Cold production footprints of heavy oil on time-lapse seismology: Lloydminster field, Alberta
Qiaozhi (Sandy) Chen, Laurence R. Lines, Joan Embleton, P. F. Daley, Larry Mayo
The simultaneous extraction of oil and sand during the cold production of heavy oil generates high permeability channels termed as "wormholes". The development of wormholes causes reservoir pressure decrease below the bubble point, resulting in dissolved gas out of solution to form foamy oil. The foamy oil could fill depressurized drainage regions (production footprints) around the borehole, leading to fluid phase changes. In this paper, the upper bound and lower bound models on the fluid mixture bulk moduli have been used to detect the sensitivity of seismic P-wave velocity. Then the Gassmann Equation has been employed to calculate the bulk modulus variations of the drainage rocks, where the velocity and density decrease dramatically due to some exolved gas. A 2D cold production model has been built to examine the seismic responses of drainage regions based on well logs in the Lloydminster cold production pool. The seismic modelling responses indicate amplitude anomalies and traveltime delays in these regions upon comparison of pre and post production results. However, because most heavy oil cold production reservoirs are very thin, with less than 10 m of net pay, seismic resolution is a challenge. Different seismic frequency bandwidths have also been tested to look at how vertical seismic resolution determines the detection of the drainage regions.