Wells – Processes – Cementing – plugging or consolidating
Reexamination Certificate
2002-12-16
2003-12-23
Marcantoni, Paul (Department: 1755)
Wells
Processes
Cementing, plugging or consolidating
C166S293000
Reexamination Certificate
active
06666268
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to methods and oil-based settable drilling fluid compositions for drilling and cementing wells.
2. Description of the Prior Art
Hydraulic cement compositions are commonly utilized in the construction of oil and gas wells. For example, hydraulic cement compositions are used in primary cementing operations whereby strings of pipe such as casings and liners are cemented in well bores. In performing primary cementing, a hydraulic cement composition is pumped into the annular space between the walls of a well bore and the exterior surfaces of a pipe string disposed therein. The cement composition is permitted to set in the annular space thereby forming an annular sheath of hardened substantially impermeable cement therein. The cement sheath physically supports and positions the pipe string in the well bore and bonds the exterior surfaces of the pipe string to the walls of the well bore whereby the undesirable migration of fluids between zones or formations penetrated by the well bore is prevented.
A variety of drilling fluids are used in drilling wells. Oil-based drilling fluids are commonly used in applications where the permeabilities of producing formations would be damaged if the formations were contacted by water-based drilling fluids. However, it has heretofore been common place in the industry to use water-based settable spotting fluids which are incompatible with the oil-based drilling fluids and often cause well bore stability problems and damage to the permeability of producing formations.
During the drilling of a well bore, the drilling fluid used is circulated through the drill pipe and drill bit and then upwardly through the well bore to the surface. The drilling fluid functions to lubricate the drill bit and carry cuttings to the surface where the cuttings and gas are removed from the drilling fluid. Heretofore, drilling fluids were not settable, i.e., they did not set into hard impermeable sealing masses when static. However, conventional drilling fluids do generally increase in gel strength over time. Typically, after a well bore is drilled to total depth, the drill pipe and drill bit are withdrawn from the well bore and the drilling fluid is left in the well bore to provide hydrostatic pressure on permeable formations penetrated by the well bore thereby preventing the flow of formation fluids into the well bore.
The next operation in completing the well bore usually involves running a pipe string, e.g., casing, into the well bore. Depending upon the depth of the well bore and whether or not problems are encountered in running the pipe string therein, the drilling fluid may remain relatively static in the well bore for a time period up to 2 weeks. During that time, the stagnate, conventional drilling fluid progressively increases in gel strength whereby portions of the drilling fluid in the well bore become increasingly difficult to displace during the cementing process.
After the pipe string has been run in the well bore, the next operation performed is usually primary cementing. That is, the pipe string disposed in the well bore is cemented by pumping a cement composition through the pipe string and into the annulus between the pipe string and the walls of the well bore whereby the drilling fluid in the annulus is displaced therefrom by the cement composition. While a variety of techniques have been developed for improving the displacement of the drilling fluid from the annulus, if the drilling fluid has developed gel strength due to remaining static in the well bore for a long period of time, portions of the drilling fluid in the well bore are bypassed by the cement composition. Since the conventional drilling fluid is not settable, i.e., it does not set into a rigid mass, formation fluids enter and flow in the well bore and this is highly undesirable.
Heretofore, settable spotting fluid compositions have been developed and used in wells for various purposes including the early displacement of drilling fluids from well bores. Water-based settable spotting fluids have included blast furnace slag and other hydraulic components which slowly set at relatively low temperatures. Slag-containing settable spotting fluids are intolerant to cement contamination; i.e., if well cement mixes with such spotting fluids, the spotting fluids prematurely set. To prevent a slag-containing spotting fluid from prematurely setting, a very strong set retarder must be added to the spotting fluid and the spotting fluid must be separated from the cement composition by a spacer fluid. If intermixing between the cement composition and the set retarded fluid occurs, the cement composition may be prevented from setting by the strong set retarder in the spotting fluid.
Oil-based settable spotting fluids have been developed which can be utilized in wells drilled with oil-based fluids and avoid well cementing problems of the types described above. However, the use of spotting fluids is an additional step in the process and may still leave some fractures with conventional, unsettable drilling fluid. Thus, there are needs for settable drilling fluid compositions which can be used for both drilling and cementing and that can avoid the problems described above.
SUMMARY OF THE INVENTION
By the present invention, methods of using oil-based settable drilling fluids and oil-based settable drilling fluid compositions are provided which meet the above described needs and overcome the deficiencies of the prior art. The methods of drilling a well bore and cementing a pipe string in the well bore basically comprise the following steps. An oil-based settable drilling fluid is prepared comprising an oil external emulsion which comprises oil, water and an emulsifying surfactant; a hydraulically settable component; and a de-emulsifying surfactant for de-emulsifying the oil-external emulsion when the emulsion is cured. The oil-based settable drilling fluid composition is then used to drill the well bore. The pipe string to be cemented is run into the well bore, the settable drilling fluid is displaced out of the pipe string and the settable drilling fluid in the annulus between the pipe string and the walls of the well bore is allowed to set into a hard impermeable mass.
The oil-based settable spotting fluid compositions of this invention for use in drilling and cementing wells basically comprise the following components: an oil external emulsion comprising oil, water and an emulsifying surfactant; a hydraulically settable component; and a de-emulsifying surfactant for de-emulsifying the oil-external emulsion when the emulsion is cured.
The objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows.
DESCRIPTION OF PREFERRED EMBODIMENTS
Preferred methods of this invention for drilling well bores and cementing pipe strings in the wells basically comprise the following steps. An oil-based settable drilling fluid is prepared comprising an oil external emulsion which comprises oil, water and an emulsifying surfactant; a hydraulically settable component; and a de-emulsifying surfactant for de-emulsifying the oil-external emulsion when the emulsion is cured. The oil-based settable drilling fluid composition is then used to drill the well bore. The pipe string to be cemented is run into the well bore. Drilling fluid is displaced out of the pipe string, and the settable drilling fluid in the annulus between the pipe string and the walls of the well bore is allowed to set into a hard impermeable mass.
The oil-based settable drilling fluid is prepared by combining a known volume of oil and emulsifying surfactant, or surfactants, which are completely mixed with the oil for uniform dispersion of the surfactant(s) in the oil. An activator, if present, is added to a known volume of water to form a slurry. The water slurry is added to the oil containing the surfactant(s) and the resulting mixture is agitated until a smooth oil-ex
Chatterji Jiten
Dennis, Jr. John L.
Griffith James E.
King Bobby J.
Dougherty, Jr. C. Clark
Halliburton Energy Service,s Inc.
Marcantoni Paul
Roddy Craig W.
LandOfFree
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