Wells – Processes – Cleaning or unloading well
Reexamination Certificate
2001-01-09
2002-12-17
Bagnell, David (Department: 3672)
Wells
Processes
Cleaning or unloading well
C166S300000, C507S269000, C507S277000, C507S140000, C507S145000
Reexamination Certificate
active
06494263
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 from a producing formation has been accomplished in the past by including an acid soluble particulate solid bridging agent in the drilling or servicing fluid for bridging over the formation pores. The filter cake formed by the drilling or servicing fluid including the acid soluble bridging agent and a polymeric suspending agent has heretofore 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 and caused their early failure. The acidic solution may have also been incompatible with the producing formation and caused 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, a metal peroxide such as an alkaline earth metal peroxide, zinc peroxide or the like has been included in the drilling and servicing fluid. The metal peroxide is deposited in the filter cake along with the bridging agent. During the filter cake removal process, a mineral acid solution is placed in contact with the filter cake which activates the metal peroxide whereby it causes polymeric materials in the filter cake to be decomposed. Thereafter, the filter cake is contacted with an under saturated aqueous solution to dissolve the filter cake. Generally, the time required for the metal peroxide and mineral acid solution to break up polymers and for the under saturated aqueous solution to dissolve the bridging agent has been relatively long making the process expensive and subjecting metal tools and parts in contact with the mineral acid 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. More specifically, the present invention provides drilling and servicing fluids which include improved bridging agents having desired properties and which can be readily removed without the use of clean-up solutions containing strong mineral acids.
The drilling and servicing fluids of this invention are basically comprised of water, a water soluble salt and a particulate solid bridging agent. The particulate solid bridging agent is a synthesized inorganic compound which is dissolvable by an aqueous clean-up solution containing a mild organic acid, a hydrolyzable ester, an ammonium salt, a chelating agent, or a mixture of an ammonium salt and a chelating agent. The inorganic bridging agent is synthesized from a class of materials generally referred to as chemically bonded ceramic compounds. The synthesized inorganic bridging agent can include weighting materials to increase or decrease the density of the bridging agent as required by the well conditions and/or certain filler materials to decrease the amount of clean-up solution required. The well drilling and servicing fluid or the bridging agent therein or the clean-up solution can also include a metal peroxide or other oxidizer or breaker which 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, a synthesized inorganic compound which is dissolvable in an aqueous clean-up solution containing a mild organic acid, a hydrolyzable ester, an ammonium salt, a chelating agent, or a mixture of an ammonium salt and a chelating agent. The filter cake formed by the drilling or servicing fluid is contacted with the clean-up solution for a period of time such that the bridging agent is dissolved thereby. In a preferred method, the bridging agent is a chemically bonded ceramic selected from magnesium oxychloride cement, magnesium oxysulfate cement, magnesium potassium phosphate hexahydrate, magnesium hydrogen phosphate trihydrate or magnesium ammonium phosphate hexahydrate. As mentioned, the bridging agent can include weighting materials and/or certain filler materials. The drilling and servicing fluid, the bridging agent therein or the aqueous clean-up solution can also include an oxidizer or other breaker which breaks 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 EMBODIMENTS
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 strong mineral acids or other hazardous chemicals. The well drilling and servicing fluids of this invention are basically comprised of water, a water soluble salt and a particulate solid bridging agent. The particulate solid bridging agent is a synthesized inorganic compound of the type generally referred to as a chemically bonded ceramic. The particulate solid bridging agent is soluble in an aqueous clean-up solution containing a mild organic acid, a hydrolyzable ester, an ammonium salt, a chelating agent or a mixture of an ammonium salt and a chelating agent. When required, a fluid loss control agent and/or a hydratable polymer solids suspending agent can optionally be included in the well drilling and servicing fluids.
The water soluble salt in the drilling and servicing fluids of this invention can be one or more of sodium chloride, sodium bromide, sodium acetate, sodium forma
Bagnell David
Dougherty, Jr. C. Clark
Halliburton Energy Service,s Inc.
Kent Robert A.
Walker Zakiya
LandOfFree
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