The effective measuring range of an electromagnetic wave resistivity instrument used in logging while drilling (LWD) is small, and the resistivity measurement is greatly influenced by the dielectric constant, especially in high-dielectric-constant formations. In this paper, the response characteristics of the instrument under a high dielectric constant are investigated by a numerical simulation algorithm, and the resistivity conversion method is determined. The results show that the higher the working frequency of the electromagnetic wave resistivity instrument while drilling, and the greater the formation of background resistivity, the greater the influence of the dielectric constant on the logging response. The existence of the dielectric constant will cause the phase shift and amplitude attenuation of the measured signal to migrate, and this migration is proportional to the formation resistivity and the dielectric constant. According to this rule, the resistivity–permittivity response library is established, and the formation permittivity is calculated by the inversion of the library. On the basis of obtaining the formation permittivity, the migration of the logging signal permittivity is corrected, the influence of the dielectric constant is eliminated, and the measuring precision and measuring range of the instrument in the high-dielectric-constant formation are enlarged.

/pdf/expanding-measuring-range-of-lwd-resistivity-instrument-in-3dju6s8w.pdf

Expanding Measuring Range of LWD Resistivity Instrument in High Permittivity Layers

The geo-sieering service provided by logging-whiledrilling technology is being more widely used with requirement of petroleum exploration and production being changed.In this article,the geo-sleering method of directional electromagnetic wave resistivity logging-while-drilling tools was studied using the magnetic-current-source dyadic Green ' s functions for horizontally stratified anisotropic media.The relative position between tool and formation boundary can be fixed by combining the orientation vector and the variation of directional geosignal,so as to eliminate the ambiguity,lower the probability of making wrong drilling decisions and place the borehole in optimal position.The orientation vector is derived from the receiver coil' s voltage and points to the conductive shoulder bed,in addition,a superposition method is applied to calculate Green' s functions in formation model with tilted boundary which is commonly encountered in underground scenarios.The information related to formation azimuth and dip can be obtained by using the azimuthal imaging of directional data,which is symmetrically compensated and free of influence exercised by formation anisotropy.Numerical results illustrate that the investigation depth and the contrast of image will increase with increasing coil spacing.The contrast of image will increase with increasing frequency and resistivity contrast between target bed and shoulder bed as well as dip angle,but the depth interval in which directional signals change significantly will narrow with increasing dip angle.The tool-toboundary distance can be estimated by interpolating real-time date into the crossplot of directional geosignal calculated by single boundary model.However,when shoulder bed resistivity is known prior to drilling,the application range of the crossplot made by two directional geosignais is severely limited,besides,the directional geosignais lost the sensitivity to tool-to-boundary distance when the transmitter coil and receiver coil are separated by formation boundary.It ' s necessary to develop some more powerful techniques to overcome the oversimplification of crossplot calculated by single boundary model and to deal with more complex underground structure better.The azimuth and distance of the boundary which has not been penetrated can be obtained by integrated utilization of above methods,and then according this,the well trajectory can be adjusted in realtime to achieve optimal wellbore placement.These conclusions provide reference to the geo-steering method of directional electromagnetic wave resistivity logging-whiie-drilling tools.

Preliminary geo-steering method of directional electromagnetic wave resistivity logging-while-drilling tools

The detection depth of azimuthal LWD electromagnetic tool determines the ability of interface prediction.There is important significance to know the detecting characteristics of electromagnetic LWD tools under different formation conditions.The response characteristics of formation boundary and the relation between the boundary strike and tool's face are simulated, and the definition of detection depth of electromagnetic LWD tools is introduced.The influence of formation conditions and tools parameters on detection depth and inverted distance to bed is analyzed by simulating the response of azimuthal LWD electromagnetic tools.The simulation results show that the difference of adjacent formation conductivity determines the amplitude of geosteering signals,the ratio and the difference of adjacent formation resistivity jointly determines the depth of detection.The small signals resolution of cross-coupling component zx voltage also determines the detection depth of the LWD electromagnetic tool,the resistivity accuracy of low resistivity formation has greater effect on the inverted distance than that of the accuracy of high resistive formation in inversion models.

Analysis on the Affecting Factors of Prediction Interface with Azimuthal LWD Electromagnetic Tool

In this article, a modified Levenberg–Marquardt inversion method is proposed for high-resolution reconstruction of resistivity distribution in multilayered formation. In forward modeling, the finite-element method (FEM) is used to obtain Jacobian matrix. In inversion process, several strategies are proposed to improve inversion performance. First, the logging data are interpolated to refine the layered formation model and improve the spatial resolution in resistivity inversion. Second, the scale of the Jacobian matrix is adjusted dynamically within a sliding window according to the sensitivity distribution obtained from the logging data to reduce the computational complexity. Third, the constrained optimization approach is applied to ensure the stability and accuracy of resistivity distribution inversion. Numerical simulation and in-field experiments were carried out to validate the performance of the proposed method. In the experiments, the proposed method was applied to the real logging data obtained in an oil field, and the accuracy of the inversion is verified using a forward modeling-based evaluation method. Results show that the proposed method has a better boundary discrimination ability and can provide a higher spatial resolution and more precise resistivity distribution of multilayered formations than the traditional apparent resistivity method. 

Modified Levenberg–Marquardt Inversion for High-Resolution Resistivity Distribution Reconstruction of Multilayered Formation

In this article, a modified Levenberg–Marquardt inversion method is proposed for high-resolution reconstruction of resistivity distribution in multilayered formation. In forward modeling, the finite-element method (FEM) is used to obtain Jacobian matrix. In inversion process, several strategies are proposed to improve inversion performance. First, the logging data are interpolated to refine the layered formation model and improve the spatial resolution in resistivity inversion. Second, the scale of the Jacobian matrix is adjusted dynamically within a sliding window according to the sensitivity distribution obtained from the logging data to reduce the computational complexity. Third, the constrained optimization approach is applied to ensure the stability and accuracy of resistivity distribution inversion. Numerical simulation and in-field experiments were carried out to validate the performance of the proposed method. In the experiments, the proposed method was applied to the real logging data obtained in an oil field, and the accuracy of the inversion is verified using a forward modeling-based evaluation method. Results show that the proposed method has a better boundary discrimination ability and can provide a higher spatial resolution and more precise resistivity distribution of multilayered formations than the traditional apparent resistivity method.

With the number of old oil fields exploited by horizontal well increased, the complexity and difficulty to extract oil from reservoir geology promote the further development of logging while drilling (LWD) technology. Thus, the LWD technology develops from the initial no-directional shallow measurements to current deep directional measurements. Based on electromagnetic wave propagation theory, electromagnetic wave resistivity logging while drilling technology is adopted to capture the resistivity from formation in real time. According to the polarization angles phenomena of resistivity curve, formation boundary can be detected. On the basis of conventional electromagnetic wave resistivity LWD, Schlumberger, Halliburton, Baker Hughes and GWDC have already carried out the research on azimuthal electromagnetic wave resistivity LWD measurement, and developed different kinds of azimuthal resistivity tools respectively, which can reflect the formation properties through 360° real-time orientation imaging technology directly. In this paper, the operating principles and characteristics of four different kinds of azimuthal resistivity tools are introduced in detail, which helps to point out the research direction on technology of azimuthal electromagnetic wave resistivity logging while drilling and application in geosteering in future.

/pdf/research-on-technology-of-azimuthal-electromagnetic-wave-3awmkzfzxh.pdf

Research on Technology of Azimuthal Electromagnetic Wave Resistivity logging While Drilling and Its Application in Geosteering

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Research on Technology of Azimuthal Electromagnetic Wave Resistivity logging While Drilling and Its Application in Geosteering