RP 2.4. SEG/Houston 2005 Annual Meeting 1513

Transcription

1 P 2.4 Measurement of sear ave velocity of eavy oil De-ua Han, Jiajin Liu, University of Houston Micael Batzle, Colorado Scool of Mines Introduction It is ell knon tat te fluids ave no sear modulus and terefore no sear ave can propagate troug fluids. But eavy oils ave properties tat are muc complex tan ligter oils. t lo temperatures, eavy oils are extremely viscous and egin to act like solids. n effective sear modulus appears alloing propagation of sear aves. Te ulk moduli of eavy oils increase since te ulk and sear moduli are related it eac oter. Terefore, it is oserved tat te compressional ave velocity of eavy oils increases faster tan tat of ligt oils at lo temperatures. noise if using te S-ave transducers instead of P- ave transducers. It is true even for very eavy oil at lo temperatures at ic te oil acts like a solid. It means it may not e feasile for direct measurement of sear velocity in eavy oil. Water S Transducer Buffer oil Heavy oil On te oter and, e kno from te viscoelastic model of Maxell tat, te sear impedance of te viscous fluid is related it its viscosity ic is one of te important control factors for ave attenuation. (a) Fig. 1 () * 2 2 (1 ) G 1/ 2 1/ 2 V S ere, * is te magnitude of te complex sear impedance, is viscosity, is density, is angle frequency and G is effective ig frequency sear modulus and is called relaxation time. It is apparent tat te sear ave velocity information is useful along it P-ave velocity and density to predict te viscosity and attenuation of te eavy oil. Tis paper descries te metod, facilities and accuracy of S-ave velocity measurements for eavy oil. Measuring Metod Te traditional metod for measurement of fluid velocity is to measure te travel time of te transmission ave and ten te velocity can e derived it te knon travel distance. specially designed camer it to transducers located at its ot ends, te distance of ic ere calirated at different temperature and pressure y distilled ater, as een used and is good for P-ave measurement for a lot of fluid samples. But te transmission signal is very ard to e recognized due to presence of strong metod is designed for indirect measurement of sear ave velocity. Figure 1 sos te principle of tis metod. Te sear ave transducer is coupled it a uffer made of some kind of plastic and te transducer is in te mode of self emission and receiving. Te measurement is done in to steps. Te first is to record te sear reflection from te ottom of te uffer tat is in contact it te reference sample (ater) and te second is to record te same reflection ave en te uffer is in contact it te real sample (eavy oil). Te difference eteen and is caused y te different reflection coefficient (eteen uffer and ater) and (eteen uffer and eavy oil) if all measurement conditions can e controlled. It is ovious tat te ratio of amplitude of reflected ave equals to te ratio of te reflection coefficient. ere, (f) and (f) are te magnitude spectra (function of frequency) of aves and. Te reflection coefficient is -1 ecause te sear impedance of ater is SEG/Houston 2005 nnual Meeting

2 P 2.4 ere, and are sear impedances of ater and uffer respectively. If te impedance of te uffer and te density of te eavy oil are knon, ten te sear velocity V s of te eavy oil can e derived. Pipe P transducer Pressure vessel Vs 1 1 Water or eavy oil Buffer S transducer ere, is te impedance of te eavy oil sample. Water is used as te reference material, since ater can e easily kept in te desired temperature and pressure. In practice, te peak-to-peak amplitude can e taken to replace te spectrum analysis in order to simplify te calculation. Experimental Facility Te scematic of experimental facility is son in figure 2. pressure vessel is used for measuring ater or eavy oil sample. Te sample pressure can e controlled y a pump troug te pipe. Te pressure vessel is put into a at tank filled it anti-freezing liquid ic can e adjusted to te desired temperature. Te S-ave transducer is used to record te reflection aves from te uffer. Meanile, a P- ave transducer is used to receive te transmitted P- ave tat is converted from sear ave. Terefore, te compressional velocity can e measured simultaneously during sear velocity measurement. It is necessary to calirate te facility first. Distilled ater is filled in te vessel and te sear reflection ave and compressional transmission ave are recorded separately at different pressures and temperatures. Te reflection aves are used to uild te relationsip of reflection aves it pressure and temperature. Te travel time of te compressional ave is used to calirate te propagation distance of compressional ave in te sample at various pressure and temperature since te velocity of te distilled ater and te uffer along it te tickness of te uffer are knon. Te calirated distance is needed to calculate P-ave velocity en te eavy oil is filled in te vessel. Virtual Instrument (softare) ritten in LBVIEW for signal spectral analysis as developed in our la. Te S-ave velocity it frequency can e derived y tis softare. Examples Fig. 2 Several eavy oil samples it different PI gravity ave een measured in te la. Figure 3 sos te P- ave and S-ave velocities versus temperature at pressure of aout 0.7 MPa for a sample of eavy oil of PI gravity of 8.0. It is clear ot velocities decreases it increasing temperature ut its a near linear relation for S-ave and non-linear for P-ave. Oter samples tat e measured support same rule. Fig. 3 Te spectral analysis can give canges in te sear velocity it frequency, ile te peak-to-peak value of te signal can only so te sear velocity near te main frequency of te transducer. Figure 4 sos te sear velocity versus frequency tat indicates sear velocity increases sligtly it increasing frequency SEG/Houston 2005 nnual Meeting

3 P 2.4 for a sample it PI of For comparison, te velocity calculated from peak-to-peak is pointed in te figure. We can find from figure 4 tat te sear velocity increases gradually it increasing frequency at various temperatures and pressures. Meanile, te value of sear velocity aout 900 khz from spectral analysis is consistent it tat using peak-to-peak ratio. Te dominant frequency of te reflection ave from spectral analysis for various temperatures is in te range of 800 to 1000 khz it 1MHz transducer. Fig. 4 Te modulus of te sample can e derived if its P-and S-ave velocities and density are knon. Figure 5 sos te ulk and sear moduli of te first sample (PI=8.0) at pressure of aout 0.7MPa. It can e seen tat te cange of te ulk modulus it temperature is very similar to tat of sear modulus. It means ot moduli are dependent on eac oter. We tink it is possile to estimate S-ave velocity from P-ave velocity. Suc relationsip ill e developed in future. Fig. 5 Velocities calculated itout spectral analysis n interesting sample is ax-ric oil it PI of It seems solid at room temperature since it contains muc ax even toug te oil is not very eavy. Te sear velocity is rater lo compared it te real eavy oil. We ave also measured sear velocity of glycerol tat is relatively lo altoug te glycerol as very ig density of gm/cc. Factors Tat ffect ccuracy of Measurement It is ell knon tat te accuracy of P-ave velocity depends on te accuracies of te travel time and calirated lengt of te camer. Te relative error of P ave velocity is less tan ±1% as per our experience. Te sear velocity measurement of eavy oil is an indirect measurement and many more factors may affect te accuracy of te measurement. Te first prolem e met in measurements is te staility of te coupling eteen te transducer and te uffer. Te state of coupling may strongly affect te amplitude of te reflection aves. Because e ave to measure ater and oil sample separately at different temperatures and pressures, e ope te canges due coupling may reverse ile canging te temperature and pressure. We tried several different materials for coupling and finally a fast epoxy is selected and te coupling staility is acceptale. Te main error is proaly from te amplitudes for aves and caused y te stailities of electronic equipment and poer. verage difference of te amplitudes of te reflection aves from statistics is in te range of 3% as per our experience. Terefore, te maximum error may occur en as 3% error and as +3% error or vice versa. s an example, e use te first sample to ceck te maximum error in te measurement of S-ave velocity. Figure 6 sos te maximum asolute and relative errors in S-ave velocity, respectively. It can e seen tat eiter one of te asolute or relative error is iger if te S-ave velocity is loer. In tis figure, te relative error of S-ave velocity may e iger tan 10% (asolute error may e larger ten 36m/s) if te S-ave velocity is less tan 0.36km/s. It means te velocity value is reliale en S-ave velocity is iger tan 0.4km/s, ut may not e accurate enoug if te S-ave velocity is relatively small. On te oter and, te material of uffer may affect te sensitivity of te measurement. Te reflection coefficient ill e close to 1 if te impedance of te uffer is very different from ater or oil; no matter te uffer is in contact eiter ater or oil. Te small difference eteen and may reduce te accuracy of te velocity calculation. Te est uffer sould ave similar impedance as ater and oil. Te density and S-ave velocity of te uffer e used are 1.277g/cm 3 and 1.05km/s respectively. In order to reduce te ave attenuation of te uffer, e select a special plastic material as te uffer it small tickness. Measurement of P-ave Velocity Te P-ave velocity can e otained simultaneously y our facility (figure 2). Te accuracy of te P-ave velocity may e questionale since te transmitted conpressional ave is te convert ave. Our measured data so te differences from te velocities y traditional metod are less tan 2% for various temperatures and pressures. Te accuracy may raise if SEG/Houston 2005 nnual Meeting

4 P 2.4 (a) te correction of travel time for delay of converted ave is taken. It is interesting tat te amplitude of te conpressional ave canges oviously it te temperature (see figure 7 as an example). Te ave amplitude can indicate te attenuation of te P-ave troug te eavy oil and te maximum attenuation in tis sample is at te temperature aout 20C since te amplitude reaces te minimum at te aove temperature. It is knon tat te maximum attenuation may occur en te ave frequency is at te resonance frequency of te material. Te resonance frequency of te eavy oil depends mainly on its viscosity tat may vary it temperature. Fig. 6 Te measurements of S-ave velocity of eavy oil demonstrate te indirect metod for measuring S-ave velocity. In order to otain certain accuracy, special care sould e taken to keep all conditions stale during measurements. Te measurement error may e rater large if te value of S-ave velocity is small and terefore, measurements of S-ave velocity of eavy oil it ig PI gravity at ig temperature may not ave ig accuracy. eferences () Batzle, M and Wang, W-P, 2004, Heavy Oils Glass Point: Fluids/DHI annual report. Beggs, H.D., and oinson, J.., 1975, Estimating te viscosity of crude oil systems: J. Petr. Tec., 27, Blitz, J., 1967, Foundamentals of ultrasonics, Plenum Press, Ne York. Conclusion Fig. 7 Greenood, M. S. and Bamerger, J.., 2002, Measurement of viscosity and sear velocity of a liquid or slurry for on0line process control, Ultrasonics, 39, Liu, J. and Han, D-H., 2004, Measurements of P-ave and S-ave velocity for eavy oil samples: Fluids/DHI annual report. SEG/Houston 2005 nnual Meeting

5 EDITED EFEENCES Note: Tis reference list is a copy-edited version of te reference list sumitted y te autor. eference lists for te 2005 SEG Tecnical Program Expanded stracts ave een copy edited so tat references provided it te online metadata for eac paper ill acieve a ig degree of linking to cited sources tat appear on te We. Measurement of sear ave velocity of eavy oil EFEENCES Batzle, M. and W.-P. Wang, 2004, Heavy Oils Glass Point: Fluids/DHI annual report. Beggs, H. D., and J.. oinson, 1975, Estimating te viscosity of crude oil systems: Journal of Petroleum Tecnology, 27, Blitz, J., 1967, Foundamentals of ultrasonics: Plenum Press. Greenood, M. S., and J.. Bamerger, 2002, Measurement of viscosity and sear velocity of a liquid or slurry for on-line process control: Ultrasonics, 39, Liu, J., and D-H. Han, 2004, Measurements of P-ave and S-ave velocity for eavy oil samples: Fluids/DHI annual report.