Effect of fluid substitution on ultrasonic velocities in chalk plugs, South Arne field, North Sea

Peter Japsen, Christian Høier, Klaus Bolding Rasmussen, Ida Fabricius, Gary Mavko, Jacob Mørch Pedersen

Research output: Contribution to journalArticleResearchpeer-review

30 Citations (Scopus)


Ultrasonic P- and S-velocities were measured for 34 chalk samples from the Ekofisk and Tor formations in the South Arne field, North Sea. V P and V S correlate strongly with porosity for both dry and saturated samples. Outlying values are found for three samples of the Ekofisk formation that regained a high water content after drying, and this may be indicative of a high clay content. The mean change in V P and V S from saturated to dry samples is a drop of 0.15 km/s and an increase of 0.21 km/s, respectively, for 31 of the samples. These changes correspond to 62% of the drop in V P predicted by Gassmann's relations, whereas the increase in V S is 154% of that predicted by Gassmann. The main reason for these deviations from Gassmann-theory is that the shear modulus in average is 0.5 GPa higher for the dry plugs than for the saturated plugs whereas Gassmann-theory predicts the shear modulus to be unchanged by fluid content. However, 94% of the change in the bulk modulus is in average predicted by Gassmann's relations. The shear modulus is found to be constant when measured for two samples at saturated and partly saturated conditions. The factors that cause the increased moduli of the dry samples is not understood, but further laboratory investigations are under way. The acoustic properties of the partly saturated chalk can, however, be estimated by applying Gassmann's relations to data for the saturated samples.

Original languageEnglish
Pages (from-to)1881-1884
Number of pages4
JournalSEG Technical Program Expanded Abstracts
Issue number1
Publication statusPublished - Jan 2002
Event72nd Annual Meeting of the Society of Exploration Geophysicists - Salt Lake City, United States
Duration: 6 Oct 200211 Oct 2002
Conference number: 72

Programme Area

  • Programme Area 3: Energy Resources


Dive into the research topics of 'Effect of fluid substitution on ultrasonic velocities in chalk plugs, South Arne field, North Sea'. Together they form a unique fingerprint.

Cite this