Stability of finite difference numerical simulations of acoustic logging-while-drilling with different perfectly matched layer schemes

In acoustic logging-while-drilling （ALWD） finite difference in time domain （FDTD） simulations, large drill collar occupies, most of the fluid-filled borehole and divides the borehole fluid into two thin fluid columns （radius -27 mm）. Fine grids and large computational models are required to model the thin fluid region between the tool and the formation. As a result, small time step and more iterations are needed, which increases the cumulative numerical error. Furthermore, due to high impedance contrast between the drill collar and fluid in the borehole （the difference is 〉30 times）, the stability and efficiency of the perfectly matched layer （PML） scheme is critical to simulate complicated wave modes accurately. In this paper, we compared four different PML implementations in a staggered grid finite difference in time domain （FDTD） in the ALWD simulation, including field-splitting PML （SPML）, multiaxial PML（M- PML）, non-splitting PML （NPML）, and complex frequency-shifted PML （CFS-PML）. The comparison indicated that NPML and CFS-PML can absorb the guided wave reflection from the computational boundaries more efficiently than SPML and M-PML. For large simulation time, SPML, M-PML, and NPML are numerically unstable. However, the stability of M-PML can be improved further to some extent. Based on the analysis, we proposed that the CFS-PML method is used in FDTD to eliminate the numerical instability and to improve the efficiency of absorption in the PML layers for LWD modeling. The optimal values of CFS-PML parameters in the LWD simulation were investigated based on thousands of 3D simulations. For typical LWD cases, the best maximum value of the quadratic damping profile was obtained using one do. The optimal parameter space for the maximum value of the linear frequency-shifted factor （a0） and the scaling factor （β0） depended on the thickness of the PML layer. For typical formations, if the PML thickness is 10 grid points, the global error can be reduced to 〈1% using the optimal PML parameters, and the error will decrease as the PML thickness increases.

Backpropagation neural network method in data processing of ultrasonic imaging logging-while-drilling

The existing methods for extracting the arrival time and amplitude of ultrasonic echo cannot eff ectively avoid the local interference of ultrasonic signals while drilling,which leads to poor accuracy of the echo arrival time and amplitude extracted by an ultrasonic imaging logging-while-drilling tool.In this study,a demodulation algorithm is used to preprocess the ultrasonic simulation signals while drilling,and we design a backpropagation neural network model to fit the relationship between the waveform data and time and amplitude.An ultrasonic imaging logging model is established,and the finite element simulation software is used for forward modeling.The response under diff erent measurement conditions is simulated by changing the model parameters,which are used as the input layer of the neural network model;The ultrasonic echo signal is considered as a low-frequency signal modulated by a high-frequency carrier signal,and a low-pass fi lter is designed to remove the high-frequency signal and obtain the low-frequency envelope signal.Then the amplitude of the envelope signal and its corresponding time are extracted as an output layer of the neural network model.By comparing the application eff ects of the various training methods,we fi nd that the conjugate gradient descent method is the most suitable method for solving the neural network model.The performance of the neural network model is tested using 11 groups of simulation test data,which verify the eff ectiveness of the model and lay the foundation for further practical application.

Joint inversion method of formation shear-wave anisotropy from logging-while-drilling acoustic data

Most sedimentary formations with fine layers can be characterized as transversely isotropic media.The evaluation of shear-wave anisotropy is critical in logging-while-drilling(LWD)applications.We developed a joint method to simultaneously invert formation shear-wave anisotropy and vertical shear velocity using LWD monopole and dipole dispersion data.Theoretical analysis demonstrates that formation shear-wave anisotropy significantly aff ects the dispersion characteristics of Stoneley and formation flexural waves.The inversion objective function was constructed based on the change in dispersion characteristics and was weighted by the spectra of multipole waves.Numerical results using synthetic examples demonstrate that the joint inversion method can not only alleviate the non-uniqueness problem but also help improve the accuracy of the inversion results.The comparison of diff erent signal-to-noise ratio inversion results proved that the weighted inversion method is more accurate and stable.

Real-time forward modeling and inversion of logging-while-drilling electromagnetic measurements in horizontal wells

Based on the pseudo-analytical equation of electromagnetic log for layered formation,an optimal boundary match method is proposed to adaptively truncate the encountered formation structures.An efficient integral method is put forward to significantly accelerate the convergence of Sommerfeld integral.By asymptotically approximating and subtracting the first reflection/transmission waves from the scattered field,the new Sommerfeld integral method has addressed difficulties encountered by the traditional digital filtering method,such as low computational precision and limited operating range,and realized the acceleration of the computation speed of logging-while-drilling electromagnetic measurements(LWD EM).By making use of the priori information from the offset/pilot wells and interactively adjusting the formation model,the optimum initial guesses of the inversion model is determined in order to predict the nearby formation boundaries.The gradient optimization algorithm is developed and an interactive inversion system for the LWD EM data from the horizontal wells is established.The inverted results of field data demonstrated that the real-time interactive inversion method is capable of providing the accurate boundaries of layers around the wellbore from the LWD EM,and it will benefit the wellbore trajectory optimization and reservoir interpretation.

2.5-Dimensional modeling of EM logging-while-drilling tool in anisotropic medium on a Lebedev grid

A 2.5D finite-difference(FD)algorithm for the modeling of the electromagnetic(EM)logging-whiledrilling(LWD)tool in anisotropic media is presented.The FD algorithm is based on the Lebedev grid,which allows for the discretization of the frequency-domain Maxwell's equations in the anisotropic media in 2.5D scenarios without interpolation.This leads to a system of linear equations that is solved using the multifrontal direct solver which enables the simulation of multi-sources at nearly the cost of simulating a single source for each frequency.In addition,near-optimal quadrature derived from an optimized integration path in the complex plane is employed to implement the fast inverse Fourier Transform(IFT).The algorithm is then validated by both analytic and 3D solutions.Numerical results show that two Lebedev subgrid sets are sufficient for TI medium,which is common in geosteering environments.The number of quadrature points is greatly reduced by using the near-optimal quadrature method.

利用LWD测井资料预测油藏衰竭程度和生产气油比

综合利用LWD、MDT测井以及生产动态资料,对衰竭式开发油藏的衰竭程度(地层压力)、单井初产气油比与LWD测井响应的关系进行了研究。研究不同衰竭程度和生产气油比时LWD体积密度和中子孔隙度测井响应特征发现,当地层压力小于饱和压力时,LWD测井密度和中子孔隙度曲线重叠区的大小与油藏衰竭程度和生产气油比具有一定关系,重叠区越大,地层压力越低,油藏衰竭程度就越严重,生产气油比也越高。经多元统计回归,得到地层压力、生产气油比与密度孔隙度和中子孔隙度之差的函数关系。通过对DLL油田Ⅱ区块实际资料的统计分析,建立了利用密度孔隙度和中子孔隙度之差预测地层压力和生产气油比的经验模型,预测结果与MDT测井压力资料和生产气油比资料相符,证明该方法有较高的精度。

Baker LWD无线随钻测井系统现场应用与维护

BakerHughes LWD无线随钻测井系统具有先进的地质导向功能,已经成为水平井、大位移井首选的随钻测量工具,但受现场维修工具和维修工艺的限制,仪器发生故障后需返厂维修,造成钻井施工被迫停工等。通过对现场维修支架结构改进,增加一对旋转轮和一对纵向移动轮,并加长升降装置的行程,使仪器在施工现场能够同时实现水平移动和水平旋转,解决了现场维修时MWD与M30插针对接的难题,同时配合现场维修工艺,使LWD随钻测井系统现场维护维修技术更加完善。该技术先后在华北油田、冀东油田等地进行了5口井现场应用,现场维修工艺技术完全可以满足维修保养LWD系统的需要。

Response simulation and theoretical calibration of a dual- induction resistivity LWD tool

In this paper, responses of a new dual-induction resistivity logging-while-drilling （LWD） tool in 3D inhomogeneous formation models are simulated by the vectorfinite element method （VFEM）, the influences of the borehole, invaded zone, surroundingstrata, and tool eccentricity are analyzed, and calibration loop parameters and calibrationcoefficients of the LWD tool are discussed. The results show that the tool has a greater depthof investigation than that of the existing electromagnetic propagation LWD tools and is moresensitive to azimuthal conductivity. Both deep and medium induction responses have linearrelationships with the formation conductivity, considering optimal calibration loop parametersand calibration coefficients. Due to the different depths of investigation and resolution, deepinduction and medium induction are affected differently by the formation model parameters,thereby having different correction factors. The simulation results can provide theoreticalreferences for the research and interpretation of the dual-induction resistivity LWD tools.

Analysis and application of the response characteristics of DLL and LWD resistivity in horizontal well

There exist different response characteristics in the resistivity measurements of dual laterolog （DLL） and logging while drilling （LWD） electromagnetic wave propagation logging in highly deviated and horizontal wells due to the difference in their measuring principles. In this study, we first use the integral equation method simulated the response characteristics of LWD resistivity and use the three dimensional finite element method （3D-FEM） simulated the response characteristics of DLL resistivity in horizontal wells, and then analyzed the response differences between the DLL and LWD resistivity. The comparative analysis indicated that the response differences may be caused by different factors such as differences in the angle of instrument inclination, anisotropy, formation interface, and mud intrusion. In the interface, the curves of the LWD resistivity become sharp with increases in the deviation while those of the DLL resistivity gradually become smooth. Both curves are affected by the anisotropy although the effect on DLL resistivity is lower than the LWD resistivity. These differences aid in providing a reasonable explanation in the horizontal well. However, this can also simultaneously lead to false results. At the end of the study, we explain the effects of the differences in the interpretation of the horizontal well based on the results and actual data analysis.

时域积分的LWD振动加速度处理电路

根据随钻测井(LWD)仪器的振动位移对随钻测井数据进行评估,是提高随钻测井准确性的有效方法。研制了一种基于时域积分方法的加速度信号处理电路,其可在井下实时测量随钻测井仪器的振动加速度,再通过积分计算获得井下实时振动位移。该电路的数字信号处理器件选用高可靠性的32位定点DSP器件TMS320F2812,加速度信号处理方法选用占用资源少、便于微型系统实时计算的时域积分方法,再采用拟合多项式极值方法,消除了积分中产生的趋势项误差。振动测试表明,该加速度测量电路所得的位移时程曲线与理论值曲线拟合的精度较高,能满足随钻测井仪器位移测量的需求。

Numerical simulation of LWD resistivity response of carbonate formation using self-adaptive hp-FEM

Most of the carbonate formation are highly heterogeneous with cavities of different sizes, which makes the prediction of cavity-filled reservoir in carbonate rocks difficult. Large cavities in carbonate formations pose serious threat to drilling operations. Logging-whiledrilling （LWD） is currently used to accurately identify and evaluate cavities in reservoirs during drilling. In this study, we use the self-adaptive hp-FEM algorithm simulate and calculate the LWD resistivity responses of fracture-cavity reservoir cavities. Compared with the traditional h-FEM method, the self-adaptive hp-FEM algorithm has the characteristics of the self-adaptive mesh refinement and the calculations exponentially converge to highly accurate solutions. Using numerical simulations, we investigated the effect of the cavity size, distance between cavity and borehole, and transmitted frequency on the LWD resistivity response. Based on the results, a method for recognizing cavities is proposed. This research can provide the theoretical basis for the accurate identification and quantitative evaluation of various carbonate reservoirs with cavities encountered in practice.

LWD测量系统在桩1-平5井中的应用

介绍了无线随钻测量 (L WD)系统的技术特性和施工要点。结合桩 1 -平 5井设计与施工要点 ,提出了应用 L WD测量井眼轨迹参数和地质参数 (含自然伽马及电磁波电阻率 )的具体方法和步骤。讨论了L WD测井资料的评价及目的层垂深的校核问题。

基于LWD算子和LOWA算子的企业知识管理绩效评价

从生产管理、人力管理、信息管理、技术管理、企业文化、外部关系等角度出发,分析了评价企业知识管理绩效水平应考虑的7个主要绩效指标。在此基础上,采用一种基于语言评价信息的多指标综合评价方法,即LWD算子和LOWA算子的综合评价方法,对企业知识管理的绩效水平进行了评价。最后,给出了一个算例说明该方法在企业知识管理绩效评价中的适用性。

LWD技术在广64平4井中的应用

结合江汉油田油藏分布在非均质油层中油层连续横向变化大、油层薄、断层多、单砂层分布面积小等地质特点,介绍了LWD在广64平4井的地质导向技术和井眼轨迹控制技术,通过及时分析、对比,使轨迹很好地控制在目的层中,全井水平段长171m,油层中累计穿行127m,实现油砂岩有效钻遇率75%,为今后江汉油田推广应用LWD地质导向技术积累了宝贵的经验。

影响LWD井深精度的因素及其简单修正

井深是地层评价测量中非常重要的一个参数,准确的井深测量使得与其相对应的地质信息更可靠,但是井深的精度却很难确定[1]。LWD测量系统现在越来越被大家所接受,并被广泛应用。但是由于钻柱拉伸、热膨胀等因素的影响,使得LWD测量井深存在误差。分析了影响LWD测量井深精度的因素,并对这些因素进行简单的修正,使其与电缆测量井深的一致性得到提高。

LWD曲线在随钻跟踪地质目标中的应用

LWD(Logging While Drilling)曲线在实时地层评价和随钻跟踪地质目标中有着重要的应用。在随钻测井曲线单一的情况，可根据邻近的直眼井或水平井的测井和录井资料，借助于回归分析法和神经网络法可模拟生成多条测井曲线。本文介绍了在水平井地质导向钻井中，如何利用实测的随钻伽马曲线和实时构造的随钻伽马、电阻率和中子孔隙度等曲线来实时跟踪地质目标层的方法和技术。将其结果用于MB油田3口水平井的实时钻井中，取得了明显的随钻跟踪地质目标效果。

随钻测井技术(LWD)在昆北油田水平钻井中的应用

随钻测井技术（LWD），在钻井进行的同时，实时采集，测取能反映地层特征的地质参数，并按需绘制成测井曲线，实现了初步的地质导向。在昆北油田水平井钻井中的应用，较好的解决了卡准层位，及时调整井眼轨迹，瞄准目的层中最佳部位钻进，为水平井钻井规避风险，降低投资提供了及时的依据和手段。

LWD测量仪器使用中的井下安全问题

介绍了LWD无线随钻测斜仪使用中出现的井下安全问题及所采取的对策措施,对同类仪器的使用具有一定借鉴作用。

随钻测井技术(LWD)在昆北油田水平钻井中的应用

随钻测井技术在钻井进行的同时实时采集、测取能反映地层特征的地质参数,并按需绘制成测井曲线,实现了初步的地质导向。在昆北油田水平井钻井中的应用较好地解决了卡准层位、及时调整井眼轨迹、瞄准目的层中最佳部位钻进,为水平井钻井规避风险,降低投资提供了及时的依据和手段。

LWD随钻测量仪器现场使用问题及解决策略

LWD随钻测量仪器属原油开采工程中非常便捷的测量装置,其应用范围正逐年扩大。本文主要研究LWD随钻测量仪器现场使用问题及解决策略。