Response analyses on the drill-string channel for logging while drilling telemetry

Downhole acoustic telemetry(DAT),using a long drill string with periodical structures as the channel,is a prospective technology for improving the transmission rate of logging while drilling(LWD)data.Previous studies only focused on the acoustic property of a free drill string and neglected the coupling between pipes and fluid-filled boreholes.In addition to the drill-string waves,a series of fluid waves are recorded in the DAT channel,which has not been investigated yet.Unpredictable channel characteristics result in lower transmission rates and stability than expected.Therefore,a more realistic channel model is needed considering the fluid-filled borehole.In this paper,we propose a hybrid modeling method to investigate the response characteristics of the DAT channel.By combining the axial wavenumbers and excitation functions of mode waves in radially layered LWD structures,the channel model is approximated to the 1-D propagation,which considers transmission,reflection,and interconversion of the drillstring and fluid waves.The proposed 1-D approximation has been well validated by comparing the 2-D finite-difference modeling.It is revealed that the transmitted and converted fluid waves interfere with the drill-string wave,which characterizes the DAT channel as a particular coherent multi-path channel.When a fluid-filled borehole surrounds the drill string,the channel responses exhibit considerable delay as well as strong frequency selectivity in amplitude and phase.These new findings suggest that the complexity of the channel response has been underestimated in the past,and therefore channel measurements on the ground are unreliable.To address these channel characteristics,we apply a noncoherent demodulation strategy.The transmission rate for synthetic data reaches 15 bps in a 94.5 m long channel,indicating that the acoustic telemetry is promising to break the low-speed limitation of mud-pulse telemetry.

Numerical simulation and dimension reduction analysis of electromagnetic logging while drilling of horizontal wells in complex structures

Electromagnetic logging while drilling(LWD)is one of the key technologies of the geosteering and formation evaluation for high-angle and horizontal wells.In this paper,we solve the dipole source-generated magnetic/electric fields in 2D formations efficiently by the 2.5D finite diff erence method.Particularly,by leveraging the field’s rapid attenuation in spectral domain,we propose truncated Gauss–Hermite quadrature,which is several tens of times faster than traditional inverse fast Fourier transform.By applying the algorithm to the LWD modeling under complex formations,e.g.,folds,fault and sandstone pinch-outs,we analyze the feasibility of the dimension reduction from 2D to 1D.For the formations with smooth lateral changes,like folds,the simplified 1D model’s results agree well with the true responses,which indicate that the 1D simplification with sliding window is feasible.However,for the formation structures with drastic rock properties changes and sharp boundaries,for instance,faults and sandstone pinch-outs,the simplified 1D model will lead to large errors and,therefore,2.5D algorithms should be applied to ensure the accuracy.

Logging-while-drilling formation dip interpretation based on long short-term memory

Azimuth gamma logging while drilling(LWD)is one of the important technologies of geosteering but the information of real-time data transmission is limited and the interpretation is difficult.This study proposes a method of applying artificial intelligence in the LWD data interpretation to enhance the accuracy and efficiency of real-time data processing.By examining formation response characteristics of azimuth gamma ray(GR)curve,the preliminary formation change position is detected based on wavelet transform modulus maxima(WTMM)method,then the dynamic threshold is determined,and a set of contour points describing the formation boundary is obtained.The classification recognition model based on the long short-term memory(LSTM)is designed to judge the true or false of stratum information described by the contour point set to enhance the accuracy of formation identification.Finally,relative dip angle is calculated by nonlinear least square method.Interpretation of azimuth gamma data and application of real-time data processing while drilling show that the method proposed can effectively and accurately determine the formation changes,improve the accuracy of formation dip interpretation,and meet the needs of real-time LWD geosteering.

A Study on the Classification and Well-Logging Identification of Eclogite in the Main Hole of Chinese Continental Scientific Drilling Project

Eclogite, one of the important lithologies in the main hole of the Chinese Continental Scientific Drilling （CCSD） Project, exists above the depth of 3 245 m and has distinctive responses of gamma-ray, compensating density and neutron well-logging, and so on. In this study, according to the diversities of minerals and chemical components and well-logging responses, edogites are classified from three aspects of origin, content of oxygen, and sub-mineral. We studied the logging identification method for eclogite sub-classes based on multi-element statistics and reconstructed 11 kinds of eclogite. As a result, eclogites can be divided into 6 types using well logs. In the light of this recognition, the eclogite in the main hole is divided into 20 sections, and the distribution characters of all sub-classes of eclogite are analyzed, which will provide important data for geological research of CCSD.

Self-adaptive inversion method of electromagnetic-propagation resistivity logging while drilling data

Because of the constraint mode of the inversion objective function in the traditional resistivity-inversion method of electromagnetic-propagation resistivity logging while drilling(EPR-LWD),obvious differences appear in the radial and vertical investigation characteristics between the amplitude-ratio and phase difference,which affect the practical application of EPR-LWD data.In this paper,according to the EPR-LWD data,a self-adaptive constraint resistivity-inversion method,which adopts a self-adaptive constraint weighted expression in the objective function to balance the contributions of the phase difference and amplitude attenuation,is proposed.A particle swarm optimization algorithm is also introduced to eliminate the dependence of the accuracy and convergence on the initial value of the inversion.According to the inversion results of multiple classical formation models for EPR-LWD,the differences between the adaptive constraint inversion-resistivity logs with the traditional amplitude-ratio and the phase difference of the resistivity logs are discussed in detail.The results demonstrate that the adaptive resistivity logs take into account the advantages of the amplitude-ratio logs in the radial investigation and phase difference logs in the vertical resolution.Further,it is superior in thin-layer identification and invasion-effect appraisal compared with the single-amplitude-ratio and phase difference logs.The inversion results can provide a theoretical reference for research on the resistivity-inversion method of electromagnetic wave LWD.

Logging while drilling electromagnetic wave responses in inclined bedding formation

For real-time inversion and fast reconstruction of formation true resistivity, the forward modeling of electromagnetic wave logging while drilling is usually based on the transversely isotropic formation model with vertical symmetry axis(VTI medium), but it only considers the horizontal and vertical resistivity. It has certain limitation during practical application. This paper presents a forward calculation method of electromagnetic wave logging while drilling in transversely isotropic(TTI) strata with inclined symmetry axis based on the Dyadic Green’s function. Anisotropic angle and azimuth are used to characterize TTI formation. The proposed algorithm is verified by numerical examples, the half-space electromagnetic wave reflection and transmission characteristics with different media are analyzed, and the necessity to use the new algorithm is pointed out. Numerical simulation also shows that there exist a critical borehole dip and critical anisotropic angle in TTI formation. Electromagnetic wave logging while drilling responses follows opposite rule before and after these two critical angles. Besides, the 'horns' at the interface are not only related to well deviation, resistivity contrast, but also related to anisotropic angle and anisotropic azimuth.

Generalized collar waves in acoustic logging while drilling

Tool waves, also named collar waves, propagating along the drill collars in acoustic logging while drilling （ALWD）, strongly interfere with the needed P- and S-waves of a penetrated formation, which is a key issue in picking up formation P- and S-wave velocities. Previous studies on physical insulation for the collar waves designed on the collar between the source and the receiver sections did not bring to a satisfactory solution. In this paper, we investigate the propagation features of collar waves in different models. It is confirmed that there exists an indirect collar wave in the synthetic full waves due to the coupling between the drill collar and the borehole, even there is a perfect isolator between the source and the receiver. The direct collar waves propagating all along the tool and the indirect ones produced by echoes from the borehole wall are summarized as the generalized collar waves. Further analyses show that the indirect collar waves could be relatively strong in the full wave data. This is why the collar waves cannot be eliminated with satisfactory effect in many cases by designing the physical isolators carved on the tool.

THE HAIF-SPACE RESPONSE ANALYSIS OF DUAL-INDUCTION LOGGING WHILE DRILLING BASED ON COMSOL

The response characteristics of the dual-induction logging tool while drilling in a half-spaceare computed and analyzed when the instrument slots opening direction, instrument height, ground conductivity is changed respectively. The results show that the haJ^-space response of the different opening direction of instrument slots has a nonlinear change with the increase of the ground conductivity. The effect of half-space response on the instrument slots downward opening direction is greatest and the upward is minimal The half-space response of the deep induction reaches the maximum near the 0.4m height when tool is above ground. The peak position does not change with the ground conductivity changes.These results have a practical significance to determine accurately the sonde error of the dual-induction logging tool while drilling.

Interest of Electrical Logging in Implementation of Technical Equipment for Water Drilling: Case of the Abrobakro Collecting Field (South-East Ivory Coast)

This work concerns the collecting field of the Abrobakro site, the objective of which is to determine the thickness of the layers crossed during drilling from electrical logging in order to propose the equipment plan for the various boreholes. The electrical logging data sheets, particularly those on resistivity and expeditious granulometry using a 1.25 mm and 2 mm mesh sieve, were used. The layer thicknesses are determined with the inflection points on the graphs. The electrical logging shows that the sands in the study area have resistivity values between 400 and 5000 Ω.m. The decrease in resistivity observed at 50 m for all boreholes shows that the static level of the groundwater is at this depth. The results of the accelerated granulometry show that the first 20 meters contain more fine particles and coarse to very coarse sands from 20 m. The granulometry of the screen laying areas shows that the 1.5 mm slot openings are best suited for all drilling in the Abrobakro collecting field. The diameter d10 of the aquiferous sands of the collecting field is close to 1.25 mm.

Rock fracture density characterization using measurement while drilling(MWD) techniques

Accurate determination of rock mass properties is a critical part of open-pit mine planning activities to enable more prescriptive blast designs to achieve improved loading and hauling and downstream process efficiency. Better and more accurate blast practice that delivers enhanced outcomes(better fragmentation, improved diggability, less dilution, etc.) is a critical and fundamental element of being able to achieve an effective Mine-Mill approach at a mining operation. Based on previous work, it has been demonstrated that an accurate representation of the rock mass properties can be obtained from the analysis of variations in blasthole drill performance as derived from measurement while drilling(MWD) systems when using tricone bits. This paper further investigates how monitored rate of penetration,pulldown force, rotary torque, rotary speed and bailing air pressure responses can be used to determine the presence of open and partially open fractures having varying dip angles. Based on a correlation of geophysically measured fracture logs and monitored drill performance variables in the same blastholes, the results show that the latter responses can accurately determine open versus closed fractures. The results also identified that variations in rate of penetration and rotary torque show the most sensitivity in the presence of open fractures that intersect a vertical blasthole at near orthogonal angles.

Study of real-time LWD data visual interpretation and geo-steering technology

LWD（logging while drilling） data has been used to explore complex subtle reservoirs by realtime visual interpretation and geo-steering.The method comprises of computer communication,well log data processing,formation recognition,reservoir modeling and model updating in real time.We studied the key technologies related to real-time LWD data visual interpretation and geo-steering and developed computer software with Chinese intellectual property rights covering the following important aspects： 1） real-time computer communication of well site LWD data;2） visualization of geological model and borehole information;3） real-time interpretation of LWD data;4） real-time geological model updating and geo-steering technology.We use field application examples to demonstrate the feasibility and validity of the proposed technologies.

Acoustic reflection well logging modeling using the frequency-domain finite-element method with a hybrid PML

In this paper, we propose a hybrid PML （H-PML） combining the normal absorption factor of convolutional PML （C-PML） with tangential absorption factor of Mutiaxial PML （M-PML）. The H-PML boundary conditions can better suppress the numerical instability in some extreme models, and the computational speed of finite-element method and the dynamic range are greatly increased using this HPML. We use the finite-element method with a hybrid PML to model the acoustic reflection of the interface when wireline and well logging while drilling （LWD）, in a formation with a reflector outside the borehole. The simulation results suggests that the PS- and SP- reflected waves arrive at the same time when the inclination between the well and the outer interface is zero, and the difference in arrival times increases with increasing dip angle. When there are fractures outside the well, the reflection signal is clearer in the subsequent reflection waves and may be used to identify the fractured zone. The difference between the dominant wavelength and the model scale shows that LWD reflection logging data are of higher resolution and quality than wireline acoustic reflection logging.

Determining the fluorescent components in drilling fluid by using NMR method

Fluorescent additives can reduce drilling operation risks, especially during high angle deviated well drilling and when managing stuck pipe problems. However, they can affect oil discovery and there is a need to reduce the level of fluorescents or change the drilling fluids to prevent loss of drilling velocity and efficiency. In this paper, based on the analysis of drilling fluids by NMR with high sensitivity, solid and liquid additives have been analyzed under conditions with different fluorescent levels and temperatures. The results show that all of the solid additives have no NMR signal, and therefore cannot affect oil discovery during drilling. For the liquid additives with different oil products, the characterizations can be quantified and evaluated through a T2 cumulated spectrum, oil peak(T2g), and oil content of the drilling fluids. NMR can improve the application of florescent additives and help us to enhance oil exploration benefits and improve drilling operations and efficiency.

Deep-detection of formation boundary using transient multicomponent electromagnetic logging measurements

The maximum distance at which an electromagnetic(EM)logging while drilling(LWD)tool detects an approaching boundary is defined as the depth of detection(DOD).Ultra-deep detection capability of the transient multicomponent EM logging measurement is investigated here.First,we adopt sine and cosine transform to calculate the transient multicomponent responses.Compared to the cosine transform,sine transform is more accurate in solving late-time responses.Then,a time-domain geosignal is introduced to sense the boundary.Results show that DOD of this transient EM measurement can be up to tens of meters,including directionally sensitivity.Additionally,by studying the decay characteristics of different components with time,cross component is confirmed to decay much faster than the coaxial/coplanar components in the formation coordinate system.A pseudo-inversion is thereby proposed to determine the dip angle of anisotropic stratified formation.Theoretical simulation results indicate that this algebraic method can determine the true dip at some particular moments.It is still stable and valid even when considering random measurement errors.Moreover,we establish the linear relationship between the time at which the half-point of geosignal curve appears and the distance to boundary(DTB),which would assist in the quick determination of DTB.

A 26ka Continuous Stratigraphic Record of Surface Rupturing Earthquakes in Drill Logs Across the Xiadian Fault,Hebei Province,China

This paper deals wiah a new method for identification of long-term slip behavior of a conceaiedfault in a plain area from tectono-stratigraphic and chronological data obtained by drilling.Chronological determination and lithological analysis and correlation of sediments in stratigraphic colunms of drills NO.1 and No.2 at Dongliuhe Village on the hanging and foot walls ofXiadian fault allow us to quantitatively reconstruct the differential sedimentary history and vertical dislocation process on the hanging and foot walls of the fault since 26 ka BP and to set upa tectono-stratigraphic indicators for identifying paleoearthquakes.On this basis,taking theaccumulative vertical displacement of both sides of a fault to be a quantitative constraint,thestate before an abrupt dislocation in surface-rupturing earthquake can be reconstructed(de-ducting the later coseismic vertical displacement),then 11 surface-rupturing paleoseismic even-ts can be identified.A close correlation between recurrence behavior of

基于正则化约束的方位伽马成像测井分辨率提高方法

随钻方位伽马测井可以用于地层放射性强度分析及地质导向、储层界面识别,但受到统计误差的影响非常大,曲线和成像分辨率不高,特别是在对比度不高的地层中,这种影响更明显。为了提高随钻方位伽马测井的成像分辨率,提出一种基于仪器响应特性对方位伽马数据进行正则化处理的方法,以获得更准确的地层放射性强度。首先根据探测器响应原理,采用数值模拟和实验方法得到方位伽马测井的响应灵敏函数,并验证得到的灵敏因子的准确性。然后,通过构造正则化计算公式、调整计算参数对测量的原始方位伽马数据进行处理。结果表明:经该方法处理后得到方位伽马曲线的聚焦性能、对比度得到提高,避免了过去使用线性求解方法所导致的过拟合问题,且伽马成像分辨率有显著增强,薄层识别能力也得到一定改善。该方法能够提供更加准确和清晰的成像结果,提高仪器的地质导向能力和储层钻遇率。

方位侧向电阻率成像随钻测井仪软聚焦仿真分析

随钻方位侧向仪器工作时,由于钻铤长度较长,使表面电位衰减严重,钻铤流出的电流会产生轴向分量,不能严格垂直于钻铤表面流出,导致测量结果不准确。针对该问题,根据方位侧向电阻率成像随钻测井仪(RIT)的电极结构,设计5种软聚焦工作模式,并给出不同工作模式下的方位侧向电极电流和视电阻率的计算表达式;软聚焦工作模式可模拟不同源距的对称天线同时工作,以保持钻铤表面等电位,并通过线性叠加差值近似的方法获得更精确的轴向电流。通过三维有限元方法计算不同软聚焦工作模式在渐变薄互层的响应,并与原始测井响应进行对比,结果表明软聚焦方法能平滑单个发射天线界面处存在的尖峰现象及台阶现象,对薄层的识别及视电阻率计算更加准确,对仪器实际测井数据资料解释有一定的指导意义。

基于深度残差网络的随钻方位电磁波电阻率测井反演方法

随钻方位电磁波电阻率测井可以提供丰富的地下信息,帮助完成储层位置确定和边界探测等任务,但常用的基于物理方程的迭代反演方法计算效率较低,在实时地质导向中受到诸多限制。为此,提出了一种基于深度残差网络的随钻方位电磁波电阻率测井资料智能反演方法。该方法将残差块中的卷积层和池化层替换为全连接层,并使用多头注意力机制来理解输入数据的关联性,以解决非线性回归问题;通过评估模型深度和宽度,并使用贝叶斯超参数调优算法找到随钻电磁波电阻率反演方法中最优的超参数,以提高反演模型的性能。该方法在模型试验中的平均准确率达到98.5%;在实际测井资料的平均准确率达到97.2%,单点反演时间约为0.01 s。研究表明,随钻方位电磁波电阻率测井反演方法能够快速准确地反演测井资料。

随钻中继式电磁波传输技术及应用研究

针对随钻条件下无线电磁波传输技术信号衰减大、传播距离短、信号频率低以及传输速率慢的难题,文章设计了基于准横电磁波(Transverse Electromagnetic Wave,TEM)激励模式的随钻中继式电磁波传输技术。该技术以钻杆作为传输载体,将电磁波在井内的随钻传输模型类比同轴线传输模型,通过使用多组载波频率,在提高传输速率的同时,利用中继接力扩展传输距离。该技术已通过不同地层环境的现场验证,是井下数据传输未来发展的重要方向。