Wells – Processes – Cementing – plugging or consolidating
Reexamination Certificate
1999-02-26
2001-03-06
Bagnell, David (Department: 3672)
Wells
Processes
Cementing, plugging or consolidating
C166S292000
Reexamination Certificate
active
06196316
ABSTRACT:
The present invention relates in general to oil and gas well completion and remedial methods.
The main objectives for drilling a well are to create a connection to the oil and/or gas reservoir and to install tubing between the reservoir and the surface. The outer steel protection is called the casing. The casing requires a gas tight seal between the reservoir and the surface. To achieve such seal, the annulus (the gap between the casing and the rock/formation) is subjected to a cementing (or grouting) operation. This treatment is normally referred to as Primary Cementing. The main aspects of primary cementing are to isolate flow between different reservoirs, to withstand the external and internal pressures acting upon the well by offering structural reinforcement and to prevent corrosion of the steel casing by chemically aggressive reservoir fluids.
A poor cementing job can result in migration of reservoir fluids, even leading to gas migration through micro-annuli in the well which not only reduces the cost-effectiveness of the well but may cause a “blow out” resulting in considerable damage. Although repair jobs (“secondary cementing”) are possible (in essence forcing more cement into the cracks and micro-annuli) they are costly and do not always lead to the desired results.
When a well has reached the end of its economically productive life, the well needs to be abandoned in compliance with local regulations. Abandonment is usually carried out by first plugging each of the casings in a large number of sequential steps, cutting and removing the steel casings and placing a large cement plug to seal the well. As only a relatively small volume of cement (typically in the order of 100 m) is used to place the plug, its quality needs to be sufficient as it will serve as a seal for a very long time.
The customary abandonment operation is very costly, especially in an off-shore environment, since it requires the use of a workover or drilling rig. It would be very beneficial if methods were available which could lead to abandonment of wells without the necessity to remove the production tubing.
One of the major drawbacks of using traditional cementing materials such as Class G Cement (e.g. OPC: Ordinary Portland Cement) in plugging is that such materials cannot achieve a gas tight seal due to the inherent shrinkage of the materials. Shrinkage is typically in the order of 4-6% by volume which causes gas migration through the micro-annuli created because of the shrinkage. The use of such cementing material in “remedial secondary cementing” has the disadvantage that the customary grain size is too large to pass freely into the micro-annuli which affects the quality of the seal.
In the search for effective cementing materials, attention has to be paid to inter alia the following requirements: the material should be gas-tight (i.e. withstand at least 2 bar per m), it should have a controllable setting time so that a range of temperatures and well depths (each requiring different conditions) can be coped with, it should be thermally stable up to 250° C. as well as being chemically stable against reservoir fluids for a very long period of time and its Theological properties should be such that pumping through existing oil field equipment can be carried out without too much problems.
A wide range of non cementious plugging agents has been suggested to cope with at least part of the problems outlined hereinabove. Examples of such materials are Epoxy Resins (R. Ng and C. H. Phelps: “Phenolic/Epoxy Resins for water/Gas Profile Modification and Casing Leak Repair”—Paper ADSPE #90, presented at the ADIPEC, held in Abu Dhabi (16-19) October 1994), Phenol-or Melamine Formaldehyde (W. V. C. de Landro and D. Attong: “Case History: Water Shut-off using Plastic Resin in a High Rate Gravel pack Well”—Paper SPE 36125 presented at the 4
th
Latin American and Caribbean Petroleum Engineering Conference, held at Port of Spain in Trinidad, Apr. 23-26, 1996) and Poly-acrylates (U.S. Pat. No. 5,484,020 assigned to Shell Oil).
Although such materials can be instrumental in solving some of the problems encountered with traditional, cement-based plugs, there are still important drawbacks to be reckoned with in terms of handling aspects, control of setting times and long term durability.
Also rubbers have been proposed in general for use as plugging materials. Reference is made to U.S. Pat. No. 5,293,938 (assigned to Halliburton Company) directed to the use of compositions consisting essentially of a mixture of a slurry of a hydraulic cement (such as Portland cement) and a vulcanisable rubber latex. Rubbers specifically referred to in said US patent specification are natural rubbers, cis-polyisoprene rubber, nitrile-rubber, ethylene-propylene rubber, styrene butadiene rubber, butyl rubber and neoprene rubber. The use of silicone rubber is also stated as a possibility but such rubber generally has less desirable physical properties, requiring incorporation of inorganic extenders.
The vulcanisation of the rubber involves the cross-linking of the polymer chains which can be accomplished by incorporating one or more crosslinking agents (the most common one being sulphur) in the rubber latex (latex having been defined as the aqueous dispersion or emulsion of the rubber concerned).
In European patent specification 325,541 (Merip Tools International S.A) the use of putty (“mastic”) has been disclosed for producing joints separating zones in wells. Suitable compounds are formed by liquid elastomers such as fluorosilicones, polysulphides, polythioethers as well as epoxy or phenolic resins.
It has now been found that a specific class of RTV (Room Temperature Vulcanising) silicone components can be advantageously employed in the repair and abandonment of wells. In case of well abandoning they can be used either in the form of a mixture with an appropriate cement compound when setting a plug or as a sealing body on top of an existing cement-based plug.
Silicone rubbers which exert sealant activity can be differentiated on the basis of their method of production. Also their properties are dependent to a certain extent on the chemical composition envisaged.
A first class of silicone sealant can be described as having been prepared by a condensation type of curing process, using a condensation catalyst, as described in (1):
{circumflex over ( )}{circumflex over ( )}{circumflex over ( )}Si—(CH
3
)
2
—O—H+C
2
H
5
—O—Si(X)(Y)—→{circumflex over ( )}{circumflex over ( )}{circumflex over ( )}Si—(CH
3
)
2
—O—Si(X)(Y)—+C
2
H
5
OH (1)
in which X and Y are inert groups and {circumflex over ( )}{circumflex over ( )}{circumflex over ( )} represents the polymer backbone of the silanol-terminated polymer.
A second, related class of silicone sealants can be described as having been produced by the termination of a silanol functional polymer by a reactive cross-linking agent. This is also a condensation reaction using a condensation catalyst, as described in (2):
{circumflex over ( )}{circumflex over ( )}{circumflex over ( )}Si(CH
3
)
2
—O—H+Z—Si(A)(B)—R→{circumflex over ( )}{circumflex over ( )}{circumflex over ( )}Si(CH
3
)
2
—O—Si—(A)(B)—R+H—Z (2)
in which each of Z, A and B is a group capable of reacting with the —O—H moiety of the silanol terminated polymer, R represents the backbone of the reactive cross-linking agent and {circumflex over ( )}{circumflex over ( )}{circumflex over ( )} represents the polymer backbone of the silanol-terminated polymer. It is also possible to subject the silicone produced according to reaction (2) to a further hydrolysis step in which the composition identified as {circumflex over ( )}{circumflex over ( )}{circumflex over ( )}Si(CH
3
)
2
—O—Si—(A)(B)—R reacts with H
2
O to give a cross-linked silicon elastomer and by-products H—A and/or H—B. This process is known as moisture-catalysed vulcanisation.
A third class of silicone sealants can be described as having been prepared by an addition-curing process, using a platinum catalyst under conditions of ele
Bosma Martin Gerard Rene
Cornelissen Erik Kerst
Edwards Paul William
Reijrink Petronella Theodora Maria
Bagnell David
Dougherty Jennifer
Shell Oil Company
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