Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Zou, Y. Articles by Bentley, L. R. Search for Related Content GeoRef GeoRef Citation

Time-lapse well log analysis, fluid substitution, and AVO

University of Calgary, Alberta, Canada

Corresponding author: zou@geo.ucalgary.ca

The first 20% of the full text of this article appears below.

Time-lapse seismic monitoring of reservoirs is based on changing seismic response due to fluid saturation, temperature, and pressure changes. The observable changes in seismic response can help locate bypassed oil, water- or gas-flood fronts, and heated zones.

However, there are risks associated with a 4D seismic project including false anomalies caused by acquisition, processing artifacts, and the ambiguity of seismic interpretation in relating seismic changes to reservoir changes. Lumley and Behrens (1998) proposed a four-step feasibility and risk assessment study before undertaking a 4D seismic project. The proposed third step is seismic modeling from sonic and density logs. Our study demonstrates a procedure for the modeling of time-lapse seismic response changes due to simulated changes to well logs. We also simulate AVO changes at a gas-oil contact (GOC) and an oil-water contact (OWC). The objective of time-lapse AVO is to distinguish between reflections from a gas or oil sand that has been flooded by gas or water. As a model, we use a well log from White Rose Field, offshore Newfoundland, Canada. Three production scenarios are investigated. The method for calculating the seismic response changes is based on the Gassmann equation and a modification of the procedure described by Bentley et al. (2000).

	Theory and method

 
Gassmann's equation relates the bulk modulus of a saturated rock K_u), to the dry rock bulk modulus K_d), the solid grain modulus K_s), the fluid bulk modulus K_f), and the porosity . Densities are calculated from

(1)

(2)

(3)

where _o, _g, _w, _s, _u, _f, are the densities of oil, gas, water, solid grains, saturated reservoir rock, and fluid mixture at reservoir conditions. S_g, S_o, and S_w are gas saturation, oil saturation, and water saturation, respectively. The density ^std is the density of oil or gas at standard conditions. R_s is the gas oil . . . [Full Text of this Article]