WO2009078744A1

WO2009078744A1 - Additive for preventing proppant flowback from hydraulic fractures

Info

Publication number: WO2009078744A1
Application number: PCT/RU2007/000707
Authority: WO
Inventors: Elena Mikhailovna Pershikova; Evgeny Borisovich Barmatov
Original assignee: Schlumberger Canada Limited; Services Petroliers Schlumberger; Schlumberger Holdings Limited; Schlumberger Technology B.V.; Prad Research And Development N.V.
Priority date: 2007-12-14
Filing date: 2007-12-14
Publication date: 2009-06-25

Abstract

This invention relates to the oil and gas industry and can be used for improving proppant flowback control and increasing the yield of production wells after a hydraulic fracturing treatment. Proppant pack strengthening additives which have arch/cellular, mesh, mesh/cellular, honeycomb, bubble, sponge-like or foam structure having at least one edge and one node are disclosed.

Description

ADDITIVE FOR PREVENTING PROPPANT FLOWBACK FROM

HYDRAULIC FRACTURES

This invention relates to hydraulic fracturing of subterranean formations, for example in the oil and gas industry. In particular, it relates to increasing fluid production from wells by limiting the closure of propped hydraulic fractures.

The following terms will be used as defined here:

- an edge: an imaginary line forming the skeleton of a cellular structure;

- a cell: a space confined by structure edges; and

- a node: an intersection point of three or more edges.

After hydraulic fracturing, the proppant remains in the resultant fracture in the form of a porous pack, the main functions of which include (1) prevention of closure of the fracture and, (2) ensuring fluid (for example hydrocarbon) flow through the channels inside the resultant structure. The quantitative parameter of the efficiency of such proppant packs is the so-called conductivity, which can be calculated using Darcy's law as follows:

C = k W = μ — ^Q

H AP ' where C is the conductivity, k is the permeability of the pack, Q is the fluid flow rate, μ is the fluid viscosity, L is the pack length, H is the pack height, W is the pack width, and AP is the pressure differential of the fluid through the proppant pack. In this case, the pack width W is determined using the following formula: C.

W =

where C_p is the proppant concentration in the fracture, φ is the porosity of the resultant pack, and γ_p is the proppant density.

Analysis of the above formulas suggests that proppant conductivity depends, among other parameters, on the width of the proppant pack, which in the ideal case will be the same as the width of the fracture. In turn, the width of the fracture will be determined by the proppant concentration in the fracture (in terms of weight of proppant per unit area of fracture face).

Currently, one of the most important factors reducing the efficiency of hydraulic fractures is proppant flowback along with the fluid production. This process reduces the proppant concentration in the fracture and hence reduces the fracture width. Proppant flowback from the fracture is also undesirable because proppants are abrasive to submersible pumps, causing their failure.

Many methods are known to be effective in reducing proppant flowback and/or the loss of other materials from hydraulic fractures.

The most commonly used approach to limiting proppant flowback is based on the application of curable resin coated proppants (for example as disclosed in US Patent No. 5,218,038). The curable resin coated proppant is pumped into the fracture at the end of the treatment. However, there are a number of considerable limitation to the application of this type of proppant; the problems are caused by chemical reactions between the resin coating and the fracturing fluid. First, this interaction results in partial degradation and disintegration of the resin coating, thus reducing the strength of the adhesion between the proppant particles and, consequently, the strength of the proppant pack. Second, the interaction between the resin coating components and the fracturing fluid leads to uncontrollable changes in the fluid rheology. This also reduces the efficiency of the hydraulic fracturing method. In addition to the above-listed factors, cyclic loads during well completion, and shutting-in of wells (especially long shut-in periods) may damage the strength of the proppant pack.

Another method of limiting proppant flowback (disclosed in US Patent No. 6,059,034) is mixing the proppant with deformable particulate material, especially in the form of bead-shaped particles. The deformable particles are made of polymer materials and are in the shape of one or more than one of beaded, cubic, bar-shaped, cylindrical and shapes with a maximal length-based aspect ratio equal to or less than 5. The deformable particles may also be in the form of plastic balls or composite particles made of a non-deformable core and a deformable coating. Typically, the non-deformable core is 50 to 95% of the overall particle size; usually the non-deformable core is made of quartz, cristobalite, graphite, gypsum or talc. In another embodiment (as disclosed in US Patent No. 6,330,916) the core consists of deformable materials and may include ground or crushed nut and seed shells, ground or crushed fruit pits and processed wood.

For limiting proppant flowback, proppant may also be mixed with adhesive polymeric materials (as disclosed in US Patent No. 5,582,249). The adhesive compounds interact mechanically with proppant particles and coat them to produce a thin and sticky layer. As a result, proppant particles stick to one another and to produced sand and crushed proppant particles, thus at least largely preventing particle flowback. Also known is the method in which proppant flowback is reduced by filling the formation with fibrous material mixed with proppant particles (as disclosed in US Patent No. 5,330,005) resulting in the fibers interweaving with the proppant particles to increase the mechanical strength of the combined pack and thus reduce proppant flowback from the fracture. Furthermore, the addition of fibers provides for more efficient load redistribution by producing membranes across the major part of the proppant pack. Fibrous structures are more flexible compared with resin coated proppants and allow movement of the proppant/fiber pack without a loss in mechanical strength.

These known proppant flowback prevention methods are characterized by high production costs and labor consumption. Furthermore, the use of the materials described above for proppant flowback prevention, including proppants with a hardening resin coating, may reduce the conductivity of proppant packs.

To address the abovementioned disadvantages, a new pack- strengthening additive has been developed for preventing proppant flowback and for producing an improved gravel pack. The pack- strengthening additive is in the form of particles having arch/cellular, mesh, mesh/cellular, honeycomb, bubble, sponge-like or foam structures with high porosity and permeability. The pack-strengthening additive is injected into the well with conventional proppants and carrier fluids. The new materials form a web that provides high mechanical strength of the proppant pack due to full or partial penetration of proppant particles into the structure of the new material, thus preventing proppant flowback during fluid production. In the meantime, due to the high structural porosity of the pack-strengthening additive, a high permeability of the proppant pack is achieved.

The technical objective achieved by the technical solution developed herein is the use of the new type of additive for preventing proppant flowback from hydraulic fractures and gravel packs in producing wells.

The technical result achieved by the implementation of the technical solution developed herein is increasing the fluid yield from formations in which the hydraulic fracturing process is used.

Summary of the Invention

An additive for preventing proppant flowback from hydraulic fractures is disclosed. The additive is in the form of particles having an arch/cellular, mesh, mesh/cellular, honeycomb, bubble, sponge-like or foam structure having at least one edge and one node. The particles are formed from a polymer or from a composite polymer containing up to 70% of a binder. The additive particles may be coated with a tackifying and/or curable material. The particles may be formed directly in a proppant pack by polymerization, hardening or cross-linking of reactant polymer foamed or homogeneously distributed between proppant particles.

A method is disclosed for increasing the production of fluid from wells. The method involves hydraulic fracturing with proppant; particles of an additive are also injected into the fracture, the particles having an arch/cellular, mesh, mesh/cellular, honeycomb, bubble, sponge-like or foam structure including at least one edge and one node. The particles are injected simultaneously with at least a portion of the proppant. The particles may be injected in only the final proppant stage or stages of the hydraulic fracturing treatment. The concentration of the additive particles may be 0.1 to 99.9% by weight proppant.

Brief Description of the Drawings

Figure 1 shows the particle structure of the pack-strengthening additive of the Invention.

Figure 2 shows the structure of a pack made up of conventional proppant and of a web of the pack-strengthening additive of the Invention.

Detailed Description of the Invention

It should be understood that throughout this specification, when a concentration or amount or other parameter range is described as being useful, or suitable, or the like, it is intended that any and every concentration or amount or other parameter within the range, including the end points, is to be considered as having been stated. Furthermore, each numerical value should be read once as modified by the term "about" (unless already expressly so modified) and then read again as not to be so modified unless otherwise stated in context. For example, "a range of from 1 to 10" is to be read as indicating each and every possible number along the continuum between about 1 and about 10. In other words, when a certain range is expressed, even if only a few specific data points are explicitly identified or referred to within the range, or even when no data points are referred to within the range, it is to be understood that the inventors appreciate and understand that any and all data points within the range are to be considered to have been specified, and that the inventors have possession of the entire range and all points within the range. Although some of the following discussion emphasizes fracturing, the composition and method of the Invention may be used in fracturing, gravel packing, and combined fracturing and gravel packing in a single operation ("frac and pack", "frac-pack", "frac-n-pack", stimpack, etc.).

The technical result is achieved by using particles of pack- strengthening material having an arch/cellular, mesh, mesh/cellular, honeycomb, bubble, sponge-like or foam structure. The main components of this structure are cells (1), edges (2) and nodes (3) as shown, for example, in Figure 1. The shapes of the particles of the pack-strengthening additive are selected to have at least one edge and one node per particle.

The material used herein has high porosity and permeability (for example, an open porosity of above 45%).

For the method disclosed herein, the new type of additive may be used either during the entire hydraulic fracturing treatment of the formation, or during only the final stages of proppant injection. In either case, the concentration of the new additive in the proppant/additive mixture may range from 0.1 to 99.9% by weight of proppant.

The pack-strengthening additive preferably are made from a polymer or a composite polymer containing up to 70% of a binder that determines the hardness, the Young's Modulus, the flow point and other mechanical and physico-chemical parameters of the additive. The admixing of the new additive with the proppant prevents proppant flowback from the fracture during well completion, cleanup, flushing, or acid treatment, and during the production stage of the well. In this case the favorable action of the new additive is mechanical capturing of proppant particles (4) in the web structure formed from particles of the pack-strengthening additive (as shown in Figure 2) and the formation of mechanical bonds inside the proppant/additive pack due to the at least partial confinement of the proppant in the web and the consequent higher rolling friction between the proppant particles.

As noted above, the pack-strengthening additive is a polymer or a composite polymer containing up to 70% of a binder that determines the hardness, the Young's Modulus, the flow point and other mechanical and physico-chemical parameters of the polymer capable of full or partial hardening or cross-linking under reservoir conditions. In this case, the favorable action of the new additive is mechanical capturing of proppant particles in the web structure described above and the formation of mechanical bonds inside the proppant pack due to the partial embedment of the proppant into the assembly of the new additive and to adhesion of proppant particles to the edges of the cellular/arch structure to form large clusters which prevent proppant flowback.

It is preferable to use co- or homopolymers of polyolefins, polyamides, polyvinyl compounds, polyimides, polyurethanes, polycarbonates, polysulfones, polyethers and their mixtures to form the pack-strengthening additive.

Alternatively, the pack-strengthening additive may be made of a ceramic material, or may be a metallic structure or a metal/ceramic composite having an arch/cellular, mesh, mesh/cellular, honeycomb, bubble, sponge-like or foam structure having at least one edge and one node.

The particles of the new additive may further be coated with any of many known tacky or adhesive materials, thus providing not only for proppant-proppant adhesion, but also for proppant adhesion to the straight arch of the arch/cellular structure. Examples of such tackifying materials include one or more than one of polyamides, quaternized polyamides,, polyesters, polycarbonates, polycarbamates, natural resins such as shellac, acrylates, silylated polyamides, and mixtures of these materials.

Hydraulic fracturing is typically performed by injecting proppant in stages characterized by differences in one or more than one of the fracturing fluid, the proppant, the proppant concentration, the injection rate, etc. The pack-strengthening additive may be added during all stages, at constant or varying concentration, or may be added only in the last stage or later stages of the injection.

The continuous arch/cellular structure may also be formed directly in the fracture due to polymerization, hardening or cross-linking of reactant pack-strengthening additive particles that are foamed or homogeneously distributed between proppant particles.

The method and pack-strengthening additive of the Invention may be used with treatment chemicals such as inhibitors, biocides, breakers, buffers, paraffin inhibitors and corrosion inhibitors, and may be used with other solid materials such as fluid loss additives and diverters. The compositions and methods of the Invention may be used when at least a portion of the proppant is resin-coated.

Suitable proppant materials include any proppant or gravel used in the industry, for example ceramic particulate, sand of different shapes, proppant or sand with cured resin coating, expanded haydite, vermiculite, agloporite, or proppants with curable resin coating, and mixtures of such materials. The Invention may be used in wells of any orientation, in open or cased holes, and with or without screens. The Invention may be used for wells for production, injection, or storage of any fluids, such as water, hydrocarbons or carbon dioxide.

The technical solution disclosed herein may be illustrated with the following implementation example.

Proppant flowback tests were carried out using an experimental apparatus including a 12x12 cm stainless steel cell having a 10 mm wide slot. The proppant pack or proppant/additive pack test specimen was placed in the cell, and water was pumped through the cell. The water pumping system was in the form of a closed loop including an up to 100 1/min flow rate water pump with adjustable delivery, a flow meter connected to a computer, a reduction valve and a settling tank. The water flow rate was adjusted manually by the operator based on the flow meter readings. The experimental system was under axially directed pressure created by a hydraulic press. The system allows measurement of the water flow rate at which the proppant pack fails.

The test was performed with 0.595 mm to 1.19 mm (16/30 mesh) ceramic proppant. The proppant was mixed with foamed polyurethane having an average cell size of 2.5 mm. The foamed polyurethane had a three-dimensional bubble structure consisting of dodecahedrons, each face of which was a pentagon. The pentagons were formed by edges between which there was a membrane or window. At least one membrane had always been destroyed, thus forming an open pore structure. The average foamed polyurethane granule size was 6 mm. Reticulated foamed polyurethane was homogeneously mixed with proppant, at a concentration of 3 % by weight of proppant, in a fracturing fluid thickened with guar gel. The resultant mixture was placed between two Ohio sandstone cores in a proppant flowback testing cell to form a proppant/additive pack, and the standard test was carried out. A closing pressure of 40 MPa was applied to the cell. Following that, the cell was heated to 90⁰C and exposed to this temperature for 2 hours. The proppant/additive pack strength was measured by pumping water containing 2% KCl heated to 90±l ⁰C through the cell. The water flow rate was gradually increased until the proppant pack was completely destroyed. Proppant pack destruction was detected by an abrupt drop in the pressure difference readings of the differential pressure gauges, and by proppant carryover to a gravity filter. For comparison, a comparative test was carried out with a pack of 0.595 to 1.19 mm (16/30 mesh) proppant alone. The test results showed that the flow rate at pack failure increased by 65±4 times when foamed polyurethane particles were added, as compared to proppant alone.

In a field test of this technical solution, the yield of a producing well in Western Siberia was increased by approximately 19%.

Claims

We claim:

1. An additive for preventing proppant flowback from hydraulic fractures in the form of particles having an arch/cellular, mesh, mesh/cellular, honeycomb, bubble, sponge-like or foam structure comprising at least one edge and one node.

2. The additive of Claim 1 wherein said particles are formed from a polymer.

3. The additive of Claim 1 wherein said particles are formed from a composite polymer containing up to 70% of a binder.

4. The additive of Claim 1 wherein said particles are further coated with a tackifying and/or curable material.

5. The additive of Claim 1 wherein said particles are formed directly in a proppant pack by polymerization, hardening or cross-linking of reactant polymer foamed or homogeneously distributed between proppant particles.

6. A method of increasing the production of fluid from wells, comprising hydraulic fracturing with proppant wherein particles of an additive are injected into the fracture, said particles having an arch/cellular, mesh, mesh/cellular, honeycomb, bubble, sponge-like or foam structure comprising at least one edge and one node.

7. The method of Claim 6 wherein said particles are injected simultaneously with at least a portion of said proppant.

8. The method of Claim 6 wherein said particles are injected in the final proppant stage or stages of said hydraulic fracturing.

9. The method of Claim 6 wherein the concentration of the additives is 0.1 to 99.9% by weight proppant.