Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Earth science
Reexamination Certificate
2000-03-03
2001-10-23
McElheny, Jr., Donald E. (Department: 2862)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Earth science
Reexamination Certificate
active
06308136
ABSTRACT:
FIELD OF THE INVENTION
The invention is related to the field of induction logging of subsurface earth formations. Specifically, it relates to the use of induction logging for obtaining structural information of the subsurface away from a borehole.
BACKGROUND OF THE INVENTION
Induction resistivity well logging devices are known in the art for measuring the electrical resistivity of earth formations penetrated by wellbores. Electrical resistivity measurements are used for, among other things, to infer the fluid content of pore spaces of the earth formations.
Induction electrical resistivity instruments known in the art, such as one described in Hunka, J. “A New Resistivity Measurement System for Deep Formation Imaging and High Resolution Formation Evaluation”, paper no. 20559, Society of Petroleum Engineers, Richardson, Tex., 1990, typically measure voltages induced in receiver coils positioned at spaced apart locations along the instrument. The voltages are induced by magnetic fields generated by eddy currents flowing in the earth formations around the instrument, in response to alternating currents of various frequencies being passed through a transmitter coil. The voltages induced in a particular one of the receiver coils are dependent on the electrical conductivity (which is inversely related to resistivity) of the media, including the earth formations, surrounding the instrument, and are dependent on the spacing of the particular receiver coil with respect to the transmitter coil. Generally, the greater the spacing between the transmitter coil and the particular receiver coil, the greater is the radial depth from the wellbore into the earth formation from which the measurement at that receiver coil corresponds. The vertical resolution of the measurements made by the closer-spaced receiver coils, however, is proportionately finer than is the vertical resolution of the measurements made by the more distant receiver coils.
When the wellbore is drilled, fluids from the drilling process may be forced into the pore spaces of some of the earth formations, changing their fluid content and therefore their resistivity. The process of fluid being forced into the pore spaces is generally referred to as “invasion”. Wellbore can be drilled with fluids having differing electrical resistivities, and the wellbore itself can have widely varying diameters over its length. The effects of variable wellbore diameter and differing wellbore fluid resistivity can indeterminately affect the total voltage being induced in each one of the receiver coils, because eddy currents also can flow within the conductive wellbore fluid and within that portion of the earth formations surrounding the wellbore subject to the invasion (the so-called “invaded zone”).
U.S. Pat. No. 5,703,773 (referred hereafter as the “'773 patent”) having the same assignee as the present application and the contents of which are fully incorporated herein by reference, discloses a method of inversion processing signals from an induction well logging instrument. The instrument includes a transmitter and a plurality of receivers at axially spaced apart locations. The method includes skin effect correcting the responses of the receivers by extrapolating the receiver responses to zero frequency. A model is generated of the media surrounding said instrument. Conductivities of elements in the model are adjusted so that a measure of misfit between the skin-effect corrected receiver responses and simulated receiver responses based on the model is minimized. The geometry of the model is adjusted so that the measure of misfit between the skin-effect corrected receiver responses and the simulated receiver responses based on the model is further minimized.
The method of the '773 patent and other prior art processing methods for well logs are developed for vertical or near vertical wells. If the well deviation exceeds 30
0
-45
0
, traditional methods may fail. To interpret the data, 3-D modeling and inversion must be carried out. However, 3-D modeling and inversion is rarely practical due to the computational time requirements and the unavailability of powerful computers. As would be known to those versed in the art, some information about the subsurface is obtained using measurement-while-drilling (“MWD”) methods in horizontal or near horizontal boreholes. In an MWD environment, there is relatively little invasion of the formation by the drilling mud and the relatively short transmitter to receiver spacings may be able to provide sufficient information about the formation resistivity to be useful in applications such as geosteering.
It is desirable to have an invention that is able to give information further away from the borehole in a near horizontal well.
FIG. 1
is an end-on view of a borehole
10
within a reservoir rock
20
. Surrounding the well is an invaded zone
12
. Also shown in
FIG. 1
are interfaces
22
and
26
marking a resistivity contrast between the zone
20
and zones
24
and
28
. Typically, the interfaces
22
and
26
could be bed boundaries marking the separation between a reservoir formation
20
and non-reservoir formations
24
and
28
. However, the boundary
26
could also be a fluid contact within a formation marking the separation between a water wet region
28
and a hydrocarbon wet region
20
while formation
22
is the caprock. Another possible configuration is that
20
is a water wet reservoir rock while
24
is the hydrocarbon saturated region with
28
being the seal beneath the reservoir.
As part of the reservoir evaluation process, it would be desirable to map the boundaries such as
22
and
26
accurately. Such information is useful in the estimation of reserves and in development of completion procedures for developing the reservoir. The present invention satisfies this need for situations such as in FIG.
1
and also in other situations where information relating to formation properties away from the borehole is needed.
SUMMARY OF THE INVENTION
The present invention is a method for making induction log measurements in an inclined borehole and determining properties of subsurface formations formation away from the borehole. Measurements are made using an induction logging instrument having a plurality of transmitter-receiver (T-R) distances. After correction of the data for skin effects and optionally correcting for eddy currents within the borehole, the shallow measurements (those from short T-R spacing or from high frequency data) are inverted to give a model of the near borehole (invaded zone resistivity and diameter) and the resistivity of the formation outside the invaded zone. Using this model, a prediction is made of the data measured by the mid-level and deep sensors (long T-R spacings). A discrepancy between these predicted values and the actual measurements made by the midlevel and deep sensors is indicative of additional layer boundaries in the proximity of the wellbore. The midlevel and deep sensor data are corrected for invasion effects and inverted using the model derived from the shallow data to give an estimate of the distance to these additional layer boundaries and of the resistivity beyond these additional boundaries. In this manner, resistivity measurements in a near horizontal borehole may be used to map subsurface layers away from the borehole. In one embodiment of the invention, the quadrature component of the signal induced in the receiver coils is used. This quadrature component is independent of T_R spacing and has a larger depth of penetration than the commonly used in-phase component of the receiver signal.
REFERENCES:
patent: 4472684 (1984-09-01), Schuster
patent: 5666057 (1997-09-01), Beard et al.
patent: 5703773 (1997-12-01), Tabarovsky et al.
patent: 5854991 (1998-12-01), Gupta et al.
patent: 5884227 (1999-03-01), Rabinovich et al.
patent: WO 98/00733 (1998-01-01), None
W. Hal Meyer; Interpretation of Propagation Resistivity Logs in High Angle Wells, SPWLA 39th Annual Logging Symposium, May 262-9, 1998, pp. 1-13.
Frank Hearn et al.; Advances in resistivi
Beard David R.
Rabinovich Michael Boris
Tabarovsky Leonty A.
Baker Hughes Incorporated
Madan Mossman & Sriram P.C.
McElheny Jr. Donald E.
LandOfFree
Method of interpreting induction logs in horizontal wells does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of interpreting induction logs in horizontal wells, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of interpreting induction logs in horizontal wells will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2591231