Wells – Processes – Repairing object in well
Reexamination Certificate
2000-07-07
2002-09-17
Suchfield, George (Department: 3672)
Wells
Processes
Repairing object in well
C166S281000, C166S295000, C166S300000, C507S224000, C507S225000, C507S903000, C523S130000, C523S131000
Reexamination Certificate
active
06450260
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to the consolidation of hydrocarbon-bearing rock formations to minimize flow of particulates into a wellbore. The consolidation is performed by the injection of a flexible gel system into the formation.
BACKGROUND OF THE INVENTION
Hydrocarbons (oil, natural gas, etc.) are obtained from a subterranean geologic formation (i.e., a “reservoir”) by drilling a well that penetrates the hydrocarbon-bearing formation. This provides a partial flowpath for the hydrocarbon to reach the surface. In order for the hydrocarbon to be “produced,” that is travel from the formation to the wellbore (and ultimately to the surface), there must be a sufficiently unimpeded flowpath from the formation to the wellbore. This flowpath is through the formation rock-e.g., sandstone, carbonates—which has pores of sufficient size, connectivity, and number to provide a conduit for the hydrocarbon to move through the formation.
When hydrocarbon is produced from a well, formation particulates may travel with the hydrocarbon from the formation, through the wellbore, to the surface. The presence of formation particulates is especially likely in soft formations comprising sand, sandstone, chalk, or limestone. The travel of particulates with the hydrocarbon is undesirable. Particulates flowing through the wellbore will erode equipment in the wellbore and at the surface, which can make replacement of such equipment necessary. Particulates in the produced hydrocarbon must also be removed before the hydrocarbon can be processed. Also, particulates can come to reside in the wellbore to the point where hydrocarbon production is greatly diminished or completely stopped.
One approach to minimize flow of formation particulates into the wellbore is by the use of a gravel pack. Typically, a screen is placed around the wellbore casing. Gravel is then packed between the screen and the casing. Gravel packs can also be used open-hole (i.e. in wellbores without a casing), or screens can be used without gravel packs. Placing gravel above the fracture pressure of the formation may be termed a “frac-pack.” As hydrocarbons are produced from the formation, they travel through the gravel pack and/or the screen before entering the wellbore. The gravel pack and/or screen inhibit the flow of particulates but, under normal conditions, do not substantially inhibit the production of hydrocarbons. However, placing a gravel pack and screen requires specialized equipment, and the gravel pack and screen create a mechanical restriction which may be plugged by scale or may be eroded by the flow of particulates. It is desirable to have a method for completing wells in unconsolidated formations that does not involve the use of a gravel pack, a screen, or both.
Another approach involves consolidating the formation by injecting a consolidating fluid comprising, for example, a resin. Conventional consolidating fluids, such as the SANDLOCK™ system (Schlumberger), comprise a resin, and optionally a curing agent, a catalyst, and an oil wetting agent. When injected into the formation, the resin (acted upon by the curing agent and catalyst, if present) hardens, causing consolidation of the formation to a rigid state and reduction in the concentration of formation particulates. These systems are designed to maintain sufficient permeability of the formation to allow production. Consolidating fluids and methods for their use are reported in U.S. Pat. Nos. 5,806,593; 5,199,492; 4,669,543; 4,427,069; and 4,291,766. U.S. Pat. No. 5,712,314 discusses the use of a flexible furan resin system for water control.
However, conventional consolidating fluids have a number of disadvantages. One is inherent to a subterranean formation consolidated by the setting of a resin: because the consolidated formation is under a great deal of stress from surrounding formations, the resin preferably imparts a very high strength to the formation. This increased strength can be assayed in the laboratory by measuring the unconfined compressive strength (UCS) of a formation sample treated with the consolidating fluid. If the strength imparted to the consolidated formation is not sufficiently high, the consolidated formation, being rigid, can fail; failure will then result in the production of sand, which is an undesirable result.
Other disadvantages of conventional consolidating fluids become apparent when a large amount of the fluid is injected into a formation to provide a sufficiently high strength. Maximizing strength requires complex treatment schedules. Increasing the concentration of resin is generally undesirable, because resins tend to be expensive and pose environmental concerns.
Therefore, it is desirable to have a consolidating fluid that, upon use to consolidate a formation, imparts a low probability of failure to the formation. Further, it is desirable for the consolidating fluid to be injected following a simple, preferably a one-step, treatment schedule. It is also desirable for the consolidating fluid to comprise agents that are relatively inexpensive and environmentally acceptable.
U.S. Pat. Nos. 5,246,073; 5,335,733; 5,486,312; and 5,617,920, assigned to Unocal, describe a fluid comprising a polyvinyl polymer, a polymethacrylamide, a cellulose ether, a polysaccharide, a lignosulfonate, an ammonium salt or alkali metal salt of the foregoing, or an alkaline earth salt of a lignosulfonate; and a crosslinking agent, such as an aldehyde, a dialdehyde, a phenol, a substituted phenol, an ether, a polyvalent metal, a chelated polyvalent metal, or a compound capable of yielding a polyvalent metal. One version of such a fluid is commercially available under the trade name “OrganoSEAL-R.” These references teach the fluid can be used to seal a wellbore to prevent contamination by water from a water-containing formation penetrated by the wellbore.
U.S. Pat. Nos. 4,683,949 and 5,947,644, assigned to Marathon Oil Co., describe a fluid comprising polyacrylamide and a chromium III/carboxylate complex crosslinking agent. The fluid is commercially available under the trade name “MARASEAL.” These references also teach the fluid can be used to seal a wellbore to prevent contamination by water from a water-containing formation penetrated by the wellbore.
Zeltmann et al., U.S. Pat. No. 6,047,773, assigned to Halliburton Energy Services, Inc., reports the use of viscous fluids, such as fluids comprising hydroxyethylcellulose, guar, or acrylic, to occupy a wellbore and provide a barrier to entry of stimulation fluids into a formation. The viscous barrier fluid itself is taught to not penetrate the formation.
U.S. Pat. No. 6,011,075 discloses a method for increasing the storage modulus G′ of a flexible gel while maintaining flexibility.
SUMMARY OF THE INVENTION
In one embodiment, the present invention relates to a method of consolidating a subterranean formation, comprising (i) providing a consolidating fluid, wherein the consolidating fluid comprises a gel component and a gel-forming agent; and (ii) injecting the consolidating fluid into the formation, under conditions wherein the consolidating fluid forms a flexible gel, thereby consolidating the formation.
In one further embodiment, the method further comprises injecting a fracturing fluid into the consolidated formation, to form a fractured formation. In a different further embodiment, the method further comprises perforating the consolidated formation, to form a perforated formation. The fractured or perforated formation can then produce hydrocarbons.
In another embodiment, the present invention relates to a method of repairing a plugged gravel pack or frac-pack. The method comprises (i) providing a consolidating fluid as described above and (ii) injecting the consolidating fluid into the gravel, under conditions wherein the consolidating fluid forms a flexible gel, thereby consolidating the gravel. Perforation through the screen and consolidated gravel, and into the formation, followed by fracturing can then be performed.
The present invention has the advantages of forming a co
Guinot Frederic J.
James Simon G.
Nelson Erik B.
Jeffery Brigitte
Menes Catherine
Nava Robin C.
Schlumberger Technology Corporation
Suchfield George
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