Method for gravel pack evaluation

• US 4,587,423 A
• Filed: 07/31/1984
• Issued: 05/06/1986
• Est. Priority Date: 07/31/1984
• Status: Expired due to Term

• Current Assignee: Schlumberger Technology Corporation (SLB)
• Original Assignee: Schlumberger Technology Corporation (SLB)
• Inventors: Boyce, James R.
• Primary Examiner(s): FIELDS, CAROLYN
• Application Number:
  US06/636,307
• Time in Patent Office: 644 Days
• Field of Search: 250/269, 250/262, 250/256, 364/422
• US Class Current: 250/269.3
• CPC Class Codes: E21B 43/04 Gravelling of wells
• CPC Class Codes: E21B 47/00 Survey of boreholes or wells monitoring pressure or flow of drilling fluid E21B21/08
• CPC Class Codes: G01V 5/12 using gamma or X-ray sources gamma sources using isotopes G21G4/00; X-ray tubes H01J35/00

Abstract

Based on Monte Carlo modeling of gravel pack conditions in a completed borehole, a straightforward expression for the determination of percent packing as a function of known or measurable borehole quantities is derived, from which an accurate quantitative gravel pack log may be obtained for purposes of evaluating gravel pack quality. The method includes using a logging tool with a gamma source and gamma detector.

Claims

1. A method for investigating a gravel pack located in the annulus between the tubing/screen and the casing of a borehole, comprising the steps of:

moving a logging tool, including a gamma ray source and at least one gamma ray detector, through the tubing/screen over the depth region of the gravel pack;

deriving a measurement (N'"'"'_T,S) of the number of gamma rays detected by said detector over a predetermined time interval; and

determining the percent packing (P) of the gravel pack at the depth of measurement in accordance with the relationship;

##EQU4## where ##EQU5## ρ

_f and ρ

_m are the density of the fluid and the material, respectively, in the annulus between the tubing/screen and the casing of the borehole;

v'"'"'_f is the volume fraction of the fluid in the annulus between the tubing/screen and the casing of the borehole;

A'"'"'_T,S is a previously determined constant A'"'"'_T or A'"'"'_S depending upon whether the depth of measurement is opposite the tubing or the screen;

B'"'"'_T,S is a previously determined constant B'"'"'_T or B'"'"'_S depending upon whether the depth of measurement is opposite the tubing or the screen; and

N'"'"'_T,S is said measured number of detected gamma rays N'"'"'_T or N'"'"'_S depending upon whether the depth of measurement is opposite the tubing or the screen.

2. The method of claim 1 further comprising the step of recording the percent packing determination as a function of depth within the borehole.

3. A method for investigating a gravel pack located in the annulus between the tubing/screen and the casing of a borehole, comprising the steps of:

deriving a measurement (N'"'"'_T,S) of the number of gamma rays detected in a predetermined time interval by a gamma ray detector located within the tubing/screen as a result of irradiation of the borehole by a gamma ray source located within the tubing/screen; and

determining the percent packing (P) of the gravel pack at the depth of measurement in accordance with the relationship;

##EQU6## where ##EQU7## ρ

_f and ρ

_m are the density of the fluid and the material, respectively, in the annulus between the tubing/screen and the casing of the borehole;

v'"'"'_f is the volume fraction of the fluid in the annulus between the tubing/screen and the casing of the borehole;

A'"'"'_T,S is a previously determined constant A'"'"'_T or A'"'"'_S depending upon whether the depth of measurement is opposite the tubing or the screen;

B'"'"'_T,S is a previously determined constant B'"'"'_T or B'"'"'_S depending upon whether the depth of measurement is opposite the tubing or the screen; and

N'"'"'_T,S is said measured number of detected gamma rays N'"'"'_T or N'"'"'_S depending upon whether the depth of measurement is opposite the tubing or the screen.

4. The method of claim 3 further comprising the step of recording the percent packing determination as a function of the depth within the borehole.