Reducing particulate flow-back in wells

This invention provides a method of treating subterranean zones to reduce particulate flow-back therefrom.

The transport of formation fines, e.g. sand and the like, from subterranean zones or formations with produced fluids is very detrimental in that the formation fines erode metal goods, plug piping and vessels and cause damage to valves, instruments and other production equipment. Such formation fines are generally available for transport from unconsolidated subterranean zones or formations.

In order to prevent the transport of formation fines from subterranean producing zones, particulate solids have been placed in the well bores or formations penetrated thereby such as by gravel packing or propped fracturing. In gravel packing treatments, particulate solids such as graded sand (referred to in the art as gravel) is suspended in a treating fluid and carried to a subterranean zone in which a gravel pack is to be placed. Once the gravel is placed in the zone, the treating fluid is recovered or allowed to dissipate into subterranean formations penetrated by the well bore. The gravel pack functions as a filter to separate formation fines from produced formation fluids while permitting the produced fluids to flow into and through the well bore. In fracturing treatments, a treating fluid is pumped through a well bore into a subterranean zone to be stimulated at a rate and pressure such that fractures are formed and extended in the subterranean zone. Particulate solids (referred to in the art as proppant particles) such as graded sand are carried into the fractures by the treating fluid. The proppant particles are deposited in the fractures and the treating fluid is recovered. The proppant particles function to prevent the formed fractures from closing whereby conductive channels are formed through which produced fluids can flow to the well bore.

While gravel packs and propped fractures have been used successfully to reduce or prevent the transport of formation fines, a problem very often encountered is the flow-back of gravel or proppant particles which leads to the transport of formation fines with hydrocarbon and other fluids produced from the subterranean zone. Like formation fines, the flow-back of gravel or proppant particles from gravel packs or propped fractures with or without formation fines erodes metal goods, plugs, piping and vessels and causes damage to valves, instruments and other production equipment.

A number of techniques have heretofore been developed to prevent gravel and proppant particle flow-back which include coating the gravel or proppant particles with a hardenable resin or tackifying agent that consolidates the gravel or proppant particles into hard permeable masses. In addition, fibers, thermoplastic particulate, ribbons, flakes and other similar materials have been mixed with the gravel or proppant particles to prevent gravel or proppant flow-back. While the techniques utilized heretofore have been successful in limiting gravel or proppant particle flow-back, gravel or proppant particle flow-back still occurs.

In EP1126131, there is provided a method of completing a subterranean producing zone containing unconsolidated sands penetrated by a well bore, which method comprises the steps of placing a sand screen in the subterranean zone to be completed, isolating the annulus between the sand screen and the well bore in the zone, and then introducing a plurality of solidified open cell foam pieces into the annulus between the sand screen and the well bore whereby the foam pieces are uniformly packed into the annulus. The open cells of the foam pieces are of a size such that the unconsolidated sand is prevented from entering the cell but produced fluids can flow therethrough. The solidified open cell foam pieces do not readily form bridges in the annulus between the sand screen and the well bore and can be uniformly packed in the annulus.

We have now devised an improved method of treating subterranean zones penetrated by well bores whereby gravel or proppant particle flow-back and/or the transport of formation fines from the subterranean zones is reduced or prevented.

The present invention provides a method of treating a subterranean zone, which method comprises introducing into said subterranean zone a treating fluid having a mixture of reticulated foam fragments and particulate solids suspended therein; and depositing said mixture of said reticulated foam fragments and said particulate solids in said subterranean zone whereby said reticulated foam fragments reduce or prevent the flow-back of said particulate solids and the transport of formation fines from said subterranean zone upon producing fluids from said zone.

In a preferred embodiment, the invention provides a method of fracturing a subterranean zone. Reticulated foam fragments are combined with a fracturing fluid having proppant particles suspended therein to thereby form a mixture of the reticulated foam fragments with the proppant particles suspended in the fracturing fluid. The reticulated foam fragments are preferably present in the fracturing fluid in an amount in the range of from about 0.1% to about 5% by weight of the proppant particles therein. The fracturing fluid is introduced into the subterranean zone at a rate and pressure sufficient to extend fractures in the subterranean zone. Thereafter, the mixture of the reticulated foam fragments and proppant particles is deposited in the subterranean zone whereby the reticulated foam fragments reduce or prevent the flow-back of the proppant particles and the transport of formation fines from the subterranean zone upon producing fluids from the zone.

In order that the invention may be more fully understood, reference is hereafter made to the accompanying drawings, in which:

• FIGURE 1 is a photograph of an example of reticulated foam fragments useful in accordance with this invention.
• FIGURE 2 is a photograph of the reticulated foam fragments of FIG. 1 having proppant entrapped therein.

The present invention provides methods of reducing or preventing the flow-back of particulate solids placed in subterranean zones as well as the transport of formation fines from the subterranean zones upon producing fluids therefrom. A method of this invention for treating a subterranean zone is comprised of the following steps. A treating fluid having a mixture of reticulated foam fragments and paraticulate solids suspended therein is provided. The treating fluid is introduced into the subterranean zone and the mixture of reticulated foam fragments and particulate solids is deposited in the subterranean zone. The reticulated foam fragments reduce or prevent the flow-back of the particulate solids and the transport of formation fines from the subterranean zone upon producing fluids from the zone.

The reticulated foam fragments useful in accordance with this invention can be formed of various materials including, but not limited to, resins, polyolefins, polyurethanes, polyvinylchlorides, metals and ceramics. The reticulated foam fragments preferably have a pore density in the range of from about 5 to about 80 pores per linear inch (about 5 to about 80 pores per linear 2.54 cm) and can have various shapes. Preferably, the fragments have lengths no longer than about 1 inch (2.54 cm) and widths or diameters no longer than about ½ inch (1.27 cm). Particularly suitable reticulated foam fragments are cubical and have lengths of about ½ inch (1.27 cm), widths of about ¼ inch (0.635 cm) and thicknesses of about ⅛ inch (0.318 cm).

Generally, the reticulated foam fragments are present in the treating fluid in an amount in the range of from about 0.1% to about 5% by weight of the particulate solids therein, more preferably in an amount of about 0.25% to about 1.5% and most preferably in an amount of about 1%.

Various treating fluids can be utilized in accordance with this invention including, but not limited to, aqueous fluids, liquid hydrocarbon fluids and foamed aqueous and liquid hydrocarbon fluids. Of these, an aqueous treating fluid is generally preferred. The viscosity of the treating fluid utilized can be increased by combining a gelling agent therewith in order to suspend the mixture of reticulated foam fragments and particulate solids therein. A variety of gelling agents well known to those skilled in the art can be utilized, including, but not limited to, natural and derivatized polysaccharides which are soluble, dispersible or swellable in aqueous liquids and biopolymers such as xanthan and succinoglycon. Of the various gelling agents which can be utilized, modified gums such as carboxyalkyl derivatives like carboxymethylguar and hydroxyalkyl derivatives like hydroxypropylguar. Modified celluloses and derivatives thereof can also be employed including, but not limited to, carboxyethylcellulose, carboxymethylhydroxyethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose and the like.

The particulate solids which can be utilized in the treating fluids include, but are not limited to, graded sand, ceramic materials, bauxite materials, glass materials, polymeric materials and wall nut hull material. Of these, graded sand is generally preferred. The particulate solids are generally included in the treating fluid in an amount in the range of from about 0.1 to about 30 pounds of particulate solids per gallon (about 120 to about 3595 kg per m³) of the treating fluid.

In order to consolidate and strengthen the mixture of the reticulated foam fragments and particulate solids after the mixture has been deposited in the subterranean zone, the particulate solid can be coated with a hardenable resin composition. The hardenable resin composition hardens after the mixture of reticulated foam fragments and particulate solids has been placed in the subterranean zone and consolidates the mixture into a hard permeable mass. A particularly suitable hardenable resin composition which can be utilized is comprised of a hardenable resin component and a hardening agent component. Hardenable resin components which can be utilized include, but are not limited to, bisphenol A-epichlorohydrin resin, polyepoxide resin, novolac resin, polyester resin, phenol-aldehyde resin, urea-aldehyde resin, furan resin, urethane resin, glycidyl ether and mixtures thereof. The hardening agent component which delayedly causes the hardenable resin component to harden can include, but is not limited to, amines, aromatic amines, polyamines, aliphatic amines, cyclo-aliphatic amines, amides, polyamides, 4,4'-diaminodiphenyl sulfone, 2-ethyl-4-methyl imidazole and 1,1,3-trichlorotrifluoroacetone, Of these 4,4'-diaminodiphenyl sulfone is generally preferred.

Most preferably, the reticulated foam fragments and the particulate solids in the treating fluid are coated with a tackifying agent. The presence of the tackifying agent prevents the segregation of the reticulated foam fragments from the particulate solids during mixing. In addition, after the mixture of reticulated foam fragments and particulate solids is deposited in the subterranean zone, the tackifying agent causes the reticulated foam fragments and particulate solids to stick together and formation fines produce from the subterranean zone to stick to the reticulated foam fragments and particulate solids. Tackifying compounds which can be utilized include, but are not limited to, liquids and solutions of polyamides, polyesters, polycarbonates, polycarbamates, natural resins and the reaction product of a polyacid with a multivalent ion. Of these, the reaction product of a polyacid with a multivalent ion is preferred. Tackifying compounds of the types set forth above are described in detail in U.S Patent No. 5,833,000 issued to Weaver et al. on November 10, 1998.

Another method of this invention for fracturing a subterranean zone is comprised of the following steps. A fracturing fluid having proppant particles suspended therein is provided. Reticulated foam fragments are combined with the fracturing fluid to thereby form a mixture of the reticulated foam fragments with the proppant particles suspended therein. The fracturing fluid is introduced into the subterranean zone at a rate and pressure to extend fractures in the subterranean zone. Thereafter, the mixture of the reticulated foam fragments and the proppant particles is deposited in the subterranean zone whereby the reticulated foam fragments reduce or prevent the flow-back of the proppant particles and the transport of formation fines form the subterranean zone upon producing fluids from the zone.

The reticulated foam fragments and the proppant particles are the same as those described above as are the other components, amounts and the like set forth above.

A preferred method of treating a subterranean zone of this invention comprises the steps of: (a) providing a treating fluid having a mixture of reticulated foam fragments and particulate solids suspended therein; (b) introducing the treating fluid into the subterranean zone; and (c) depositing the mixture of the reticulated foam fragments and the particulate solids in the subterranean zone whereby the reticulated foam fragments reduce or prevent the flow-back of the particulate solids and the transport of formation fines from the subterranean zone upon producing fluids from the zone.

Another preferred method of fracturing a subterranean zone of this invention comprises the steps of: (a) providing a fracturing fluid having proppant particles suspended therein; (b) combining reticulated foam fragments with the fracturing fluid to thereby form a mixture of the reticulated foam fragments and the proppant particles suspended therein; (c) introducing the fracturing fluid into the subterranean zone at a rate and pressure sufficient to extend fractures in the subterranean zone; and (d) depositing the mixture of the reticulated foam fragments and the proppant particles in the subterranean zone whereby the reticulated foam fragments reduce or prevent the flow-back of the proppant particles and the transport of formation fines from the subterranean zone upon producing fluids from the zone.

In order to further illustrate the methods of this invention, the following examples are given.

Example 1

Without Tackifying Agent

An amount of 300 grams of bauxite proppant was used to form a slurry with water prior to adding 3 grams of reticulated foam particulate having a pore density of 30 pores per linear inch (ppi) (30 pores per linear 2.54 cm) and dimensions of 3/8 inch (0.953 cm) in length, ¼ inch (0.635 cm) in width and 1/8 inch (0.318 cm) in thickness. The reticulated foam particulate used is shown in FIG 1. Stirring was continued until a homogeneous slurry was formed. The mixture was then packed into a visual flow chamber. A ½ inch (1.27 cm) perforation was installed at the outlet of the chamber. The inlet of the flow chamber was connected to tap water faucets. Flow was established one the flow chamber was filled with water. A slow flow rate (250 mL/min) was initiated and steadily increased until the faucets were fully opened whereby the flow rate was greater than 16 L/min. Only a very small amount of proppant was produced during the initial flow and no additional proppant was produced afterward, even as the flow was cycled from 0 to more than 16L/mon.

With Tackifying Agent

A proppant slurry was prepared as described in Example 1 except that a polyamide-type tackifying agent in the amount of 4.5 mL was first dry coated onto the proppant before mixing the proppant with water to form the slurry. Three grams of 30 ppi (30 pores per linear 2.54 cm) reticulated foam particulate was added to the slurry as the slurry was being stirred. The mixture of proppant and reticulated foam was then packed into the flow chamber and was subjected to a flow test as described above. During the flow test the proppant pack remained stable during increasing and cycling flow rates of from 0 to 16 L/min. Only a very small amount of proppant was produced as the initial flow was established. It was also observed that the proppant grains were embedded and entrapped within the reticulated foam fragments, forming small, stable individual proppant "pillows" within reticulated foam fragments, forming small, stable individual "pillows" within the reticulated foam fragments, forming small, stable individual proppant "pillows" within the proppant pack as shown in FIG. 2.