DIRECT RESERVOIR SIGNATURE USING THE DRAG WAVE

摘要

A monofrequency signal is used to record signature properties of subsurface reservoir formations. While recording conventional Vibroseis data after certain prescribed distances, the monofrequency signal is transmitted to evaluate the presence of reservoir rocks underneath that source location. When a compressional wave travels through a permeable and fluid-saturated reservoir formation, the Drag Wave travels through reservoir fluid interconnections at a slower velocity than the compressional wave in the rock matrix. Due to the Doppler Effect, a unique lower frequency is generated. This lower frequency becomes an indicator of the presence of reservoir formations. Its character depends on the tortuosity of pore interconnections, presence of pore fluids, and permeability. A transfer function is calculated to convert the swept frequency signal used for conventional seismic recording. This converted swept frequency signal is cross-correlated with the normally recorded signal. Only the presence of the reservoir formation is highlighted; non-reservoir formations are not displayed.

主权项

1. A new seismic acquisition method of determining and directly mapping the presence, location and extent of the reservoir formations, highlighting their presence in a separate image by transmitting a monofrequency and obtaining the unique signal generated from within the reservoir itself, using a conversion factor to cross-correlate a new swept signal with the normal recorded data, and observing the signature of each reservoir, comprising the steps of:
using reflection seismic recording methods with frequency-generating source, that transmits a short duration seismic compressional wave; transmitting a normal Vibroseis sweep, also known as a production sweep, transmitted from the source location into the earth, with the determined parameters of the operation; this invention is characterized by the unique step of transmitting a separate monofrequency signal, also called the primary signal, from the source location into the earth at every nth station of the normal operation, with no limitation on the quantity and variety of monofrequencies transmitted at each of the nth stations; characterized by transmitting each of the signals separately into the earth and not simultaneously; characterized by synchronizing the normal Vibroseis sweep signal and the monofrequency signal with respect to the duration-time of the signal;