Development and prospect of downhole monitoring and data transmission technology for separated zone water injection

This article outlines the development of downhole monitoring and data transmission technology for separated zone water injection in China.According to the development stages,the principles,operation processes,adaptability and application status of traditional downhole data acquisition method,cable communications and testing technology,cable-controlled downhole parameter real-time monitoring communication method and downhole wireless communication technology are introduced in detail.Problems and challenges of existing technologies in downhole monitoring and data transmission technology are pointed out.According to the production requirement,the future development direction of the downhole monitoring and data transmission technology for separated zone water injection is proposed.For the large number of wells adopting cable measuring and adjustment technology,the key is to realize the digitalization of downhole plug.For the key monitoring wells,cable-controlled communication technology needs to be improved,and downhole monitoring and data transmission technology based on composite coiled tubing needs to be developed to make the operation more convenient and reliable.For large-scale application in oil fields,downhole wireless communication technology should be developed to realize automation of measurement and adjustment.In line with ground mobile communication network,a digital communication network covering the control center,water distribution station and oil reservoir should be built quickly to provide technical support for the digitization of reservoir development.

Response characteristics of drill-string guided wave in downhole acoustic telemetry

Modeling of a drill-string acoustic channel has been an important topic in downhole telemetry for a long time.The propagation of drill-string guided waves in the borehole contains excitation,attenuation,and mode conversion issues that have not been considered by existing modeling methods.In this article,we formulate a hybrid modeling method to investigate the response characteristics of a fundamental-mode drill-string wave in various borehole environments.This hybrid method provides channel functions,including transmitting and receiving deployments,periodicity of the structure,and formation property changes.The essential physics of the drill-string wave propagation is captured with a one-dimensional model.The analytical solutions of the wavefield in multilayered cylindrical structures are introduced into a propagation matrix to express drill-string-wave interactions with the borehole environments.The effectiveness of the proposed method is confirmed through comparison with the finite-difference method.In addition,by designing numerical models,we investigate the conversion effect of the drill-string wave at the tool joint.We demonstrate that the conversion intensity of the drill-string wave is positively correlated not only with the cross-sectional area of the tool joint but also with the wave impedance of the outer formation.Hard formation outside the borehole reduces the energy leakage while intensifying the conversion of drill-string waves to Stoneley waves,and the opposite is true for the drill string in an infinite fluid.The converted Stoneley waves interfere with the drill-string waves,resulting in variations of bandgap distribution,which challenges the reliability of the data transmission.

Numerical simulation of downhole temperature distribution in producing oil wells

An improved numerical simulation method is presented to calculate the downhole temperature distribution for multiple pay zones in producing oil wells. Based on hydrodynamics and heat transfer theory, a 2-D temperature field model in cylindrical coordinates is developed. In the model, we considered general heat conduction as well as the heat convection due to fluid flow from porous formation to the borehole. We also take into account the fluid velocity variation in the wellbore due to multiple pay zones. We present coupled boundary conditions at the interfaces between the wellbore and adjacent formation, the wellbore and pay zone, and the pay zone and adjacent formation. Finally, an alternating direction implicit difference method （ADI） is used to solve the temperature model for the downhole temperature distribution. The comparison of modeled temperature curve with actual temperature log indicates that simulation result is in general quite similar to the actual temperature log. We found that the total production rate, production time, porosity, thickness of pay zones, and geothermal gradient, all have effects on the downhole temperature distribution.

基于Downhole工艺的海底静力触探及其设备研制

论述基于Downhole CPT的海底静力触探工艺和实施方案,并在此基础上研制了适用于水深10～100 m,触探最大深度120 m的海底静力触探设备。对设备中的管内锥探总成、海底机座以及推进速度控制策略等核心问题进行了探讨。码头与海底试验中,触探数据结果与钻探取样基本符合,验证了工艺方案与触探设备达到了预期的工艺要求。

Numerical simulation of surface and downholedeformation induced by hydraulic fracturing

Tiltmeter mapping technology infers hydraulic fracture geometry by measuringfracture-induced rock deformation, which recorded by highly sensitive tiltmeters placed atthe surface and in nearby observation wells. By referencing Okada＇s linear elastic theory andGreen＇s function method, we simulate and analyze the surface and downhole deformationcaused by hydraulic fracturing using the homogeneous elastic half-space model and layeredelastic model. Simulation results suggest that there is not much difference in the surfacedeformation patterns between the two models, but there is a significant difference in thedownhole deformation patterns when hydraulic fracturing penetrates a stratum. In suchcases, it is not suitable to assume uniform elastic half-space when calculating the downholedeformation. This work may improve the accuracy and reliability of the inversion results oftiltmeter monitoring data.

Using the curve moment and the PSO-SVM method to diagnose downhole conditions of a sucker rod pumping unit

Downhole working conditions of sucker rod pumping wells are automatically identified on a computer from the analysis of dynamometer cards. In this process, extraction of feature parameters and pattern classification are two key steps. The dynamometer card is firstly divided into four parts which include different production information according to the ＂four point method＂ used in actual oilfield production, and then the moment invariants for pattern recognition are extracted. An improved support vector machine （SVM） method is used for pattern classification whose error penalty parameter C and kernel function parameter g are optimally chosen by the particle swarm optimization （PSO） algorithm. The simulation results show the method proposed in this paper has good classification results.

Downhole Microseismic Source Location Based on a Multi-Dimensional DIRECT Algorithm for Unconventional Oil and Gas Reservoir Exploration

Downhole microseismic data has the significant advantages of high signal-to-noise ratio and well-developed P and S waves and the core component of microseismic monitoring is microseismic event location associated with hydraulic fracturing in a relatively high confidence level and accuracy.In this study,we present a multidimensional DIRECT inversion method for microseismic locations and applicability tests over modeling data based on a downhole microseismic monitoring system.Synthetic tests inidcate that the objective function of locations can be defined as a multi-dimensional matrix space by employing the global optimization DIRECT algorithm,because it can be run without the initial value and objective function derivation,and the discretely scattered objective points lead to an expeditious contraction of objective functions in each dimension.This study shows that the DIRECT algorithm can be extensively applied in real downhole microseismic monitoring data from hydraulic fracturing completions.Therefore,the methodology,based on a multidimensional DIRECT algorithm,can provide significant high accuracy and convergent efficiency as well as robust computation for interpretable spatiotemporal microseismic evolution,which is more suitable for real-time processing of a large amount of downhole microseismic monitoring data.

Study of Structural Parameters of the Inlet of Downhole Hydrocyclones

Three different inlets of hydrocyclone are studied in combination with the construction of a dowrahole system and hydrocyclone. By comparing the relationship between the inlet structure ＆ dimensional parameter of hydrocyclone and separation efficiency ＆ pressure loss, the highest efficiency is obtained from the inlet of an involute curve with increasing depth-width ratio from the three types, in which the separation efficiency and pressure loss all drops slowly, for the length of the channel decreases, while it drops rapidly in the other two. The flow guiding ability of the inlet affects the separation efficiency greatly, so the corresponding involute type of inlet of hydrocyclone fits for downhole oil-water separation is optimized, which serves as a basis for the structural design of downhole hydrocyclone.

Study on the Source Characteristics of Downhole Airgun with Different Excitation Environments

The measurement of underground medium variation using a repeated artificial source has gradually become an important goal to pursue. In recent years,we have developed and improved a technology system with large capacity airguns excited in land reservoirs by transplanting marine seismic exploration technology. The excitation effect has a close relationship to airgun capacity,water environment,and excitation conditions. In view that large capacity airgun must be excited without a water environment,we expand the system to use in downhole. Based on the BHS-2200 LL downhole airgun with a capacity of250in3,this paper carries out a comparative analysis on the characteristics of an airgun source excited in 0. 2m- and 5. 0m-diameter wells,and the results show that:( 1) The dominant frequency of the airgun signal excited in a 5. 0m well is mainly from 10 Hz to40Hz,lower than that in a 0. 2m well,and the larger body of water is good for bubble oscillation.( 2) In terms of exciting energy,the signal excited in a 5. 0m well has stronger energy than in a 0. 2m well,with a difference of 1 order in magnitude,and the signal can be detected up to 9km excited in a 5. 0m well with a single shot.( 3) The airgun signal has good repeatability in both excitation wells. The downhole airgun excitation technology system has potential application in dynamic monitoring near a fault zone with a small scale range, exploration of oil and mineral resources, and modern urban geophysical environment.

Design and Analysis of an Active Helical Drive Downhole Tractor

During oil-gas well drilling and completion, downhole tools and apparatus should be conveyed to the destination to complete a series of downhole works. Downhole tractors have been used to convey tools in complex wellbores, however a very large tractive force is needed to carry more downhole tools to accomplish works with high efficiency. A novel serial active helical drive downhole tractor which has significantly improved performance compared with previous work is proposed. All previously reported helical drive downhole tractors need stators to balance the torque generated by the rotator. By contrast, the proposed serial downhole tractor does not need a stator; several rotator-driven units should only be connected to one another to achieve a tractive force multifold higher than that was previously reported. As a result, the length of a single unit is shortened, and the motion flexibility of the downhole tractor is increased. The major performance indicators, namely, gear ratio, velocity, and tractive force, are analyzed. Experimental results show that the maximum tractive force of a single-unit prototype with a length of 900 mm is 165.3 kg or 1620 N. The analysis and experimental results show that the proposed design has considerable potential for downhole works.

OFDM Wireless Downhole Transmission Systems and Proposed SLM Method for PAPR Reduction

At present, mud pulse transmission systems are widely used in downhole data transmission. But the systems are very low in transmission efficiency, only 5-10 bits/s, with very large anti-inter-symbol-interference (ISI). It cannot meet high requirements for high-speed transmission of modern logging system. The development of communication technology has laid some foundation for this requirement. For this purpose, the Orthogonal Frequency Division Multiplexing (OFDM) Wireless Downhole Transmission Systems are proposed for the first time because of their high transmission rate, anti-inter-symbol-interference (ISI), and high spectral efficiency, etc. Due to non-linear power amplifier (PA) of logging systems with limited dynamic range, the drawbacks of high peak-average power ratio (PAPR) may outweigh all the potential benefits of OFDM wireless downhole transmission systems. Selective mapping (SLM) method can reduce the PAPR of OFDM logging signals without distortion. But at the receiver, the conventional SLM method needs exact bits of side information (SI) to recover the data signal. The probability of erroneous SI detection has a significant influence on the error performance of the system. And individual transmissions of SI result in the reduction of bandwidth efficiency. To restore the exact data signal, our scheme codes the SI bits by linear block codes (LBC), and is easily decoded by syndrome decoding. And then the coding SI bits are superimposed onto the logging signals to omit SI bits transmission. The theory and simulation results show that the proposed method has better performance than the conventional one. Accordingly, the OFDM wireless downhole transmission systems can tackle the high PAPR problem, and highten the transmission rate of logging signals.

Introduction to the theory and technology on downhole control engineering and its research progress

On the basis of reviewing the development history of drilling engineering technology over a century, this paper describes the technical and scientific background of downhole control engineering, discusses its basic issues, discipline frame and main study contents, introduces the research progress of downhole control engineering in China over the past 30 years, and envisions the development direction of downhole control engineering in the future. The author proposed the study subject of well trajectory control theory and technology in 1988, and further proposed the concept of downhole control engineering in 1993. Downhole control engineering is a discipline branch, which applies the perspectives and methods of engineering control theory to solve downhole engineering control issues in oil and gas wells; meanwhile, it is an application technology field with interdisciplinarity. Downhole control engineering consists of four main aspects; primarily, investigations about dynamics of downhole system and analysis methods of control signals; secondly, designs of downhole control mechanisms and systems, research of downhole parameters collections and transmission techniques; thirdly, development of downhole control engineering products; fourthly, development of experimental methods and the laboratories. Over the past 30 years, the author and his research group have achieved a number of progress and accomplishments in the four aspects mentioned above. As a research field and a disciplinary branch of oil and gas engineering, downhole control engineering is stepping into a broader and deeper horizon.

An analysis of the uniformity of multi-fracture initiation based on downhole video imaging technology: A case study of Mahu tight conglomerate in Junggar Basin, NW China

To solve the problem that the production of Mahu conglomerate reservoir is not up to expectation after the multi-cluster plus temporary plugging fracturing technology is applied in horizontal wells, stages 2–6 in the test well MaHW6285 are selected to carry out erosion tests with different pumping parameters. The downhole video imaging technology is used to monitor the degree of perforations erosion, and then the fracture initiation and proppant distribution of each cluster are analyzed. The results showed that proppant entered 76.7% of the perforations. The proppant was mainly distributed in a few perforation clusters, and the amount of proppant entered in most of the clusters was limited. The proppant distribution in Stage 4 was relatively uniform, and the fracture initiation of each cluster in the stage is more uniform. The proppant distribution in stages 2, 3, 5, and 6 was significantly uneven, and the uniform degree of fracture initiation in each cluster is low. More than 70% of the proppant dose in the stage entered clusters near the heel end, so the addition of diverters did not promote the uniform initiation of hydraulic fractures. There was a positive correlation between the amount of proppant added and the degree of perforations erosion, and the degree of perforations erosion ranged from 15% to 352%, with an average value of 74.5%, which was far higher than the statistical results of shale reservoir tests in North America. The use of 180° phase perforation(horizontal direction) can reduce the “Phase Bias” of perforations erosion, promote uniform perforations erosion and fluid inflow. The research results provide the basis for optimizing the pumping procedure, reducing the perforation erosion and improving the success rate of diversion.

A Mathematical Model and a Method for the Calculation of the Downhole Pressure in Composite-Perforation Technological Processes

Using the conservation equations for mass,momentum and energy,a model is elaborated to describe the dynamics of high-energy gases in composite-perforation technological processes.The model includes a precise representation of the gunpowder combustion and related killing fluid displacement.Through numerical solution of such equations,the pressure distribution of the high-energy gas in fractures is obtained,and used to determine crack propagation.The accuracy of the model is verified by comparing the simulation results with actual measurements.

Downhole microseismic data reconstruction and imaging based on combination of spline interpolation and curveletsparse constrained interpolation

When cause of the aliasing lack probl using borehole sensors and microseimic events to image, spatial aliasing often occurred be- of sensors underground and the distance between the sensors which were too large. To solve em, data reconstruction is often needed. Curvelet transform sparsity constrained inversion was widely used in the seismic data reconstruction field for its anisotropic, muhiscale and local basis. However, for the downhole ease, because the number of sampling point is mueh larger than the number of the sensors, the advantage of the cnrvelet basis can＇t perform very well. To mitigate the problem, the method that joints spline and curvlet-based compressive sensing was proposed. First, we applied the spline interpolation to the first arri- vals that to be interpolated. And the events are moved to a certain direction, such as horizontal, which can be represented by the curvelet basis sparsely. Under the spasity condition, curvelet-based compressive sensing was applied for the data, and directional filter was also used to mute the near vertical noises. After that, the events were shifted to the spline line to finish the interpolation workflow. The method was applied to a synthetic mod- el, and better result was presented than using curvelet transform interpolation directly. We applied the method to a real dataset, a mieroseismic downhole observation field data in Nanyang, using Kirchhoff migration method to image the microseimic event. Compared with the origin data, artifacts were suppressed on a certain degree.

Optimization of shut-in time based on saturation rebalancing in volume-fractured tight oil reservoirs

Based on imbibition replacement of shut-in well in tight oil reservoirs, this paper expounds the principle of saturation rebalancing during the shut-in process after fracturing, establishes an optimization method for shut-in time after horizontal well volume fracturing with the goal of shortening oil breakthrough time and achieving rapid oil breakthrough, and analyzes the influences of permeability, porosity, fracture half-length and fracturing fluid volume on the shut-in time. The oil and water imbibition displacement in the matrix and fractures occurs during the shut-in process of wells after fracturing. If the shut-in time is too short, the oil-water displacement is not sufficient, and the oil breakthrough time is long after the well is put into production. If the shut-in time is too long, the oil and water displacement is sufficient, but the energy dissipation in the formation near the bottom of the well is severe, and the flowing period is short and the production is low after the well is put into production. A rational shut-in time can help shorten the oil breakthrough time, extend the flowing period and increase the production of the well. The rational shut-in time is influenced by factors such as permeability, porosity, fracture half-length and fracturing fluid volume. The shortest and longest shut-in times are negatively correlated with porosity, permeability, and fracture half-length, and positively correlated with fracturing fluid volume. The pilot test in tight oil horizontal wells in the Songliao Basin, NE China, has confirmed that the proposed optimization method can effectively improve the development effect of horizontal well volume fracturing.

油气井井下切割技术发展现状及趋势

油气开发后期,退役井数量急剧增加,完井修井作业中套管磨损、卡钻等问题突出,退役经济耗费显著增加。为最大限度减少卡钻和退役经济耗费,有必要开展新型套管切割技术及装备的研发与应用。首先,总结了现阶段井下管柱切割技术的主要类型、工作原理和配套装备,包括机械切割、磨料射流切割、聚能切割、化学切割、电弧切割以及激光切割;对比机械切割、磨料射流切割以及特种切割方式的技术发展现状和趋势,分析上述切割方式的工程应用及优缺点;在此基础上,提出面向高效套管切割工程需求的主要切割技术及工具。结合目前切割技术及工具的发展现状,对未来井下管柱切割技术给出优化割刀性能、加强磨料射流切割的控制、研制新型切割工具及切割工具智能化等建议。

中国石油井下作业数字化监督发展问题与对策

阐述了中国石油井下作业数字化监督在监督人员数字化管理、施工队伍数字化监督、施工作业数字化监督、井场环境数字化监督4个方面的发展现状。分析了井下作业数字化监督发展面临数字化监督管理制度不健全、监督数据标准不统一、数字化智能监督技术不完善、缺少统一的数字化智能监督平台、监督数据价值挖掘不深入5个方面的主要问题。提出了制定井下作业数字化监督管理制度、建立井下作业监督数据标准、攻关数字化智能监督关键技术、研发井下作业数字化智能监督平台、提升监督大数据分析应用水平5项数字化监督发展对策。展望了井下作业数字化监督建设发展后在提升监督人员履职效率、降低监督人力资源成本、提升工程质量、保障施工安全与环保4个方面的预期成效。

钻井利器的故事之“井下动力钻具”

钻井是能源矿产勘探开发最直接的工程技术手段,井下动力钻具作为破碎地层岩土的有利器具,或直接驱动钻头形成滑动钻进,或与顶驱(或转盘)的回转共同组合驱动钻头形成复合钻进,具有降耗增速、减小井下事故风险等优点。为促使井下动力钻具被更多技术人员了解和认识,物尽其用充分发挥其钻井优势并利用技术特点开发新功能、新器具,本文从科普的角度介绍了井下动力钻具的用途、主要种类、工作原理及发展历程,并综合对比不同井下动力钻具的优劣势。最后,结合深井、超深井等钻井新形势对钻探器具、工艺等的新要求,以及材料、测控、智能化等新科技的在钻井工程中的应用趋势,指出了当前主流井下动力钻具的更新换代、技术革新的发展方向。