Well Yuetan-1 is a high-pressure gas well in the offshore area of Liaodong Bay.During cementing of the third casing section,the Ø244.5 mm casing string was damaged and fractured at 1 238 m,which led to the sealing loss across high-pressure gas reservoir intervals from 2 626 m to 3 690 m.In order to effectively restore well integrity and meet the drilling requirements of the fourth casing section,a cement slurry system with low water loss,low flow resistance,high thixotropy and high channeling prevention capacity and thus suitable for cement squeezing operations was developed,according to the inspection results of the downhole cable camera and the downhole complex situation of Well Yuetan-1.A casing damage remedial cementing technology for high-pressure gas wells was formed,in which casing damage cracks are sealed by choke cement squeeze,and the high-pressure gas reservoirs are isolated by retainer cement squeezing and intermittent cement squeezing cement.After the treatment,the casing string was pressure-tested to 20 MPa with no pressure drop and no annular pressure,and the high-pressure gas reservoir was well sealed.The daily gas production in the trial production reached 19 000 m3/d.This technology and field application provide technical references for the treatment of similar complexities such as casing damage.
Downhole throttling can effectively prevent hydrate generation at wellhead,simplify surface processes and reduce costs.However,when this technology is applied in water-producing gas wells with ultrahigh pressure,the mutual influence between gas-liquid two-phase flow and nozzle flow may lead to significant discrepancies between the daily gas production and the designed values for some wells.Accurately predicting the flow rate and pressure drop of gas and liquid through downhole throttler is crucial to process design.To address this issue,one study was conducted based on a constructed visualization experimental apparatus to perform downhole throttling simulation experiments.The dynamics of gas-liquid two-phase nozzle flow under different flow patterns was analyzed.Data were divided based on the upstream flow pattern before the throttler,and the performance of four commonly used engineering nozzle flow models under different flow patterns was evaluated.The research results show that among the mathematical models used to predict mass and flow rate for slug flow,turbulent flow and annular flow,it is recommended to apply Ashford model(with correlation coefficient R2 is 0.92),Sachdeva model(with correlation coefficient R2 is 0.80),and Al-Safran model(with correlation coefficient R2 is 0.96),respectively.To verify the accuracy of the model evaluation results.Well Shuangtan 8 was selected for field application.The depth of the downhole throttler was determined to be 3 000 meters,the flow pattern was judged to be turbulent flow,and the calculated nozzle diameter was 5.3 mm according to the selected Sachdeva model.The evaluation results of the model can provide theoretical basis and guidance for the design of downhole throttling technology in water producing gas wells,and have certain promotion value.
Natural fractures are well developed in fractured-vuggy carbonate gas reservoirs,which are prone to lost circulation during plugging after formation testing or killing before production.Moreover,such lost circulation presents large volumes and high rates,and the complex cases of high lost circulation proneness and high difficulties in plugging,and lost circulation associated with kickoff are sometimes encountered.An integrated pipe string for formation testing-temporary plugging-production was designed,and an integrated formation test and production technology,enabled by the core tool of the pressure-controlled downhole disconnection on/off valve,was developed.With the presented technology,the reservoir can be quickly plugged by annulus pressurization;the upper pipe string can be tripped out without killing;the completion string can be tied back in clear water or low-density working fluids to connect the reservoir,which allows for production with no induced flow.Field applications showed that this technology can effectively avoid lost circulation during well killing after formation testing in fractured-vuggy carbonate gas reservoirs,significantly reduce reservoir damage,and improve recovery factor of primary production.The presented technology has excellent prospects for application promotion.
The Menggulin conglomerate reservoir is an ordinary heavy oil reservoir undergoing water flooding development.Various stimulation measures have been implemented in this reservoir,and it has now entered a high-water-cut period,showing limited potential in further increasing the recovery rate through water flooding.In order to improve the development efficiency,a field test of fire flooding was conducted.In comparison with other successful fire flooding projects in China,this block is relatively low in crude oil viscosity,porosity,and permeability,while thick in oil layer,which poses high challenges on technological processes.Therefore,based on the characteristics of an ordinary heavy oil reservoir,the fire flooding gas injection and ignition process were optimized.The commonly used four-stage gas injection process was replaced by a three-stage gas injection process,and the four-stage gradual heating ignition was simplified to one-stage heating ignition.As a result,the gas injection duration of the tubing was shortened from 3 d to 1-2 h,and the igniter temperature rose to 400℃after 19 hours of ignition.This reduced the gas injection duration of the tubing and increased the temperature rise rate during ignition,achieving safe ignition.Within three months after ignition,the oil well showed initial positive results.As of May 2023,the daily oil production had increased by 230.5%,and it is still steadily increasing,accompanied by a 16.5%decrease in overall water cut.In comparison with other fire flooding blocks,this one exhibited early and rapid response.Additionally,during the initial production stage,N2 was the main component of the produced gas,while O2 and CO2 were relatively low.The produced crude oil also showed significant improvement,with increased saturation hydrocarbon content and decreased heavy components.These findings provide valuable insights for implementing fire flooding in similar reservoirs.
Dual-layer coiled tubing drilling is a novel dual-gradient drilling technique.In order to analyze the ECD distribution characteristics in the well during dual-layer coiled tubing drilling,a computational model for calculating well ECD based on the characteristics of dual-layer coiled tubing drilling technology was developed,taking into account parameters such as well temperature,pressure and cuttings concentration.The impacts of drilling fluid displacement and density on well ECD were analyzed.The case study indicate that the well ECD increases with the increase of drilling fluid displacement and density,while slightly influenced by the increase of penetration rate.And the dimensions of the dual-layer coiled tubing need to be optimized based on the well size and circulating pressure loss.The dual-layer coiled tubing dual-gradient drilling technique can effectively reduce the bottomhole ECD,and achieve dynamic control of well pressure by adjusting drilling fluid displacement and density during drilling,providing an effective solution for addressing challenges such as narrow pressure windows in deepwater drilling and shallow leakage.
Shale oil reservoirs in the Jiyang Depression of Shengli Oilfield are developed in continental faulted basin,and correspond to multiple sets of high-quality source rocks,implying a great potential for development.However,these reservoirs are challenged by complex geological conditions for drilling,wellbore instability and difficult bit selection.Through researches on overall optimization of well group design,optimization and control of wellbore trajectory,structural optimization and selection of drilling tools,associated ROP enhancement technology,and precise managed pressure drilling(MPD),an efficient and fast shale oil cluster well drilling technology was developed.So far,12 of the test wells have been drilled.For Well Niuye-XX,in the 53 d drilling period,the average rate of penetration(ROP)was 22.3 m/h in the second spud-in,47.3%higher than that in the early stage;the ROP reached 13.04 m/h in the third spud-in by using the assembly of NOV bit + rotary steering + steering motor + hydraulic oscillator;in the middle-late stage of drilling in horizontal section,the assembly of high temperature-resistant downhole motor + double hydraulic oscillator enabled a high reservoir penetration.Coupling with actual drilling data,suggestions and focuses on future development of the efficient and fast shale oil cluster well drilling technology are proposed.
To improve the drainage performance of the low-pressure low-rate wells with co-production of gas and water in the Sulige tight sandstone gas reservoir,the composite gas production technology of negative-pressure production and foam-assisted dewatering was developed.The applicability of the composite production technology was analyzed in accordance with the gas production of wells per unit drawdown pressure,remaining recoverable reserves in the low-pressure low-rate production stage and production system nodal analysis of the representative Sulige block.Moreover,the well candidate criteria were proposed for the composite production technology,considering the applicability analysis,production stimulation mechanisms and key parameters of the negative-pressure production equipment,and field testing was performed in three wells selected correspondingly.The results showed that the presented technology is highly applicable to gas wells that can no maintain normal commingled flow of water and gas in the case of low pressure and low production rates.As the tubing pressure at the wellhead drops to zero,normal mixed flow of water and gas can be maintained even with the gas production of about 0.2×104 m3/d.The quit-flowing pressure can be further lowered,with the help of foam-assisted dewatering.Three wells of Type-Ⅰ,Ⅱand Ⅲ,respectively were selected for field testing.The average daily production gains were 0.50×104 m3/d,0.39×104 m3/d and 0.28×104 m3/d respectively during the testing,and the minimal wellhead tubing pressure reached-0.05 MPa.Hence,the composite production technology can effectively lower down wellhead pressure of gas wells and tap the gas production potential.Also,better performance of the presented production technology is expected in reservoirs with higher quality.
Well Hutan 1 is an ultra-deep well with high pressure and high temperature.To address the challenges posed by complex geological conditions,adverse well conditions,and extreme operational conditions during the well testing process,a risk assessment of the construction was conducted.The well testing operation primarily faces three potential risks:pipe sticking in the well,well safety and well control risk.Innovative measures were taken to mitigate these risks.An integrated pipe string,optimized for perforation and testing,was used to avoid the risk of pipe sticking in the well.On the base of well safety check,sand production prediction and casing pressure control calculation,the maximum casing pressure limit was set,and the production pressure difference was controlled on-site,eliminating well safety risk.Through optimization of surface testing processes,real-time tracking and analysis as well 000 emergency measures,well control risk was effectively controlled.The safe and smooth well testing operation in Well Hutan gained a high-yield industrial flow of oil and gas,with daily gas production of 61×104 m3 and daily oil production of 106 m3,the recorded reservoir pressure reached an impressive 146.07 MPa.The research results provide technical reference for oil testing in high-temperature,high-pressure and ultra-deep wells.
Two-phase flow of gas and water is vital for the production capacity of deep shale gas wells,and it is of great significance to investigate the two-phase production performance of gas and water,for evaluating the reservoir stimulation effects.The production forecast model of multi-stage fractured horizontal wells of deep shale gas was built,considering the two-phase gas-water flow in the fracturing fluid-invaded zone(water invasion zone)and fractures.The presented model was combined with the material balance equation,and the semi-analytical solutions of this model were obtained via the successive iteration approach.The liability and practicability of this model were validated using both the commerical numerical simulator and field production data,and the effects of the sensitive parameters of the water invsion zone(width,water saturation and permeability of the water invasion zone)on production capacity of wells were analyzed.The results showed that the built model can deliver reasonable prediction of production capacity of deep shale gas wells.The shale gas production drops with the expanding width and increasing water saturation of the water invasion zone,and yet climbs up,with the growing permeability of the water invasion zone.The shale gas production capacity is subjected to the joint effects of the multiple parameters of the water invasion zone.Specifically,among the width,water saturation and permeability of the water invasion zone,the water invasion zone width has the largest effects on the 20-year cumulative gas production and water production time,while the intial gas production is most affected by the water saturation of the water invasion zone.The new model provides a theoretical basis and scientific basis for improving the accuracy of productivity prediction in deep shale gas wells.
To deal with the incompetence of the current injection-production well pattern of the Shuang 6 Underground Gas Storage(UGS),the first three large-diameter injection-production wells were deployed.Given the intensive alternating load during injection and production,insufficient cutting-carrying of drilling fluids and low cement slurry displacement efficiency in large wells,optimize the design of the wellbore structure of the cover layer,seal the top of the cover layer with technical casing,seal the middle of the cover layer with production casing,and seal the bottom of the cover layer with a half way cementing of the Ø177.8 mm oil layer tail pipe,improving wellbore integrity;the continuous cutting weighting was performed to monitor cutting return in real time and reduce risks of downhole accidents;the cementing tools and parameters were optimized and the casing centering was enhanced for better cementing quality.These efforts resulted in excellent effects in practice.The cement bond logging showed the cementing qualification rates of the Ø339.7 mm intermediate casing and Ø244.5 mm production casing of the drilled well Shuang 6-H431 reach 93.1%and 99.9%,respectively,and the high-quality cemented section along the caprock is 221 m long.These indicators are far higher than those specified in the industrial standard of underground gas storage.This research provides practical experience for drilling engineering of large-diameter wells in the Liaohe UGS as well as other UGS in China.
Given the high difficulties in formation damage prevention,low efficiency of well clean-up and high risks of well control of well completion and workover of horizontal openhole gas wells,a novel mechanical reservoir isolation valve was developed.This mechanical ball valve with repeatable switching is opened and closed by a specialized switching tool.The isolation system composed of the reservoir isolation valve and suspension packer forbids both the downward flow of fluids above the ball valve and upward flow of fluids below the ball valve and gas in the reservoir.The ball valve sealing performance,switch operation and ball valve re-entry sealing performance of the reservoir isolation valve were investigated via laboratory experiments,which validates the safety and performance reliability of the invention.Field testing demonstrated that the presented tool,with reasonable structures and reliable performance,can achieve zero leakage of working fluids and deliver high efficiency of well clean-up and cost-effectiveness of operations.This invention provides a safe and effective technical approach for life-cycle formation damage prevention in oil and gas wells.
Axe-shaped PDC cutter is well performed in rock breaking owing to its unique structure,but its rock-breaking performance and optimal working angle remain unclear.An evaluation method of total specific energy for rock breaking by cutting combining with pressing was established.By using the rock-breaking simulation model,the working angle optimization of axe-shaped PDC cutter was investigated,and a simulation was conducted on the axe-shaped PDC cutter with optimized working angle.The results show that the composite rock-breaking specific energy of the axe-shaped PDC cutter changes in an"N"pattern as the working angle increases.The axe-shaped PDC cutter with the working angle of 130° is excellently performed in hard sandstone,with the cutting force,cutting rock-breaking specific energy,pressing rock-breaking specific energy,and composite rock-breaking specific energy of 35%,20%,5.9%and 10.5%lower respectively than that of conventional PDC cutter.Laboratory experiment shows that the cutting rock-breaking specific energy of the axe-shaped PDC cutter reduces by 35.2%and shows a greater penetration.The research provides a theoretical foundation for customization of PDC cutter for hard sandstone of Shaximiao Formation in northeastern Sichuan Basin.
The geological conditions in the deep and ultra-deep wells are complex,high temperature and pressure may cause overflow.After the overflow,the well needs to be shut down in time,and the appropriate well killing mode should be selected to re-establish the downhole pressure balance.In order to provide a scientific quantitative selection method,this paper presents a well killing selection method based on quantitative evaluation of overflow capacity.In this paper,the concept of formation overflow energy is proposed,which represents the power of overflow fluid under specific pressure differential.Furthermore,the formation overflow energy computation model is established to evaluate the formation overflow capacity quantitatively.Finally,the selection criterion of well killing method is given,with the pressure return method and the maximum allowable pressure and the critical flow overflow energy as the evaluation index.This method has been tested in the overflow well in middle Tarim region,with wide applicability and an accuracy of 93.75%,which is of guiding significance for selecting the well killing method on site and realizing safe drilling.
Artificially synthesized polyacrylamides and natural plant gums such as guar gum are often used as fracturing fluid thickeners.Compared with natural plant gums such as guar gum,artificially synthesized polyacrylamides have distinct advantages in terms of performance,cost,and environmental cleanliness,as a result,they are widely used in hydraulic fracturing operations in oilfields.The acrylamide fracturing fluid thickeners were investigated,and then classified according to the number of reaction monomers involved in the synthesis of polyacrylamide fracturing fluid thickeners(ranging from 1 to 5).The synthesis methods and conditions for the acrylamide fracturing fluid thickeners were summarized,and the reasons for the synergy of some reaction monomers were explained.Furthermore,certain issues,such as the lack of reactivity ratio measurement and the absence of structural design of the polymers,in the synthesis process wore proposed,which may be critical factors affecting their performance.This research can serve as a reference for selecting monomers and synthesis methods when synthesizing acrylamide fracturing fluid thickeners.
Accurate prediction of well trajectory is fundamental to well trajectory control,and therefore,extremely important for improving drilling efficiency.However,there are many factors that may change well trajectory,and the downhole mechanical behavior is complex,which leads to high difficulties in accurately predicting well trajectory.This presents a dual-input sequence-to-sequence(Di-S2S)model.The model considers time series features,such as WOB and ROP,and non-time series features,such as drilling mode,formation stratigraphy and BHA structure.The non-time series features were numerically characterized with dimensionality reduction via a natural language processing process,and a dynamic updating mechanism based on incremental training was built for the model.The data of 12 wells were analyzed with the Di-S2S model,and the results were compared with those of the LSTM and BP models.The results show that the average absolute error of well inclination angles is reduced by 49%and 8%respectively,and the average absolute error of azimuths is reduced by 49%and 24%,respectively,compared with the LSTM and BP models.Moreover,compared with the offline model,the average absolute errors of well inclination and azimuth of the dynamic updating model,both lower than 0.2°,are reduced by 61%and 67%respectively.The presented Di-S2S model has high accuracy and enables real-time prediction.This research provides technical support for steerable drilling.
This research investigated the property variation and corrosion mechanisms of sulfoaluminate cement in highly sour services.The variations of the specific area and pore structure of the cement after corrosion were measured by cryogenic nitrogen adsorption tests(the BET and BJH methods).The changes in hydration products after corrosion were tested using the X-ray diffractometer(XRD)and thermal analyser(TG/DTG).Finally,the micro-scale morphological variations of hydration products of cement after corrosion were observed using the scanning electron microscope(SEM).The results showed that SAC presents a desirable strength at 60℃.The hydration products are mainly Aft after 14-day corrosion at 60℃and CaSO 4·2H2O after 14-day corrosion at 90℃.Notable stratification of the set cement is observed after corrosion by H2S.The outer layer is first corroded,while the inner layer presents short-term strength growth due to swelling.The mechanism of H2S corrosion is that C-S-H and CH in the hydration products of cement react with H2S respectively and produce swelling Aft and CaSO4·2H2O,which results in cracking of cement and reduction in compressive strengths.The findings of this research provide the experimental and theoretical basis for applications of sulfoaluminate cement in cementing of oil and gas wells with highly sour gas.
Reservoir stimulation of coal seams is one of the important techniques to increase the production of coalbed methane.However,due to the unique cleat system and lithologic characteristics of coal reservoirs,the conventional hydraulic fracturing technology is found inapplicable in field applications.Based on the characteristics of low temperature,high safety,adsorption partial pressure and phase-change pressurization of liquid carbon dioxide,the cryogenic fracturing technology of coal reservoirs with liquid carbon dioxide was developed.The first coal seam freezing test was performed in Well X150-1 of the Qinnan Basin.The field test shows that liquid carbon dioxide forms ice crystals and also temporary plugging to divert fractures and enable continuous fracture propagation.Compared with the production data of the adjacent well X150-2,the technology reflects the advantages of short desorption time and high gas production of a single well after transformation from the perspective of later drainage and production effects.From the long-term drainage effect,after the liquid level drops to near the coal seam in the later stage,the daily drainage of Well X150-1 is relatively high,indicating better gas production potential.This technology is an effective supplement and development of conventional hydraulic fracturing technology.
深水钻井一旦钻遇浅水流极易出现井漏甚至井喷等重大事故.常规地震剖面进行定性预测浅水流的准确性较低,为此提出了一种基于模拟实验的定量预测浅水流压力并对风险等级进行评价的方法.根据声波在水中及饱和岩石介质中的传播速度特征,进行了浅水流声学模拟实验.研究表明:纵波在深水浅水流地层中的传播速度随着地层压力的增大而增大,地层孔隙度越大,声波传播速度越小;通过数据拟合得到纵波速度与浅水流地层压力、孔隙度之间呈幂指数函数关系,根据实验结果建立了声速与浅水流地层压力、孔隙度的双参数模型,用于根据声速预测浅水流地层压力;利用有限元软件进行了浅水流地层的地质建模及放喷模拟,定义浅水流对钻井造成不同风险等级的压力系数范围.在中国南海深水区进行了浅水流声学预测及风险评价方法现场应用,验证了深水浅水流声波识别预测技术的可行性.
传统基于采油工程理论的抽油机举升系统设计方法难以有效处理复杂矿场实际情况,设计方案的可靠性有待提升.建立涵盖稠油、低渗、复杂断块等多个油藏类型的数据库,应用协同过滤推荐技术从数据库的抽油机井举升系统设计方案中探索规律,辅助优化设计,提升抽油机井举升系统的效益.通过对搜集的 3万余套历史举升方案相关数据规范化处理,得到涵盖油井地质、流体、生产等维度的抽油机井举升系统设计样本库.在此基础上,分析基于用户的协同过滤推荐系统的典型架构,建立了面向抽油机井举升系统设计的推荐算法,能够根据待设计井的地质开发特征,从数据库的历史样本中匹配得到地质开发条件相似度高且运行效果良好的举升设计方案进行推荐.分析 15口井的实例,协同过滤举升系统设计的平均泵效提升 7.84%,百米吨液耗电下降 24%,推荐方案相比于当前方案均有显著效果提升.研究成果为抽油机井举升方案设计提供了新的思路和方法,为油田大数据应用提供了有益借鉴和参考.
在气候变化、碳排放问题的大背景下,高等院校亟需采取应对措施积极开设碳储科学与工程专业,在人才培养、科学研究等方面助力国家实现碳达峰、碳中和的宏伟目标.通过系统调研全球二氧化碳捕集、利用与封存(CCUS)产业背景、国内外公司CCUS发展规划战略以及CCUS领域人才需求情况,详细分析了高等院校开设碳储科学与工程专业的必要性,阐述了国外高校CCUS教育和科研进展,通过对比国内首批开设碳储科学与工程专业 4所高校的实践情况总结了该专业目前面临的挑战,并提出了应对建议.研究结果表明,目前国内外碳储科学与工程专业人才需求量大,并且具有良好的就业前景和发展态势,高校开设碳储科学与工程专业十分必要.
