Stand-off compensated formation measurements apparatus and method

• US 5,250,806 A
• Filed: 03/18/1991
• Issued: 10/05/1993
• Est. Priority Date: 03/18/1991
• Status: Expired due to Term

• Current Assignee: Schlumberger Technology Corporation 5000 Gulf Freeway
• Original Assignee: Schlumberger Technology Corporation (Schlumberger NV)
• Inventors: Holenka, Jacques M., Evans, Michael, Rhein-Knudsen, Erik
• Primary Examiner(s): FIELDS, CAROLYN
• Application Number:
  US07/670,819
• Time in Patent Office: 932 Days
• Field of Search: 250/254, 250/264, 250/265, 250/266, 250/268, 250/269, 250/270
• US Class Current: 250/254
• CPC Class Codes: E21B 17/1078 Stabilisers or centralisers for casing, tubing or drill pipes devices for off-center positioning E21B17/10; E21B17/1007 - E21B17/1064 take precedence
• CPC Class Codes: E21B 47/01 Devices for supporting measuring instruments on drill bits, pipes, rods or wirelines; Protecting measuring instruments in boreholes against heat, shock, pressure or the like
• CPC Class Codes: E21B 47/085 using radiant means, e.g. acoustic, radioactive or electromagnetic
• CPC Class Codes: G01V 5/08 using primary nuclear radiation sources or X-rays , e.g. for inducing radioactivity; investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays, neutrons G01N23/00

Abstract

Apparatus and method for measuring density, porosity and other formation characteristics while drilling is disclosed. The apparatus, preferably housed in a drill collar and placed within a drill string, includes a source of neutrons and a source of gamma rays placed within a tubular body which is adapted to provide for the flow of drilling through it. Two sets of stabilizer blades are provided. One set, associated with the neutron source, includes secondary radiation detectors that are placed radially beyond the nominal outer radius of the body. Formation porosity measurement accuracy is substantially enhanced since the standoff of the detectors from the formation is substantially decreased. Another set, associated with the gamma ray source, includes one or more gamma ray detection assemblies in a single blade. Each of the gamma ray detector assemblies is also placed radially beyond the nominal outer radius of the tubular wall. Formation density or absorption coefficient accuracy is substantially enhanced since the standoff between the detection assembly and the borehole wall is decreased. In a particularly preferred embodiment, ultrasonic sensors incorporated either or both sets of blades provide a measurement of the borehole diameter and/or standoff of the detectors from the borehole. The bulk density measurement and neutron porosity measurement data can be corrected with information derived from the standoff or borehole diameter.

Claims

1. Apparatus for measuring characteristics of earth formations surrounding a borehole while drilling tool comprising:

a tubular body having upper and lower ends and adapted to be coupled to a drill string and adapted to provide a fluid flow path between its upper and lower ends, said tubular body having a nominal tubular outer radius, and having a source of neutrons disposed coaxially within said body;

a plurality of stabilizer blades secured symmetrically about the outer periphery of said tubular body, said blades having a maximum outer radius greater than said tubular outer radius, each of said blades having a longitudinal length and an angular width dimensions such that the angular width of each blade is substantially less than the angular distance between each blade;

a plurality of detector cavities in registration with each of said stabilizer blades, each of said cavities formed by an outwardly facing slot of said body which faces an inwardly facing slot of a stabilizer blade, said cavities characterized by an outer radial extend substantially greater than said nominal tubular outer radius,

longitudinally spaced secondary radiation detectors associated with each of said cavities; and

means responsive to said longitudinally spaced radiation detectors to generate first radiation signals useful for determining porosity of said earth formations.

2. The apparatus of claim 1 further comprising:

means including ultrasonic sensors carried by said body for measuring standoff of said body from said borehole, said measuring of standoff being performed while the borehole is being drilled, wherein said determining of porosity from said first radiation signals may be corrected as a function of measured standoff of said body.

3. The apparatus of claim 1 further comprising:

a gamma ray source positioned within said tubular body;

a second plurality of stabilizer blades disposed about the outer periphery of said tubular body, each of said second plurality of stabilizer blades extending radially outwardly from said tubular body at a second maximum radial distance;

at least one gamma ray detection assembly associated with at least one of said second plurality of stabilizer blades, each gamma ray detection assembly placed radially at least partially beyond said nominal outer radius of said tubular wall of said body in an associated gamma ray detection assembly cavity, said gamma ray detection assembly cavity extending radially into an associated blade; and

means responsive to said at least one gamma ray detection assembly to generate second radiation signals useful for determining a second characteristic of said earth formations.

4. The apparatus of claim 3 further comprising:

means including ultrasonic sensors carried by said body for measuring standoff of said body from said borehole, said measuring of standoff being performed while the borehole is being drilled, wherein said determining of porosity from said first radiation signals may be corrected as a function of measured standoff of said body.

5. Apparatus for measuring characteristics of earth formations surrounding a borehole while drilling comprising:

a) a tubular body having upper and lower ends and adapted to be coupled to a drill string and adapted to provide a fluid flow path between its upper and lower ends, said tubular body having a tubular wall with a nominal outer radius and a fin section comprising a plurality of fins of increased outer radius;

b) a neutron source positioned within said tubular body, said source emitting high energy neutrons into the formation which produce secondary radiation as a result of neutron-formation interaction;

c) a first plurality of stabilizer blades disposed about the periphery of said tubular body, each one of said first plurality of stabilizer blades placed about one of said fins, said blades extending radially outwardly from said tubular body at a first maximum radial distance;

d) longitudinally spaced secondary radiation detectors associated with at least one of said fins and said first plurality of stabilizer blades, each secondary radiation detector placed radially at least partially beyond said increased outer radius of at least one of said fins in an associated secondary radiation detector cavity, said secondary radiation detector cavity extending radially into an associated blade;

e) means responsive to said longitudinally spaced secondary radiation detectors to generate first radiation signals useful for determining a first characteristic of said earth formations;

f) a gamma ray source positioned within said tubular body;

g) a second plurality of stabilizer blades disposed about the outer periphery of said tubular body, each of said second plurality of stabilizer blades extending radially outwardly from said tubular body at a second maximum radial distance;

h) at least one gamma ray detection assembly associated with at least one of said second plurality of stabilizer blades, each gamma ray detection assembly placed radially at least partially beyond said nominal outer radius of said tubular wall of said body in an associated gamma ray detection assembly cavity, said gamma ray detection assembly cavity extending radially into an associated blade; and

i) means responsive to said at least one gamma ray detection assembly to generate second radiation signals useful for determining a second characteristic of said earth formations.

6. The apparatus of claim 5 wherein said first characteristic of said earth formations is porosity and wherein said second characteristic of said earth formations is density or photoelectric absorption coefficient.

7. The apparatus of claim 5 wherein said fins are defined by a longitudinal length and a peripheral width;

and wherein each of said first and said second plurality of stabilizer blades includes an outer blade section that is secured to said tubular body and extends radially outwardly from said fins.

8. The apparatus of claim 7 wherein said outer blade section extends beyond each side of said peripheral width of said fins and extends beyond each end of said longitudinal length, whereby said outer blade section envelopes one of said fins.

9. The apparatus of claim 5 wherein said secondary radiation detector cavity is defined by a longitudinal outwardly facing slot in at least one of said plurality of fins and an inwardly facing slot in said outer blade section which is in registration with said outwardly facing slot.

10. The apparatus of claim 5 further comprising:

means for generating standoff signals indicative of the standoff of said at least one gamma ray detection assembly from said surrounding borehole, said means comprising at least one ultrasonic sensor disposed in at least one of said second plurality of stabilizer blades, said at least one ultrasonic sensor facing radially outwardly from said tubular body; and

means for combining said second radiation signals and said standoff signals to correct said second earth formation characteristic.

11. Apparatus for measuring characteristics of earth formations surrounding a borehole while drilling comprising:

a) a tubular body having upper and lower ends and adapted to be coupled to a drill string and adapted to provide a fluid flow path between its upper and lower ends, said tubular body having a tubular wall with a nominal outer radius and a fin section comprising a plurality of fins of increased outer radius;

b) a neutron source positioned within said tubular body, said source emitting high energy neutrons into the formation which produce secondary radiation as a result of neutron-formation interaction;

c) a first plurality of stabilizer blades disposed about the periphery of said tubular body, each one of said first plurality of stabilizer blades placed about one of said fins, said blades extending radially outwardly from said tubular body at a first maximum radial distance, and

a second plurality of stabilizer blades disposed about the periphery of said tubular body, said first and second sets of stabilizer blades being axially separated from each other;

d) longitudinally spaced secondary radiation detectors associated with at least one of said fins and said first plurality of stabilizer blades, each secondary radiation detector placed radially at least partially beyond said increased outer radius of at least one of said fins in an associated secondary radiation detector cavity, said secondary radiation detector cavity extending radially into an associated blade;

e) means responsive to said longitudinally spaced secondary radiation detectors to generate first radiation signals useful for determining a first characteristic of said earth formations;

f) means for generating borehole diameter signals indicative of the diameter of said borehole, said means comprising at least one ultrasonic sensor disposed in at least one of said second plurality of stabilizer blades, said at least one ultrasonic sensor facing radially outwardly from said tubular body; and

g) means for combining said first radiation signals and said borehole diameter signals to correct said first earth formation characteristic.

12. Apparatus for measuring characteristics of earth formations surrounding a borehole while drilling comprising:

a) a tubular body having upper and lower ends and adapted to be coupled to a drill string and adapted to provide a flow path between its upper and lower ends, said tubular body having a tubular wall with a nominal outer radius and a fin section comprising a plurality of fins of increased outer radius;

b) a gamma ray source positioned within said tubular body;

c) a first plurality of stabilizer blades disposed about the outer periphery of said tubular body, each one of said stabilizer blades placed about each one of said plurality of fins, said blades extending radially outwardly from said tubular body at a maximum radial distance, at least one of said first plurality of stabilizer blades being designated as a gamma ray detection blade;

d) at least one gamma ray detection assembly placed radially at least partially beyond said increased outer radius of at least one of said fins in an associated gamma ray detection assembly cavity which extends radially into said gamma ray detection blade;

e) means responsive to said at least one gamma ray detection assembly to generate gamma ray signals useful for determining a first characteristic of said earth formations;

f) at least one ultrasonic sensor disposed in one of said first plurality of stabilizer blades, said at least one ultrasonic sensor facing radially outwardly from said tubular body; and

g) means responsive to said at least one ultrasonic sensor for generating standoff signals indicative of the standoff between said at least one gamma ray detection assembly and said borehole.

13. The apparatus of claim 12 wherein said standoff signals are combined with said gamma ray signals to provide a correction to said first characteristic of said earth formations.

14. The apparatus of claim 12 wherein said stabilizer blade in which said at least one ultrasonic sensor is disposed is a blade other than said gamma ray detection blade.

15. Apparatus for measuring characteristics of earth formations surrounding a borehole while drilling comprising:

a) a tubular body having upper and lower ends and adapted to be coupled to a drill string and adapted to provide a flow path between its upper and lower ends, said tubular body having a tubular wall with a nominal outer radius and a fin section comprising a plurality of fins of increased outer radius;

b) a gamma ray source positioned within said tubular body;

c) a first plurality of stabilizer blades disposed about the outer periphery of said tubular body, each one of said stabilizer blades placed about each one of said plurality of fins, said blades extending radially outwardly from said tubular body at a maximum radial distance, at least one of said first plurality of stabilizer blades being designated as a gamma ray detection blade;

d) at least one gamma ray detection assembly placed radially at least partially beyond said increased outer radius of at least one of said fins in an associated gamma ray detection assembly cavity which extends radially into said gamma ray detection blade;

e) means responsive to said at least one gamma ray detection assembly to generate gamma ray signals useful for determining a first characteristic of said earth formations;

f) at least one ultrasonic sensor disposed in one of said first plurality of stabilizer blades, said at least one ultrasonic sensor facing radially outwardly from said tubular body;

g) means responsive to said at least one ultrasonic sensor for generating standoff signals indicative of the standoff between said at least one gamma ray detection assembly and said borehole,

h) a neutron source positioned within said tubular body, said source emitting high energy neutrons into the formation which produce secondary radiation as a result of neutron-formation interaction;

i) a second plurality of stabilizer blades disposed about the periphery of said tubular body at a vertical distance separated from said first plurality of stabilizer blades, each of said second plurality of stabilizer blades extending radially outwardly from said tubular body;

j) at least one secondary radiation detector associated with at least one of said second plurality of stabilizer blades, each secondary radiation detector placed radially at least partially beyond said nominal outer radius of said tubular wall of said body in a secondary radiation detector cavity, said secondary radiation detector cavity extending radially into an associated stabilizer blade;

k) means responsive to said at least one secondary radiation detector to generate secondary radiation signals useful for determining a second characteristic of said earth formations; and

l) means responsive to said at least one secondary radiation detector to generate secondary radiation signals useful for determining a second characteristic of said earth formations.

16. The apparatus of claim 15 further comprising;

means for generating borehole diameter signals from said at least one ultrasonic sensor indicative of the diameter of said borehole; and

means for combining said borehole diameter signals and said secondary radiation signals to provide a correction to said second characteristic of said earth formations.

17. The apparatus of claim 15 further comprising:

means for generating standoff signals from said at least one ultrasonic sensor indicative of the standoff of said gamma ray detection assembly from said surrounding borehole, and means for generating borehole diameter signals from said at least one ultrasonic sensor indicative of the diameter of said borehole; and

means for combining said standoff signals with said gamma ray signals to correct said first formation characteristic, and means for combining said borehole diameter signals with said secondary radiation signals to correct said second formation characteristic.

18. The apparatus of claim 17 wherein said standoff signals are combined with said gamma ray signals and said borehole diameter signals are combined with said secondary radiation signals in downhole instrumentation and wherein the corrected first and second formation characteristics are transmitted uphole.