Electromagnetic Telemetry System Research Articles

Demodulation of EM Telemetry Data Using Fuzzy Wavelet Neural Network with Logistic Response

Data telemetry is a critical element of successful unconventional well drilling operations, involving the transmission of information about the well-surrounding geology to the surface in real-time to serve as the basis for geosteering and well planning. However, the data extraction and code recovery (demodulation) process can be a complicated system due to the non-linear and time-varying characteristics of high amplitude surface noise. In this work, a novel model fuzzy wavelet neural network (FWNN) that combines the advantages of the sigmoidal logistic function, fuzzy logic, a neural network, and wavelet transform was established for the prediction of the transmitted signal code from borehole to surface with effluent quality. Moreover, the complete workflow involved the pre-processing of the dataset via an adaptive processing technique before training the network and a logistic response algorithm for acquiring the optimal parameters for the prediction of signal codes. A data reduction and subtractive scheme are employed as a pre-processing technique to better characterize the signals as eight attributes and, ultimately, reduce the computation cost. Furthermore, the frequency-time characteristics of the predicted signal are controlled by selecting an appropriate number of wavelet bases “N” and the pre-selected range for pij3 to be used prior to the training of the FWNN system. The results, leading to the prediction of the BPSK characteristics, indicate that the pre-selection of the N value and pij3 range provides a significantly accurate prediction. We validate its prediction on both synthetic and pseudo-synthetic datasets. The results indicated that the fuzzy wavelet neural network with logistic response had a high operation speed and good quality prediction, and the correspondingly trained model was more advantageous than the traditional backward propagation network in prediction accuracy. The proposed model can be used for analyzing signals with a signal-to-noise ratio lower than 1 dB effectively, which plays an important role in the electromagnetic telemetry system.

Electromagnetic telemetry simulation in vertical drillings

Electromagnetic (EM) telemetry is one of the key research subjects that has increased application in transmitting real-time data between the borehole and surface during drilling. There are several methods that can be used to model an EM telemetry system, including the method of moments (MoM) and the electric field integral equation method. We have developed a pulse basis function for the MoM, which assists in the analytical estimation of thin wire kernel integrations and avoids singular problems when simulating current distributions. The scattering field is solved using the current distribution. We examine the method using a simple example of vertical drilling. In the model, a vertically placed drill string is driven through a layered earth model. The drill string represents a long, thin wire antenna with a source located near the drill bit. The validity of the method is confirmed by comparing our results to the analytical solution in a half-space model as well as the current distributions along the drill string derived from the proposed method with those derived from a commercial finite-element solver, COMSOL-Multiphysics. Furthermore, the efficiency of this method is demonstrated by comparing its computational costs with those of COMSOL. The simulated EM telemetry in a known geologic setting is then compared with a field data example. These comparisons show that the proposed method is accurate and efficient. Moreover, we develop insights into how the parameters needed for calculations alter current distributions along the drill string and the signal received at the surface. The proposed method is therefore useful for obtaining the optimal design parameters for EM telemetry systems.

Fast and accurate simulation of electromagnetic telemetry in deviated and horizontal drilling

Electromagnetic (EM) telemetry systems are widely used for measurement-while-drilling (MWD), especially in unconventional drilling. In this paper, a numerical method for the simulation of EM telemetry systems in deviated and horizontal drilling is introduced. The underground formation is assumed to be horizontally layered media, and the long, metal drill string acts as an antenna that may be treated as a thin wire excited by a gap voltage source located near the drill bit. The numerical model employs the electric field integral equation (EFIE) and the method of moments (MoM) to obtain a linear system for the axial current distribution on the drill string, which is subdivided into several one-dimensional segments. By using the thin wire kernel, near-field interactions can be evaluated accurately and efficiently, while also reducing problem dimensionality and singularity order of the homogeneous medium contribution to the layered medium Green's function (LMGF). The latter typically takes the form of a dyadic spectral domain integral, the asymptotics of whose integrands may be estimated and combined with Kummer's method to accelerate its evaluation, with the asymptotic correction terms evaluated in closed or easily evaluated forms. Numerical results are presented to verify the fast and accurate performance of the proposed approach. Results for signal voltage receivability by a surface antenna are also presented and discussed.

Multiscale Modeling of Electromagnetic Telemetry in Layered Transverse Isotropic Formation

Electromagnetic telemetry (EMT) systems are utilized for measurement while drilling to transmit data from borehole to the ground surface during drilling or vice versa. To help predict the successful deployment of the EMT system within complex formation and environmental noise, a reliable numerical algorithm is developed and applied to model the EMT system for directional drilling in layered transverse isotropic (TI) formation. In the telemetry system, the long and thin drill string having three-dimensional trajectory acts as an underground antenna that can be modeled as a thin wire excited by a delta gap voltage/current source near the drill bit. Using the thin wire assumption, the developed algorithm calculates the thin wire kernel in homogeneous uniaxial media with high accuracy to reduce the dimension and complexity of the problem. The mixed-potential form of layered media Green's function and electric field integral equation are used to model the electromagnetic interaction of the drill string and layered TI media. The effect of drilling fluid outside the pipe is modeled using the volumetric equivalence principle. The accuracy and efficiency of the new algorithm are demonstrated by several numerical examples.

Modeling an electromagnetic telemetry system for signal transmission in oil fields

Some finite element techniques for modeling an electromagnetic-based telemetry device known as the EM-MWD (electromagnetic measurement-while-drilling) used in oil fields are described. Results obtained from field tests at the test rig of GTI Gas Research Facility, Catoosa, OK, are compared with numerical results obtained using finite-element methods. The finite element technique used is based on the 2D-Axisymmetric H formulation.

Digital electromagnetic telemetry system for studying behaviour of decapod crustaceans.

1 year and the receiving system batteries are replaced by divers at intervals of up to 4 weeks. In field tests, crab (Cancer pagurus L.) and lobster (Homarus gammarus (L.)) activity was monitored at an artificial reef for 14 months. Examples of the type of information acquired are presented to illustrate the capabilities of the system and potential applications are discussed. Limitations of digital electromagnetic telemetry stem mainly from the short range of detection, the need for cables on the seabed and the size and shape of the transmitting tag.

Movement and activity patterns of the European lobster, Homarus gammarus , revealed by electromagnetic telemetry

European lobsters, Homarus gammarus (L.), were tracked on an artificial reef in Poole Bay on the south coast of England using an electromagnetic telemetry system which monitored movements between reef units and recorded body movements (pitching and rolling) detected with a tilt switch incorporated into the transmitting tag. Several environmental variables (water temperature, light, hydrostatic pressure, current velocity and direction) were recorded simultaneously by the telemetry system, which was self-contained on the seabed. Movements between units of the artificial reef (excursions outside shelter) were predominantly nocturnal, peaking 1.5 to 3 h after sunset and returning to low levels shortly before dawn. A marked decline in the number of inter-reef unit movements from late summer to winter was related to decreasing water temperature rather than to daytime light level, wave height or tidal range. Activity indicated by the tilt switch was also greater at night, but declined gradually from a peak early in the night to a minimum at around midday, on average, implying a degree of activity within reef units during daylight. As with movements between reef units, activity declined seasonally with decreasing water temperature; in addition, the diel pattern of activity disappeared in winter.

Attenuation predictions at extremely low frequencies for measurement-while-drilling electromagnetic telemetry system

Extremely low frequencies (ELFs) are employed to transmit data from underground to the ground surface in the measurement-while-drilling electromagnetic (MWD-EM) telemetry system. Based on electromagnetic field theory, the present work is aimed at predicting the receivability of the signals at the surface. A unified analytic method that is suitable for vertical, directional, or horizontal wells is presented. Attenuation properties are examined for various parameters, including the Earth's conductivity, operating frequency and the length of the drill string. The frequency dependence of the receivability in reference to a noise level is illustrated for different depths of well and different cases. It is also demonstrated that the electric field distributions at the surface have the same features for the three types of well, and that the measurements should be carried out near the well heads for any type of well. A scale model experiment is made to test the authors' theoretical results. The measured data and the computed results are comparable. >