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Acoustic velocity log numerical simulation and saturation estimation of gas hydrate reservoir in Shenhu area, South China Sea.

Xiao K, Zou C, Xiang B, Liu J - ScientificWorldJournal (2013)

Bottom Line: In depth of 50 to 245 m below seafloor (mbsf), as sediment porosity decreases, P wave velocity increases gradually; as gas hydrate saturation increases, P wave velocity increases gradually; as free gas saturation increases, P wave velocity decreases.This rule is almost consistent with the previous research result.In depth of 195 to 220 mbsf, the actual measurement of P wave velocity increases significantly relative to the P wave velocity of saturated water modeling, and this layer is determined to be rich in gas hydrate.

View Article: PubMed Central - PubMed

Affiliation: School of Geophysics and Information Technology, China University of Geosciences, Beijing 10083, China.

ABSTRACT
Gas hydrate model and free gas model are established, and two-phase theory (TPT) for numerical simulation of elastic wave velocity is adopted to investigate the unconsolidated deep-water sedimentary strata in Shenhu area, South China Sea. The relationships between compression wave (P wave) velocity and gas hydrate saturation, free gas saturation, and sediment porosity at site SH2 are studied, respectively, and gas hydrate saturation of research area is estimated by gas hydrate model. In depth of 50 to 245 m below seafloor (mbsf), as sediment porosity decreases, P wave velocity increases gradually; as gas hydrate saturation increases, P wave velocity increases gradually; as free gas saturation increases, P wave velocity decreases. This rule is almost consistent with the previous research result. In depth of 195 to 220 mbsf, the actual measurement of P wave velocity increases significantly relative to the P wave velocity of saturated water modeling, and this layer is determined to be rich in gas hydrate. The average value of gas hydrate saturation estimated from the TPT model is 23.2%, and the maximum saturation is 31.5%, which is basically in accordance with simplified three-phase equation (STPE), effective medium theory (EMT), resistivity log (Rt), and chloride anomaly method.

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Related in: MedlinePlus

Relation between P wave velocity and sediment porosity, gas hydrate saturation at site SH2. (Because of the effect of variation of borehole conditions and actual sediments, the sediment porosity in some intervals does not reduce with the increasing depth and causes the curved surface unsmooth growth. In depth of 195 to 220 mbsf of gas hydrate reservoir, P wave velocity surface of forward simulation subsides as the sediment porosity relatively increases.)
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fig5: Relation between P wave velocity and sediment porosity, gas hydrate saturation at site SH2. (Because of the effect of variation of borehole conditions and actual sediments, the sediment porosity in some intervals does not reduce with the increasing depth and causes the curved surface unsmooth growth. In depth of 195 to 220 mbsf of gas hydrate reservoir, P wave velocity surface of forward simulation subsides as the sediment porosity relatively increases.)

Mentions: In order to study the dependence of P wave velocity on sediment porosity, gas hydrate saturation, it is assumed that values of gas hydrate saturation increase from 0 to 1 in the interval of 0.1. Using gas hydrate model of the TPT to model the corresponding P wave velocity of the previous gas hydrate saturations, the relation surface of previous three properties can be formed as Figure 5 shows. With the increase of the sediment burial depth in depth of 50 to 245 mbsf at site SH2, the porosity presents a decreasing trend except for the abnormality caused by borehole conditions in some intervals, and P wave velocity of forward stimulation (Sh = 0) slowly increases from 1743 to 1795 m/s. But with the increase of gas hydrate saturation, the increase rate of P wave velocity is obviously accelerated, and P wave velocity (burial depth is 51 mbsf) increases from 1743 to 3961 m/s. From the above analysis, the general rule between P wave velocity of forward stimulation and sediment porosity, gas hydrate saturation at site SH2 is the smaller the sediment porosity, the greater the P wave velocity; the higher the gas hydrate saturation, the greater the P wave velocity. This result is basically in accordance with the research result made by Tinivella [35].


Acoustic velocity log numerical simulation and saturation estimation of gas hydrate reservoir in Shenhu area, South China Sea.

Xiao K, Zou C, Xiang B, Liu J - ScientificWorldJournal (2013)

Relation between P wave velocity and sediment porosity, gas hydrate saturation at site SH2. (Because of the effect of variation of borehole conditions and actual sediments, the sediment porosity in some intervals does not reduce with the increasing depth and causes the curved surface unsmooth growth. In depth of 195 to 220 mbsf of gas hydrate reservoir, P wave velocity surface of forward simulation subsides as the sediment porosity relatively increases.)
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3713345&req=5

fig5: Relation between P wave velocity and sediment porosity, gas hydrate saturation at site SH2. (Because of the effect of variation of borehole conditions and actual sediments, the sediment porosity in some intervals does not reduce with the increasing depth and causes the curved surface unsmooth growth. In depth of 195 to 220 mbsf of gas hydrate reservoir, P wave velocity surface of forward simulation subsides as the sediment porosity relatively increases.)
Mentions: In order to study the dependence of P wave velocity on sediment porosity, gas hydrate saturation, it is assumed that values of gas hydrate saturation increase from 0 to 1 in the interval of 0.1. Using gas hydrate model of the TPT to model the corresponding P wave velocity of the previous gas hydrate saturations, the relation surface of previous three properties can be formed as Figure 5 shows. With the increase of the sediment burial depth in depth of 50 to 245 mbsf at site SH2, the porosity presents a decreasing trend except for the abnormality caused by borehole conditions in some intervals, and P wave velocity of forward stimulation (Sh = 0) slowly increases from 1743 to 1795 m/s. But with the increase of gas hydrate saturation, the increase rate of P wave velocity is obviously accelerated, and P wave velocity (burial depth is 51 mbsf) increases from 1743 to 3961 m/s. From the above analysis, the general rule between P wave velocity of forward stimulation and sediment porosity, gas hydrate saturation at site SH2 is the smaller the sediment porosity, the greater the P wave velocity; the higher the gas hydrate saturation, the greater the P wave velocity. This result is basically in accordance with the research result made by Tinivella [35].

Bottom Line: In depth of 50 to 245 m below seafloor (mbsf), as sediment porosity decreases, P wave velocity increases gradually; as gas hydrate saturation increases, P wave velocity increases gradually; as free gas saturation increases, P wave velocity decreases.This rule is almost consistent with the previous research result.In depth of 195 to 220 mbsf, the actual measurement of P wave velocity increases significantly relative to the P wave velocity of saturated water modeling, and this layer is determined to be rich in gas hydrate.

View Article: PubMed Central - PubMed

Affiliation: School of Geophysics and Information Technology, China University of Geosciences, Beijing 10083, China.

ABSTRACT
Gas hydrate model and free gas model are established, and two-phase theory (TPT) for numerical simulation of elastic wave velocity is adopted to investigate the unconsolidated deep-water sedimentary strata in Shenhu area, South China Sea. The relationships between compression wave (P wave) velocity and gas hydrate saturation, free gas saturation, and sediment porosity at site SH2 are studied, respectively, and gas hydrate saturation of research area is estimated by gas hydrate model. In depth of 50 to 245 m below seafloor (mbsf), as sediment porosity decreases, P wave velocity increases gradually; as gas hydrate saturation increases, P wave velocity increases gradually; as free gas saturation increases, P wave velocity decreases. This rule is almost consistent with the previous research result. In depth of 195 to 220 mbsf, the actual measurement of P wave velocity increases significantly relative to the P wave velocity of saturated water modeling, and this layer is determined to be rich in gas hydrate. The average value of gas hydrate saturation estimated from the TPT model is 23.2%, and the maximum saturation is 31.5%, which is basically in accordance with simplified three-phase equation (STPE), effective medium theory (EMT), resistivity log (Rt), and chloride anomaly method.

Show MeSH
Related in: MedlinePlus