METHOD OF AND APPARATUS FOR MEASURING IN SITU THE FORMATION FACTOR

• US 3,728,622 A
• Filed: 09/28/1971
• Issued: 04/17/1973
• Est. Priority Date: 09/28/1971
• Status: Expired due to Term

• Current Assignee: Cecil E. Williams
• Original Assignee: Cecil E. Williams
• Inventors: Williams, Cecil E.
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US05/184,446
• Time in Patent Office: 567 Days
• Field of Search: 324/1,3,4,9,10,64,65,62 340/4E
• US Class Current: 324/71.1
• CPC Class Codes: G01V 3/06 using ac
• CPC Class Codes: Y02A 90/30 Assessment of water resources

Abstract

A method of and apparatus for measuring in situ the formation factor is disclosed. The formation factor is the ratio of the resistivity of a water saturated sediment to the resistivity of the interstitial water of the sediment. To this end the sediment is insulated from the water by an insulating sheet provided with a circumferential electrode and two opposed electrodes disposed on opposite surfaces of the sheet. By applying an alternating current between these three electrodes the ratio of the resistivity between the electrode in contact with the sediment and the circumferential or counter electrode on the one hand and the resistivity between the opposed electrode in contact with the water and the counter electrode may be measured. This may conveniently be effected by a Wheatstone bridge to which an alternating current is applied. The bridge may be balanced by adjusting one of the resistors thereby to measure the ratio of the resistance of the sediment to the resistance of the water. The electrode arrangement may be modified to form in essence a sled which may be moved by a boat or a ship across the watersediment interface.

Claims

1. Apparatus for measuring in situ the formation factor at the interface of a body of water and a sediment comprising:

a. an insulating member of elongated shape having two opposed, substantially flat surfaces;

b. a first counter electrode surrounding at least a portion of the circumference of said member and adapted to be in contact with the water and with the sediment;

c. a second electrode disposed on one surface of said member and adapted to be in contact with the water;

d. a third electrode disposed on the opposite surface of said member and adapted to be in contact with the sediment to be measured; and

e. apparatus coupled to said electrodes and including an electronic oscillator for measuring the ratio of the resistance between said first and said third electrode on the one hand and that between said first and second electrode on the other hand, the smallest lateral dimension of said member extending beyond said third electrode being no less than the desired depth of penetration into the sediment of the alternating current generated by said oscillator, thereby to determine directly the formation factor.

2. Apparatus as defined in claim 1 wherein said second and said third electrodes are each of hemispherical shape.

3. Apparatus as defined in claim 1 wherein said second and said third electrodes each project from opposite sides of said member into the water and the sediment respectively.

4. Apparatus as defined in claim 1 wherein said second and third electrodes are substantially flat.

5. Apparatus as defined in claim 1 wherein said insulating member has a conductivity less than that of the water.

6. Apparatus as defined in claim 1 wherein said member is of substantially circular shape.

7. Apparatus as defined in claim 6 wherein said first electrode extends over the entire circumference of said member and is of circular shape.

8. Apparatus as defined in claim 1 wherein said insulating member is of an elongated shape having a curved portion and an opposite flat portion and wherein said first electrode is substantially U-shaped.

9. An electrode arrangement for measuring in situ the formation factor at the interface of a body of water and a sediment comprising:

a. an elongated, insulating member having two opposed, substantially flat surfaces;

b. a first counter electrode surrounding at least a portion of the circumference of Said member and adapted to be in contact with the water and with the sediment;

c. a second water-resistance measuring electrode disposed on one surface of said member and adapted to be in contact with the water, and d. a third sediment-resistance measuring electrode disposed on the opposite surface of said member and adapted to be in contact with the sediment, said second and third electrodes having substantially identical forms, said member extending beyond said third electrode in all directions by no less than the desired depth of penetration into the sediment of an applied alternating current.

10. An electrode arrangement as defined in claim 9 wherein said second and third electrodes are each substantially of hemispherical shape.

11. An electrode arrangement as defined in claim 9 wherein said second and third electrodes are substantially flat.

12. An electrode arrangement as defined in claim 9 wherein said insulating member has one upturned end portion whereby said electrode arrangement is adapted to be dragged across said interface.

13. The method of measuring in situ the formation factor at the interface of water and a sediment comprising the steps of:

a. insulating a first predetermined area at the interface of water and the sediment to be measured;

b. applying a first alternating current between the circumference of the insulated area and a second area small compared to the predetermined area and disposed between the insulated area and the water;

c. applying a second alternating current between the circumference of the insulated area and a third area small compared to the predetermined area and disposed between the insulated area and the sediment, the distance between the third area and the outer edge of the first area being no less than the desired depth of penetration into the sediment of the second alternating current; and

d. determining the ratio of the resistances of the sediment and water by determining the ratio of the resistances encountered by the second and first alternating currents, thereby to obtain the formation factor.