Wells – Processes – Placing fluid into the formation
Patent
1996-02-28
1997-10-21
Neuder, William P.
Wells
Processes
Placing fluid into the formation
E21B 4327
Patent
active
056786328
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the use of enzymes in the production of oil, gas or water from an underground reservoir.
One third to a half of the world's hydrocarbon reserves are found in carbonate rock structures, in particular a large area of the Texas and Oklahoma oil and gas fields in the US, the Albertan oil and gas fields in Canada, the oil and gas reservoirs of Argentina and Oman and many onshore areas in Europe. Carbonate rock tends to have very low permeability particularly when there are no connected fractures present. Groundwater is often pumped from boreholes or irrigation wells in chalk or other carbonate formations.
In many sandstone reservoirs, the rock structure may be cemented together by carbonate, or carbonate scales may accumulate close to production wells as a result of carbon dioxide being released from solution due to a pressure drop. Another type of scale that can accumulate around production wells is iron scale, in particular iron oxides and hydroxides. Low permeability, drilling damage and accumulation of scale all impede the flow of oil to the production well and the conventional method used to open up channels around the well bore to improve the flow rate is the injection of acid (known as acidising or acid stimulation). There are two types of acid treatment: fracture acidising (injection of acid at rates above fracture pressure to etch the faces of the resultant fractures) and matrix acidising (injection of acid at rates below fracture pressure to dissolve flow channels in the rock or to remove scale or damage caused by drilling). Acid treatments are employed in all types of oil wells and occasionally in water wells: they may be used to open fractures or remove damage in newly drilled wells or to rehabilitate old wells from which production has declined. Acid (usually hydrochloric acid though acetic and formic acids are used on occasion when it is desirable to delay the spending of the acid) is pumped into the well, where it reacts with the calcium carbonate according to the following stoichiometry:
Calcium chloride (CaCl.sub.2) is highly soluble in water and the acid etches channels in the rock, thus improving the oil or gas flow towards the production well. Hydrochloric acid reacts immediately with carbonate rock and tends to form a few large channels known as "wormholes" through the rock, rather than opening up the pore structure. The acid penetration distance is limited to a few feet at most.
Because hydrochloric acid reacts so rapidly when contacted with carbonate rock, a number of products have been developed which aim to reduce the reaction rate, allowing acid to penetrate further into the formation or to react more uniformly around the wellbore. The reaction of hydrochloric acid may be retarded by emulsifying, gelling or chemically retarding the acid. The reaction of acetic acid is naturally retarded because a build up of the reaction product, carbon dioxide, reduces the reaction rate. As carbon dioxide bleeds off into the formation or is absorbed by the oil, water or hydrocarbon gas, the reaction of acetic acid continues.
The benefits of retarded acids over conventional hydrochloric acid have been limited to date, since a significant permeability increase extending out at least 10 feet from the wellbore is necessary in order to obtain significant improvements in oil production rate (Williams, Gidley and Schechter, 1979 Ch. 10 in Acidizing Fundamentals, Soc. Petrol. Eng. of AIME, New York, Dallas).
Conventionally hydrocarbon wells in carbonate reservoirs are acidised immediately after drilling before production commences and often repeat treatments are conducted every two to three years.
In an alternative fracturing treatment to acid fracturing, fractures may be created by injecting sand suspended in an aqueous fluid (known as proppant) into a well at a rate above fracture pressure. When the injection pressure is removed, the sand remains in place, propping the fracture open. It is very unusual for a propped fracture subsequently to be treated with hydrochloric acid,
REFERENCES:
patent: 2863832 (1958-12-01), Perrine
patent: 3630285 (1971-12-01), Claytor, Jr. et al.
patent: 4506734 (1985-03-01), Nolte
patent: 5560737 (1996-10-01), Schuring et al.
Cadmus et al.; "Bacterial Degradation Of Xanthan Gum;" Industrial Polysaccharides: Genetic Engineering, Structure/Property Relations And Applications; 1987; pp. 101-107.
William, Gidley & Schechter; "Chapter 10: Matrix Acidizing Of Carbonates;" Soc. Petrol. Eng. Of Aime; 1979; pp. 86-91.
NTIS TECH NOTES, No. 9, Sep. 1984m Springfield, Va., p. 626, `bacteria aid in oil production and utilsation`.
Harris Ralph
Moses Vivian
Cleansorb Limited
Neuder William P.
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