Acoustics – Geophysical or subsurface exploration – Well logging
Reexamination Certificate
2000-04-26
2001-06-12
Dang, Khanh (Department: 2837)
Acoustics
Geophysical or subsurface exploration
Well logging
C181S112000, C367S025000, C166S250010
Reexamination Certificate
active
06244375
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to production of hydrocarbons from subsurface formations and more particularly to in-hole seismic data acquisition to map advancing fluid fronts within a field or around a single wellbore.
2. Description of the Related Art
In order to relatively precisely map advancing fluid fronts within a field or around a single wellbore requires the use of deep reading measurements at spatial resolutions of less than five (5) meters but with the spatial extents of several hundred meters, depending upon the reservoir location, size and the number of wells in the field. Conventional three dimensional (“3D”) seismic acquisition and repeated 3D seismic acquisitions (also referred to as the 4D seismic acquisition) and seismic data acquisition techniques known as vertical seismic profiling (“VSP”), 3D VSP and Reverse VSP or Reverse 3D VSP are often utilized to model the reservoirs and/or to determine the advancing fluid fronts in the producing formations. The conventional 3D and 4D surface seismic acquisitions are performed by deploying detectors at or near the surface and the survey area is usually substantially large. The conventional 3D and 4D surveys provide data with limited spatial resolution and no near real-time ability to utilize results because of the lengthy time span required to acquire and process the data, which can take several months. The subsurface VSP and 3D VSP also suffer from long data processing cycles and have limited spatial extent.
Water breakthrough can occur rapidly, especially after a new horizontal well is drilled. Reservoir engineers can take timely action if the fluid front information is available timely.
Another related problem is the expense of acquiring repeat 3D seismic data over a relatively small geographical area, such as between 10-20 Km
2
. The current seismic surveying vessels using surface towed cables are designed to acquire vast volumes of data over a large region. Ocean bottom cable surveys, wherein seismic sensor or detector cables are deployed on the sea bottom, provide an alternative surveying method but are more expensive than the towed streamer cable acquisition methods.
Co-pending U.S. Pat. application Ser. No. 08/948,150, now U.S. Pat. No. 6,065,538, assigned to the assignee of this application, provides yet another alternative, wherein seismic sensors are deployed in wells formed for such purposes as close to the producing zones. Such techniques also are relatively expensive as they require drilling of additional wells.
The present invention provides systems and methods for acquiring seismic data by deploying movable clusters of seismic detectors in wells to acquire data as needed. Such a system provides seismic data with relatively high spatial resolution and with small spatial extent. Because of the relatively small number of detectors, the data can be processed substantially in real-time and utilized to provide 4D maps of the advancing fluid fronts. Use of such systems in multiple wells in a common field provides maps of the advancing fluid fronts within that field.
SUMMARY OF THE INVENTION
In one aspect, this invention provides near real-time systems and methods for acquiring seismic data in reservoirs at very high spatial resolution such that advancing fluid fronts can be mapped substantially in real time. The systems allow large spatial extents to be investigated at arbitrarily fine spatial intervals or resolution. In one system, one or more autonomous devices are deployed in the well to detect seismic data. Each device includes at least one seismic receiver and may also include an acoustic energy source. The device may include multiple spaced apart receivers. An acoustic energy source, preferably at the surface, induces acoustic waves into the subsurface formations. The autonomous devices move in the well and detect seismic waves traveling to the receivers at known discrete locations in the well. The devices store the seismic data in on-board memory. After the data acquisition, the devices dock at the receiver stations in the well. The receiver stations provide power to the devices and download the stored data from the memory. A two way data link between a surface control unit, such as a computer system, and the downhole receiver is used to transmit data from the receiver to the surface computer. The surface computer system also sends command signals to the downhole receiver to control the operation of the individual devices. The receiver stations can be programmed to control the operation of the devices, which may include resident programs to perform the survey operations at specified intervals.
The data gathered by the devices is used to update existing seismic maps in determining the boundary conditions of the fluid fronts. The amount of the data is relatively small compared to conventional seismic methods, such as VSP, RSVP or surface seismic methods using land cables or streamer cables, and thus can be processed to update the prior 3D data to locate fluid fronts substantially in real time. The data collection spacing defines the spatial resolution, which is selected by the operator based upon the need.
In an alternative method, the devices are deployed in the wellbore and at sea bottom. The devices travel along predefined paths at the sea bottom and in the wells to collect seismic data. Tracks are used to guide the devices in the wells and at the ocean bottom. Coiled tubing laid at the ocean bottom may be used as tracks. A subsea control station or receiver provides power and data transmission function for the subsea devices. A source on a vessel may be used to induce acoustic energy into the subsurface formations. The data from both the wells and the sea bottom is then used to update the 3D maps to obtain 4D maps and to model the reservoirs.
Examples of the more important features of the invention thus have been summarized rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto.
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patent: 5259452 (1993-11-01), Wittrisch
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patent: 5481502 (1996-01-01), Cretin et al.
patent: 5550785 (1996-08-01), Laurent et al.
patent: 5597042 (1997-01-01), Tubel et al.
patent: 5721538 (1998-02-01), Tubel et al.
patent: 5798982 (1998-08-01), He et al.
patent: 6065538 (2000-05-01), Reimers et al.
Burge Philip
Norris Michael W.
Baker Hughes Incorporated
Dang Khanh
Madan Mossman & Sriram P.C.
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