Controlling wellbore pathways by manipulating the surface area to mass ratio of the diverting material

Abstract

A mixture of at least two shapes of a dissolvable diverter material. The shapes range from a flake having a high surface area to mass ratio to beads having a low surface area to mass ratio. The density of the various shapes may be manipulated by including voids or low-density materials within the shape. The density manipulation allows matching the transport properties of the at least two shapes to the transport fluid so that both shapes may arrive at the desired location at the desired time.

Claims

1. A diverter system for downhole use comprising: a plurality of first particles, second particles, and third particles, wherein the first particles, the second particles, and the third particles comprise at least a first dissolvable material, wherein the first particles define a bead shape formed to incorporate within the first particles a second material of less density than the first dissolvable material to reduce the overall density of the first particles, wherein the reduced overall density of the first particles is less than a density of the second particles, wherein the second particles define a flake shape having at least a fifty percent greater surface area than the first particles, wherein the third particles define a powder, and wherein the plurality of first particles, second particles, and third particles are configured such that the second particles, then the third particles, and then the first particles arrive at a fracture within a hydrocarbon bearing formation.

2. The diverter system of claim 1, wherein the first dissolvable material is a polylactic acid.

3. The diverter system of claim 1, wherein the first particles have a thickness of between 0.01 inches and 0.1 inches.

4. The diverter system of claim 1, wherein the first particles have a thickness of between 0.015 inches and 0.025 inches.

5. A diverter system for downhole use comprising: a plurality of first particles, second particles, and third particles wherein the first particles define a flake shape, the second particles define a bead shape, and the third particles define a powder, wherein the first particles, the second particles, and the third particles comprise at least a first dissolvable material, wherein the second particles are formed to incorporate within the second particles a second material of less density than the first dissolvable material to reduce the overall density of the second particles, further wherein the reduced overall density of the second particles is less than a density of the first particles, wherein the reduced overall density of the second particles allows the second particles to remain entrained in a low viscosity fluid, wherein the low viscosity of the fluid is between about 1 and about 100 centipoise, further wherein the first particles have at least a fifty percent greater surface area than the second particles, and wherein the plurality of first particles, second particles, and third particles are configured such that the first particles, then the third particles, and then the second particles arrive at a fracture within a hydrocarbon bearing formation.

6. The diverter system of claim 5, wherein the first dissolvable material is polylactic acid.

7. The diverter system of claim 6, wherein the first particles have a thickness of between 0.01 inches and 0.1 inches.

8. The diverter system of claim 6, wherein the first particles have a thickness of between 0.015 inches and 0.025 inches.

9. The diverter system of claim 6, wherein the low viscosity fluid is slickwater.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 depicts a dissolvable material that is manipulated in order to vary its surface area or general density with regard to its mass.

(2) FIG. 2 depicts a flake of polylactic acid having a first mass and a bead of polylactic acid having a second mass.

(3) FIG. 3 depicts a disk of a diverter material.

(4) FIG. 4 depicts a chiclet of a diverter material.

DETAILED DESCRIPTION

(5) FIG. 1 depicts an embodiment of the invention where the dissolvable material is manipulated in order to vary its surface area or general density with regard to its mass. For example a particle 10 of the dissolvable material has a height 12, a width 14, and a length 16. The particle 10 may be a material where the overall density of the particle 10 is controlled by the incorporation of less dense materials or by the inclusion of voids into the particle 10, such as by turning the material into a foam. For instance the particle 10 has voids 18, 20, 22, 24, and 26. The total displacement of the voids within particle 10 is subtracted from the overall volume of particle 10 with the result then multiplied by the density of the dissolvable material to determine the overall density of the particle. The various embodiments may be utilized alone or in conjunction with other embodiments.

(6) FIG. 2 depicts a further example of a flake 50 of polylactic acid having a first mass, such as 1.3 grams, and a bead 60 of polylactic acid having a second mass of 1.3 grams. Because polylactic acid generally has a density of about 1.3 g/cm.sup.3, both flake 50 and bead 60 have a volume of about 1 cm.sup.3. In order to turn to determine the radius 62 of bead 60 the volume equation for a sphere may be used.
V.sub.B=(4πr.sup.3)/3

(7) Where the volume of the bead 60 is known. In this case V.sub.B is 1 cm.sup.3 giving a radius 62 of 0.62 cm.

(8) Once the radius 62 of bead 60 is known we can determine the area of the bead 60 using the equation:
A.sub.B=4πr.sup.2

(9) Which leads to an area of the bead 60, A.sub.B, of 4.83 cm.sup.2.

(10) Using a similar methodology we can determine the area of flake 50 to provide a much higher area for a given volume. In this case the volume of the flake 50 may be determined by the formula:
V.sub.F=L×W×H

(11) Where length 52, L, is 2 cm and width 54, W, is 2 cm providing us with a height 56, H, of 0.25 cm.

(12) Knowing the dimensions of flake 50 we can determine the area, A.sub.F, of flake 50 using the formula:
A.sub.F=2×(L×W)+2×(L×H)+2×(W×H)

(13) Which leads to an area of the flake 50, A.sub.F, of 10 cm.sup.2.

(14) In this example the flake 50 has more than twice the surface area of a bead 60 of an equivalent mass, of 1.3 g. It has been found that the preferred size of a flake 50 has a length of about 0.134 inches, a width of about 0.148 inches, and a thickness of about 0.02 inches although the length and width may range as high as 0.5 inches and as small as 0.1 inches. The particle thickness may range as low as 0.01 inches and as high as 0.05. The preferred size of the bead is about 0.125 inches.

(15) In the event that both the 1.3 gram bead 60 and the 1.3 gram flake 50 are both placed in 2⅞ inch tubing with a low viscosity fluid flowing at 3 barrels per minute the 1.3 gram bead 60 is not able to be effectively placed while a 1.3 g flake 50 is able to be effectively placed at the desired location. In such an instance it may be desirable to foam or otherwise manipulate the bead 60 in order to either decrease its density or increase its surface area, A.sub.B, so that the 1.3 g bead 60 has similar fluid transport characteristics as the 1.3 g flake 50.

(16) The fluid transport characteristics of the diverter may be manipulated by changing either the surface area of the diverter material, the density of the diverter material, or both. The transport properties of the diverter can be changed by forming the particles into various shapes in addition to the flake 50 and bead 60 of FIG. 2. FIG. 3 depicts a disk 70 of a diverter material where the disk 70 has a radius 72 and a thickness 74. FIG. 4 depicts a chiclet 80 having a thicker midsection as compared to its side, in this case the midsection has a thickness or height 82 and an edge or periphery thickness 80 that may vary from between 0% to as much as 25% of the height 82 of the diverter material. The density of the diverter may also be varied by inducing bubbles or including a second material having a non-homogenous density, such as air, within the material.

(17) Preferably the diverter is utilized in conjunction with a low viscosity fluid, such as slick water. Generally slick water has no or a very low loading of viscosifier and is generally a Newtonian fluid. In such instances the transport effects of high surface area to mass increases with the reduction in viscosity. In an extreme example, in a cross-linked system, such as in a guar based non-newtonian fluid, the diverter particles are immune to settling regardless of their fluid transport characteristics. However as viscosity drops the impact of the ratio of surface area to mass increases. In one embodiment particles are formed from a dissolvable polymer having variable internal density. In one instance density may be manipulated by mixing a less dense material with the polymer to decrease its density such as by mixing air into the polymer or other material. In other words bubbles may be trapped within the material rendering the material less dense. In other instances voids within the dissolvable polymer may be a vacuum. Similarly in highly turbulent flow the diverter particles are immune to settling regardless of their fluid transport characteristics. While at the other extreme in a low viscosity fluid such as slick water, at low flow rates in laminar flow, the bead, where its density is not controlled, settles out of the fluid at low spots or other points where the beads may be trapped prior to reaching the desired location or at least tending to reach the desired location at some time after any particles having other transport properties have reached the location. Generally water has a viscosity of about 1 centipoise at 20 degrees Celsius is a low viscosity fluid and low viscosity ranges from less than 1 to about 100 centipoise.

(18) In general fluid flow having a high Reynolds number (“Re”) has more turbulent flow and particles moving in such fluid flow are less dependent upon the fluid flow characteristics of the particles. The Reynolds number (Re) is a dimensionless quantity in fluid mechanics used to help predict flow patterns in different fluid flow situations. In general a Reynolds number greater than 10,000 is indicative of turbulent flow, while a Reynolds number of less than 2000 is indicative of laminar flow. Re is generally defined as:

(19) $\mathrm{Re}=\frac{\rho uDH}{\mu }=\frac{uDH}{v}=\frac{QDH}{vA}$

(20) D.sub.H is the hydraulic diameter of the pipe (the inside diameter if the pipe is circular) (m).

(21) Q is the volumetric flow rate (m.sup.3/s).

(22) A is the pipe's cross-sectional area (m.sup.2).

(23) u is the mean velocity of the fluid (m/s).

(24) μ is the dynamic viscosity of the fluid (Pa.Math.s=N.Math.s/m.sup.2=kg/(m.Math.s)).

(25) v (nu) is the kinematic viscosity (v=μ/ρ) (m.sup.2/s).

(26) ρ is the density of the fluid (kg/m.sup.3).

(27) In an embodiment there is a first particle wherein the first particle has a density that is varied depending upon the viscosity. The first particle may be a bead having a variable internal density and a flake, wherein the flake has a surface area providing flow characteristics comparable to the flow characteristics of the bead. In certain instances the flake may have a variable internal density. The fluid may be pumped at a flow rate dependent upon the density of the first particle, the transport properties of the flake, and/or the viscosity of the fluid.

(28) In certain embodiments all of the particles do not have the same transport properties. In such cases the flakes tend to arrive first, then the dust, and then the beads. In such instances the flakes may be compared to a sailboat where due to the large surface area to mass ratio of the flakes the flakes mimic the flow rate of the fluid and therefore arrive first. The powder or dust arrive slightly after the flakes with the beads trailing behind. With the flakes arriving first and just prior to the powder. Flakes are then able to bridge off, the powder packs and seals while the beads give increased pressure tolerance. The flakes also enable bridging against the formation face.

(29) In certain embodiments, for instance when used in uncemented liner applications, the thin cross section and elasticity of the material allow the flakes to deform and pass through the openings in the liner while allowing for bridging against the formation face.

(30) In certain embodiments when used in openhole applications, the greater surface area results in more comprehensive coverage of the formation face, allowing a distinctly new fracture to develop.

(31) The methods and materials described as being used in a particular embodiment may be used in any other embodiment. While the embodiments are described with reference to various implementations and exploitations, it will be understood that these embodiments are illustrative and that the scope of the inventive subject matter is not limited to them. Many variations, modifications, additions and improvements are possible.

(32) Plural instances may be provided for components, operations or structures described herein as a single instance. In general, structures and functionality presented as separate components in the exemplary configurations may be implemented as a combined structure or component. Similarly, structures and functionality presented as a single component may be implemented as separate components. These and other variations, modifications, additions, and improvements may fall within the scope of the inventive subject matter.