METHOD FOR PLACING CEMENT IN A WELL

• US 3,866,683 A
• Filed: 02/01/1974
• Issued: 02/18/1975
• Est. Priority Date: 02/01/1974
• Status: Expired due to Term

• Current Assignee: George P. Maly, Paul W. Fischer
• Original Assignee: George P. Maly, Paul W. Fischer
• Inventors: Maly, George P., Fischer, Paul W.
• Primary Examiner(s): Purser, Ernest R.
• Assistant Examiner(s): Ebel, Jack E.
• Application Number:
  US05/438,526
• Time in Patent Office: 382 Days
• Field of Search: 166/285,291,292,312
• US Class Current: 166/292
• 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: E21B 33/14 for cementing casings into boreholes

Abstract

The integrity and strength of cement placed in a well drilled with a drilling fluid containing an ingredient that deleteriously affects curing of the cement can be improved by (1) displacing the drilling fluid from the well with a highly gelled aqueous suspension of a hydrated clay that is substantially free of deleterious agents and that has a density at least equal to that of the drilling fluid, (2) introducing a cement slurry into the well, and (3) displacing the cement slurry to the proper location in the well with an additional quantity of highly gelled, aqueous hydrated clay suspension. The gelled preflush fluid can contain an abradant solid to facilitate the removal of the filter cake from the wall of the borehole. Also, filter cake removal can be facilitated by jetting the gelled preflush fluid against the borehole wall.

Claims

1. A METHOD FOR PLACING CEMENT IN A WELL DRILLED WITH A DRILLING MUD CONTAINING AGENTS THAT DELETERIOUSLY AFFECT THE SETTING OF THE CEMENT, WHICH COMPRISES:

DISPLACING THE DRILLING MUD FROM THE WELL WITH A PREFLUSH FLUID COMPRISING A HIGHLY GELLED AQUEOUS SUSPENSION OF A HYDRATED CLAY THAT IS SUBSTANTIALLY FREE OF THE DELETERIOUS CEMENT RETARDING AGENTS AND THAT HAS A DENSITY AT LEAST EQUAL TO THAT OF THE DRILLING MUD;

PUMPING A CEMENT SLURRY INTO THE WELL;

DISPLACING THE CEMENT SLURRY TO A DESIRED LOCATION IN THE WELL WITH A DISPLACING FLUID COMPRISING A HIGHLY GELLED AQUEOUS SUSPENSIONOF A HYDRATED CLAY THAT IS SUBSTANTIALLY FREE OF THE DELETERIOUS CEMENT RETARDING AGENTS;

AND PERMITTING SAID CEMENT TO SET IN SAID WELL.

2. The method defined in claim 1 wherein said preflush fluid exhibits a Fann viscosity of at least about 250 seconds and a yield above about 40.

3. The method defined in claim 1 wherein said hydratable clay is bentonite.

4. The method defined in claim 1 wherein said preflush fluid also contains a weighting agent to increase the density of said fluid.

5. The method defined in claim 4 wherein said weighting agent is selected from the group consisting of barites and calcium carbonate.

6. The method defined in claim 1 wherein said preflush fluid also contains an abrasive solid material.

7. The method defined in claim 1 wherein a stream of said preflush fluid is jetted against the wall of said well to remove the mud cake therefrom.

8. A method for placing cement in a well drilled with a drilling mud containing agents that deleteriously affect the setting of the cement, which comprises:

displacing the drilling mud from the well with a preflush fluid comprising a highly gelled aqueous suspension of bentonite that is substantially free of deleterious cement retarding agents and that contains a weighting material in an amount sufficient to increase the density of said fluid to at least equal to that of the drilling mud, said preflush fluid exhibiting a Fann viscosity of at least about 250 seconds and a yield above about 35;

pumping a cement slurry to the well;

displacing the cement slurry to a desired location in the well with a displacing fluid comprising a highly gelled aqueous suspension of bentonite that is substantially free of the deleterious cement retarding agents; and

permitting said cement to set in said well.

9. The method defined in claim 8 wherein said weighting agent is selected from the group consisting of barites and calcium carbonate.

10. The method defined in claim 8 wherein said preflush fluid contains an abrasive solid material.

11. The method defined in claim 8 wherein a stream of said preflush fluid is jetted against the wall of said well to remove the mud cake therefrom.