Wells – Processes – With indicating – testing – measuring or locating
Reexamination Certificate
2000-06-27
2001-10-16
Schoeppel, Roger (Department: 3672)
Wells
Processes
With indicating, testing, measuring or locating
C166S402000, C166S272200, C166S373000, C367S039000, C367S057000, C181S112000, C340S853100
Reexamination Certificate
active
06302204
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the placement of wellbores and management of the corresponding reservoirs and more particularly to selectively drilling one or more wellbores for conducting seismic surveys therefrom to improve the seismographs and utilizing the improved seismographs to determine the type and course of wellbores for developing a field. The method of the present invention further relates to obtaining seismic information during drilling of the wellbores and during production of hydrocarbons for improving hydrocarbon production from the reservoirs. The method of the present invention further relates to using the derived seismic information for automatically controlling petroleum production wells downhole computerized control systems.
BACKGROUND OF THE INVENTION
Seismic surveys are performed from surface locations to obtain maps of the structure of subsurface formations. These surveys are in the form of maps (referred herein as seismographs”) depicting cross-section of the earth below the surveyed region or area. Three dimensional (“3D”) surveys have become common over the last decade and provide significantly better information of the subsurface formations compared to the previously available two-dimension (“2D”) surveys. The 3D surveys have significantly reduced the number of dry wellbores. Still, since such seismic surveys are performed from the surface, they lose resolution due to the distance between the surface and the desired hydrocarbon-bearing formations, dips in and around the subsurface formations, bed boundary delineations, which is typically several thousand feet.
Surface seismic surveys utilize relatively low frequency acoustic signals to perform such surveys because such signals penetrate to greater depths. However, low frequency signals-provide lower resolution, which provides low resolution seismographs. High frequency signals provide relatively high resolution boundary delineations, but attenuate relatively quickly and are, thus, not used for performing seismic surveys from the surface.
Only rarely would an oil company drill a wellbore without first studying the seismographs for the area. The number of wellbores and the path of each wellbore is typically planned based on the seismographs of the area. Due to the relatively low resolution of such seismographs, wellbores are frequently not drilled along the most effective wellpaths. It is therefore desirable to obtain improved seismographs prior to drilling production wellbores. Additionally, more and more complex wellbores are now being drilled, the placement of which can be improved with high definition seismographs. Furthermore, relatively recently, it has been proposed to drill wellbores along contoured paths through and/or around subsurface formations to increase potential recovery or to improve production rates of hydrocarbons. In such cases, it is even more critical to have seismographs that relatively accurately depict the delineation of subsurface formations.
Conventionally, seismographs have been updated by (a) performing borehole imaging, which is typically conducted while drilling a wellbore and (b) by cross-well tomography, which is conducted while between a number of producing wells in a region. In the case of borehole imaging, a seismic source seismic source generates acoustic signals during drilling of the wellbore. A number of receivers placed on the surface receive acoustic reflections from subsurface formation boundaries, which signals are processed to obtain more accurate bed boundary information about the borehole. This technique helps improve the surface seismographs in piecemeal basis. Data from each such well being drilled is utilized to continually update the seismographs. However, such wellbores are neither planned nor optimally placed for the purpose of conducting subsurface seismic surveys. Their wellpaths and sizes are determined based upon potential recovery of hydrocarbons. In the case of crosswell tomography, acoustic signals are transmitted between various transmitters and receivers placed in producing wellbores. The effectiveness of such techniques are reduced if the wellbores are not optimally placed in the field. Such techniques would benefit from wellbores which are planned based on improved seismographs.
In the control of producing reservoirs, it would be useful to have information about the condition of the reservoir away from the borehole. Crosswell techniques are available to give this kind of information. In seismic tomography, a series of 3-D images of the reservoir is developed to give a 4-D model or the reservoir. Such data has usually been obtained using wireline methods in which seismic sensors are lowered into a borehole devoted solely for monitoring purposes. To use such data on a large scale would require a large number of wells devoted solely to monitoring purposes. Furthermore, seismic data acquired in different wireline runs commonly suffers from a data mismatch problem where, due to differences in the coupling of the sensors to the formation, data do not match.
The present invention addresses the above-noted problems and provides a method of conducting subsurface seismic surveys from one or more wellbores. These wellbores may be drilled for the purpose of conducting such surveys. Alternatively, permanently implanted sensors in a borehole that could even be a production well could be used to gather such data. The data from such subsurface surveys is utilized to improve the previously available seismographs. The improved seismographs are then utilized to plan the production wellbores. Borehole seismic imaging and cross-well tomography can be utilized to further improve the seismographs for reservoir management and control.
SUMMARY OF THE INVENTION
The present invention provides a method for forming wellbores. In one method, one or more wellbores are drilled along preplanned paths based in part upon seismic surveys performed from the surface. An acoustic transmitter transmits acoustic signals at one or more frequencies within a range of frequencies at a plurality of spaced locations. A plurality of substantially serially-spaced receivers in the wellbores and/or at surface receive signals reflected by the subsurface formations. While the acoustic receivers are permanently deployed downhole, the acoustic transmitter may optionally be positioned permanently or temporarily downhole; or may be positioned permanently or temporarily at the surface of the well. The receiver signals are processed by conventional geophysical processing methods to obtain information about the subsurface formations. This information is utilized to update any prior seismographs to obtain higher resolution seismographs. The improved seismographs are then used to determine the profiles of the production wellbores to be drilled. Borehole seismic imaging may then be used to further improve the seismographs and to plan future wellbores. Information gathered from tomographic surveys carried out over a period of time can be used to map changes in the reservoir conditions away from the boreholes and appropriate control measures may be taken. Fiber optic sensors, along with a light source, can also be used to detect the acoustic and seismic signals.
Another embodiment of the present invention includes permanent downhole formation evaluation sensors which remain downhole throughout production operations. These formation evaluation sensors for formation measurements may include, for example, gamma ray detection liar formation evaluation, neutron porosity, resistivity, acoustic sensors and pulse neutron which can, in real time, sense and evaluate formation parameters including important information regarding water migrating from different zones. Permanently installed fiber optic sensors can also be used to measure acoustic signals, pressure, temperature and fluid flow. These are utilized to in the seismic mapping as well as in obtaining and upodating reservoir models and in managing the production of hydrocarbons.
On particularly advantageous permanent downhole sen
Harrell John W.
Reimers Nils
Tubel Paulo S.
Baker Hughes Incorporated
Madan Mossman & Sriram P.C.
Schoeppel Roger
LandOfFree
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