Evaluation of the oil and gas preservation conditions, source rocks, and hydrocarbongenerating potential of the Qiangtang Basin: New evidence from the scientific drilling project

The Qiangtang Basin of the Tibetan Plateau,located in the eastern Tethys tectonic domain,is the largest new marine petroliferous region for exploration in China.The scientific drilling project consisting primarily of well QK-1 and its supporting shallow boreholes for geological surveys(also referred to as the Project)completed in recent years contributes to a series of new discoveries and insights into the oil and gas preservation conditions and source rock evaluation of the Qiangtang Basin.These findings differ from previous views that the Qiangtang Basin has poor oil and gas preservation conditions and lacks high-quality source rocks.As revealed by well QK-1 and its supporting shallow boreholes in the Project,the Qiangtang Basin hosts two sets of high-quality regional seals,namely an anhydrite layer in the Quemo Co Formation and the gypsum-bearing mudstones in the Xiali Formation.Moreover,the Qiangtang Basin has favorable oil and gas preservation conditions,as verified by the comprehensive study of the sealing capacity of seals,basin structure,tectonic uplift,magmatic activity,and groundwater motion.Furthermore,the shallow boreholes have also revealed that the Qiangtang Basin has high-quality hydrocarbon source rocks in the Upper Triassic Bagong Formation,which are thick and widely distributed according to the geological and geophysical data.In addition,the petroleum geological conditions,such as the type,abundance,and thermal evolution of organic matter,indicate that the Qiangtang Basin has great hydrocarbon-generating potential.

A review of light amplification by stimulated emission of radiation in oil and gas well drilling

The prospect of employing Light Amplification by Stimulated Emission of Radiation(LASER) for well drilling in oil and gas industry was examined.In this work,the experimental works carried out on various oil well drilling operations was discussed.The results show that,LASER or LASER-aided oil and gas well drilling has many potential advantages over conventional rotary drilling,including high penetration rate,reduction or elimination of tripping,casing,bit costs,enhanced well control,as well as perforating and side-tracking capabilities.The investigation also reveals that modern infrared LASERs have a higher rate of rock cuttings removal than that of conventional rotary drilling and flame-jet spallation.It also reveals that LASER can destroy rock without damaging formation permeability but rather,it enhances or improves permeability and that permeability and porosity increases in all rock types.The paper has therefore provided more knowledge on the potential value to drilling operations and techniques using LASER.

Formation damage mechanism and control strategy of the compound function of drilling fluid and fracturing fluid in shale reservoirs

For the analysis of the formation damage caused by the compound function of drilling fluid and fracturing fluid,the prediction method for dynamic invasion depth of drilling fluid is developed considering the fracture extension due to shale minerals erosion by oil-based drilling fluid.With the evaluation for the damage of natural and hydraulic fractures caused by mechanical properties weakening of shale fracture surface,fracture closure and rock powder blocking,the formation damage pattern is proposed with consideration of the compound effect of drilling fluid and fracturing fluid.The formation damage mechanism during drilling and completion process in shale reservoir is revealed,and the protection measures are raised.The drilling fluid can deeply invade into the shale formation through natural and induced fractures,erode shale minerals and weaken the mechanical properties of shale during the drilling process.In the process of hydraulic fracturing,the compound effect of drilling fluid and fracturing fluid further weakens the mechanical properties of shale,results in fracture closure and rock powder shedding,and thus induces stress-sensitive damage and solid blocking damage of natural/hydraulic fractures.The damage can yield significant conductivity decrease of fractures,and restrict the high and stable production of shale oil and gas wells.The measures of anti-collapse and anti-blocking to accelerate the drilling of reservoir section,forming chemical membrane to prevent the weakening of the mechanical properties of shale fracture surface,strengthening the plugging of shale fracture and reducing the invasion range of drilling fluid,optimizing fracturing fluid system to protect fracture conductivity are put forward for reservoir protection.

Stability analysis of seabed strata and casing structure during the natural gas hydrates exploitation by depressurization in horizontal wells in South China Sea

Natural gas hydrates(NGHs)are a new type of clean energy with great development potential.However,it is urgent to achieve safe and economical NGHs development and utilization.This study established a physical model of the study area using the FLAC^(3D) software based on the key parameters of the NGHs production test area in the South China Sea,including the depressurization method,and mechanical parameters of strata,NGHs occurrence characteristics,and the technological characteristics of horizontal wells.Moreover,this study explored the law of influences of the NGHs dissociation range on the stability of the overburden strata and the casing structure of a horizontal well.The results are as follows.With the dissociation of NGHs,the overburden strata of the NGHs dissociation zone subsided and formed funnelshaped zones and then gradually stabilized.However,the upper interface of the NGHs dissociation zone showed significant redistribution and discontinuity of stress.Specifically,distinct stress concentration and corresponding large deformation occurred in the build-up section of the horizontal well,which was thus prone to suffering shear failure.Moreover,apparent end effects occurred at the end of the horizontal well section and might cause the deformation and failure of the casing structure.Therefore,it is necessary to take measures in the build-up section and at the end of the horizontal section of the horizontal well to prevent damage and ensure the wellbore safety in the long-term NGHs exploitation.

The Effects of Carbon Dioxide Laser Irradiation on Drilling of Limestone Included Crude Oil

Laser rock spallation is a rock removal process that utilizes laser induced thermal stress to fracture and cause a break through the rock by creating small fragments before melting of the rock. In this paper we investigated the effects of CO2 laser irradiation on limestone of Iran Sarvak formation. Since the limestone included heavy and light oil, we studied the amount of laser beam absorption by this oils for determining thermal fractured during the laser drilling laboratory process. In order to characterize this limestone spectrophotometry (from UV to NIR), scanning electron microscopy (SEM) have been used.

Theoretical Progress and Key Technologies of Onshore Ultra-Deep Oil/Gas Exploration

Oil/gas exploration around the world has extended into deep and ultra-deep strata because it is increasingly difficult to find new large-scale oil/gas reservoirs in shallow–middle buried strata. In recent years, China has made remarkable achievements in oil/gas exploration in ultra-deep areas including carbonate and clastic reservoirs. Some (ultra) large-scale oil and gas fields have been discovered. The oil/gas accumulation mechanisms and key technologies of oil/gas reservoir exploration and development are summarized in this study in order to share China’s experiences. Ultra-deep oil/gas originates from numerous sources of hydrocarbons and multiphase charging. Liquid hydrocarbons can form in ultradeep layers due to low geothermal gradients or overpressures, and the natural gas composition in ultra-deep areas is complicated by the reactions between deep hydrocarbons, water, and rock or by the addition of mantle- or crust-sourced gases. These oils/gases are mainly stored in the original highenergy reef/shoal complexes or in sand body sediments. They usually have high original porosity. Secondary pores are often developed by dissolution, dolomitization, and fracturing in the late stage. The early pores have been preserved by retentive diageneses such as the early charging of hydrocarbons. Oil/gas accumulation in ultra-deep areas generally has the characteristics of near-source accumulation and sustained preservation. The effective exploration and development of ultra-deep oil/gas reservoirs depend on the support of key technologies. Use of the latest technologies such as seismic signal acquisition and processing, low porosity and permeability zone prediction, and gas–water identification has enabled the discovery of ultra-deep oil/gas resources. In addition, advanced technologies for drilling, completion, and oil/gas testing have ensured the effective development of these fields.

Novel Water-Based Drilling and Completion Fluid Technology to Improve Wellbore Quality During Drilling and Protect Unconventional Reservoirs

The efficient exploration and development of unconventional oil and gas are critical for increasing the self-sufficiency of oil and gas supplies in China.However,such operations continue to face serious problems(e.g.,borehole collapse,loss,and high friction),and associated formation damage can severely impact well completion rates,increase costs,and reduce efficiencies.Water-based drilling fluids possess certain advantages over oil-based drilling fluids(OBDFs)and may offer lasting solutions to resolve the aforementioned issues.However,a significant breakthrough with this material has not yet been made,and major technical problems continue to hinder the economic and large-scale development of unconventional oil and gas.Here,the international frontier external method,which only improves drilling fluid inhibition and lubricity,is expanded into an internal-external technique that improves the overall wellbore quality during drilling.Bionic technologies are introduced into the chemical material synthesis process to imitate the activity of life.A novel drilling and completion fluid technique was developed to improve wellbore quality during drilling and safeguard formation integrity.Macroscopic and microscopic analyses indicated that in terms of wellbore stability,lubricity,and formation protection,this approach could outperform methods that use typical OBDFs.The proposed method also achieves a classification upgrade from environmentally protective drilling fluid to an ecologically friendly drilling fluid.The developed technology was verified in more than 1000 unconventional oil and gas wells in China,and the results indicate significant alleviation of the formation damage attributed to borehole collapse,loss,and high friction.It has been recognized as an effective core technology for exploiting unconventional oil and gas resources.This study introduces a novel research direction for formation protection technology and demonstrates that observations and learning from the natural world can provide an inexhaustible source of ideas and inspire the creation of original materials,technologies,and theories for petroleum engineering.

Multistring analysis of wellhead movement and uncemented casing strength in offshore oil and gas wells

This paper presents a theoretical method and a finite element method to describe wellhead movement and uncemented casing strength in offshore oil and gas wells.Parameters considered in the theoretical method include operating load during drilling and completion and the temperature field,pressure field and the end effect of pressure during gas production.The finite element method for multistring analysis is developed to simulate random contact between casings.The relevant finite element analysis scheme is also presented according to the actual procedures of drilling,completion and gas production.Finally,field cases are presented and analyzed using the proposed methods.These are four offshore wells in the South China Sea.The calculated wellhead growths during gas production are compared with measured values.The results show that the wellhead subsides during drilling and completion and grows up during gas production.The theoretical and finite element solutions for wellhead growth are in good agreement with measured values and the deviations of calculation are within 10％.The maximum von Mises stress on the uncemented intermediate casing occurs during the running of the oil tube.The maximum von Mises stress on the uncemented production casing,calculated with the theoretical method occurs at removing the blow-out-preventer （BOP） while that calculated with the finite element method occurs at gas production.Finite element solutions for von Mises stress are recommended and the uncemented casings of four wells satisfy strength requirements.

The impacts of gas impurities on the minimum miscibility pressure of injected CO_2-rich gas–crude oil systems and enhanced oil recovery potential

An effective parameter in the miscible-CO_2 enhanced oil recovery procedure is the minimum miscibility pressure(MMP)defined as the lowest pressure that the oil in place and the injected gas into reservoir achieve miscibility at a given temperature. Flue gases released from power plants can provide an available source of CO_2,which would otherwise be emitted to the atmosphere, for injection into a reservoir. However, the costs related to gas extraction from flue gases is potentially high. Hence, greater understanding the role of impurities in miscibility characteristics between CO_2 and reservoir fluids helps to establish which impurities are tolerable and which are not. In this study, we simulate the effects of the impurities nitrogen(N_2), methane(C_1), ethane(C_2) and propane(C_3) on CO_2 MMP. The simulation results reveal that,as an impurity, nitrogen increases CO_2–oil MMP more so than methane. On the other hand, increasing the propane(C_3)content can lead to a significant decrease in CO_2 MMP, whereas varying the concentrations of ethane(C_2) does not have a significant effect on the minimum miscibility pressure of reservoir crude oil and CO_2 gas. The novel relationships established are particularly valuable in circumstances where MMP experimental data are not available.

Key technologies, engineering management and important suggestions of shale oil/gas development: Case study of a Duvernay shale project in Western Canada Sedimentary Basin

The Duvernay project in Canada was taken as an example to summarize the advanced technology and engineering management model of shale oil and gas development in North America.Preliminary suggestions were put forward to accelerate the commercial development of domestic continental shale oil and gas.The advanced technologies,valuable knowledge and rich experience were introduced,including the evaluation of geological target area of the project,rapid long horizontal drilling and completion,high-intensity fracturing,and well spacing optimization.In particular,the concept and connotation of the full-life cycle management of North American unconventional resource projects were analyzed.Its emphasis on early evaluation and risk management,and a highly competitive market environment have played an important role in promoting technological innovation and management innovation.In addition,the low-cost sharing system of industry-wide knowledge and experience and the management mode were applied.These management approaches are of great significance for reference in accelerating the exploration and development of unconventional resources in China.China possesses abundant shale oil and gas resources,which are an important replacement to guarantee the national oil and gas energy supply.However,due to the late start and special geological characteristics and engineering difficulties in China,there is a large gap in technology level and management mode compared with North America.According to the advanced experience and enlightenment of the shale oil and gas development in North America,a preliminary proposal to accelerate the development of shale oil and gas in China was made.

Real Time Application of Bearing Wear Prediction Model Using Intelligent Drilling Advisory System

The real-time prediction of bearing wear for roller cone bits using the Intelligent Drilling Advisory system （IDAs） may result in better performance in oil and gas drilling operations and reduce total drilling cost. IDAs is a real time engineering software and being developed for the oil and gas industry to enhance the performance of complex drilling processes providing meaningful analysis of drilling operational data. The prediction of bearing wear for roller cone bits is one of the most important engineering modules included into IDAs to analyze the drilling data in real time environment. The Bearing Wear Prediction module in IDAs uses a newly developed wear model considering drilling parameters such as weight on bit （WOB）, revolution per minute （RPM）, diameter of bit and hours drilled as a function of International Association of Drilling Contractors （IADC） bit bearing wear. The drilling engineers can evaluate bearing wear status including cumulative wear of roller cone bit in real time while drilling, using this intelligent system and make a decision on when to pull out the bit in time to avoid bearing failure. The wear prediction module as well as the intelligent system has been successfully tested and verified with field data from different wells drilled in Western Canada. The estimated cumulative wears from the analysis match close with the corresponding field values.

Effect of Cassava Starch and Sodium Carbonate on the Properties of Local Drilling Mud: Beneficiation to Improve the Rheological and Flow Properties of Locally Formulated Mud

Drilling mud is a key component in drilling operations and in accessing oil and gas reservoirs. Bentonite is applied as a viscosifier, fluid loss control agent, and as a weighting material in water-based drilling mud. The type of bentonite used in drilling mud formulation is sodium bentonite due to its high dispersion properties and high swelling capacity. Nigeria has a huge bentonite clay deposit resources which can be evaluated and enhanced in order to be utilized as drilling mud. However, bentonite clay from different parts of Nigeria was investigated and found to be calcium bentonite which is not suitable for drilling mud, because it has low swelling capacity and poor rheological properties. In this study, local bentonite obtained from Afuze, Edo state was used to formulate different samples of drilling mud with each treated using thermo-chemical beneficiation process with sodium carbonate and cassava starch, and then undergo characterization to identify the changes in physical properties and finally, draw comparison with API values for standard drilling mud. The results obtained from this study indicates that, the flow and rheological properties of the beneficiated drilling mud developed through thermo-chemical treatment, showed significant improvement compared to the untreated mud. Therefore, pure calcium bentonite from natural deposits in Nigeria can be modified to sodium bentonite and sufficiently used in drilling mud formulation.

Fracture evolution and pressure relief gas drainage from distant protected coal seams under an extremely thick key stratum

When an extremely thick rock bed exists above a protected coal seam in the bending zone given the condition of a mining protective seam, this extremely thick rock bed controls the movement of the entire overlying stratum. This extremely thick rock bed, called a ＂main key stratum＂, will not subside nor break for a long time, causing lower fractures and bed separations not to close and gas can migrate to the bed separation areas along the fractures. These bed separations become gas enrichment areas. By analyzing the rule of fracture evolution and gas migration under the main key stratum after the deep protective coal seam has been mined, we propose a new gas drainage method which uses bore holes, drilled through rock and coal seams at great depths for draining pressure relief gas. In this method, the bores are located at a high level suction roadway （we can also drill them in the drilling field located high in an air gateway）. Given the practice in the Haizi mine, the gas drainage rate can reach 73% in the middie coal group, with a gas drainage radius over 100 m.

优快钻井工艺在海上钻井平台上的应用

面对复杂多变的海洋环境,海上钻井平台不但要为作业人员提供相对稳定的钻井作业条件,还要确保在狭小空间内钻井工艺安全运行。传统的原油开采技术很难应对海上油气开采过程中的困难和挑战。与传统的原油开采技术相比,优快钻井工艺在海上钻井平台上更具应用优势,可以提高海上油气开采效率,缩短海上油气开发周期。基于此,文章分析了优快钻井工艺在海上钻井平台上的技术优势、应用特点及应用流程,为海洋钻井作业人员提供参考和借鉴。

油气田地热开发前景潜力分析

全世界地热资源丰富,开发利用潜力巨大,地源热泵技术和地热发电技术的进步加速了地热资源开发利用的步伐。中国中、低温地热资源十分丰富,地热直接利用走在世界前列,地热发电具有一定的基础。中国石油矿权区面积广,区内地热资源总量大。介绍了我国地热资源分布及特点,分析了我国地热资源开发存在的问题,阐述了中国石油地热利用的进展和模式,中国石油具有地热资源开发利用的先天优势,其部分石油钻井可转换为地热开发井,油田采出水也可进行地热资源开发。中国石油地热资源开发利用应坚持依托油田,发挥优势,降低能耗,改善油区工作和生活环境。

国内分支井技术应用面临的主要难题及研究进展

介绍了分支井的技术特点及其在国内外的应用情况,分析认为国内分支井应用面临的主要技术难题有分支井眼参数设计、分支井叉口部位的处理以及分支系统设计的尺寸限制3个方面,总结了国内在分支井领域的研究进展及存在的问题,提出预开窗分支井、地面塑性预成型的6级分支井系统与智能完井技术结合是分支井技术的发展方向。

膨胀套管的研究现状

综述了国内外膨胀套管的研究现状,表明我国在高性能膨胀套管制造技术领域与发达国家之间存在着较大差距;探讨了不同作业类型下膨胀套管用钢的选材、性能要求及组织设计目标;展望了膨胀套管的未来发展趋势及对我国油气勘探开发的重要意义。建议加快高端膨胀套管的国产化研发进程,为我国深海钻井和勘探开发西部油气藏急需的膨胀套管钻井关键技术提供装备支持。

我国海上油田钻井完井投资测算方法研究

本文分析了我国海上油田钻井完井投资测算的现有方法,针对存在的问题和不足,从内生变量的选择、相关系数、变量的影响程度等方面进行分析研究,提出以作业周期、井深、水深三个因素进行测算的新方法。