Use of dual density spacer fluids to improve cementing efficiency in horizontal wellbores

• US 5,402,849 A
• Filed: 11/01/1993
• Issued: 04/04/1995
• Est. Priority Date: 09/28/1992
• Status: Expired due to Fees

• Current Assignee: Mobil Oil Corporation (Exxon Mobil Corporation)
• Original Assignee: Mobil Oil Corporation (Exxon Mobil Corporation)
• Inventors: Jennings, Alfred R. Jr.
• Primary Examiner(s): Suchfield, George A.
• Application Number:
  US08/143,707
• Time in Patent Office: 519 Days
• Field of Search: 166/50, 166/285, 166/291, 166/292, 166/312
• US Class Current: 166/291
• CPC Class Codes: C09K 8/42 Compositions for cementing, e.g. for cementing casings into boreholes; Compositions for plugging, e.g. for killing wells compositions for plastering C09K8/50
• CPC Class Codes: C09K 8/424 using "spacer" compositions
• CPC Class Codes: E21B 33/14 for cementing casings into boreholes

Abstract

A well completion process for improved cement placement in a horizontal wellbore. Initially, a cleaning fluid is circulated down the wellbore for conditioning and cleaning it. Afterwards, a production tube containing centralizers is positioned centrally within the wellbore. Next, "spacer fluids" of higher and lower densities are circulated within an annulus formed by the space between the tube and the wellbore so as to more substantially clean the annulus out. Subsequently, a cement having a density greater than the spacer fluid is pumped into the annulus. Thereafter, a light weight cement is pumped into the annulus thereby overriding the heavier cement and removing voids in the annulus resulting in more efficient cement placement.

Claims

1. A well completion process for improved cement placement in a horizontal wellbore located in a formation comprising:

a) circulating a cleaning fluid down the wellbore in an amount and for a time sufficient to condition and clean it for cementing a production tubing or casing in place;

b) directing a production tubing with centralizers therearound into the wellbore thereby locating the tubing centrally within the wellbore;

c) directing a first cement spacer fluid of a known density down an annulus formed between the tubing and wellbore so as to substantially clean-out the wellbore;

d) ceasing the introduction of the first cement spacer fluid down said annulus thereby allowing said first cement spacer fluid to equilibrate;

e) introducing into said annulus a second cement spacer fluid having a specific gravity of at least 0.1 less than the specific gravity of said first cement spacer fluid whereby said second cement spacer fluid overrides said first spacer fluid so as to contact contaminants in the top section of said annulus while said first fluid contacts contaminants in the bottom section of said annulus;

f) ceasing the introduction of said second cement spacer fluid into the annulus and allowing both fluids to equilibrate;

g) removing both cement spacer fluids containing said contaminants from said wellbore thereby cleaning said annulus;

h) directing a first cement slurry down the annulus and up the tubing which cement slurry has a density greater than the cement spacer fluid and is in an amount sufficient to fill the annulus; and

i) directing a second cement slurry down the annulus which cement slurry has a density less than the density of the first cement slurry and which overrides the first cement slurry thereby filling any voids that were unfilled by the first cement slurry so as to effectively isolate the casing from the formation.

2. The method as recited in claim 1 where said first spacer fluid is selected from a member of the group consisting of aqueous potassium chloride, sodium chloride, calcium chloride, zinc chloride, potassium bromide, sodium bromide, calcium bromide, and zinc bromide.

3. The method as recited in claim 1 where said second fluid is selected from a member of the group consisting of diesel fuel, kerosene, xylene, aqueous potassium chloride, sodium chloride, and calcium chloride.

4. The method as recited in claim 1 where after step g), steps c) through f) are repeated and additional wellbore volumes of said fluids are introduced into said wellbore and removed.

5. The method as recited in claim 1 where the apparent viscosities of the first and second fluids in said annulus are less than about 100 cps at the temperature existing in said wellbore.

6. The method as recited in claim 1 wherein said second fluid has a specific gravity range of about 0.50 to about 1.20 at room temperature.

7. The method as recited in claim 1 where the first fluid has a viscosity of about 5 to about 80 times greater than the viscosity of the second fluid.

8. The method as recited in claim 1 where in step c) the first cement spacer fluid has a specific gravity of about 1.0 to about 1.4 at room temperature.

9. The method as recited in claim 1 where in step c) said first fluid mixes with solid contaminants and said contaminants remain suspended in the first fluid.

10. The method as recited in claim 1 where the apparent viscosities of the first and second fluids in said annulus are less than about 100 cps at the temperature existing in said wellbore and where the first cement slurry comprises a hydraulic cement and the second cement slurry comprises a light weight or foamed cement.

11. The method as recited in claim 1 where the first spacer fluid has a viscosity of about 5 to about 80 times greater than the viscosity of the second fluid and where the first cement slurry comprises a hydraulic cement and the second cement slurry comprises a light weight or foamed cement.