OA10549A

OA10549A - A hole-finding apparatus having integrated sensors

Info

Publication number: OA10549A
Application number: OA70159A
Authority: OA
Inventors: Thomas R Stanley; Gary A Hazen
Original assignee: Petroleum Res & Dev Nv
Priority date: 1996-12-05
Filing date: 1997-12-05
Publication date: 2002-05-31

Description

1 010549 20.2661

A HOLE-FINDING APPARATUS HAVING INTEGRATED SENSORS

Background of the Invention 1. Field of the Invention 5 The invention relates to well logging apparatus combined with hole-finding apparatus. 2. Background of the Prior Art

Hole-finding with a transversely flexible device on the bottom of instrumentation 10 or equipment is common in the logistics of downhole measurements. Such a device ischaracteristically constructed of a homogeneous elastomeric or other similariy flexiblematerial. As shown in Figures 1-2, a fundamental form is a slick, tapered profile,uniformly increasing in cross section with proximity to the instrumentation or equipmentto provide increasingly stiffer bending moment against latéral flexure toward the tool 15 end. Multiple variations of material choice, cross-sectional profiles, lengths, andapplications of protubérances are possible. Regardless of the spécifies of themechanical design of such an apparatus, the objective of the apparatus is to guide apiece of equipment or instrumentation down a subsurface hole to its intended locationregardless of the orientation, curvature or size of borehole, or condition, texture or other 20 properties of the borehole wall.

Summary of the Invention

Measuring or sensing the downhole environment electrically, acoustically,mechanically, or by nuclear means, of either the borehole fluid or surrounding 25 subsurface strata (the formation), is well established practice. However, the techniques of measuring the downhole environment and performing the hole-finding 2 010549 fonction are currently mutually exclusive. To combine the ability to measure or sensethe downhole or formation environment actively from within (such as by means of anuclear source/sensor), or as part of a hole-finding apparatus so that such a device canprovide both mechanical and sensing fonctions simultaneously, or serially, is the focusof the présent invention.

One such embodiment is a tool which intégrâtes a sériés of électrodes as aprobe on the tip of the hole-finding apparatus such that the hole-finder can measureborehole fluid resistivity Rm and spontaneous potential Sp as it guides the equipmentthrough the borehole. Orientation and position of the électrodes with respect to eachother and the surrounding environment is germane to the design. Extensive modelinghas shown that the electrode arrangement used herein as an illustratiave and preferredembodiment has a superior measurement quality, minimizing borehole size andproximity effects.

Brief Description of the Drawings

Figure 1 is a view of a prior art hole-finding apparatus having a thread protectorattached.

Figure 2 is a view of the prior art hole-finding apparatus of Figure 1 (with the threadprotector removed), partly in cross-section to show the means for attaching the hole-finder to a logging tool.

Figure 3 is a view of a prior-art probe containing electrode sensors.

Figure 4 is a view of the présent invention with the probe electrode sensors ofFigure 3 integrated into the bottom end of the hole-finder apparatus.

Figure 5 is a cross-section view of the présent invention taken along the line 5-5 ofFigure 4. 3 010549

Description of the Preferred EmbodimentsU. S. Patent 5,574,371 to Tabanou et al describes a probe, shown in Figure 3, that can be integrated into the end of the hole-finding apparatus. This patent disclosure isincorporated by référencé into this disclosure. The measurement probe 26 is securelyconnected and bonded into the bottom (i.e., end) of the hole-finder as shown in Figure 4. (For ease of description, the référencé designators used herein for the probe 26 ofFigures 3-5 are the same as those used in Figure 5 of the '371 patent). Themeasurement probe 26 is adapted for measuring the spontaneous potential Spand theresistivity Rm of a mud in the mud-filled borehole. The measurement probe includes abottom electrode 32 (A 0) disposed on a bottom of the probe 26 when the loggingapparatus is disposed in a borehole, a second electrode 34 (A , ) for measuringspontaneous potential Sp and at least one measurement electrode 36 (Μ , M 2)disposed adjacent the bottom electrode 32 (A 0) for measuring a voltage potential dropin a région of the mud which is disposed directly adjacent and below the bottomelectrode 32 (A 0) of the measurement probe 26. When the measurement probe 26 isenergized, a current flows in the mud between bottom electrode 32 (A 0) and thesecond electrode 34 (A 1 ). The current is initially emitted into the mud from the bottomelectrode 32 (A 0) and flows in a direction which is approximately parallel to alongitudinal axis of the logging apparatus tool string. Since the measurement electrode36 (Μ , M 2) is disposed adjacent the bottom electrode 32 θ), the measurement electrode 36 (M 1 M 2) measures the voltage potential drop, i.e., correlating toresistivity, Rm , in the région of the mud disposed directly below the bottom electrode 32(A „). In addition, the voltage potential drop in such région measured by themeasurement electrode 36 (M , M 2) is controlled by the current being emitted from,or received in, the bottom electrode 32 (A 0) and flowing in such région.

Since the current being initially emitted from, and received in, the bottom electrode32 (A „) of the measurement probe 26 propagates in the mud in a direction which is 4 010549 approximately parallel to a longitudinal axis of the probe 26, only a very small quantityof such current crosses an interface between the mud in the borehole and a formationpenetrated by the borehole. As a resuit, the voltage potential drop being measured bythe measurement electrode 36 (Μ , M 2) is controlled primarily by the potential dropwhich exists in the région of the mud disposed adjacent and directly below the bottomelectrode 32 (A 0). Therefore, even though a large contrast in resistivity may exist at aninterface between the conductive mud in the borehole and the formation penetrated bythe borehole, since most of the current received in and emitted from the bottomelectrode 32 (A 0) faits to cross such interface, that resistivity contrast faits toadversely affect the accuracy of the measurement of the mud resistivity Rm taken bythe measurement probe 26.

The spontaneous potential measurement, Sp , can be made from any of theélectrodes. In this illustrative example, the upper electrode has been chosen due to itssize and proximity to the borehole. The Sp measurement is well known and consists ofmeasuring the DC voltage downhole with respect to an electrode at the surface. Thismeasurement is used for delineating permeable beds, estimating shale content,determining formation water resistivity, and corrélation. It is very advantageous to hâvethis measurement near the bottom extremity of the surveying instrument due to itsfundamental importance and wide usage.

Figures 1 and 2 show views of a prior art hole finder 10, partly in cross-section. Inthese figures, an attachment piece 12 (known as a threaded field joint) having threads13 connects the hole-finder 10 to the bottom of a logging tool (not shown), A material14, such as rubber, forms the body of the hole-finder and engages the attachmentpiece 12 by means of internai geometry (such as shown at 12a of Figure 2) which isconducive to supporting a metal-to-rubber bond. A thread protector 15 protects thethreads 13 during transportation (i.e., non-use) and also serves as a carrying handle.However, with this configuration, a probe (e.g., such as 26 in Figure 3) could not belocated atthe bottom of the hole-finder 10 of Figures 1 and 2 because such a design 5 010549 does not provide a ready means to communicate with such a probe. The capability ofthis tool would be limited to the hole-finding fonction only, and would not provide anyborehole characteristic measuring function. 5 Figures 4 and 5 show an implémentation of the présent invention shown generallyat 10a. A probe such as 26 in Figure 3 is attached to the end of the hole-finder/probe10a. Electrical wires 16 pass through a passageway 19 molded or drilled through thehole-finder/probe 10a. If attachment to the drill string is to be made by means of anattachment piece such as 12 in Figure 2, i.e., by a threaded field joint, the piece 12 10 must be modified by extending the passageway 19 therethrough to provide for communication between the probe 26 électrodes and other measurement equipmentlocated either in the logging tool or at ground level. In the embodiment of Figures 4and 5, the hole-finder/probe 10a is attached directly to the drill string by means of boltsor set-screws (not shown) through boit holes 17 in the insert 18 and communication is 15 made possible by wires 16 through the passageway 19 in the hole-finder/probe 10a.As previously stated, the hole-finder/probe 10a guides the tool through the boreholeand around obstructions and borehole curvatures while the probe 26 makesmeasurements of borehole or formation environment characteristics, i.e., resistivity Rmand spontaneous potential Sp in this illlustrative example. The hole-finder/probe 10a is 20 made of a flexible material 14a, e.g., an elastomeric material such as 90 duro nitrilerubber. Another preferred material is neoprene 80-85 Shore "A" (Maloney Compound330-R supplied by Maloney Technical Products, S&B Technical Products of Fort Worth,Texas). It will be appreciated that the hole-finder can be constructed of other polymers,springs, composites of such, or with other physical materials which provide changing 25 stiffness to latéral forces.

FiGURE 5 is a cross-section view of the hole-finder/probe 10a taken along the line 5-5 of Figure 4. This view is on a section taken through the bolt-holes 17 which receivebolts or set screws (not shown) used to attach the hole-finder/probe 10a to the logging 6 010549 tool (not shown). The boit holes 17 are made through an insert 18 imbedded in theflexible material 14a, the insert 18 being preferably made of low-carbon Steel.

Different physical constructions of this described hole-finder/probe are possible, andit is not intended to be limited to any particular combination of manufacturingprocess/technique, or sequences of processes/techniques in its construction.

The présent invention provides significant advantages over the prior art, namely, itprovides borehole characteristic measurements having little effect on, or influencefrom, the formation while providing the hole-finding capability to assist in navigatingthe tool down a borehole. Additionally, the sense point for the spontaneous potentialSp measurement is moved to the bottom of the sensing instrument, thus allowingformation measurements to be made at the bottom of the borehole.

The invention has been described in connection with the preferred embodiments ofspontaneous potential Sp and mud resistivity measurement Rm apparatus as shown inthis illustrative embodiment. However, it will be appreciated that the invention is notlimited solely to these measurements but can be expanded to measuring otherborehole or formation characteristics with instruments of the aforementioned electrical,acoustic, mechanical or nuclear type, for example. Changes, variations andmodifications to the basic design may be made without departing from the inventiveconcept in this invention. In addition, these changes, variations and modificationswould be obvious to those skilled in the art having the benefit of the foregoing teachingscontained in this application. Ail such changes, variations and modifications areintended to be within the scope of the invention which is limited by the following daims.

Claims

7 010549 We claim:

1. An apparatus adapted to be connected to the bottom of a tool string in aborehole, drilled through an earth formation, for navigating said tool string in saidborehole and for measuring a borehole or formation parameter, comprising: a flexible member attached to the bottom of said tool string for navigating saidtool string in said borehole, said flexible member having a bottom surface extendinginto said borehole below said tool string; and a measuring means included in said bottom of said flexible member formeasuring a borehole or formation characteristic.
2. The apparatus of claim 1 further including: means for acquiring information relating to said borehole or formationcharacteristic and for communicating said information to a point distant from saidapparatus.
3. The apparatus of claim 1 wherein said borehole or formation characteristic isresistivity.
4. The apparatus of claim 1 wherein said borehole or formation characteristic isspontaneous potential.
5. The apparatus of claim 1 wherein said borehole or formation characteristic isdetected by a radiation sensor located within said flexible member.
6. The apparatus of claim 1 wherein said borehole or formation characteristic isdetected by an acoustic sensor located within said flexible member. 8 010549
7. The apparatus of claim 1 wherein said borehole or formation characteristic isdetected by mechanical means.
8. The apparatus of claim 1 wherein said flexible member is tapered toward saidbottom surface of said flexible member and wherein said flexibility of said flexiblemember increases toward said bottom of said flexible member.
9. The apparatus of claim 1 wherein said flexible member is made of anelastomeric material.
10. The apparatus of claim 9 wherein said elastomeric material is rubber.
11. The apparatus of claim 10 wherein said rubber is 90 duro nitrile.
12. The apparatus of claim 9 wherein said elastomeric material is neoprene.
13. The apparatus of claim 1 wherein said measuring means comprises: a first plurality of surfaces included in said bottom surface of said flexiblemember, said plurality of surfaces being occupied by an electrode adapted to measurea borehole or formation characteristic; and a second plurality of surfaces included in said bottom surface of said flexiblemember, said second plurality of surfaces not being occupied by électrodes andproviding séparation between said électrodes.
14. The apparatus of claim 13 wherein a bottom electrode occupying one of said firstplurality of surfaces is adapted to émit a first current into said borehole and a secondelectrode occupying another of said first plurality of surfaces is adapted to receive saidfirst current from said borehole and wherein said second electrode is adapted for 9 010549 emitting a second current into said borehole and said bottom electrode is adapted to receive said second current from said borehole.
15. The apparatus of daim 14 further comprising at least one measurementelectrode occupying still another of said First plurality of surfaces and having ameasurement electrode adjacent said bottom electrode and said borehole adapted formeasuring a voltage potential in said borehole, said voltage potential being determinedby said current flowing in said borehole.
16. The apparatus of daim 15 wherein said first plurality of surfaces including saidbottom electrode surface, said second electrode surface and said measurementelectrode are joined together with said second plurality of surfaces to form onesubstantially continuous bottom surface.
17. The apparatus of daim 15 further comprising a second measurement electrodeoccupying still another of said First plurality of surfaces and having a secondmeasurement electrode surface and disposed adjacent said one measurementelectrode adapted for measuring said voltage potential in said borehole, said Firstplurality of surfaces joining together with said second plurality of surfaces to form onecontinuous measurement electrode surface.
18. The apparatus of daim 14 wherein substantially ail of said First currentpropagates in a direction which is approximately parallel to a longitudinal axis of saidapparatus when said First current is initially emitted from said bottom electrode.
19. The apparatus of daim 14 wherein substantially ail of said second currentpropagates in a direction which is approximately parallel to the longitudinal axis of saidapparatus when said second current is received in said bottom electrode. 10 010549
20. A method for navigating a tool string through a borehole drilled through an earthformation and measuring a characteristic parameter of said borehole or formation,comprising the steps of: integrating a measuring means into the bottom end of a flexible member, saidmeasuring means being adapted to measure a characteristic parameter of saidborehole or formation; attaching said flexible member to the bottom end of a tool string; inserting said tool string and said attached flexible member into said borehole; providing means for communicating between said measuring means and saidtool string; acquiring data relating to said characteristic parameter of said borehole orformation; and communicating said data relating to said characteristic parameter of saidborehole or formation to a point distant from said flexible member.