Abstract: 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.

Abstract: 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.

Abstract: The propagation of a compressional wave in a reservoir rock causes the pore fluids to flow within the pores and pore connections; this internal flow of the pore fluid exhibits hysteretic and viscoelastic behavior. This nonlinear behavior is directly related to the viscosity of the pore fluids. Pore fluids that have higher viscosity like oil, after being disturbed due to a sudden change in pressure applied by a seismic impulse, require a larger time-constant to return to its original state of equilibrium. This larger time-constant generates lower seismic frequencies, and becomes the differentiating characteristic on a seismic image between the lower-viscosity pore fluid like water against the higher-viscosity pore fluid like oil. Mapping these lower frequencies on a seismic reflection image highlights the oil-bearing volume of the reservoir rock formations versus the volume of the reservoir rock formations saturated with water or gas.

Abstract: Permeability is one of the most important factors in influencing the commercial viability of a hydrocarbon reservoir. So far, permeability cannot be measured directly in-situ in reservoir formations. This invention relates to the field of estimating in-situ permeability of the reservoir rock formations. The measurements can be made across two wells or in a single well. Due to the morphology of their pore interconnections and the pore fluids in the rock, permeable rocks are elastically nonlinear. In a permeable rock, which is elastically nonlinear, the interactions between two elastic waves can be used in a unique way to map its physical properties. In this invention, the interaction of an elastic wave generated within the permeable rock with an externally generated seismic signal is used to determine the bulk tortuosity and bulk permeability of a reservoir rock formation.

Abstract: Elastic nonlinear effects, which cause frequency spectral broadening and the effects of the presence of the Slow-Wave in the reservoir rocks, are investigated. The creation of new frequencies due to elastic nonlinearity of the reservoir rocks and their presence in the reflected seismic signals is used to map the location and extent of the reservoir formations. The large differences in the velocities of the Compressional Wave and the Slow-Wave cause changes in their reflection and refraction characteristics. The reflection due to Slow-Wave appears as a low-frequency artifact, delayed in time. The delay time of this artifact is used to calculate the Slow-Wave velocity and the tortuosity of the reservoir rocks. Based on the tortuosity and the wellbore data, permeability can be estimated.

Abstract: This invention relates to mapping the open fractures in the reservoir subsurface formations. To map these open fractures, the elastically nonlinear interaction of the two surface generated seismic waves, as they propagate through the open fractures and are reflected back from the subsurface boundaries, is recorded using conventional 3-D seismic receiver configurations. Recorded data are processed for standard 3-D reflection imaging and additionally for mapping the location and orientation of the subsurface open fractures.

Abstract: This invention relates to mapping the hydrocarbon reservoir characteristics by mapping the reservoir formations that display dynamic elastic nonlinearity responses to the seismic signals. The main reason of this nonlinear behavior in the reservoir rocks is their bulk rock property: the porosity, fractures, differential pressure and pore saturation. To map these bulk rock properties, the interaction of the two seismic waves as they propagate through elastically nonlinear rocks is recorded. Two compressional seismic signals are transmitted from the surface. Seismic reflection data using surface or borehole detectors are recorded. One of the transmitted signals is a conventional swept frequency and the other is a mono-frequency signal. During the propagation of these two signals through the elastically nonlinear reservoir rocks, there is an interaction between the two signals. The sum and difference frequencies of the two primary seismic signals that were transmitted from the surface are created.

Abstract: This invention relates to using elastically nonlinear seismic imaging methods, to identify the bypassed hydrocarbons and the movement of the reservoir fluids in the reservoir due to injection and production processes. Time-lapse seismic recording is used to monitor the changes in the hysteretic nonlinear behavior of the pore fluids in the reservoir rocks. Since the nonlinear hysteretic behavior of the saturated reservoir rock generates harmonics of the primary seismic signal that propagates through it, the measurement of these harmonics is used to determine the changes in the reservoir fluids due to hydrocarbon production over time.

Abstract: This Patent describes a method for determining the location and orientation of the open natural fractures in an earth formation by analyzing the interaction of the two seismic signals. One is a low frequency signal transmitted from the earth's surface and the other a high frequency signal transmitted from a wellbore. The compressional and the rarefaction cycles of the lower frequency signal are used to modulate the width of the open fractures, which changes their transmission characteristics. As a result, the amplitude of the high frequency signal gets modulated as it propagates through the open fractures. The result of the interaction of the high and low frequency seismic signals is recorded in another wellbore. The spectral analysis of the modulated signal that is recorded during compression and rarefaction cycles of the lower frequency surface generated signal is used to determine the location and the orientation of the open natural fractures.