Methods and compositions for controlling lost circulation in subterranean operations

A lost circulation composition, that comprises a first portion of particles having a weight mean particle size of less than about 20 microns, a second portion of particles having a weight mean particle size in the range of from about 25 microns to about 400 microns, and a third portion of particles having a weight mean particle size in the range of from about 450 microns to about 1,500 microns, wherein the lost circulation composition has a multimodal particle size distribution, is provided, wherein resilient particles, particles comprising a thermoset polymer laminate, or a combination thereof are present in the lost circulation composition in an amount of at least about 20% by weight of the lost circulation composition, is provided. Drilling fluids, methods of controlling lost circulation, and methods of increasing an effective fracture gradient while drilling also are provided.

BACKGROUND

The present invention relates to subterranean operations. More particularly, the present invention relates to lost circulation compositions and methods of using such lost circulation compositions.

During the drilling of a well bore, a drilling fluid may be circulated down through the inside of the drill string, through the drill bit, and to the surface through the arnnulus between the walls of the well bore and the drill string. The drill string may be a drill pipe, a casing string, or any other suitable conduit. Among other things, the circulating drilling fluid lubricates the drill bit, carries drill cuttings to the surface, and balances the formation pressure exerted on the well bore. One problem associated with the drilling of a well bore may be the undesirable loss of large amounts of the drilling fluid into the subterranean formation. This problem may be referred to as “lost circulation” and the sections of the formation into which the drilling fluid may be lost may be referred to as “lost circulation zones.” The loss of drilling fluid into the formation is undesirable, inter alia, because of the expense associated with the drilling fluid lost into the formation. In addition to drilling fluids, problems with lost circulation may also be encountered with other fluids, for example, spacer fluids, completion fluids (e.g., completion brines) and workover fluids that may be circulated in a well bore. A variety of factors may be responsible for lost circulation. For example, the subterranean formation penetrated by the well bore may be highly permeable or may contain fractures or crevices therein. Furthermore, the formation may breakdown under the hydrostatic pressure applied by the fluid, thereby allowing the fluid to be lost into the formation. For instance, fractures in the subterranean formation may be created or enhanced due to the hydrostatic pressure of the drilling fluid with the resulting loss of drilling fluid into those fractures. As referred to herein, the “effective fracture gradient,” refers to the minimum hydrostatic pressure plus frictional losses that may be required to create or enhance a fracture in a potential lost circulation zone.

A number of methods have been developed to control lost circulation. One method involves the introduction of a settable composition into a problematic zone to prevent and/or reduce the flow of the drilling fluid into the lost circulation zone. However, this method may require an undesired interruption in the drilling process. Another method commonly used to control lost circulation involves the placement of lost circulation materials into the lost circulation zone. These conventional lost circulation materials may be placed into the formation, inter alia, as part of a drilling fluid or as a separate lost circulation pill in an attempt to control and/or prevent lost circulation. Conventional lost circulation materials may include graphitic carbon, ground battery casings, ground tires, ground nut shells (e.g., walnut shells, peanut shells, and almond shells), sized-calcium carbonate, petroleum coke, glass, mica, ceramics, polymeric beads, and the like. To increase the effectiveness of these conventional lost circulation materials, the particle sizes of the lost circulation materials have been optimized. For instance, petroleum coke having from about 35% to about 90% by weight particles between 10 mesh and 60 mesh has been used as a lost circulation material. Additionally, lost circulation materials have been added to drilling fluids in an attempt to increase the effective fracture gradient to allow for continued drilling and prevent lost circulation. For instance, the inclusion of lost circulation materials having between about 250 microns and about 600 microns in the drilling fluid may induce a screenout in the fracture tip that may reduce propagation or creation of fractures in the formation. These conventional methods for combating lost circulation, however, may not provide a desirable level of lost circulation control.

SUMMARY

The present invention relates to subterranean operations. More particularly, the present invention relates to lost circulation compositions and methods of using such lost circulation compositions.

In one embodiment, the present invention provides a lost circulation composition that comprises a first portion of particles having a weight mean particle size of less than about 20 microns; a second portion of particles having a weight mean particle size in the range of from about 25 microns to about 400 microns, and a third portion of particles having a weight mean particle size in the range of from about 450 microns to about 1,500 microns, wherein the lost circulation composition has a multimodal particle size distribution, wherein resilient particles, particles comprising a thermoset polymer laminate, or a combination thereof are present in the lost circulation composition in an amount of at least about 20% by weight of the lost circulation composition.

In another embodiment, the present invention provides a fluid that comprises a lost circulation composition having a multimodal particle size distribution, the lost circulation composition comprising a first portion of particles having a weight mean particle size of less than about 20 microns, a second portion of particles having a weight mean particle size in the range of from about 25 microns to about 400 microns, and a third portion of particles having a weight mean particle size in the range of from about 450 microns to about 1,500 microns, wherein resilient particles, particles comprising a thermoset polymer laminate, or a combination there are present in the lost circulation composition in an amount of at least about 20% by weight of the lost circulation composition.

In another embodiment, the present invention provides a method of controlling lost circulation that comprises contacting a lost circulation zone in a subterranean formation with a lost circulation composition having a multimodal particle size distribution, the lost circulation composition comprising a first portion of particles having a weight mean particle size of less than about 20 microns, a second portion of particles having a weight mean particle size in the range of from about 25 microns to about 400 microns, and a third portion of third particles having a weight mean particle size in the range of from about 450 microns to about 1,500 microns, wherein resilient particles, particles comprising a thermoset polymer laminate, or a combination thereof are present in the lost circulation composition in an amount of at least about 20% by weight of the lost circulation composition.

In another embodiment, the present invention provides a method of controlling lost circulation that comprises adding to a fluid a lost circulation composition having a multimodal particle size distribution, the lost circulation composition comprising a first portion of particles having a weight mean particle size of less than about 20 microns, a second portion of particles having a weight mean particle size in the range of from about 25 microns to about 400 microns, and a third portion of particles having a weight mean particle size in the range of from about 450 microns to about 1,500 microns, wherein resilient particles, particles comprising a thermoset polymer laminate, or a combination thereof are present in the lost circulation composition in an amount of at least about 20% by weight of the lost circulation composition.

In another embodiment, the present invention provides a method of increasing an effective fracture gradient in a portion of a subterranean formation while drilling a well bore that penetrates the portion of the subterranean formation, the method comprising providing a fluid that comprises a lost circulation composition having a multimodal particle size distribution, the lost circulation composition comprising a first portion of particles having a weight mean particle size of less than about 20 microns, a second portion of particles having a weight mean particle size in the range of from about 25 microns to about 400 microns, and a third portion of particles having a weight mean particle size in the range of from about 450 microns to about 1,500 microns, wherein resilient particles, particles comprising a thermoset polymer laminate, or a combination thereof are present in the lost circulation composition in an amount of at least about 20% by weight of the lost circulation composition; placing the fluid into the well bore; and allowing the fluid to contact the portion of the subterranean formation penetrated by the well bore.

In yet another embodiment, the present invention provides a method of controlling lost circulation that comprises providing a fluid that comprises a lost circulation composition having a multimodal particle size distribution, the lost circulation composition comprising a first portion of particles having a weight mean particle size of less than about 20 microns, a second portion of particles having a weight mean particle size in the range of from about 25 microns to about 400 microns, and a third portion of particles having a weight mean particle size in the range of from about 450 microns to about 1,500 microns, wherein resilient particles, particles comprising a thermoset polymer laminate, or a combination thereof are present in the lost circulation composition in an amount of at least about 20% by weight of the lost circulation composition.; placing the fluid into a well bore; and allowing the fluid to contact a lost circulation zone penetrated by the well bore.

The features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of the specific embodiments which follows.

DESCRIPTION

The present invention relates to subterranean operations. More particularly, the present invention relates to lost circulation compositions and methods of using such lost circulation compositions.

The present invention provides lost circulation compositions with improved particle size distributions. In certain embodiments, the present invention provides a lost circulation composition that comprises a first portion of particles having a weight mean particle size (“d50”) of less than about 20 microns; a second portion of particles having a d50 in the range of from about 25 microns to about 400 microns, and a third portion of particles having a d50 in the range of from about 450 microns to about 1,500 microns, wherein the lost circulation composition has a multimodal size distribution. As used herein, the term “particle(s)” refers to particles having a well-defined physical shape as well as those with irregular geometries, including any particles having the physical shape of platelets, shavings, fibers, flakes, ribbons, rods, strips, spheroids, toroids, pellets, tablets, or any other physical shape. The lost circulation compositions having a multimodal particles size distribution may have a bimodal particle size distribution, trimodal particle size distribution, or other suitable particle size distribution as desired by one of ordinary skill in the art based, inter alia, on the particular application.

Generally, resilient particles, particles comprising a thermoset polymer laminate, or a combination thereof are present in the loss circulation composition in an amount of at least about 20% by weight of the lost circulation composition. For example, resilient particles may be present in the lost circulation composition in an amount of at least about 20% by weight. Alternatively, particles comprising a thermoset polymer laminate may be present in the lost circulation composition in an amount of at least about 20% by weight. In yet other embodiments, resilient particles may be present in the lost circulation composition in an amount of at least about 10% by weight and particles comprising a thermoset polymer laminate may be present in the lost circulation composition in an amount of at least about 10% by weight. In some embodiments, at least a portion of the particles comprising the thermoset polymer laminate may be in the form of platelets.

The first portion of particles included in the lost circulation compositions should have a d50 of less than about 20 microns. Generally, the first portion of particles may comprise any materials suitable for use as lost circulation materials, including, but not limited to, minerals (e.g., mineral fibers such as basalt, wollastonite, and sepiolite), thermoset polymer laminates, graphitic carbon-based materials, ground battery casings, ground tires, ground nut shells (e.g., walnut shells, peanut shells, almond shells, etc.), sized-calcium carbonate, petroleum coke, vitrified shale, calcium clay, glass (e.g., ground glass, glass fibers, hollow glass beads, etc.), mica, ceramics, polymeric materials (e.g., hollow or solid polymeric beads, such as styrenedivinyl benzene crosslinked beads, vinylidene chloride beads, polystyrene beads, and the like), synthetic materials (e.g., fibers such as polypropylene fibers), and mixtures thereof. Of these, graphitic carbon-based materials and sized-calcium carbonate are preferred. An example of suitable sized-calcium carbonate having a d50 of less than about 20 microns is “BARACARB® 5” sized-calcium carbonate, which is commercially available from Halliburton Energy Services, Duncan, Okla. Generally, the graphitic carbon-based materials of the present invention may comprise graphite and a carbon matrix. In certain embodiments, the graphite may be present in the graphitic carbon-based materials in an amount of at least about 20% by weight and, in other embodiments, in an amount of from about 80% to about 95% by weight. An example of a suitable calcium clay having a d50 of less than about 20 microns are calcium montmorrillonite clay, commonly referred to as “Rev Dust,” that is commercially available from Baroid Drilling Fluids, Houston, Tex. Other suitable clays and minerals include kaolinite, attapulgite, zeolite, silica, and combinations thereof. Furthermore, in addition to the above-listed materials, the first portion of particles may also comprise drill solids, such as weighting materials (e.g., barite) and bentonite, that are commonly included in drilling fluids, which also may serve as lost circulation materials for the purposes of the present invention when they fall within the specified size range. The appropriate type and amount of the first portion of particles to include in a lost circulation composition of the present invention will vary dependent upon a variety of factors known to those skilled in the art, including formation characteristics and conditions, such as circulation loss rates, fracture geometry, and the like.

In some embodiments, the first portion of particles may comprise resilient particles. As used herein, the phrase “resilient particles” refers to particles that rebound and do not fail when a compaction pressure is applied. Suitable resilient particles may comprise a variety of suitable materials, including graphitic carbon-based materials or elastomeric styrene butadiene block or random copolymers. Graphitic carbon-based materials generally are considered resilient if they have a resiliency of at least about 20% after compression at 10,000 psi. As used herein, the term “resiliency” refers to the percentage increase in sample volume after release of a compaction pressure and is defined by the following formula:

%⁢⁢Resiliency=100⁢(hrho-1)
wherein hois the height of a column of the material being tested under the compaction pressure and hris the height of the column of the material being tested after the compaction pressure is released. An exemplary resiliency test procedure is described in U.S. Pat. No. 5,826,669, the relevant disclosure of which is incorporated by reference herein. An example of suitable resilient carbon-based materials having a d50 of less than about 20 microns is “DESULCO® 9090 RGC” carbon additive having a d50 of about 15 microns, which is commercially available from Superior Graphite, Chicago, Ill. An example of suitable particles comprising elastomeric styrene butadiene block or random copolymers is “Finaprene® 411,” which is commercially available from TOTAL Petrochemicals Elastomers USA, Inc., Houston, Tex. In some embodiments, resilient particles are present in the first portion of particles in an amount of at least about 30% by weight of the first portion. One of ordinary skill in the art will be able to determine additional resilient particles suitable for a particular application.

The second portion of particles included in the lost circulation compositions of the present invention should have a d50 in the range of from about 25 microns to about 400 microns. In some embodiments, the second portion of particles may have a d50 in the range of from about 75 microns to about 350 microns. Generally, the second portion of particles may comprise any materials suitable for use as lost circulation materials, including, but not limited to, minerals (e.g., mineral fibers such as basalt, wollastonite, and sepiolite), thermoset polymer laminates, graphitic carbon-based materials, ground battery casings, ground tires, ground nut shells (e.g., walnut shells, peanut shells, almond shells, etc.), sized-calcium carbonate, petroleum coke, vitrified shale, calcium clay, glass (e.g., ground glass, glass fibers, hollow glass beads, etc.), mica, ceramics, polymeric materials (e.g., hollow or solid polymeric beads, such as styrenedivinyl benzene crosslinked beads, vinylidene chloride beads, polystyrene beads, and the like), synthetic materials (e.g., fibers such as polypropylene fibers), and mixtures thereof. Of these, thermoset polymer laminates at least a portion of which are in the form of platelets, graphitic carbon-based materials, and sized-calcium carbonate are preferred. Examples of suitable sized-calcium carbonate having a d50 in the range of from about 25 microns to about 400 microns include “BARACARB® 25” sized-calcium carbonate, “BARACARB® 50” sized-calcium carbonate, and “BARACARB® 150” sized-calcium carbonate, which are commercially available from Halliburton Energy Services, Duncan, Okla. Generally, the graphitic carbon-based materials of the present invention may comprise graphite and a carbon matrix. In certain embodiments, the graphite may be present in the graphitic carbon-based materials in an amount of at least about 20% by weight and, in other embodiments, in an amount of from about 80% to about 95% by weight. Examples of suitable thermoset laminate materials include those that comprise melamine formaldehyde polymers, urea-formaldehyde type of thermoset polymers, and combinations thereof. One example of a commercially available thermoset polymer laminate material is “FORMICA®” brand laminate from Formica Corporation, Cincinnati, Ohio. An example of commercially available particles comprising thermoset polymer laminates is “PHENOSEAL™ ground laminate from Forta Corporation, Philadelphia, Pa. “PHENOSEAL™ ground laminate is available in Fine, Medium, and Coarse grades. Of these, the Fine Grade material about 55% of which passes through a 250 micron (60 mesh) screen is preferable. The appropriate type and amount of the second portion of particles to include in the lost circulation compositions of the present invention will vary dependent upon a variety of factors known to those skilled in the art, including formation characteristics and conditions, such as circulation loss rates, fracture geometry, and the like.

In some embodiments, the second portion of particles may comprise resilient particles. Suitable resilient particles may comprise a variety of suitable materials, including graphitic carbon-based materials or elastomeric styrene butadiene block or random copolymers. Graphitic carbon-based materials generally are considered resilient if they have a resiliency of at least about 20% after compression at 10,000 psi. Examples of suitable resilient carbon-based materials having a d50 in the range of from about 25 microns to about 400 microns include “STEELSEAL®” carbon additive and “STEELSEAL® Fine” carbon additive, which are commercially available from Halliburton Energy Services, Inc., Duncan, Okla. An example of suitable particles comprising elastomeric styrene butadiene block or random copolymers is “Finaprene® 411,” which is commercially available from TOTAL Petrochemicals Elastomers USA, Inc., Houston, Tex. One of ordinary skill in the art will be able to determine additional resilient particles suitable for a particular application. In some embodiments, resilient particles, particles comprising a thermoset polymer laminate, or combinations thereof are present in the second portion of particles in an amount of at least about 30% by weight of the second portion.

The third portion of particles that may be included in the lost circulation compositions of the present invention should have a d50 in the range of from about 450 microns to about 1,500 microns. In some embodiments, the third portion of particles may have a d50 in the range of from about 450 microns to about 800 microns. Generally, the third portion of particles may comprise any materials suitable for use as lost circulation materials, including, but not limited to, minerals (e.g., mineral fibers such as basalt, wollastonite, and sepiolite), thermoset polymer laminates, graphitic carbon-based materials, ground battery casings, ground tires, ground nut shells (e.g., walnut shells, peanut shells, almond shells, etc.), sized-calcium carbonate, petroleum coke, vitrified shale, calcium clay, glass (e.g., ground glass, glass fibers, hollow glass beads, etc.), mica, ceramics, polymeric materials (e.g., hollow or solid polymeric beads, such as styrenedivinyl benzene crosslinked beads, vinylidene chloride beads, polystyrene beads, and the like), synthetic materials (e.g., fibers such as polypropylene fibers), and mixtures thereof. Of these, thermoset polymer laminates at least a portion of which are in the form of platelets, graphitic carbon-based materials, and sized-calcium carbonate are preferred. An example of suitable sized-calcium carbonate having a d50 in the range of from about 450 microns to about 1,500 microns is “BARACARB® 600” sized-calcium carbonate, which is commercially available from Halliburton Energy Services, Duncan, Okla. Generally, the graphitic carbon-based materials of the present invention may comprise graphite and a carbon matrix. In certain embodiments, the graphite may be present in the graphitic carbon-based materials in an amount of at least about 20% by weight and, in other embodiments, in an amount of from about 80% to about 95% by weight. Examples of suitable thermoset laminates include those that comprise melamine formaldehyde polymers, urea-formaldehyde type of thermoset polymers, and combinations thereof. One example of a commercially available thermoset polymer laminate material is “FORMICA®” brand laminate from Formica Corporation, Cincinnati, Ohio. An example of commercially available particles comprising thermoset polymer laminates is “PHENOSEAL™ ground laminate from Forta Corporation, Philadelphia, Pa. “PHENOSEAL™ ground laminate is available in Fine, Medium, and Coarse grades. Of these, the Fine Grade material about 79% of which passes through a 850 micron (20 mesh) screen is preferable. For wider fracture widths, the Medium Grade material or the Coarse Grade material may be preferable. About 75% of the PHENOSEAL™ Medium Grade ground laminate particles pass through a 1190 micron (14 mesh) screen but not through a 850 micron (20 mesh) screen. About 70% of the PHENOSEAL™ Coarse Grade ground laminate particles pass through a mesh screen between 1190 microns (14 mesh) and 2000 microns (10 mesh). The appropriate type and amount of the third portion of particles to include in the lost circulation compositions of the present invention will vary dependent upon a variety of factors known to those skilled in the art, including formation characteristics and conditions, such as circulation loss rates, fracture geometry, and the like.

In some embodiments, the third portion of particles may comprise resilient particles. Suitable resilient particles may comprise a variety of suitable materials, including graphitic carbon-based materials or elastomeric styrene butadiene block or random copolymers. Graphitic carbon-based materials generally are considered resilient if they have a resiliency of at least about 20% after compression at 10,000 psi. An example of suitable particles comprising elastomeric styrene butadiene block or random copolymers is “Finaprene® 411,” which is commercially available from TOTAL Petrochemicals Elastomers USA, Inc., Houston, Tex. One of ordinary skill in the art will be able to determine additional resilient particles suitable for a particular application. In some embodiments, resilient particles, particles comprising a thermoset polymer laminate, or combinations thereof are present in the third portion of particles in an amount of at least about 30% by weight of the third portion.

The lost circulation compositions of the present invention may provide, among other things, improved lost circulation control over conventional lost circulation compositions. For example, the lost circulation compositions of the present invention may effectively seal the pores and fractures that may be present in shales, sandstones, carbonate rock, and the like. It is believed that due, inter alia, to fluid leak off into the formation the particles present in the lost circulation compositions of the present invention may concentrate in areas leading up to the tip of fractures in the formation, wherein these fractures may be preexisting fractures in the formation or fractures induced by the pressure of fluid (e.g., a drilling fluid). As the concentration of these particles within the fractures and at the fracture tip increases, the transmission of fluid pressure from the fluid to the fracture tip may be reduced, thereby causing a “tip screenout” and a resulting reduction in the effective fracture gradient and prevention of fracture propagation. By including resilient particles in the lost circulation composition, the functionality of the lost circulation composition may be improved. For example, their resiliency may allow the resilient particles to absorb the imposed pressure by reduction in volume and/or to mold themselves into the fracture tip when pressure is applied, thereby rebounding to plug the fracture when the pressure is released. Presence of platelets (e.g., particles comprising a thermoset polymer laminate) of suitable sizes in relation to the fracture width is believe to provide a strong bridging mesh type scaffold network between the walls of the fracture. Generally, resilient particles, particles comprising a thermoset polymer laminate, or a combination thereof may be present in the lost circulation compositions of the present invention in an amount of at least about 20% by weight of the lost circulation composition. Furthermore, the first portion of particles of the present invention may act to improve the functionality of the lost circulation compositions of the present invention. Among other things, it is believed that the first portion of particles may plug the interstices between the second and/or third portion of particles when the lost circulation compositions of the present invention are concentrated within fractures in the subterranean formation, and it is believed that the second portion of particles may plug interstices between the third portion of particles when the lost circulation compositions of the present invention are concentrated within fractures in the subterranean formation.

The lost circulation compositions of the present invention may be included in a variety of fluids in order to prevent or control lost circulation. For example, the lost circulation compositions of the present invention may be included in fluids which are circulated in a well bore, including drilling fluids, spacer fluids, completion fluids (e.g., completion brines), and workover fluids. Generally, the drillings fluids may comprise any suitable fluids, including water-based fluids, oil-based fluids, or combinations thereof. Furthermore, the lost circulation compositions of the present invention may be included in lost circulation treatment fluids that may be used in remedial treatments to control lost circulation. Generally, the lost circulation treatment fluids may comprise any suitable fluids, including water-based fluids, oil-based fluids, or combinations thereof. In some embodiments, the lost circulation treatment fluids may be foamed. One of ordinary skill in the art, with the benefit of this disclosure, will recognize that spacer fluids may need to be used to separate a lost circulation treatment fluids from other fluids in the well bore, for example, where the lost circulation treatment fluid is not compatible with the other fluids in the well bore.

The amount of the lost circulation composition to include in these fluids depends, inter alia, on formation characteristics and conditions, the downhole equipment, the desired application, and other factors known to those skilled in the art. In some embodiments, a lost circulation composition of the present invention may be included in a fluid in an amount of less than about 100 pounds of the lost circulation composition per barrel of the fluid. In certain embodiments, for example, where the lost circulation composition is included in a drilling fluid, a lost circulation composition of the present invention may be included in a drilling fluid in an amount in the range of from about 10 pounds to about 30 pounds of the lost circulation composition per barrel of the drilling fluid. In certain embodiments, for example, where the lost circulation composition is included in a lost circulation treatment fluid, a lost circulation composition of the present invention may be included in a lost circulation treatment fluid in an amount in the range of from about 30 pounds to about 80 pounds of the lost circulation composition per barrel of the fluid. One of ordinary skill in the art, with the benefit of this application, will know the appropriate amount of a lost circulation composition of the present invention to include in a fluid for a particular application.

The lost circulation compositions of the present invention may be prepared in a variety of ways. For example, the components of the lost circulation compositions may be dry blended and then mixed into the fluid at the point of usage. In other embodiments, the components of the lost circulation composition may be simultaneously added to the fluid. In yet other embodiments, the components of the lost circulation composition may be individually added to the fluid. For example, where added to a drilling fluid, the drilling fluid already may comprise at least a portion of the particles (e.g., drill solids) that form the lost circulation compositions of the present invention. Therefore, only the particles not present in the drilling fluid may be added to such drilling fluid to form the lost circulation compositions of the present invention.

In one embodiment, the present invention provides a lost circulation composition that comprises a first portion of particles having a weight mean particle size of less than about 20 microns; a second portion of particles having a weight mean particle size in the range of from about 25 microns to about 400 microns, and a third portion of particles having a weight mean particle size in the range of from about 450 microns to about 1,500 microns, wherein the lost circulation composition has a multimodal particle size distribution, wherein resilient particles, particles comprising a thermoset polymer laminate, or a combination thereof are present in the lost circulation composition in an amount of at least about 20% by weight of the lost circulation composition.

In another embodiment, the present invention provides a drilling fluid that comprises a lost circulation composition having a multimodal particle size distribution, the lost circulation composition comprising a first portion of particles having a weight mean particle size of less than about 20 microns, a second portion of particles having a weight mean particle size in the range of from about 25 microns to about 400 microns, and a third portion of particles having a weight mean particle size in the range of from about 450 microns to about 1,500 microns, wherein resilient particles, particles comprising a thermoset polymer laminate, or a combination there are present in the lost circulation composition in an amount of at least about 20% by weight of the lost circulation composition.

In another embodiment, the present invention provides a method of controlling lost circulation that comprises contacting a lost circulation zone in a subterranean formation with a lost circulation composition having a multimodal particle size distribution, the lost circulation composition comprising a first portion of particles having a weight mean particle size of less than about 20 microns, a second portion of particles having a weight mean particle size in the range of from about 25 microns to about 400 microns, and a third portion of third particles having a weight mean particle size in the range of from about 450 microns to about 1,500 microns, wherein resilient particles, particles comprising a thermoset polymer laminate, or a combination thereof are present in the lost circulation composition in an amount of at least about 20% by weight of the lost circulation composition.

In another embodiment, the present invention provides a method of controlling lost circulation that comprises adding to a fluid a lost circulation composition having a multimodal particle size distribution, the lost circulation composition comprising a first portion of particles having a weight mean particle size of less than about 20 microns, a second portion of particles having a weight mean particle size in the range of from about 25 microns to about 400 microns, and a third portion of particles having a weight mean particle size in the range of from about 450 microns to about 1,500 microns, wherein resilient particles, particles comprising a thermoset polymer laminate, or a combination thereof are present in the lost circulation composition in an amount of at least about 20% by weight of the lost circulation composition.

In another embodiment, the present invention provides a method of increasing an effective fracture gradient in a portion of a subterranean formation while drilling a well bore that penetrates the portion of the subterranean formation, the method comprising providing a fluid that comprises a lost circulation composition having a multimodal particle size distribution, the lost circulation composition comprising a first portion of particles having a weight mean particle size of less than about 20 microns, a second portion of particles having a weight mean particle size in the range of from about 25 microns to about 400 microns, and a third portion of particles having a weight mean particle size in the range of from about 450 microns to about 1,500 microns, wherein resilient particles, particles comprising a thermoset polymer laminate, or a combination thereof are present in the lost circulation composition in an amount of at least about 20% by weight of the lost circulation composition; placing the fluid into the well bore; and allowing the fluid to contact the portion of the subterranean formation penetrated by the well bore.

In yet another embodiment, the present invention provides a method of controlling lost circulation that comprises providing a fluid that comprises a lost circulation composition having a multimodal particle size distribution, the lost circulation composition comprising a first portion of particles having a weight mean particle size of less than about 20 microns, a second portion of particles having a weight mean particle size in the range of from about 25 microns to about 400 microns, and a third portion of particles having a weight mean particle size in the range of from about 450 microns to about 1,500 microns, wherein resilient particles, particles comprising a thermoset polymer laminate, or a combination thereof are present in the lost circulation composition in an amount of at least about 20% by weight of the lost circulation composition.; placing the fluid into a well bore; and allowing the fluid to contact a lost circulation zone penetrated by the well bore.

To facilitate a better understanding of the present invention, the following examples of specific embodiments are given. In no way should the following examples be read to limit, or define, the scope of the invention.

Particles sizes for various materials that may be used to prepare lost circulation compositions of the present invention were measured using Malvern equipment. In particular, particles sizes for BARACARB® 150 sized-calcium carbonate, BARACARB® 600 sized-calcium carbonate, STEELSEAL® carbon additive, Mica, and Rev Dust were measured and are presented in Table 1.

Particle sizes for the “PHENOSEAL™ ground laminate were beyond the measuring ability of the Malvern Particle Size Analyzer. The manufacturer provided data is summarized as follows. The material is available in Fine, Medium, and Coarse grades. About 79% of the Fine Grade material passes through a 850 micron (20 mesh) screen. About 75% of the Medium Grade material passes through a 1190 micron (14 mesh) screen but not through a 850 micron (20 mesh) screen. And about 70% of the Course Grade material passes through a mesh screen between 1190 microns (14 mesh) and 2000 microns (10 mesh).

Tests were conducted using various sample lost circulation treatment fluids and a Hassler sleeve test cell containing a synthetic core. Synthetic cores, having a length of 4.2 inches and a diameter of 1 inch, were prepared by mixing different grades of sand (5% 12/20 mesh sand; 25% 20/40 mesh sand; 70% Oklahoma No. 1 sand) with mixed with a resin mixture. The resin mixture for a single synthetic core comprised a bisphenol-A epoxide resin (ER-1™, 4 ml), a gamma-aminopropyl tri-alkoxy silane coupling agent (PLASTIC FIXER, 0.3 ml), and a diamine hardener (EH-2™, 4 ml). The mixture was charged into a TEFLON™ tube containing, in the center of the tube, a TEFLON™ rectangular stick or a stainless steel stick which had been machined to have the desired tapering width along the length of the stick. The height of the stick was 12 mm. When the sand mix was partially cured, the stick was pulled out and the mix was allowed to set in the tube at 140° F. for at least 6 hrs. Therefore, the synthetic core was formed with a simulated fracture therein where the width of the simulated fracture was based on the tapering of the stick. Thus, synthetic cores were formed having a wider end of about 3 mm and a narrower end ranging from about 1 mm to about 3 mm, depending on the tapering of the stick.

Referring now toFIG. 1, the test equipment used in this example is illustrated. A synthetic core, prepared as described above, was fitted into a rubber sleeve (not shown), inserted a metal receptacle (not shown), and mounted in a Hassler sleeve test cell2, having one end thereof designated as the well bore side4and one end thereof designated as the formation side6. The synthetic core was mounted so that the wider end of the simulated fracture faced well bore side4. The pressure on well bore side4of test cell2was measured by a pressure transducer8mounted on well bore side4of test cell2. The metal cylinder containing the core inside the rubber sleeve was connected to a pump5with which a desired pressure can be applied on the rubber sleeve to achieve an impermeable fit between the core and the rubber sleeve. The test cell2also was connected to a thermostat (not shown) to the control the temperature during testing.

A drilling fluid reservoir10and a brine reservoir12were provided and the bottoms of these two reservoirs were connected to a three-way valve14by conduits16and17, respectively. Drilling fluid reservoir10contains a control drilling fluid, and brine reservoir12contains an API brine. The outlet of three-way valve14was connected to the inlet of a pump18by conduit20. Pump18had a programmable flow rate and pressure. The outlet of pump18was connected to the entrance of well bore side4of test cell2by a conduit22. Thus, by appropriate manipulation of three-way valve14, pump18was used to direct either the control drilling fluid or the API brine to test cell2. Also, conduit22was connected to valve23which was connected to atmosphere.

A sample reservoir24was also provided, and the top of sample reservoir24was connected to a source of pressurized nitrogen, generally designated by numeral26. Sample reservoir24contained a sample lost circulation treatment fluid. The bottom outlet of sample reservoir24was optionally connected to the top to the entrance of well bore side4of test cell2by a conduit28. Test cell2had a three-way design to connect sample reservoir24to test cell2by conduit28without having to disconnect conduit22.

The exit of formation side6of test cell2was connected to a three-way valve30by conduit31. One outlet connection of three-way valve30was connected to atmosphere. The other outlet connection of three-way valve30was connected to the bottom of an oil reservoir32that contained a mineral oil by conduit34. The top of oil reservoir32was connected to a back pressure regulator36, the pressure of which was adjusted with nitrogen pressure. The other side of back pressure regulator36was connected to atmosphere.

The test procedure was designed to determine the ability of a lost circulation composition to withhold pressure applied from a drilling fluid when applied on the wider end of the simulated fracture, as described in the Forward Flow Procedure listed below. Additionally, if the lost circulation composition withstood the pressure during the forward flow procedure, the ability of the lost circulation composition to withstand pressure applied from formation fluids was determined, as described in the Reverse Flow Procedure listed below.

Forward Flow Test Procedure

First, pump18was used to pass the control drilling fluid from drilling fluid reservoir10through the synthetic core within test sleeve2, from well bore side4to formation side6. Three-way valve30was open to atmosphere. Once synthetic core was wet with the control drilling fluid, the pump was stopped and the three-way design into test cell2at well bore side4was altered to allow for drilling fluid flow from conduit28through which sample reservoir was connected to test cell2. The three-way design restricted flow back into conduit22. The sample lost circulation treatment fluid was then prepared by adding the components thereof into a separate beaker (directly into sample reservoir24if it the fluid viscosities too quickly) and stirring for about one minute with a spatula. Upon preparation, the sample lost circulation treatment fluid was charged into sample reservoir24. Next, pressure from source of pressurized nitrogen26was used to push the lost circulation treatment fluid through the synthetic core within test sleeve2, from well bore side4to formation side6. The lost circulation treatment fluid was pushed through the synthetic core until it extruded though the formation side6of test cell2. Hopefully, the lost circulation composition within the sample lost circulation treatment fluid plugged the simulated fracture of the synthetic core, which was indicated by stoppage of fluid drainage with minimum applied pressure of about 500 psi. Subsequently, test cell2should be disconnected from conduit28and conduit31, and any solid on the face or bottom of the synthetic core or any conduits was cleaned. Once cleaned, test cell2was reconnected conduit31and conduit22so that the outlet of pump18was connected to test cell2.

Next, pump18was used to pump the control drilling fluid from drilling fluid reservoir10to fill conduit22with the control drilling fluid. Also, conduit31and conduit34were filled with mineral oil from oil reservoir32by controlling three-way valve30, after which three-way valve30was closed to atmosphere. Next, the drilling fluid in drilling fluid reservoir10and test cell2were heated to 180° F. After 30 minutes at 180° F., pump18was set at a flow rate of 2 milliliters per minute (ml/min) and a pressure of 100 psi. In addition, a back pressure of 100 psi was applied to back pressure regulator36with nitrogen gas. Additionally, pump5was used to apply a pressure on the rubber sleeve of 300 psi to about 600 psi higher than the pressure applied by pump on well bore side4. The pressure at the face of the synthetic core on well bore side4of test cell2was measured using pressure transducer8. If the lost circulation composition withstood the initial pressure, the pressure applied to well bore side4(using pump18) and the pressure applied to the rubber sleeve (using pump5) were steadily increased in 100 psi increments up to the maximum operating pressure of test cell2while observing the flow rate of oil dripping through back pressure regulator36. If the flow rate of oil dripping through back pressure regulator36reaches 2 ml/min or the pressure read by pressure transducer8dropped to zero, the plug of the lost circulation composition in the simulated fracture of the synthetic core failed to withstand the pressure applied thereto by the control drilling fluid. When the pressure of pump18reached the maximum operating pressure of test cell2, the pressure was held for 30 minutes and the flow of oil through back pressure regulator36was observed.

Reverse Flow Test Procedure

First, while maintaining temperature at 180° F., test cell2was reversed within the system, as shown inFIG. 2. Accordingly, pump18was connected to the formation side6of test cell2by conduit22. Likewise, well bore side4was connected to three-way valve30by conduit31. Also, pressure transducer8was positioned to measure the pressure on formation side6of test cell2.

Next, pump18was used to flush any of the control drilling fluid in conduit22through valve23to atmosphere. Next, pump18was set to provide the API brine to the formation side6of test cell2at flow rate of 2 ml/min and a pressure of 100 psi. In some tests, pump18provided the control drilling fluid. Because test cell2was reversed, the pressure from the API brine was applied to the narrow end of the simulated fracture in the synthetic core. In addition 100 psi was applied to back pressure regulator36with nitrogen gas. Additionally, pump5was used to apply a pressure on the rubber sleeve of 300 psi to 600 psi higher than that applied by pump18on formation side6. The pressure at the face of the synthetic core on formation side6of test cell2was measured using pressure transducer8. If the lost circulation composition withstood the initial pressure, the pressure applied to it by the API brine (using pump18) and the pressure applied to the rubber sleeve (using pump5) were steadily increased in 100 psi increments up to the maximum operating pressure test cell2while observing the flow rate of oil dripping through back pressure regulator36. If the flow rate of oil dripping through back pressure regulator36reaches 2 ml/min or the pressure read by pressure transducer8drops to zero, the plug of the lost circulation composition in the simulated fracture of the synthetic core failed to withstand the pressure applied thereto by the control drilling fluid. When the pressure of pump18reached the maximum operating pressure of test cell2or the lost circulation composition failed, the heat was turned off and pump18and back pressure regulator36were stopped.

Sample Lost Circulation Treatment Fluids

These series of tests were conducted using a control drilling fluid and various sample lost circulation treatment fluids. The components of the fluids were mixed and either hot rolled or, when large quantities were made, kept in a water bath overnight at 150° F. for about 16 hours to about 18 hrs. When BARACARB® 150, BARACARB® 600, STEELSEAL®, and Rev Dust, were added to the sample lost circulation treatment fluid, these components were stirred into the fluid just prior to use, unless otherwise stated. Generally, these lost circulation compositions have different amounts, sizes, and types of particles therein, as lost circulation compositions. Referring now toFIG. 3, a graphical illustration of the percent volume change per unit particle size increase versus particle size is shown for the control drilling fluid, Sample Lost Circulation Treatment Fluid No 3, and Lost Circulation Treatment Fluid No. 4. The formulations of the control drilling mud and Sample Lost Circulation Treatment Fluids Nos. 1-5 are provided in Table 2.

TABLE 2ControlSample Lost Circulation Treatment FluidComponentDrilling FluidNo. 1No. 2No. 3No. 4No. 5Water (ppb)278278278271278278Bentonite (ppb)444444NaCl (ppb)727272637272BARITE1(ppb)939393819393XAN VIS2(ppb)1.31.31.31.31.31.3PAC L ™3(ppb)0.250.250.250.250.250.25NaOH (ppb)0.50.50.50.50.50.5DEXTRID1.01.01.01.01.01.0LT ™4(ppb)BARACARB ™None301515NoneNone600 (ppb)BARACARB ™NoneNoneNoneNone30100150 (ppb)STEELSEAL ™ (ppb)NoneNone1515NoneNoneMica (ppb)NoneNoneNoneNoneNoneNoneRev Dust (ppb)NoneNoneNone79NoneNoneDensity, ppg11.411.711.712.211.812.51Barite is a barium sulfate that is commercially available from Baroid Drilling Fluids, Houston, TX.2XAN VIS is a xanthan based viscosifying that is commercially polymer available from Baroid Drilling Fluids, Houston, TX.3“PAC L ™” filtration control agents is a polyanionic cellulose that is commercially available from Baroid Drilling Fluids, Houston, TX.4“DEXTRID LT ™” filtration control agent is a modified starch product that is commercially available from Baroid Drilling Fluids, Houston, TX.

The formulations of Sample Lost Circulation Treatment Fluids Nos. 6-10 are provided in Table 3.

TABLE 3Sample Lost Circulation Treatment FluidComponentNo. 6No. 7No. 8No. 9No. 10Water (ppb)278278278278278Bentonite (ppb)44444NaCl (ppb)7272727272BARITE1(ppb)9393939393XAN VIS2(ppb)1.31.31.31.31.3PAC L ™3(ppb)0.250.250.250.250.25NaOH (ppb)0.50.50.50.50.5DEXTRID1.01.01.01.01.0LT ™4(ppb)BARACARB ™NoneNone7.5None22.5600 (ppb)BARACARB ™151007.5NoneNone150 (ppb)STEELSEAL ™151515157.5(ppb)Mica (ppb)NoneNoneNone15NoneRev Dust (ppb)NoneNoneNoneNoneNoneDensity, ppg11.712.611.911.811.81Barite is a barium sulfate that is commercially available from Baroid Drilling Fluids, Houston, TX.2XAN VIS is a xanthan based viscosifying that is commercially polymer available from Baroid Drilling Fluids, Houston, TX.3“PAC L ™” filtration control agents is a polyanionic cellulose that is commercially available from Baroid Drilling Fluids, Houston, TX.4“DEXTRID LT ™” filtration control agent is a modified starch product that is commercially available from Baroid Drilling Fluids, Houston, TX.

The results of the tests using the above-described sample lost circulation treatment fluids are provided in Table 4.

Thus, Example 2 illustrates that varying the particle size distribution within a lost circulation treatment fluid may impact the ability of the lost circulation treatment fluid to prevent circulation losses.

Additional tests were performed on a variety of sample lost circulation treatment fluids using the same procedures as in Example 2. For this series of tests, the control drilling fluid was a synthetic oil-based drilling fluid that is commercially available under the trademark “PETROFREE®” fluid from Baroid Drilling Fluids, Houston, Tex. Additionally, an oil wetting lecithin-based agent was added to the control drilling fluid in an amount of 2 pounds per barrel of the drilling fluid, the oil wetting lecithin-based agent is commercially available under the trademark “DRILTREAT®” additive from Baroid Drilling Fluids, Houston, Tex. An additional additive, that is commercially available under the trademark “EZ MUL® NT” emulsifier from Baroid Drilling Fluids, Houston, Tex., was also added to the control drilling fluid in an amount of 6 pounds per barrel of the drilling fluid to improve the oil wetting ability of the control drilling fluid. To prepare the sample lost circulation treatment fluids used in the present example, the control drilling fluid, prepared as described above, was mixed with particles of the type and amount shown in Table 5. Referring now toFIG. 4, a graphical illustration of the percent volume change per unit particle size increase versus particle size is shown for the control drilling mud, Sample Lost Circulation Treatment Fluid No. 12, and Sample Lost Circulation Treatment Fluid No. 13.

The results of the tests utilizing the above-described sample lost circulation treatment fluids are provided in Table 6.

Thus, Example 3 illustrates that varying the particle size distribution within a lost circulation treatment fluid may impact the ability of the lost circulation treatment fluid to prevent circulation losses.

Additional tests were performed on a variety of sample lost circulation treatment fluids utilizing the same procedures as in Example 2. For this series of tests, the control drilling fluid was a synthetic oil-based drilling fluid of 12 ppg that is commercially available under the trademark “PETROFREE®” fluid from Baroid Drilling Fluids, Houston, Tex. To prepare the sample lost circulation treatment fluids used in the present example, the control drilling fluid, prepared as described above, was mixed with particles of the type and amount shown in Table 7.

The results of the tests utilizing the above-described sample lost circulation treatment fluids are provided in Table 8. The resulted listed for Sample Lost Circulation Treatment Fluids in Table 8 are from Example 3 and are listed in Table 8 for comparative purposes.