Method and apparatus for delayed flow or pressure change in wells

Abstract

degradable polylactic or polyhydroxyalkanoate polymers may be used to viscosify aqueous fluids for use in wells, Sand control screen or liner can be coated with a solid degradable polymer during placement in a well. Mechanical changes or flow changes in a well can be caused by solid degradable polymer that changes physical properties after it is placed in a well. Parts of devices or entire devices can be made of solid degradable polymer that converts to a fluid after selected times in an aqueous environment in a well.

Description

This application is a divisional application of application Ser. No. The use of a water-degradable solid polymer that decreases in molecular weight with time is not disclosed.

FIG. 2 shows a cross-section of a wire-wrapped sand control screen. The screen includes basepipe 130, stand-offs 134 and wire 136. Washpipe or tail pipe 132 is shown inside the screen. The protective coating on the screen is designated 122. It should be understood that a screen is illustrated, but a perforated liner or permeable sintered medium may be protected by a protective coating such as coating 122.

The use of PLA, PHA and other polyester polymers makes possible a timed degradation of the coating, rather than the employment of temperature alone or dissolution in a fluid as disclosed in the '919 Publication. The properties of the polyester may be selected to maintain sufficient mechanical strength to prevent displacement of the polymer from the screen as it is placed in a well. This time may be from several hours to days, depending on the time required to place the coated screen in a well. An example of the decrease in molecular weight of poly (DL-lactide) with time is provided in the paper “Further investigations on the hydrolytic degradation of poly (DL-lactide),” Biomaterials 20 (1999) 35-44. The data in the paper were obtained at 37° C. and at 60° C. As can be noted in the U.S. Pat. No. 4,716,964, referenced above, the rate of degradation is much more rapid at temperatures more typical of the temperature in wells. The polymer coating initially should have a melting point higher than the temperature expected in the well. The polymer should degrade to form a material that can be displaced from the well. If the polymer should flow outwardly from the screen, the polymer should not permanently damage permeability of the gravel placed in the well. Some or the entire polymer may be produced from the well as a viscous liquid. The initial strength of the solid polymer should be sufficient to prevent flow across the screen, in the area where the polymer is applied, under pressure differentials across the screen as it is placed in the well. The polymer coating may be used, for example, to prevent flow through only selected areas of the screen as it is put in a well. To increase initial strength of the polymer, a composite may be formed with the polymer by incorporating particles of a rigid solid, which may be a soluble crystalline material, for example, in the polymer before it is placed on the screen. Polymers having varying degradation rates may be used on different areas of a screen. For example, a more rapidly degrading polymer may be used over the lower portion of a screen.

Degradable polymer, such as PLA, may be applied to the screen, for example, by heating the polymer to allow flow or extrusion and coating the polymer on the finished screen. The screen may be heated before application of the polymer to allow more uniform flow of polymer into the screen. Alternatively, the polymer may be applied from solution in a solvent and the solvent removed to form a solid polymer. Alternatively, the base pipe or mandrel of the screen may be coated and the holes plugged with hot PLA or other water-degradable polymer before the wire of a screen is applied. Alternatively, blank pipe to be run into a well may be coated with the degradable polymer. The degradable polymer may be formulated to contain any or all the additives taught by the '919 Publication. The additives would then be released to enter the fluids around the screen or blank pipe as the polymer degrades.

There are reasons to attach various mechanical devices to the outside of tubulars as they are placed in a well. The devices may be used to measure physical or chemical variables or to modify flow conditions in the well, for example. A change in the position, status or operation of the device after a selected time may be desirable. A degradable polymer, such as PLA or a PHA, may be used to form a mechanical part of the device or a support for the device. The degradation rate of the degradable polymer may be selected to allow the desired change to occur in a selected range of time after placement of the device in a well. For example, FIG. 3 is adapted from U.S. Pat. No. 5,509,474. In this example, tubing 106 has been placed in a well inside casing 12. The annulus between tubing and casing will ordinarily be filled by an aqueous fluid. Sensors 111 are designed to be released from the vicinity of the outside surface of tubing 106 and then to spring against the inside wall of casing 12. An electromechanical device could be used to release the spring-loaded sensors. Alternatively, groove 200 may be formed in insulating material collar 114 and the spring-loaded sensors may be held in groove 200 by placing a selected solid water-degradable polymer over the sensor, shown at 111(a), in the groove, using techniques of placement such as described above for a screen. After tubing 106 is placed in a well in an aqueous fluid environment, polymer in groove 200 degrades to a range of mechanical properties (determined by the decrease in molecular weight of the degradable polymer) that allows sensor 111 to be released and to spring into the position shown at 111, which is in contact with the inside surface of casing 12.

The applications of degradable polymers disclosed herein to allow a timed change in location of a part or parts of mechanical devices can be readily seen by one of skill in the art of each device. The degradable polymer may easily be configured to allow the change to occur as compressive strength of the polymer degrades, as tensile strength degrades, as bending strength degrades, or as a combination of properties changes. The time of change can be determined by selecting a degradable polymer that changes in properties at a rate to allow the change to occur in a desired time range. This range may be hours, days or months, depending on the mechanical configuration and the polymer selected.

In other applications, flow configuration or pressure changes may be desired in a well after a selected time. For example, a port may preferably be opened after a selected time, in the range of hours, days or months. The port may be inaccessible or require expensive operations to open. For example, the port may be used to co-mingle fluid streams being produced from a well and be in an aqueous environment. A plug may be formed from a degradable polymer as disclosed herein. Tests can be performed with different polymer compositions to select the polymer providing the opening of the port in the desired time range and at the pressure differential existing across the port when in the well. Measurements of physical properties of a selected degradable polymer as a function of time and at selected temperatures in an aqueous environment may also be used to predict the time of opening of a selected port under selected conditions. Alternative, the polymer can be made in the form of a seal or gasket that degrades in time to allow flow. Such measurements and tests should take into account the dimensions of the degradable polymer body that is degrading, since such changes in properties are known to be affected by dimensions of the body, which affect the length of the diffusion path of water molecules into the degradable material and the diffusion path of reaction products from the polymer.

In another embodiment, mechanical devices or selected parts of mechanical devices that are placed in a well may be formed from solid degradable polymer such as PLA or PHA. For example, parts of a packer, a bridge plug or a cement retainer may be formed of water-degradable polymer. After a selected range of time, from hours, to days or months, the device or selected parts of the device may be designed to decrease in properties so as to release the device and facilitate retrieval. Alternatively, the entire device may be formed of a degradable polymer where strength of the polymer is adequate. For example, a nipple or pipe section may be formed of degradable polymer. The nipple or pipe may degrade and later be produced from a well. The pipe may be the “tail pipe” used in a sand control screen, for example.

Whereas the PLA used in fluids is preferably amorphous, as described above, the PLA used in mechanical or flow control devices may be amorphous or crystalline. The bending strength of rods of poly (D-lactide) (PLA) (which would be crystalline) when made by routine injection molding has been measured to be in the range of 40-140 MPA. Rods formed by solid state extrusion had bending strengths up to 200 MPA (“Enhancement of the mechanical properties of polylactides by solid-state extrusion,” Biomaterials 17, (March, 1996, 529-535). Further information about PLA and its properties is provided in a chapter entitled “Present and Future of PLA Polymers” in the book Degradable Polymers, Recycling, and Plastics Waste Management. Ed. by Ann-Christine Albertsson and S. J. Huang, Marcel Dekker, Inc. It is well known that strength may be increased by the use of composites made of the thermoplastic polymer. Where added strength is desired, composite formed from a degradable polymer may be used. PLA, for example, can be molded as other thermoplastic materials are formed or it may be formed by extrusion other processing steps known in industry.

An example of a simple mechanical device that may be formed or partially formed from PLA or other water-degradable polymer is a flotation container to be attached to casing being run into a horizontal well. Such flotation devices made of metal are well known. The walls and ends of such a container may be formed from degradable polymer, with adequate supports of degradable polymer between the ends to prevent collapse, or the ends and supports may be formed of degradable polymer and designed to allow walls to collapse after a selected time in the well (and before cementing).

Other mechanical parts that may be more easily left in a well than retrieved may also be formed from degradable polymer such as PLA. For example, the case or container of perforating devices may be formed of degradable polymer. After a selected time, the device may then be easily flowed from the well, if desired.

Although the present invention has been described with reference to specific details, it is not intended that such details should be regarded as limitations on the scope of the invention, except as and to the extent that they are included in the accompanying claims.

Claims

1. A method for changing a flow pattern in a well having a casing comprising placing a solid degradable polymer piece in an internal device or internal flow channel in apparatus within the casing in the well such that decrease of a strength of the degradable polymer after a selected range of time causes changing of the flow pattern in the well, wherein the solid degradable polymer piece comprises polylactic acid.

2. The method of claim 1 wherein the solid degradable polymer piece is in the form of a plug, seal or gasket.

3. The method of claim 1 wherein the changing of flow pattern in the well causes co-mingling of fluid streams produced from the well.

4. A method for changing a pressure in a well having a casing comprising placing a solid degradable polymer piece in an internal device or internal flow channel in apparatus within the casing in the well such that decrease of a strength of the degradable polymer after a selected range of time causes changing of the pressure in the well, wherein the solid degradable polymer comprises polylactic acid.

5. The method of claim 4 wherein the solid degradable polymer piece is in the form of a plug, seal or gasket.

6. A method for changing a flow pattern or pressure in a well having a casing comprising placing a solid hydrolytically degradable polymer piece in an internal device or internal flow channel in apparatus within the casing in the well such that decrease of a strength of the degradable polymer after a selected range of time causes changing of the flow pattern in the well, wherein the solid degradable polymer is chemically degraded to polymers having shorter chains that are water soluble.

7. The method of claim 6 wherein the solid degradable polymer piece is in the form of a plug, seal, or gasket.