Method for determining the placement of perforations in a well casing

• US 4,631,677 A
• Filed: 06/01/1984
• Issued: 12/23/1986
• Est. Priority Date: 06/01/1984
• Status: Expired due to Term

• Current Assignee: Halliburton Energy Services Incorporated (Halliburton Company)
• Original Assignee: Diamond Oil Well Drilling Company Incorporated
• Inventors: Wilson, Bob T., Park, Arthur
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Meyer, Charles B.
• Application Number:
  US06/616,410
• Time in Patent Office: 935 Days
• Field of Search: 364/422, 364/420, 250/253, 250/256, 73/38, 73/151, 73/152, 73/153, 73/155, 175/59, 175/40, 324/376, 367/31, 367/35
• US Class Current: 702/13
• CPC Class Codes: E21B 25/06 the core receiver having a flexible liner or inflatable retaining means
• CPC Class Codes: E21B 25/08 Coating, freezing, consolidating cores E21B25/06 takes precedence; Recovering uncontaminated cores or cores at formation pressure
• CPC Class Codes: E21B 49/00 Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells
• CPC Class Codes: E21B 49/02 by mechanically taking samples of the soil

Abstract

A method for determining the productivity of a well site includes extracting a core with sponge coring techniques and measuring the parameters of the core. The parameters measured are porosity, permeability and percent mobile oil. A core factor is calculated which is the square root of the product of permeability and porosity and indicates the space available in the core for oil production. The core factor is multiplied by the percent mobile oil to provide a Production Index. The Production Index indicates the capacity of a given oil well to produce oil. With the Production Index data, perforations are selectively placed in various areas along the longitudinal axis of a well casing (38) to selectively allow communication between the interior of the well casing and a formation of interest. In this manner, only areas having high oil mobility are communicated within a given region of the formation of interest.

Claims

1. A method for determining the productivity of a well site, comprising:

extracting a representative core sample of a formation of interest from the well site utilizing sponge coring techniques, the portion of the total oil that bleeds out of the core sample absorbed by the sponge utilized in sponge coring techniques;

measuring the porosity of the core sample at predetermined depth increments;

measuring the fraction of the core space in the core sample occupied by total oil at each of the predetermined depth increments, the total oil equal to the oil remaining in the core on the surface of the well in addition to the oil that bleeds out of the core sample upon extraction thereof, the fraction equal to the percent mobile oil;

determining a Production Index to indicate the producibility of the well as a function of depth increments, the Production Index varying directly with the product of the porosity, permeability and percent mobile oil; and

placing a well casing in a well that is disposed in the formation of interest and placing perforations in the well casing at selected positions determined by the Production Index such that the selected perforations are located at depths having a Production Index greater than a predetermined number along the formation of interest.

2. The method of claim 1 and further comprising determining the percent of water saturation in the core.

3. The method of claim 2 wherein the Production Index further varies inversely with respect to the water saturation.

4. The method of claim 1 wherein the Production Index is equal to the square root of the product of the permeability and porosity multiplied by the percent mobile oil.

5. A method for determining the productivity of a well site, comprising:

extracting a representative core sample of a formation of interest from the well with sponge coring techniques such that the sponge traps fluids that bleed off from the core samples;

measuring the porosity of the core sample at predetermined depth increments;

measuring the permeability of the core sample at each of the predetermined depth increments;

measuring the oil saturation in the core sample at the predetermined depth increments, the oil saturation equal to the percent of the pore space of the core sample which is occupied by oil;

measuring the percentage of oil in the pore space absorbed by the sponge at each of the predetermined depth increments;

calculating the total percentage of oil saturation which is equal to the sum of the oil in the core plus the oil in the sponge as a percent of the pore space of the core sample at the predetermined depth increments;

calculating percent mobile oil, the percent mobile oil equaling the fraction of the total percentage of oil saturation that is absorbed by the sponge as a percentage;

calculating a core factor, the core factor equaling the square root of the product of the porosity times the permeability;

calculating the Production Index, the Production Index equaling the product of the core factor and the percent mobile oil;

the Production Index providing an indication of the producibility of a well, a high value for the Production Index indicating a more producible zone than a low value;

placing a well casing in the well; and

disposing perforations in the walls of the well casing as a function of peaks in the Production Index where the value of the Production Index is greater than a predetermined value.

6. The method of claim 5 and further comprising measuring the water saturation of the core sample at the predetermined depth increments and calculating the Productivity Index to equal the product of the core factor and the percent mobile oil divided by the percent water saturation.

7. A method for placement of perforations in a well casing to maximize producibility in a well site, comprising:

extracting a representative core sample of a formation of interest in the well;

measuring the porosity of the core sample at predetermined depth increments;

measuring the permeability of the core sample at each of the predetermined depth increments;

measuring the fraction for the pore space in the core sample occupied by total oil at each of the predetermined depths, the total oil equal to the oil remaining in the core on the surface of the well in addition to the oil that bleeds out of the core sample upon extraction thereof, the fraction equal to the percent mobile oil;

determining a Production Index to indicate the productivity of the well, the Production Index varying directly with the product of porosity, permeability and percent mobile oil and as a function of the predetermined depth increments;

placing a well casing in the well; and

perforating the well casing at locations determined by the Production Index such that the perforations are placed at depths having a Production Index that is greater than a predetermined value such that perforations are located proximate peaks in the value of the production index rather than valleys in the value thereof.

8. The method of claim 7 wherein the step of extracting a representative core sample comprises utilizing sponge coring technique with a sponge disposed around the core such that the portion of the total oil that bleeds out of the core sample is absorbed by the sponge.

9. The method of claim 7 and further comprising determining the percent of water saturation in the core.

10. The method of claim 7 wherein the Production Index further varies inversely with respect to the water saturation of the core.

11. The method of claim 7 wherein the Production Index is equal to the square root of the product of the permeability and porosity multiplied by the percent mobile oil.

12. A method for placement of perforations in a well casing to maximize production in a well site, comprising:

extracting a representative core sample of a formation of interest from the well with sponge coring techniques such that the sponge utilized in the sponge coring techniques traps fluids that bleed off from the core samples as a result of removing the core sample from a high pressure region at the depths of the well to a low pressure region at the service of the well;

measuring the porosity of the core sample at predetermined depth increments along its longitudinal axis;

measuring the permeability of the core sample at each of the predetermined depth increments;

measuring the oil saturation in the core sample at the predetermined depths, the oil saturation equal to the percent of the pore space of the core sample which is occupied by oil;

measuring the percentage of oil in the pore space absorbed by the sponge at each of the predetermined depth increments;

calculating the total percentage of oil saturation which is equal to the sum of the oil in the core plus the oil in the sponge as a percent of the pore space of the core sample at the predetermined depth increments;

calculating percent mobile oil, the percent mobile oil equaling the fraction of the total oil saturation that bleeds into the sponge as a percentage;

calculating a core factor, the core factor equaling the square root of the product of the porosity times the permeability;

calculating the Productivity Index, the Productivity Index equaling the product of the core factor and the percent mobile oil;

the Production Index providing an indication of the productivity of a well, a high value for the Production Index indicating a more producible zone than a low value;

placing a well casing in the well; and

perforating the well casing at locations determined by the Production Index such that the perforations are placed at depths having a Production Index that is greater than a predetermined value such that perforations are located proximate peaks in the value of the Production Index rather than valleys in the value thereof.

13. The method of claim 12 and further comprsing measuring the water saturation of the core sample at the predetermined depth increments and calculating the Productivity Index to equal the product of the core factor and the percent mobile oil divided by the product of the percent water saturation and a constant.