Earth boring – well treating – and oil field chemistry – Well treating – Contains enzyme or living micro-organism
Reexamination Certificate
2000-04-20
2003-05-27
Tucker, Philip (Department: 1712)
Earth boring, well treating, and oil field chemistry
Well treating
Contains enzyme or living micro-organism
C507S241000, C507S244000, C507S925000
Reexamination Certificate
active
06569814
ABSTRACT:
BACKGROUND OF THE INVENTION
The present Invention relates to novel fluids and techniques to optimize/enhance the production of hydrocarbons from subterranean formations. To recover hydrocarbons (e.g., oil, natural gas) it is of course necessary to drill a hole in the subsurface to contact the hydrocarbon-bearing formation. This way, hydrocarbons can flow from the formation, into the wellbore and to the surface. Recovery of hydrocarbons from a subterranean formation is known as “production.” One key parameter that influences the rate of production is the permeability of the formation along the flowpath that the hydrocarbon must travel to reach the wellbore. Sometimes, the formation rock has a naturally low permeability, other times, the permeability is reduced during, for instance, drilling the well. When a well is drilled, a fluid is circulated into the hole to contact the region of the drill bit, for a number of reasons—including, to cool the drill bit, to carry the rock cuttings away from the point of drilling, and to maintain a hydrostatic pressure on the formation wall to prevent production during drilling.
Drilling fluid is expensive particularly in light of the enormous quantities that must be used during drilling. Additionally, drilling fluid can be lost by leaking off into the formation. To prevent this, the drilling fluid is often intentionally modified so that a small amount leaks off and forms a coating on the wellbore, or a “filtercake.”
Yet once drilling is complete, and production is desired, then this coating or filtercake must be removed. The present fluids and techniques are directed to removing this filtercake or other such damage in the wellbore and near-wellbore region, that results either intentionally (in the case of drilling fluid) or unintentionally (in the case of scale deposits from produced water or dewatered fluids from workover/stimulation operations performed on the well).
Conventional treatments for removing filtercake include: aqueous solution with an oxidizer (such as persulfate), hydrochloric acid solution, organic (acetic, formic) acid, combination of acid and oxidizer, and aqueous solutions containing enzymes. For instance, the use of enzymes to remove filtercake is disclosed in U.S. Pat. No. 4,169,818, Mixture of Hydroxypropylcellulose and Poly(Maleic Anhydride/Alkyl Vinyl Ether) as a Hydrocolloid Gelling Agent (1979) (col. 1, In. 42); U.S. Pat. No. 3,515,667, Drilling Fluid Additive (1970); U.S. Pat. No. 3,509,950, Well Drilling Mud and Screen Composition of Use Thereof; U.S. Pat. No. 2,259,419, Well Drilling (1941). Chelating agents (e.g., EDTA) are also used to promote the dissolution of calcium carbonate. See, C. N. Fredd and H. S. Fogler,
Chelating Agents as Effective Matrix Stimulation Fluids for Carbonate Formations
, SPE 372212 (1997); C. N. Fredd and H. S. Fogler,
Alternative Stimulation Fluids and Their Impact on Carbonate Acidizing
, SPE 31074 (1996), both articles are hereby incorporated by reference in their entirety. According to conventional teaching, the oxidizer and enzyme attack the polymer fraction of the filtercake; the acids mainly attack the carbonate fraction (and other minerals). Generally speaking, oxidizers and enzymes are ineffective in degrading the carbonate fraction; likewise, acids have very little effect on polymer.
In addition, numerous problems plague conventional techniques of filtercake removal. Perhaps the most troublesome is the issue of “placement.” For instance, one common component in filtercake is calcium carbonate. The substance of choice to remove calcium carbonate is hydrochloric acid. Hydrochloric acid reacts very quickly with calcium carbonate. What happens then, is that the filtercake begins to dissolve, therefore dramatically increasing the permeability of the wellbore face, so that the wellbore region is no longer “sealed off” from the formation. Once this happens, the entire clean-up fluid may then leak off into the formation through this zone of increased permeability (“thief zones,” or discrete zones within the interval of very high permeability where more filtercake dissolution has occurred than at other places along the interval).
A second problem with removal of filtercake is that it is comprised of several substances, and which are, as mentioned earlier, not generally removable with a single substance. Calcium carbonate and organic polymers (e.g., starch and other polysaccharide) are two primary constituents of conventional drilling fluids that form a filtercake on the wellbore. Treating these successively—i.e., with two different fluids, one after the other—is problematic since, it requires at least two separate treatments. Combining two different breakers (one for the polymer fraction, one for calcite) is problematic since each has a distinct activity profile (or optimal window of activity, based on temperature, pH, etc.) and the activity profiles of two different breakers may not coincide. This is particularly likely if one of the breakers is an enzyme, which are notoriously temperature and pH sensitive.
Moreover, if the calcium carbonate is removed first—as it often is—then, once the hydrochloric acid contacts the filtercake, regions of higher permeability are created in the wellbore (where the filtercake has dissolved). Hence, fluid will leak-off into the formation during subsequent phases of the filter-cake removal treatment.
Hence, the ideal fluid must be easy to “spot” or place in wellbore over the entire length of the desired zone, contiguous with the producing zone (e.g., a two thousand foot horizontal zone)—before any filtercake dissolution occurs. If the fluid begins to dissolve the filtercake too quickly, then the fluid will be lost through the thief zones and the entire fluid treatment will be destroyed. In other words, a hypothetical ideal fluid would be completely unreactive for a period of time to enable it to be spotted along the entire length of the producing interval, then, once in place, react sufficiently slowly and uniformly, so that no thief zones are. Again, if thief zones form, then the entire mass of fluid can leak off through that zone. Hence, reasonably uniform/controlled dissolution is necessary to ensure that the fluid remains in contact with the filtercake along the entire interval until near-complete dissolution of the filtercake has occurred along the entire interval.
Moreover, removing filtercake is an expensive and time-consuming procedure. Therefore, it is desirable to do this at the same time that another treatment is being performed, if possible. For instance, if a material must be delivered to one portion of the formation into the wellbore (e.g., in conjunction with a remedial treatment), then the fluid used to carry that material can be an acid solution which will also dissolve portions of the filtercake. Again, if the carrier fluid leaks off into the formation through a thief zone, then the remedial operation is completely destroyed.
One common treatment performed on wells, particularly wells in the Gulf Coast region of the United States, is known as a “gravel pack.” Gravel pack operations are performed to prevent the production of sand along with hydrocarbon, which often occurs in formations of weakly consolidated sands. To prevent sand production, a filter (or screen) can be placed around the portion of the wellbore in which production occurs. A more long-term solution for sand control is achieved if the region between the screen and the formation is filled with gravel, which is properly sized to prevent the sand from moving through the gravel and into the wellbore—to function as a filter—so that when the sand tries to move through the gravel, it is filtered and held by the gravel or screen, but hydrocarbon continues to flow unhindered (by either the gravel or screen) into the wellbore.
Again, it would be highly advantageous if the fluid used to deliver the gravel could also be used to dissolve the filtercake, Which would eliminate the need for a separate treatment just to dissolve the filtercake. This would result in substantial cost sav
Brady Mark E.
Frenier Wayne W.
Vinod Palathinkara S.
Jeffrey Brigitte
Menes Catherine
Nava Robin
Schlumberger Technology Corporation
Tucker Philip
LandOfFree
Fluids and techniques for hydrocarbon well completion does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Fluids and techniques for hydrocarbon well completion, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fluids and techniques for hydrocarbon well completion will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3054260