Electricity: measuring and testing – Of geophysical surface or subsurface in situ – With radiant energy or nonconductive-type transmitter
Reexamination Certificate
2001-09-04
2003-10-07
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Of geophysical surface or subsurface in situ
With radiant energy or nonconductive-type transmitter
C343S787000
Reexamination Certificate
active
06630831
ABSTRACT:
BACK GROUND TO INVENTION
1. Field of Use
Any medium containing electrically conductive material can be monitored for changes in the electrical resistivity of the electrically conductive material. An important and well-known example is the measurement of the electrical resistivity of underground geologic formations. Such formations often contain salt water, which is a relatively high electrically conductive material and/or hydrocarbons which are less electrically conductive and therefore more electrically resistive. The resistivity of geologic formations containing these materials is measurable, thereby providing information relative to the concentrations of oil, water and gas at various locations within a geologic formation.
It has been demonstrated that it is possible to measure the resistivity of an underground geologic formation through a ferromagnetic well casing penetrating the formation, as well as through other materials that are electrically conductive and magnetically permeable. These materials are referred herein as “EM barriers” or “barrier materials.” The technology is based upon inductive magnetic coupling; therefore the measuring apparatus does not need to be in physical contact to the barrier material comprising the well casing or production tubing. It has also been shown that magnetic flux may be transmitted through metals that have a permeability of one weber/amp. These metals can be considered non-permeable, i.e., there is little or no absorption of magnetic flux. However, due to the rapid spreading of the magnetic flux, the flux intensity drops off with respect to distance as the inverse cube of the distance.
The invention subject of this specification utilizes the technique of inductive magnetic coupling of Electromagnetic waves to EM barrier materials in combination with transmission of Electromagnetic waves through non-permeable material to facilitate the measurement of resistivity of geologic formation beyond the well casing.
Hydrocarbon production wells typically utilize an outer casing made of a ferromagnetic material. Common outside diameters of the casing may be of a range of 7 to 10 inches or larger. The interior diameter is of varying dimensions. The thickness of the casing also varies but may typically be ½ inch or more in thickness. Placed inside the permanent casing is a smaller production tubing. The outer diameter of the production tubing may be in a range of 1 to 4 inches. Hydrocarbon, such as crude oil mixed with salt water or solid particles such as sand, flows through the production tubing at a high velocity. This environment is harsh and corrosive, sometimes requiring the replacement of the production tubing. It will be appreciated that well casing is required to maintain an open channel for the flow of production and minimize interruption due to a “cave in” or crumbling of the bore hole wall.
Note that throughout this specification, the terms “casing,” “well bore casing” and “well casing” will be deemed to include hydrocarbon production tubing or other ancillary structures such as casing or tubing connectors, collars or couplings.
The sensor tool of this invention may create a “Metallic Transparency”™ region local to its oscillating magnetic flux transmitter (transmitter) or its flux receiver (receiver) by means of a strong magnetic flux field saturating an EM barrier near the transmitter and receiver. It may also utilize near practical saturation and “Magnetic Lens”™ focus to direct the oscillating flux of the transmitter in a controlled manner.
The present invention relates generally to measuring resistivity of media such as liquids, gases or other objects within a geologic formation surrounding a well casing. Specifically, the present invention relates to through casing resistivity measurement in downhole hydrocarbon production environments. The present invention provides a sensor apparatus and method for measuring the resistivity of a formation proximate to a well. The current invention, in one embodiment, is an apparatus for measuring the resistivity of the surrounding formation. The apparatus records electrical responses corresponding to magnetic fluxes that relate to the resistivity of the geologic formation at various depths or locations within the formation penetrated by the cased well. The apparatus can thereby detect the location and amplitude of said resistivity in single or multiple directions, and at distances that will help operators of wells adjust their production management and their reservoir management activities. The apparatus can also be used to detect changes in the resistivity over time by comparison of recorded fluxes at various time intervals.
The invention includes a sensor tool that can travel through the relatively narrow diameter of well casing (or production tubing), means to raise and lower the tool to a specified location of the casing string proximate to a non magnetically permeable section, means to supply power and receive data, as well as recording and display devices.
The invention subject of this specification allows the transmission of Electromagnetic waves through well casing, thereby permitting information of the lithology to be obtained from sensors within the well. Recent developments have shown that magnetic flux may be transmitted though ferromagnetic or paramagnetic materials, such as carbon steel. Ferromagnetic metals or paramagnetic metals, being electrically conductive and magnetically permeable have previously been barriers to the transmission of Electromagnetic energy.
2. Summary of Related Art
In the development and production of oil and gas reservoirs, there is a very significant need to increase the amount and accuracy of information regarding the composition and changes in the composition of the resource-bearing zones of the formation. Resistivity measurement has long been used to characterize properties of the immediately surrounding substrates prior to the inception of production. However, it has typically only been possible to take such measurements prior to setting casing or while the formation itself is otherwise “exposed” to a logging tool, i.e., an “open hole” without an interceding material that acts as a barrier between the logging tool and the formation substrate. Existing methods of measuring the resistivity of the media within a geologic formation have therefore required that the measurements be taken with logging tools deployed prior to commencement of actual production. After casing is placed in the well and production is underway, it is generally not possible to measure the resistivity of the surrounding geologic formation without interruption of the well production and penetration or removal of the well casing.
As is known to those skilled in the industry, the electrical resistivity of a geologic formation varies as a result of (among other reasons) the changing proportion of hydrocarbon to water contained within the formation. Having the ability to measure at selected locations and directions over time would provide for the unique ability to monitor, for example, the change in the percentage of water versus either oil, gas, or other electrically conductive materials approaching the well, far in advance of such change in fluids actually entering the well. The benefits of such measurements include the ability to see changes in the composition of the formation, i.e., hydrocarbon and water by measuring changes in the resistivity of the formation through the barrier material comprising the well casing.
Numerous attempts have been made to provide an apparatus or method for measuring the electrical resistivity of the surrounding geologic formation through a well casing. See for example U.S. Pat. No. 5,654,639 entitled “Induction Measuring Devices in the Presence of Metal Wall,” but requiring an electric current to be passed into the metal pipe wall. The contact device is then disengaged from the wall when the apparatus is moved. Also U.S. Pat. No. 5,426,367, entitled “Logging of Cased Well by Induction Logging to Plot an Induction Log of the Well” and stating the d
Em-Tech Sensors LLC
Le Toan
Lefkowitz Edward
McEwing David
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