Jinhai Hu

Water cut measurement of oil–water flow in vertical well by combining total flow rate and the response of a conductance probe

In this paper, a conductance probe-based well logging instrument was developed and the total flow rate is combined with the response of the conductance probe to estimate the water cut of the oil?water flow in a vertical well. The conductance probe records the time-varying electrical characteristics of the oil?water flow. Linear least squares regression (LSR) and nonlinear support vector regression (SVR) were used to establish models to map the total flow rate and features extracted from the probe response onto the water cut, respectively. Principal component analysis (PCA) and partial least squares analysis (PLSA) techniques were employed to reduce data redundancy within the extracted features. An experiment was carried out in a vertical pipe with an inner diameter of 125?mm and a height of 24 m in an experimental multi-phase flow setup, Daqing Oilfield, China. In the experiment, oil?water flow was used and the total flow rate varied from 10 to 200 m3 per day and the water cut varied from 0% to 100%. As a direct comparison, the cases were also studied when the total flow rate was not used as an independent input to the models. The results obtained demonstrate that: (1) the addition of the total flow rate as an input to the regression models can greatly improve the accuracy of water cut prediction, (2) the nonlinear SVR model performs much better than the linear LSR model, and (3) for the SVR model with the total flow rate as an input, the adoption of PCA or PLSA not only decreases the dimensions of inputs, but also increases prediction accuracy. The SVR model with five PCA-treated features plus the total flow rate achieves the best performance in water cut prediction, with a coefficient of determination (R2) as high as 0.9970. The corresponding root mean squared error (RMSE) and mean quoted error (MQE) are 0.0312% and 1.99%, respectively.

Manchester code telemetry system for well logging using quasi-parallel inductive-capacitive resonance.

In this paper, a quasi-parallel inductive-capacitive (LC) resonance method is proposed to improve the recovery of MIL-STD-1553 Manchester code with several frequency components from attenuated, distorted, and drifted signal for data telemetry in well logging, and corresponding telemetry system is developed. Required resonant frequency and quality factor are derived, and the quasi-parallel LC resonant circuit is established at the receiving end of the logging cable to suppress the low-pass filtering effect caused by the distributed capacitance of the cable and provide balanced pass for all the three frequency components of the Manchester code. The performance of the method for various encoding frequencies and cable lengths at different bit energy to noise density ratios (Eb/No) have been evaluated in the simulation. A 5 km single-core cable used in on-site well logging and various encoding frequencies were employed to verify the proposed telemetry system in the experiment. Results obtained demonstrate that the telemetry system is feasible and effective to improve the code recovery in terms of anti-attenuation, anti-distortion, and anti-drift performances, decrease the bit error rate, and increase the reachable transmission rate and distance greatly.

Water holdup measurement of oil-water two-phase flow in a horizontal well using a dual-circle conductance probe array

This paper presents a minimum root-mean-square error (RMSE)-based method for a dual-circle conductance probe array to measure the water holdup of an oil–water two-phase flow in a horizontal oil well. The dual-circle conductance probe array consisting of 24 conductance probes, half of which are equidistantly distributed on a 34 mm radius inner circle and the other half on a 48 mm radius outer circle, is used to estimate the oil–water interface and hence the water holdup in the horizontal oil well. For the same water holdup, the number of probes immersed in water may vary with varying the azimuth angle due to the limited number of probes. The limited number of probes and unknown azimuth angle of the probe array in the oil well limit the measurement accuracy of the water holdup. In order to obtain a better water holdup estimate, a water holdup measurement method based on the minimum RMSE was proposed to decrease the effects of the limited number of probes and unknown azimuth angle of the probe array. To verify the proposed method, numerical simulations were carried out and compared with the commonly used equi-weight estimate method; results showed that the RMSE of the water holdup estimates obtained using the proposed method is smaller than that when using the equi-weight estimate method. Experiments were implemented in a 16 m long and 125 mm inner diameter horizontal pipe on an industrial-scale experimental multiphase flow setup in the Daqing Oil Field, China. The RMSEs of water holdup estimates obtained using the proposed and equi-weight estimate methods are 0.0632 and 0.0690, respectively, showing that the proposed method is better than the equi-weight estimate method.

Identification of Oil–Water Flow Patterns in a Vertical Well Using a Dual-Ring Conductance Probe Array

In this paper, a dual-ring conductance probe array-based well logging instrument was developed and a method based on the support vector classification (SVC) and voting methods was proposed to identify the oil-water flow patterns in a vertical well. The patterns of the oil-water flow in a vertical well are classified into five patterns, i.e., pure oil phase, pure water phase, water-in-oil, oil-in-water, and transition. The conductance probe records the time-varying electrical characteristics of the oil- water flow, which is referred to as the original signals. Various features are extracted to characterize each original signal. The features are first treated through principal component analysis (PCA) to decrease data redundancy in the original features. A nonlinear SVC model is then established to map the PCA-treated features into a flow pattern. To identify the flow pattern, it can be voted by an individual probe or by probe combinations. Experiments were carried out in a vertical pipe with an inner diameter of 125 mm and a height of 24 m on the industrial-scale experimental multiphase flow setup in Daqing Oilfield, China. In the experiment, the oil-water two-phase flow was tested and the total flow rate was varied from 10 to 200 m3 per day, equivalent to 0.0094 to 0.1886 m · s-1, and the water cut was varied from 0% to 100%. The results obtained demonstrate that the developed probe array-based instrument can increase the reliability of flow pattern recognition, compared with the single probe-based instrument. The identification accuracy obtained using the optimal probe combination and the proposed method is 97.95% ± 2.01% (mean ± std), and higher than that obtained using a single probe and the SVC model.

DC bias compensation in digital AC-based capacitance measurement for ECT

The AC-based capacitance measuring circuits are widely used in electrical capacitance tomography. In the circuit, the desired exciting and measuring signals are alternative current (AC) ones that should have a zero direct current (DC) component. However, because of the non-deal characteristics of the operational amplifiers and other electronic components, DC biases, i.e., nonzero DC components always exist in actual AC signals. The DC biases have negative influences on capacitance measurement. In the paper, theoretical analysis was carried out and a method of compensating the effect of the DC bias was introduced. A digital AC-based capacitance measuring system was constructed to implement the compensation method. Experimental results show that the signal-to-noise ratio of the system is improved by employing the proposed method.

A new cylindrical capacitance sensor for measurement of water cut in a low-production horizontal well

In a horizontal well with low flow rate, oil-water two-phase flow is stratified due to gravity. For measuring water cut accurately in a low-production horizontal well, a novel cylindrical capacitance sensor is proposed in this paper. The structure of the sensor is cylindrical and hollow with multi-layer structure which is consisted of inside insulation layer, electrode layer, outside insulation layer and metal casing from inside to outside. And the measurement principle is analyzed in this paper. The mathematical model is established, which shows that theoretically, there is a good relationship between the sensor response and water holdup. The response curve is monotone and the sensor has a good resolution and a high sensitivity in the whole range of water holdup. The electric field of cylindrical capacitance sensor was simulated respectively by using ANSYS software when the sensor is filled with pure water, pure oil and oil-water mixture. The results of the simulation are consistent with the mathematical model. Static experiments with the sensor filled with oil-water mixture were conducted finally. The results have verified the theoretical analysis and show that the proposed sensor is a viable solution to measuring water cut in a low-production horizontal well. Cylindrical capacitance sensor provides a good reference for the water cut in low-production horizontal well and has a good application prospect.

Identification of oil-water flow patterns using conductance probe in vertical well

In this paper, a sensor of conductance probe is proposed to detect the electrical characteristics of the oil-water flow in vertical well. Statistic and wavelet packet decomposition are employed to extract the features of the voltage response of conductance probe. A method based on principal component analysis (PCA) and support vector classification (SVC) is proposed to identify the flow patterns from the water-in-oil, transition, and oil-in-water flow patterns. Experiments were carried out in a 125 mm vertical well within the flow rate range of 10~200 m3/d and the water content range of 10~90% in Daqing Oilfield, China. Experimental results reveal that the optimal identification accuracy of training set is obtained as 100%, and that of testing set is achieved as 96.25%. Corresponding quantity of of principal component is 7, and cross validation accuracy is 95%. Consequently, the proposed method is feasible and effective to identify the flow patterns of oil-water flow using conductance probe sensor in vertical well.

Experimental study on cylindrical capacitance sensor

In this paper, a cylindrical capacitance sensor with a multi-layer structure was presented. The mathematical model in stratified flow was established and the sensor response in non-stratified flow was also discussed. Results of static experiments agreed well with the stratified model and showed a monotonic relationship between the sensor response and the water holdup. Dynamic experiments were carried out using a long pipeline with inner diameter (ID) 20 mm. A section of plexiglas pipe with the same ID was installed on the line through which pictures of flow state could be shot by a camera. The mathematical model, experiments and results were detailed in the paper.