Determination of Acoustic Velocities for Natural Gas

Abstract:In coal seam gas (CSG) wells, water is periodically removed from the wellbore in order to keep the bottom-hole flowing pressure at low levels, facilitating the desorption of methane gas from the coal bed. In order to calculate gas flow rate and further optimize well performance, it is necessary to accurately monitor the liquid level in real-time. This paper presents a novel method based on autocorrelation function (ACF) analysis for determining the liquid level in CSG wells under intense noise conditions. The method involves the calculation of the acoustic travel time in the annulus and processing the autocorrelation signal in order to extract the weak echo under high background noise. In contrast to previous works, the non-linear dependence of the acoustic velocity on temperature and pressure is taken into account. To locate the liquid level of a coal seam gas well the travel time is computed iteratively with the non-linear velocity model. Afterwards, the proposed method is validated using experimental laboratory investigations that have been developed for liquid level detection under two scenarios, representing the combination of low pressure, weak signal, and intense noise generated by gas flowing and leakage. By adopting an evaluation indicator called Crest Factor, the results have shown the superiority of the ACF-based method compared to Fourier filtering (FFT). In the two scenarios, the maximal measurement error from the proposed method was 0.34% and 0.50%, respectively. The latent periodic characteristic of the reflected signal can be extracted by the ACF-based method even when the noise is larger than 1.42 Pa, which is impossible for FFT-based de-noising. A case study focused on a specific CSG well is presented to illustrate the feasibility of the proposed approach, and also to demonstrate that signal processing with autocorrelation analysis can improve the sensitivity of the detection system.

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“…It can be derived from energy balance around a stationary wave undergoing an infinitesimal perturbation [34,35]:…”

Section: Acoustic Velocity In Annulusmentioning

confidence: 99%

“…The acoustic velocity in annulus is mainly related to the composition, temperature and pressure of the annulus. It can be derived from energy balance around a stationary wave undergoing an infinitesimal perturbation [34,35]:…”

Section: Modeling Of Annulus Temperaturementioning

confidence: 99%

A Novel Acoustic Liquid Level Determination Method for Coal Seam Gas Wells Based on Autocorrelation Analysis

Zhang

Fan

et al. 2017

Energies

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“…To make the calculation of the properties of mixtures more systematic, Batzle and Wang normalized pressure and temperature by the pseudocritical values, which are the weighted molar average of the pure compounds. Thomas et al (1970) found a relation to calculate these then called pseudoreduced values by the gravity G of the gas composition.…”

Section: Appendix a Comparison Of Equations Of Statementioning

confidence: 99%

“…But for pure methane Batzle and Wang found differences of several percent between calculated and measured velocities, which result from errors in the calculation of the volume in the BWR equation by Thomas et al (1970). Setzman and Wagner went a very different way.…”

Section: Appendix a Comparison Of Equations Of Statementioning

confidence: 99%

Seismic Monitoring in the Framework of the Pilot Project CLEAN

Houpt¹

2010

72nd EAGE Conference and Exhibition Incorporating SPE EUROPEC 2010

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“…The LCF corrects the liquid density to account for the effect of the gas phase. In modern terms, the LCF is related to liquid holdup, H L , by: (1) and the F y term is simply (v SG ) sc /P 0.4 . Apparently the P 0.4 term is used to approximately convert standard condition gas flow rate to in-situ conditions, thereby approximating v SG .…”

Section: Introductionmentioning

confidence: 99%

Estimation of Bottomhole Pressure in Pumping Oil Wells: Effect of High-Viscosity Fluids and Casinghead Pressure

An¹,

Scott²,

Langlinais³

2000

Proceedings of SPE Annual Technical Conference and Exhibition

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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe ability to monitoring bottomhole flowing pressure in pumping oil wells provides important information regarding both reservoir and artificial lift performance. Converting surface pressure measurements to bottomhole is currently accomplished by locating the fluid level in the annulus using a sonic device and then applying a correlation to estimate the density of the gas-cut liquid column above the perforations. This gascut liquid column exhibits Zero Net Liquid Flow (ZNLF) conditions where the casing head gas flows through a nearly stagnant liquid. A review of literature reveals that the correlations currently in use by the industry are based on low pressure and low viscosity data. Increasingly, operators are encountering high viscosity fluids and in some instances, casinghead gas flows into gathering systems which are not the typical low pressure systems. This paper presents recent experimental measurements for ZNLF under high viscosity and pressure conditions. The results indicate that viscosity and pressure have a significant effect on the calculated bottomhole pressures and that these effects are not accounted for in the currently applied methods. New methods are presented to calculate multiphase density, i.e. gradient correction factor, under high viscosity and high pressure conditions.

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Determination of Acoustic Velocities for Natural Gas

Cited by 40 publications

References 0 publications

A Novel Acoustic Liquid Level Determination Method for Coal Seam Gas Wells Based on Autocorrelation Analysis

A Novel Acoustic Liquid Level Determination Method for Coal Seam Gas Wells Based on Autocorrelation Analysis

Seismic Monitoring in the Framework of the Pilot Project CLEAN

Estimation of Bottomhole Pressure in Pumping Oil Wells: Effect of High-Viscosity Fluids and Casinghead Pressure

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