Wells – Processes – Cleaning or unloading well
Reexamination Certificate
2000-08-01
2002-07-23
Bagnell, David (Department: 3672)
Wells
Processes
Cleaning or unloading well
C166S300000, C175S072000, C507S140000, C507S145000, C507S269000, C507S277000
Reexamination Certificate
active
06422314
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to well drilling and servicing fluids utilized in producing formations and the removal of filter cake deposited by the fluids in the formations.
2. Description of the Prior Art
The use of special fluids for drilling or servicing hydrocarbon producing formations penetrated by well bores is well known. The drilling fluids are utilized when well bores are drilled into producing formations to minimize damage to the permeability of the formations and their ability to produce hydrocarbons. Servicing fluids are utilized when completion operations are conducted in producing formations and when conducting work-over operations in the formations. The drilling and servicing fluids deposit filter cake on the walls of the well bores within the producing formations which prevents the drilling and servicing fluids from being lost into the formations and prevents solids from entering the porosities of the producing formations. After the drilling or servicing of a producing formation has been completed, the filter cake is removed prior to placing the formation on production.
The removal of the filter cake has heretofore been accomplished by including a particulate solid bridging agent in the drilling or servicing fluid for bridging over the formation pores which is acid soluble. The filter cake formed by the drilling or servicing fluid which includes the bridging agent and a polymeric suspending agent has been contacted with a strongly acidic solution, and the acidic solution has been allowed to remain in contact with the filter cake for a period of time sufficient to dissolve the bridging particles and polymer. In spite of efforts to avoid it, the strongly acidic solution has often corroded metallic surfaces and completion equipment such as sand screens which caused their early failure. The acidic solution may also be incompatible with the producing formation and cause damage thereto.
Water soluble particulate solid bridging agent has also been utilized in drilling or servicing fluids, and the filter cake containing the water soluble bridging agent has been contacted with an aqueous salt solution which is undersaturated with respect to the water soluble bridging particles. However, such undersaturated aqueous solutions require a relatively long period of time to dissolve the particles primarily due to the polymeric suspending agents included in the drilling or servicing fluids. That is, the polymer or polymers present in the filter cake shield the water soluble bridging particles from the aqueous solution.
In order to remove the polymeric materials in the filter cake and thereby allow the bridging agent in the filter cake to be dissolved by aqueous solutions, the filter cake has heretofore been contacted with an aqueous salt solution containing a peroxide such as alkaline earth metal peroxides, zinc peroxides and the like. An acid has also been included in the aqueous solution containing the metal peroxide to activate the peroxide. The aqueous solution has been maintained in contact with the filter cake for a period of time such that the polymers in the filter cake are decomposed and the bridging agent dissolved. Thereafter, the walls of the well bore are contacted with a wash solution to remove the remaining filter cake therefrom. Generally, the time required for the solution containing the metal peroxide and acid to break-up polymers and dissolve the bridging agent has been relatively long making the process expensive and subjecting metal tools and parts in contact with the solution to acid corrosion.
Thus, there are continuing needs for improved drilling and servicing fluids and methods of removing filter cake deposited by the fluids from producing formations.
SUMMARY OF THE INVENTION
The present invention provides improved well drilling and servicing fluids for use in producing formations which meet the needs described above and overcome the deficiencies of the prior art. The drilling and servicing fluids of this invention are basically comprised of water, a density increasing water soluble salt, a fluid loss control agent, a hydratable polymer solids suspending agent and a particulate solid bridging agent comprised of an inorganic compound which is dissolvable by a clean-up solution comprised of water and an ammonium salt. In a preferred embodiment, the inorganic bridging agent is magnesium oxide and the ammonium salt in the clean-up solution is ammonium chloride. A chelating agent such as citric acid and its salts is also preferably included in the clean-up solution. The well drilling and servicing fluid additionally can include a metal peroxide or other oxidizer or breaker which is activated by the ammonium salt in the clean-up solution and functions to oxidize and break-up polymer in the filter cake deposited by the fluid.
The present invention also provides methods of removing filter cake from the walls of well bores penetrating producing formations deposited therein by drilling or servicing fluids. The methods include utilizing, as the particulate solid bridging agent in the drilling or servicing fluid, an inorganic compound which is dissolvable in a clean-up solution comprised of water and an ammonium salt. The filter cake formed by the drilling or servicing fluid is contacted with the clean-up solution comprised of water and an ammonium salt for a period of time such that the bridging agent is dissolved thereby. In a preferred method, the bridging agent is magnesium oxide and the ammonium salt in the clean-up solution is ammonium chloride. The clean-up solution also preferably includes a chelating agent.
In addition to the bridging agent, the drilling or servicing fluid can also include an oxidizer or other breaker which is deposited in the filter cake and is activated by the ammonium chloride in the cleaning solution to break-up polymer in the filter cake.
It is, therefore, a general object of the present invention to provide improved well drilling and servicing fluids for use in producing formations and methods of removing filter cake therefrom.
Other and further 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 EMBODIMENT
The present invention provides improved well drilling and servicing fluids for use in producing formations which deposit filter cake that can be readily removed without the use of acids or other hazardous chemicals. The well drilling and servicing fluids of this invention are basically comprised of water, a density increasing water soluble salt, a fluid loss control agent, a hydratable polymer solids suspending agent and a particulate solid bridging agent which is soluble in a clean-up solution comprised of an aqueous ammonium salt solution. The density increasing water soluble salt can be one or more of sodium chloride, sodium bromide, sodium acetate, sodium formate, sodium citrate, potassium chloride, calcium chloride and calcium bromide. Common oilfield brines can be utilized and are preferred due to their ready availability in the oilfield.
A variety of fluid loss control agents can be utilized in the well drilling or servicing fluids of this invention, including, but not limited to, starch, starch ether derivatives, hydroxyethylcellulose, cross-linked hydroxyethylcellulose and mixtures thereof. Of these, starch is the most preferred. The fluid loss control agent is generally included in the salt solution or brine in an amount in the range of from about 0% to about 2% by weight of the salt solution or brine, more preferably in the range of from about 1% to about 1.3% and most preferably about 1.3%.
A variety of hydratable polymer solid suspending agents can be utilized, including, but not limited to, biopolymers such as xanthan and succinoglycon, cellulose derivatives such as hydroxyethylcellulose and guar and its derivatives such as hydroxypropyl guar. Of these, xanthan is preferred. The hydratable polymer is genera
Fisk, Jr. James V.
Kercheville James D.
Reddy B. Raghava
Todd Bradley L.
Bagnell David
Dougherty, Jr. C. Clark
Halliburton Energy Service,s Inc.
Kent Robert A.
Walker Zakiya
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