is only 67.5%. According to the core sensitivity evaluation and casting thin section analysis results of Well Tangdong 9X6, a reservoir protection technology system was developed for the drilling of the Tangdong exploration and appraisal wells, according to the potential damage factors. The protection system adopts the film-forming plugging reservoir protection technology and combines the applications of the single-well multi-layer/multi-point design method. The efficient implementation of the developed technology system is ensured with the help of refined technology implementation management and high-quality real-time evaluation. The film-forming plugging reservoir protection technology was applied to five wells in this block. The dynamic fluid loss of drilling fluids was reduced by 25.7%, and the permeability recovery rate was increased by 13.1%. All the five wells met the geological expectations. Two wells have delivered high production, with initial daily production of 61.3 t and 101.1 t, respectively, which indicates good performance.
One of the main reasons for rheology out-of-control of high density water-based drilling fluid is the increase of inferior solid phase content. Inferior solid phase is dispersed in high density water-based drilling fluid，which enhances the system architecture，resulting in increased drilling fluid viscosity and higher shearing force. Based on the principle of viscosity reduction by competitive adsorption，WNTHIN，a low molecular weight polymer viscosity reducer was synthesized with 2-acrylamide-2-methylpropanesulfonic acid，styrene，maleic anhydride，N and N-dimethylacrylamide in a molar ratio of 1∶2∶1∶1.Test results of the viscosity reducer show that WNTHIN can significantly reduce the viscosity and shearing force of high density potassium polysulfonate water-based drilling fluid with a density of 2.40 g/cm3，with plastic viscosity reduced by 42.85%，static shearing force reduced by 51.35%，and the recommended WNTHIN dosage addition is 1.5%. The field application of WNTHIN in a well in Penglai Gas Field showed improved rheology of high density potassium polysulfonate water-based drilling fluid. The plastic viscosity dropped from 58 mPa·s to 30 mPa·s，the yield point dropped from 29 Pa to 14 Pa，and the 10 min static shearing force dropped from 28 Pa to 16 Pa. The performance of the high density water-based drilling fluid has been improved to meet the technical requirements for safe drilling in deep wells.
To prevent the water block damage induced by any extraneous fluid's invasion during drilling and completion operations in low-permeability gas reservoirs，a high-performance anti-water blocking agent（FWB），which is composed of hydrogen-rich block silicone oil and some additives such as organosilicon surfactant and deformer，was developed for low-permeability gas reservoirs. The infrared spectroscopy was used to characterize the molecular structure of the block silicone oil，and a series of tests，which include surface tension test，contact angle test，core imbibition test，permeability recovery ratio test，and drilling fluid compatibility test，were conducted to comprehensively evaluate the performance of this anti-water blocking agent. The test results show that，at the mass concentration of 1%，it can dramatically reduce the surface tension of the aqueous phase to 22.28 mN/m，increase the contact angle of the aqueous phase from 29° to 120°，decrease the core imbibition amount by 69.2%，and improve the permeability recovery ratio to 89.3%，and that it has good compatibility with drilling fluids. This anti-water blocking agent can significantly reduce the water block damage during drilling and completion operations and provide effective protection for low-permeability oil and gas reservoirs.
The post-frac flowback and production of the alkali-salt layers of Fengcheng Formation in Mahu Sag suffer from wellbore salt deposition，but the salt deposition law remains unclear. Therefore，through static and dynamic salt precipitation evaluation experiments，the reservoir conditions affecting the salt precipitation rate and the impacts of flow rate and gas production on wellbore salt deposition in the production process are investigated to clarify the wellbore salt deposition law. The results show that the three typical salts，with their solubility from most to least sensitive to temperature，are sodium carbonate，sodium bicarbonate and sodium chloride. Moreover，the boundary conditions （total salinity and ion composition） and salt crystal types of salt crystal precipitation are defined for composite salt solutions with different compositions. Under the same salinity，the precipitation degrees of composite salts with different compositions are between those of the individual salt，and the priority orders of salt precipitation are sodium bicarbonate，sodium carbonate and sodium chloride，which is consistent with the change of solubility of various salts with temperature. With the increasing flow rate and gas production，the salt deposition first grows and then declines. The salt deposition peaks in the case of the daily liquid production of 40 m3/L and the gas-liquid ratio of 200 m3/L.The study on the salt deposition law in alkali-salt wells helps to set reasonable drainage parameters，delay the salt deposition during flowback，ensure the smooth completion of formation testing after fracturing，and provide a theoretical basis for on-site salt prevention measures in the later production from Fengcheng Formation alkali-salt layers.
Analysis of Factors Affecting the Productivity of Radial Multilateral Horizontal Wells in Low Permeability Reservoirs
Radial multilateral horizontal well technology can be used to improve the productivity of low permeability reservoirs by drilling multilateral branches in the oil intervals of horizontal wellbores，which increases the oil displacement area. However，the factors affecting the productivity of radial multilateral horizontal wells are not clear and，to date，there has been little research on methods of prediction. This paper describes a numerical model for radial multilateral horizontal wells，using numerical simulation software COMSOL，and its application in evaluating the influence of factors such as reservoir and well type on well production. The mathematical model was solved using the finite element method and radial horizontal well output predicted using the material balance method. The focus of the study is to analyze the effects of changes in radial multilateral well parameters and formation heterogeneity on production behavior and transient pressure distribution. The results show that branch length has a significant effect on productivity，effectively expanding the control area. The number of branches，their angles，and formation heterogeneity，are found to be the principal controlling factors.
Simulation and Countermeasures of Casing Erosion at Downhole Decoupled Sandblaster During Fracturing
During long-time fracturing，the high speed proppant-carrying fluid flowing will cause serious erosion for downhole tools and casings. Therefore，it is important to understand the flow field distribution inside the tool and the casing erosion pattern during fracturing，propose improvement measures，optimize fracturing parameters，and protect wellbore integrity. A finite element mechanical model of casing erosion at the decoupled sandblaster during fracturing was developed，and a systematic analysis and study of erosion in an ultra-deep well was conducted. The results show that without sheath protection，the erosion rate of the casing at the outlet reaches 1.46×10-3 kg/（m2·s），with a casing thickness reduction of 1.35 mm，which decreases the casing strength，and the pipe string with erosion defect is more prone to stress concentration. After the sheath is added，the wall thickness reduction of the casing caused by erosion is significantly lower than that of the working condition without sheath protection. The finite element model developed allows a complete and quantitative study and analysis on all the points near the outlet of the sandblaster. The safety window of wall thickness thinning of the eroded sheath under different injection rate of fracturing fluid and proppant ratio was predicted. The safety window can quantitatively provide guidance for the operators to ensure effective protection of the casings and prevent casing erosion by controlling the injection rate and proppant ratio. The study is of great significance to parameter optimization and wellbore protection during fracturing.
Exploration of Nitrogen Injection Production Resuming Technology for Offshore Bottom Water Coning Gas Wells
底水锥进会使气井产量快速递减和采出程度大幅下降，尤其在海上高采气速度下底水锥进影响更显著。为了能够使此类井成功复产，开展了注氮气压水锥研究和现场试验。通过数值模拟研究，确定了水锥面的物理形态，并据此优化氮气的注入量和焖井时间。A3井实施两轮次累计注入38×104 m3氮气。现场试验表明：通过高压注入氮气可以有效突破水锥面对气相的封堵，建立气相与井筒的通道。两轮次分别返排出10%~15%的氮气后，天然气的含量即可达100%，说明只需要较少的注入量即可突破水锥面；但底水能量强，现场处理能力有限，频繁更换生产制度导致大量产水，累计自喷15×104 m3天然气后停喷。在后期的治理中需要控制油嘴，防止井底流压波动加剧产水，影响复产效果。本次注氮气压水锥工艺探索对同类底水气藏的复产有一定的借鉴和指导意义。
Simulation of Prefilm of Water-Based Corrosion Inhibitors on the Inner Wall of Production Tubing in Sour Gas Wells
Sour gas wells are often associated with the corrosion of metal materials caused by CO2 and H2S. The prefilm anticorrosion technology by water-based corrosion inhibitor injection is relatively advanced and low-cost. However，no systematic research has been carried out on the prefilm time，thickness and distribution of liquid film and corrosion inhibitor spray cycle. Based on RNG k- ε model，the multiphase flow theory and the EWF model were coupled to simulate the formation and flow of the water-based corrosion inhibitor liquid film，and the flow law of corrosion inhibitors subjected gas stream flushing after injection was analyzed. The results showed that the gas stream in the sour gas well can entrain water-based corrosion inhibitors and form a liquid film with a thickness of about 2 mm on the pipe wall under production conditions，and the prefilm performance is better in the pipe section between the 20~60 m positions. After the injection of water-based corrosion inhibitor is stopped，the liquid film of corrosion inhibitors on the pipe wall is gradually destroyed and thinned due to the flushing of gas streams. Therefore，it is recommended to install a corrosion inhibitor injection nozzle at an interval of 60 m along the pipe and place the corrosion inhibitor nozzles along the wellbore in a spiral manner.
Leakage of crude oil storage tanks can cause serious consequences，and risk identification and analysis of crude oil storage tank leakage is an important part of tank farm safety management. Based on the fault tree analysis （FTA） model and analytical hierarchical process （AHP），this research identified and incorporated a total of 18 basic events，and quantified the structural importance of each basic event through the minimum cut set. The judgment factor was determined as per the structural importance，and then a judgment matrix was constructed to analyze the risks of tank leakage. The analysis results showed that valve failure，design defects，overfilling，tank defects and overhaul operations are the main contributors to tank leakage risks. The findings of this research provide a theoretical basis for tank leakage risk prevention and control. The FTA-AHP method was also proved to be able to objectively analyze the risk of tank leakage and provide theoretical support for the daily safety management of storage tanks.
The metaverse represents the next generation of internet and is also an immersive virtual world connected to the real world on which it is having a profound effect. It is capable，for example，of real time rendering of digital twin scenarios and high-precision simulations that follow the laws of physics. Carbon Capture，Utilization，and Storage （CCUS） has come to be regarded as a critical core technology for China to achieve its double carbon goal. Compared with conventional Carbon Capture and Storage （CCS） technology，it offers tangible economic benefits and practical operability. The metaverse can energize every aspect of CCUS. However，current CCUS engineering technology is not standardized，which means high industrialization costs. Our analysis of the current development status of CCUS technology at home and abroad reveals that machine learning based on supervised and unsupervised algorithms can play a huge role in CO2 capture using adsorption techniques；in particular on the selection of adsorbent materials. In addition，process simulation and optimization using quantum computing offers a lower cost option for CO2 capture than the technologies currently in use. This paper proposes an intelligent，integrated，on and offline management system—using metaverse technology clusters （particularly machine learning）—as a vision for the future to solve the industrialization issues facing CCUS and help to achieve its large scale application.
