Elastic waves push organic fluids from reservoir rock

Elastic waves have been observed to increase productivity of oil wells, although the reason for the vibratory mobilization of the residual organic fluids has remained unclear. Residual oil is entrapped as ganglia in pore constrictions because of resisting capillary forces. An external pressure gradient exceeding an ‘‘unplugging’’ threshold is needed to carry the ganglia through. The vibrations help overcome this resistance by adding an oscillatory inertial forcing to the external gradient; when the vibratory forcing acts along the gradient and the threshold is exceeded, instant ‘‘unplugging’’ occurs. The mobilization effect is proportional to the amplitude and inversely proportional to the frequency of vibrations. We observe this dependence in a laboratory experiment, in which residual saturation is created in a glass micromodel, and mobilization of the dyed organic ganglia is monitored using digital photography.We also directly demonstrate the release of an entrapped ganglion by vibrations in a computational fluid-dynamics simulation

Acoustic imaging of underground storage tank wastes: A feasibility study. Final report

The objectives for this underground storage tank (UST) imaging investigation are: (1) to assess the feasibility of using acoustic methods in UST wastes, if shown to be feasible, develop and assess imaging strategies; (2) to assess the validity of using chemical simulants for the development of acoustic methods and equipment. This investigation examined the velocity of surrogates, both salt cake and sludge surrogates. In addition collected seismic cross well data in a real tank (114-TX) on the Hanford Reservation. Lastly, drawing on the knowledge of the simulants and the estimates of the velocities of the waste in tank 114-TX the authors generated a hypothetical model of waste in a tank and showed that non-linear travel time tomographic imaging would faithfully image that stratigraphy

Imaging and Characterizing the Waste Materials Inside an Underground Storage Tank Using Seismic Normal Modes

It is necessary to know something about the nature of the wastes in a Hanford underground storage tank (UST) so that the correct hardware can be inserted into a tank for sampling, sluicing, or pumping operations. It is also important to know if a layer of gas exists beneath solid and liquid layers of waste. Given that the tank will have only one liquid observation well (LOW), the authors examined the information that could be obtained from the natural seismic vibrations of a tank as a whole; that is, the normal modes of that tank. As in the case of a bell, the natural vibration, or normal modes, of a tank depend on many things, including the construction of the tank, the kinds of waste materials in the tank, the amount of each material in the tank, and where the energy is placed that excites the vibrations (i.e., where you will ''hit'' the tank). The nature of a normal mode of vibration can be given by its frequency and amplitude. For any given frequency, the amplitude of vibration can be given as a function of position in and around the tank. Since they assumed that one would be ''listening'' to a tank from locations along a LOW, they show their computed amplitudes as a function of position inside and around the tank, and in the case of the physical models they display the observations along various lines inside the tank model. This allowed us to see the complex geometry of each mode of oscillation as a function of increasing frequency

Imaging and characterizing the waste materials inside an underground storage tank using seismic normal modes. Annual progress report, September 15, 1996--September 14, 1997

'This report covers the initial year of investigation of the normal modes of oscillation of underground storage tanks. This work is directed toward finding a way to estimate the properties of the waste in tanks on the Hanford Reservation with the minimal use of instrumentation in a tank. Theoretical work, as well as laboratory-sized physical modeling was undertaken this first year and the satisfying corroboration between the two methods has given us confidence to go forward. The physical model results presented here are for a tank containing a single layer of liquid wastes, while the theoretical formulation is valid for both the single-layer and multi-layer cases. Given this solid foundation the authors proceed to tanks containing multiple layers of solids.

Reservoir characterization by cross-hole seismic imaging. Final report, September 15, 1989--June 30, 1994

Better characterization of reservoirs requires better images of those reservoirs. This report documents the research undertaken at the Massachusetts Institute of Technology`s Earth Resources Laboratory (ERL) to improve seismic tomographic images. In addition, the new imaging method was applied to a data set collected in a producing oil field. The method developed is nonlinear travel time tomography. This technique uses the travel time of the first arriving energy at a receiver and distributes that time back along realistic ray paths. This is an important distinction between this method and previous methods that used either straight ray paths from source to receiver or fixed ray paths (ray paths fixed by an a priori model). The nonlinearity arises during each iteration in the matching of observed travel times with those determined from a model. In this technique the model is updated during each iteration (the velocity structure is changed) and new ray paths are computed in that update model. Thus the resulting image is based on physically realistic ray paths. Tomography resolution is not merely a simple function of the wavelength of the seismic energy used but also involves a measure of how well a given region has been sampled by ray paths. Moreover, the ray paths must represent a wide variation in inclination as they pass through a given spatial cell. This imaging technique was applied to a compressional wave data set collected at ERL`s Michigan Test Site located in the Northern Reef Trend of MI. It consists of two deep boreholes that straddle a producing reef. Two hundred source positions and two hundred receiver positions were used to obtain 40,000 ray paths. Although ERL`s boreholes are 2,000 ft apart, kilohertz data was obtained. The resulting image of the reservoir showed a low velocity zone inside the reef and a thin layer of low velocity that intersected one of the boreholes. The presence of this thin layer was confirmed by logs and borehole engineering

Elastic waves push organic fluids from reservoir rock

Elastic waves have been observed to increase productivity of oil wells, although the reason for the vibratory mobilization of the residual organic fluids has remained unclear. Residual oil is entrapped as ganglia in pore constrictions because of resisting capillary forces. An external pressure gradient exceeding an ‘‘unplugging’’ threshold is needed to carry the ganglia through. The vibrations help overcome this resistance by adding an oscillatory inertial forcing to the external gradient; when the vibratory forcing acts along the gradient and the threshold is exceeded, instant ‘‘unplugging’’ occurs. The mobilization effect is proportional to the amplitude and inversely proportional to the frequency of vibrations. We observe this dependence in a laboratory experiment, in which residual saturation is created in a glass micromodel, and mobilization of the dyed organic ganglia is monitored using digital photography.We also directly demonstrate the release of an entrapped ganglion by vibrations in a computational fluid-dynamics simulation.This article is from Geophysical Research Letters 32 (2005): L13303, doi:10.1029/2005GL023123. Posted with permission.</p

Seafloor borehole array seismic system (SEABASS)

The Seafloor Borehole Array Seismic System (SEABASS) has been developed to measure the pressure and three dimensional particle velocity of the VLF sound field (2-50HZ) below the seafloor in the deep ocean (water depths of up to 6km). The system consists off our three-component borehole seismometers (with an optional hydrophone), a borehole digitizing unit, and a seafloor control and recording package. The system can be deployed using a wire line re-entry capability from a conventional research vessel in Deep Sea Drilling Project (DSDP) and Ocean Drilling Project (ODP) boreholes. Data from below the seafloor are acquired either on-board the research vessel via coaxial tether or remotely on the seafloor in a self-contained package. If necessary the data module from the seafloor package can be released independently and recovered on the surface. This paper describes the engineering specifications of SEABASS, the tests that were carried out, and preliminary results from an actual deep sea deployment. Ambient noise levels beneath the seafloor acquired on the Low Frequency Acoustic-Seismic Experiment (LFASE) are within 20dB of levels from previous seafloor borehole seismic experiments and from land borehole measurements. The ambient noise observed on LFASE decreases by up to 12dB in the upper 100m of the seafloor in a sedimentary environment.This work was carried out under JHU Contract # 602809-0 and under ONR contracts #N00014-89-C-0018, #N00014-89-J-1012, and #N00014-90-C-0098