Earth boring – well treating – and oil field chemistry – Earth boring – Contains organic component
Reexamination Certificate
1999-08-05
2001-10-09
Tucker, Philip (Department: 1712)
Earth boring, well treating, and oil field chemistry
Earth boring
Contains organic component
C507S140000, C507S145000, C507S212000, C507S269000, C507S272000, C507S277000, C507S906000, C507S925000
Reexamination Certificate
active
06300286
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to clay-free aqueous well drilling and servicing fluids, methods of preparation thereof, and method of drilling a well therewith.
The use of fluids for conducting various operations in the boreholes of subterranean oil and gas wells which contact a producing formation are well known. Thus drill-in fluids are utilized when initially drilling into producing formations. Completion fluids are utilized when conducting various completion operations in the producing formations. Workover fluids are utilized when conducting workover operations of previously completed wells.
One of the most important functions of these fluids is to seal off the face of the wellbore so that the fluid is not lost to the formation. Ideally this is accomplished by depositing a filter cake of the solids in the fluid over the surface of the borehole without any loss of solids to the formation. In other words, the solids in the fluid bridge over the formation pores rather than permanently plugging the pores. This is particularly critical in conducting horizontal drilling operations within hydrocarbon containing formations.
Many clay-free fluids have been proposed for contacting the producing zone of oil and gas wells. See for example the following U.S. Patents: Jackson et al. U.S. Pat. No. 3,785,438; Alexander U.S. Pat. No. 3,872,018; Fischer et al. U.S. Pat. No. 3,882,029; Walker U.S. Pat. No. 3,956,141; Smithey U.S. Pat. No. 3,986,964; Jackson et al. U.S. Pat. No. 4,003,838; Mondshine U.S. Pat. No. 4,175,042; Mondshine U.S. Pat. No. 4,186,803; Mondshine U.S. Pat. No. 4,369,843; Mondshine U.S. Pat. No. 4,620,596; Dobson, Jr. et al. U.S. Pat. No. 4,822,500, and Johnson U.S. Pat. No. 5,504,062.
These fluids generally contain polymeric viscosifiers such as certain polysaccharides or polysaccharide derivatives, polymeric fluid loss control additives such as lignosulfonates, polysaccharides or polysaccharide derivatives, and bridging solids. As disclosed in Dobson, Jr. et al. U.S. Pat. No. 4,822,500, a xanthan biopolymer and an epichlorohydrin crosslinked hydroxypropyl starch fluid loss control additive synergistically interact to provide suspension and fluid loss control in certain of these fluids.
Magnesium oxide has been disclosed for use in various polysaccharide-containing fluids to increase the thermal stability thereof. See for example the following U.S. patents: Jackson U.S. Pat. No. 3,852,201; Jackson U.S. Pat. No. 3,953,335; Hartfield U.S. Pat. No. 3,988,246; Jackson U.S. Pat. No. 4,025,443; and Dobson, Jr. U.S. Pat. No. 5,514,644.
It is well known that certain biopolymer-containing fluids are shear thinning, exhibiting a high low shear rate viscosity and a low high shear rate viscosity. A near zero shear rate (0.06 to 0.11 sec
−1
) viscosity provides a numerical value related to the ability of a fluid to suspend particles or cuttings under static conditions. Conversely, viscosity measured at shear rates above 20 sec
−1
relates to the hole cleaning capability of a fluid under annular flow conditions.
It is known to use dense brines as the base aqueous liquid for high density drilling and well servicing fluids. Such fluids contain minimal soluble bridging solids concentration and viscosifying polymer additives. The most commercially available dense brines contain calcium chloride, calcium bromide, and zinc bromide. However, utilization of the brines has been limited. Generally, water-soluble polymers used for viscosity and filtration control do not perform well in calcium bromide and zinc bromide brines. Examples of the use of dense brines for use in well drilling and servicing fluids are as follows: Swartwout et al. U.S. Pat. No. 5,612,293; Dobson, Jr. et al. U.S. Pat. No. 5,616,541; Dobson, Jr. et al. U.S. Pat. No. 5,728,652; Dobson, Jr. et al. U.S. Pat. No. 5,728,654; Vollmer et al. U.S. Pat. No. 5,785,747; and Dobson, Jr. et al. U.S. Pat. No. 5,804,535.
Clean-up of the filter cake deposited on the sides of the borehole is a critical part of the completion process to ensure maximum productivity from a wellbore. Poor wall cake development allows particulates or liquids to enter the formation resulting in internal formation damage. Solids or polymers which have not been removed from the surface of a borehole can also impede the flow of hydrocarbons by plugging a prepacked screen during production. Filter cake removal is generally undertaken by treating the wellbore with concentrated acid solution, particularly hydrochloric acid. Dobson, Jr. et al. U.S. Pat. No. 5,607,905 discloses the incorporation of certain inorganic peroxides into the filter cake which enhance the removal of the filter cake upon contacting it with an acidic solution. Brannon et al. U.S. Pat. No. 5,881,813 discloses an enzyme-containing clean-up fluid for degrading the residual polymeric viscosifiers present in filter cakes from drill-in fluids or present in the formation from other well treating fluids.
While these improvements in formulating well drilling and servicing fluids from high density brines have had commercial success, there is still a need for such fluids which exhibit enhanced particulate suspension characteristics at lower viscosities and which are easier and more completely removed from wellbores, screens, and the like present in hydrocarbon-containing formations.
SUMMARY OF THE INVENTION
The invention provides clay-free well drilling and servicing fluids comprising an aqueous brine which contains at least 0.6 equivalents per liter of a water soluble divalent cation salt, a particulate bridging agent which is insoluble in the aqueous brine, and a starch derivative which functions as a combination suspending agent and fluid loss control agent. The starch derivative is used in a concentration sufficient to provide the fluid with the following characteristics: (a) a low shear rate viscosity less than about 10,000 centipoise; (b) a high shear rate viscosity at 511 sec
−1
in the range from about 15 to about 70 centipoise measured at 120° F.; (c) a fluid loss less than about 10 milliliters as measured at 185° F. and 250 psi differential pressure across a 5 micron disk for 30 minutes; and (d) anti-settling characteristics as exhibited upon static aging the fluid for 16 hours at 185° F. The invention further provides that the low shear rate viscosity can be increased without raising the high shear rate viscosity above about 70 centipoise by incorporating magnesium oxide and/or dipotassium hydrogen phosphate in the fluids.
The preferred modified starch comprises amylopectin, such as a waxy starch, that has been crosslinked to the extent that the viscosity of a basic aqueous amylopectin starch suspension undergoing crosslinking is within about 25% to about 60% of the maximum viscosity that can be obtained, preferably from about 25% to less than about 50%, and pre-gelatinized.
The invention further comprises a process for preparing the clay-free fluids, and a process of drilling, completing, or working over a well with the clay-free fluids.
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof will hereinafter be described in detail and shown by way of example. It should be understood, however, that it is not intended to limit the invention to the particular forms disclosed, but, on the contrary, the invention is to cover all modifications and alternatives falling within the spirit and scope of the invention as expressed in the appended claims.
The compositions can comprise, consist essentially of, or consist of the stated materials. The method can comprise, consist essentially of, or consist of the stated steps with the stated materials.
REFERENCES:
patent: 4175042 (1979-11-01), Mondshine
patent: 4427556 (1984-01-01), House et al.
patent: 4822500 (1989-04-01), Dobson, Jr. et al.
patent: 5514644 (1996-05-01), Dobson
patent: 5612293 (1997-03-01), Swartwoot et al.
patent: 5616541 (1997-04-01), Dobson, Jr. et al.
patent: 5641728 (1997-06-01), Dobson, Jr. et al.
patent: 5728654 (1998-03-01), Dobson
Dobson, Jr. James W.
Lay Jeffrey S.
Tresco Kim O.
House Roy F.
Texas United Chemical Company, L.L.C.
Tucker Philip
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