Wells – Processes – Chemical inter-reaction of two or more introduced materials
Patent
1988-02-22
1992-01-21
Suchfield, George A.
Wells
Processes
Chemical inter-reaction of two or more introduced materials
166307, 252 8553, E21B 4327
Patent
active
050820583
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains to the stimulation of wells to improve the permeability of such wells to the flow of fluids. The invention is especially useful in improving the flow of hydrocarbons from wells which have suffered from formation damage due to clay deposits.
2. Description of the Prior Art
It is well known that oil production in siliceous sub-terranean formations, over the useful life of a well, usually decreases with time. To reestablish a higher flow of oil, one of the first methods usually employed is pumping. Frequently, however, after a period of time, even pumping will not make the well economical. Unfortunately in many wells such flow reduction occurs long before the oil, or other fluid in the reservoir reached by the wellbore, has become depleted. Low permeability frequently results from the deposition of clay and other finely divided material in the pore structure or flow passages of the formation. Clay particles, capable of forming such undesirable deposits, generally exist throughout the formation and are carried by the oil and deposited in the flow passages leading to the wellbore. Formation damage can also be caused by the swelling of the clay upon contact with foreign liquids injected for well development or stimulation purposes. Formation damage of the above types is often referred to as clay deposits, clay dispersions, particle plugging, clay swelling, etc., which hereinafter will simply be referred to collectively as "pore deposits."
It is known that pore deposits can be solubilized more or less by treatment with mineral acid solutions, for example, hydrochloric acid and hydrofluoric acid. Aqueous solutions containing about 2 to 6 weight percent hydrofluoric acid and 5 to 15 weight percent hydrochloric acid, sometimes referred to as "mud acids" have been used to treat damaged formations in hopes of restoring to the formation its initial permeability. Mud acids have also been used to treat formations which are naturally tight.
Unfortunately, hydrochloric acid is usually not effective in solubilizing the more tenuous pore deposits such as those deposits that are mainly siliceous in composition. By the term "siliceous" as used herein is meant silica and/or silicate. By the term "siliceous material" as used herein is meant silica-containing and/or silicate-containing materials. Examples of siliceous materials are sandstone and certain clays. Non-limiting example of clays which are silicates, usually aluminosilicates are attapulgite, bentonite, chlorite, halloysite, illite, kaolinite, montmorillonite, and various mixtures of the aforementioned substances. It is known that hydrofluoric acid will solubilize siliceous material readily; however, because of its high reactivity hydrofluoric acid, unmixed with other mineral acids such as hydrochloric acid, generally is not used to increase oil production. Other serious problems also exist with the use of hydrofluoric acid. For example, since the rate of reaction of hydrofluoric acid with siliceous materials is very rapid, most of the acid is spent within a zone of about one or two feet or less radially from the wellbore. In formations having high formation temperatures the acid becomes spent at even shorter distances from the wellbore thereby causing the acidizing operation to be even less effective.
Since the mineral content of the matrix of many formations is usually sandstone or silica or a similar siliceous material, hydrofluoric acid can dissolve the matrix itself as well as the undesirable pore deposits in the matrix. As a consequence hydrofluoric acid can cause permanent damage to the formation by the dissolving of the pore structure or matrix itself, or by allowing the precipitation of reaction products and/or creation of fines within the pores of the formation. To prevent permanent damage from occurring the concentration of hydrofluoric acid is usually adjusted so that no more than minor damage to the formation can occur. As a consequence, clay deposits distant from the wellbore do
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Logan F. Eugene
Oxy USA Inc.
Suchfield George A.
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