BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of logging of material properties and, in one possible specific embodiment, relates to methods and/or devices for making a log in layered environments. One possible non-limiting example includes producing a log of material properties with respect to borehole depth.

2. Description of the Background

Subsurface geological formations typically comprise layers of various types of formations. While the present invention is not limited to use in producing logs of a layered environment comprising subsurface geological formations, an embodiment of the invention is conveniently described in terms of this environment.

Most oil and gas was originally deposited in an ocean environment. As a consequence, such formations may contain fluids such as salt water and/or oil. Salt water, with its mobile sodium and chlorine ions makes the formation conductive to electricity, while the oil/gas makes the formation resistive. The oil companies typically utilize logging tools to produce a log of material properties of a wellbore. As one example, when the desired rock formation or depth is reached, the drill pipe and the bit are removed from the hole. An instrument is lowered into the wellbore to measure the electrical conductivity versus depth. In this way, a log or a record of the geologic formation is produced. Other instruments may generate a log of a wellbore while drilling. Generally, if the rocks are relatively conductive, they contain salt water. If the rocks are relatively resistive, they contain oil and/or gas.

The earliest instruments used direct current and were first used in 1927. In the 1950's, electromagnetic or induction tools were introduced. These electromagnetic instruments had coaxial coils, and measured just one component of the conductivity tensor of the rock. There are many different electromagnetic tools which measure various physical quantities. The standard induction tools measure a voltage while the measurement-while-drilling (MWD) tools measure phase differences and/or amplitude ratios. Other tools comprise many configurations such as laterolog tools, normal and lateral tools, e-log tools and the like. The present invention may be utilized with these and other tools.

Oil is often deposited in a layered environment. There is an exact mathematical solution to an electromagnetic instrument penetrating a parallel layered environment at any angle as per an article by the inventor. See, for example, Hardman and Shen, “Theory of Induction Sonde in Dipping Beds,” Geophysics Vol. 51, No. 3, March 1986, p. 800-809. However, in the real world, the interface between the layers is not necessarily parallel.

Other background material may include Hardman and Shen, “Charts for Correcting Effects of Formation Dip and Hole Deviation on Induction Logs,” The Log Analyst, Vol. 28, No. 4, p 349-356, July-August 1987; Hardman, “Four-Term Decomposition Techniques for a Faster Inversion of Induction Responses,” SPE 84606, October 2003; Wang, Barber, et al., “Triaxial Induction Logging: Theory, Modeling, Inversion, and Induction,” SPE 103897, December 2006; Anderson, Barbara et al., “Effect of Dipping Beds on the Response of Induction Tools”, SPE Formation Evaluation (March 1988), pp. 29-36; Barber, Anderson, et al, “Determining Formation Resistivity Anisotropy in the Presence of Invasion, SPE 90526, September 2004; Anderson, Barbara et al., “Response of 2-MHZ LWD Resistivity and Wireline Induction Tools in Dipping Beds and Laminated Formations”, SPWLA 31st Annual Logging Symposium, Jun. 24-27, 1990, Paper A, pp. 1-25; Barber, Thomas D. et al., “Interpretation of Multiarray Induction Logs in Invaded Formations at High Relative Dip Angles”, The Log Analyst, vol. 40, No. 3 (May-June 1999), pp. 202-21; Sommerfeld Partial Differential Equations in Physics, Academic Press 1949; U.S. Pat. Nos. 3,808,520; 6,304,086; 6,573,722; 6,216,089; 3,510,757; US 2006/0038571; US 2007/0256832; US 2003/0222651; US 2003/0146753; US 2003/0155924; US 2005/0127917; US 2004/0017197; US 2006/0192562; US 2003/0146751; US 2009/0018775; US 2008/0078580; US 2008/0210420; US 2008/0215241; US 2008/0258733; US 2008/0078580; US 2008/0278169; and US 2005/0256642.

Since around 2000, the tools have transmitter and receiver coils in the x, y and z directions. These tri-axial instruments measure all the components of the conductivity tensor and are able to orient the individual bed boundaries. A change in bed boundary orientation may be indicative of a change in the depositional environment. Information concerning the orientation of the bed boundary may be very useful in the geologic interpretation of the formation.

Consequently, there remains a long felt need for improved methods which may be utilized to produce more accurate logs in layered environments wherein the layers may or may not be parallel. Moreover, it sometimes desirable to more quickly calculate or invert logs. Because those skilled in the art have recognized and attempted to solve these problems in the past, they will appreciate the present invention, which addresses these and other problems.

SUMMARY OF THE INVENTION

An object of the invention is to provide an improved method of logging physical properties.

Another possible object of the present invention is to provide a faster method of computing and inverting a log.

Another possible object of the present invention is provide the ability to compute the log when any boundary has an individually variable orientation whereby the bed boundary effects are accurately accounted for in the log. (FIG. 1)

Another possible object of the invention is to provide improved accuracy of the positions and/or orientations of bed boundaries and/or the material properties of the beds.

Another possible object of the invention is to provide an improved method for geosteering a well.

Another possible object of a specific embodiment of the present invention is to determine a conductivity log from the composite magnetic field.

These and other objects, features, and advantages of the present invention will become apparent from the drawings, the descriptions given herein, and the appended claims. However, it will be understood that the above-listed objectives and/or advantages of the invention are intended only as an aid in understanding aspects of the invention, are not intended to limit the invention in any way, and therefore do not form a comprehensive or restrictive list of objectives, and/or features, and/or advantages.

Accordingly, the present invention comprises a method for making a log of material properties in a plurality of beds from an instrument which produces an electromagnetic field. (SeeFIG. 11) In one embodiment, the invention may comprise steps such as, for example, estimating material properties for the plurality of beds and/or estimating positions for a plurality of bed boundaries and/or estimating orientations for the plurality of bed boundaries wherein the bed boundary orientations are individually variable. Other steps may comprise utilizing the positions, and/or the orientations, and/or the material properties to compute the log. (SeeFIG. 1)

In one possible embodiment, an inversion process can be utilized to invert the log.

In one embodiment, the method may comprise varying the orientation for a selected one of a plurality of bed boundaries and utilizing the resulting orientations of the bed boundaries and/or the positions and/or the material properties of the beds to compute the log. The method may comprise varying a position for the selected bed boundary and utilizing the resulting positions of the bed boundaries and/or the orientations and/or the material properties to compute the log. The method may also comprise varying the material properties for a selected bed and utilizing the resulting material properties and/or positions and/or the orientations of the bed boundaries to compute the log.

In one embodiment, the method may comprise selecting a bed boundary from the plurality of bed boundaries, computing a transverse magnetic term one, and utilizing the transverse magnetic term one to compute the log. (SeeFIG. 6) The method may also comprise computing a transverse magnetic term two and a transverse magnetic term three and/or a transverse magnetic term four for the bed boundary and utilizing the transverse magnetic term one and/or the transverse magnetic term two and the transverse magnetic term three and/or the transverse magnetic term four to compute the log.

In one possible embodiment, the method may comprise selecting a bed from the plurality of beds wherein the bed has an upper bed boundary and a lower bed boundary (SeeFIG. 5), computing a first transverse magnetic term one for the upper bed boundary, computing a second transverse magnetic term one for the lower bed boundary, combining the first transverse magnetic term one and the second transverse magnetic term one to provide a combined transverse magnetic term one. (SeeFIG. 9) Other steps may comprise utilizing the combined transverse magnetic term one to compute the log. The method may also comprise computing a transverse magnetic term two for the upper bed boundary, computing a transverse magnetic term three for the lower bed boundary, and utilizing the combined transverse magnetic term one, the transverse magnetic term two, and the transverse magnetic term three to compute the log. (SeeFIG. 8)

In another embodiment, the method may comprise selecting a bed boundary from the plurality of bed boundaries, computing a transverse electric term one, and utilizing the transverse electric term one to compute the log. The method may comprise computing a transverse electric term two and a transverse electric term three for the bed boundary and/or utilizing the transverse electric term one and/or the transverse electric term two and the transverse electric term three to compute the log.

In another embodiment, the method may comprise selecting a bed from the plurality of beds wherein the bed has an upper bed boundary and a lower bed boundary, computing a first transverse electric term one for the upper bed boundary, computing a second transverse electric term one for the lower bed boundary, and combining the first transverse electric term one and the second transverse electric term one to provide a combined transverse electric term one. (SeeFIG. 9) The method may utilize the combined transverse electric term one to compute the log. The method may further comprise computing a transverse electric term two for the upper bed boundary, computing a transverse electric term three for the lower bed boundary, and utilizing the combined transverse electric term one, the transverse electric term two, and the transverse electric term three to compute the log. (SeeFIG. 8)

In yet another embodiment, the method may comprise selecting a bed boundary from the plurality of bed boundaries, computing a transverse electric up for the bed boundary and computing a transverse electric down for the bed boundary. (SeeFIG. 10) The method may comprise utilizing the transverse electric up and the transverse electric down to compute the log. The method may also comprise computing a transverse magnetic term one and utilizing the transverse magnetic term one, the transverse electric up, and the transverse electric down to compute the log. The method may comprise computing a transverse magnetic term one, a transverse magnetic term two, and a transverse magnetic term three for the bed boundary, and utilizing the transverse magnetic term one, the transverse magnetic term two, the transverse magnetic term three, the transverse electric up, and the transverse electric down to compute the log.

In another embodiment, the method of claim1may comprise selecting a bed from the plurality of beds wherein the bed has an upper bed boundary and a lower bed boundary (SeeFIG. 10), computing a transverse electric down for the upper bed boundary and computing a transverse electric up for the lower bed boundary. The method may utilize the transverse electric down and the transverse electric up to compute the log. The method may also comprise computing a first transverse magnetic term one for the upper bed boundary, computing a second transverse magnetic term one for the lower bed boundary, combining the first transverse magnetic term one and the second transverse magnetic term one to provide a combined transverse magnetic term one, and utilizing the combined transverse magnetic term one, the transverse electric up, and the transverse electric down to compute the log. The method may also comprise computing a first transverse magnetic term one for the upper bed boundary, computing a second transverse magnetic term one for the lower bed boundary, combining the first transverse magnetic term one and the second transverse magnetic term one to provide a combined transverse magnetic term one, computing a transverse magnetic term two for the upper bed boundary, computing a transverse magnetic term three for the lower bed boundary, and utilizing the combined transverse magnetic term one (SeeFIG. 9), the transverse magnetic term two, the transverse magnetic term three, the transverse electric up and the transverse electric down to compute the log. (SeeFIG. 10)

In another embodiment, the method may comprise computing a first and/or a new transverse electric up for the bed boundary, computing a first and/or a new transverse electric down for the bed boundary and utilizing the transverse magnetic term one, the transverse electric up and the transverse electric down to compute the log.

In another embodiment, the method may comprise computing a first and/or a new transverse electric up for the bed boundary, computing a first and/or a new transverse electric down for the bed boundary, and utilizing the transverse magnetic term one, the transverse magnetic term two, the transverse magnetic term three, the first and/or new transverse electric up and/or the first and/or new transverse electric down to compute the log.

In another embodiment, the method may comprise computing a first and/or new transverse electric down for the upper bed boundary, computing a first and/or new transverse electric up for the lower bed boundary, utilizing the combined transverse magnetic term one, the first and/or new transverse electric down and/or the first and/or transverse electric up to compute the log.

In another embodiment, the method may comprise computing a first and/or new transverse electric down for the upper bed boundary, computing a first and/or new transverse electric up for the lower bed boundary and/or utilizing the combined transverse magnetic term one, the transverse magnetic term two, the transverse magnetic term three, and/or the first and/or new transverse electric down and the first and/or new transverse electric up to compute the log.

In yet another embodiment, the method may comprise determining a change in a transverse electric part to estimate bed material property derivatives for the plurality of beds (SeeFIG. 12), and/or estimating new material properties for the plurality of beds using the bed material property derivatives for the plurality of beds. If desired, the above steps can be iterated until a convergence criteria is reached. A change in a constant related to the material property in the transverse electric part can be utilized for determining the bed material derivatives. In one embodiment, the constant can be described utilizing k2, where k2is ω2με.

The transverse electric part may comprise an upper bed boundary term and a lower bed boundary term for each of the plurality of beds. The transverse electric part can be a transverse electric part of a dipole. The dipole can comprise a vertical dipole component and/or a horizontal dipole component. (SeeFIG. 7)

The invention provides improved accuracy because th plurality of bed boundaries may or may not comprise non-parallel bed boundaries.

In one embodiment, the method may comprise a method geo-steering the instrument relative to a first bed boundary. The method may comprise determining an orientation between the instrument and the first bed boundary. The method may also comprise determining a relative position between the instrument and the first bed boundary.

The method may comprise estimating apparent dip angles for the plurality of bed boundaries. Another advantageous feature of the present invention is that the estimation of the apparent dip angles includes the possibility that the apparent dip angle calculations include the possibility the dip angle is changing within the bed rather than assuming the dip angle is constant within a bed.

In another embodiment, a method for determining a conductivity log may comprise determining a composite magnetic field at a receiver of an instrument and generally determining the conductivity log from the composite magnetic field. As noted above, the method may comprise determining a relative position between the instrument and a bed boundary and/or determining a relative angle between the instrument and a bed boundary.

In another embodiment, a method is provided for making a log of material properties in a plurality of beds from an instrument which produces an electromagnetic field. The method may comprise estimating a first material property for the plurality of beds and/or estimating a first orientation and/or a first position for a plurality of bed boundaries. Additional steps may call for utilizing the first orientation and/or the first position and/or first material property to compute the log. Additional steps may comprise comparing the so-computed log with a measured log from the instrument. The method may further comprise iteratively varying at least one of the first material property, the first orientation, and/or the first position for at least one of the plurality of bed boundaries and/or beds and subsequently comparing until the log is within a convergence criteria of the measured log.

