# Patent

## Title
Subterranean treatment fluid composition and method of treatment

## Abstract

A thickened composition comprising a polymer, a divalent ions source, water and cement is disclosed. Such composition enables fluid loss reduction and higher gel strength. This may be useful for treating a well for example as a fluid spacer or a scavenger; this may also be used a hydraulic fracturing fluid.

## Background
RELATED APPLICATION DATA
The current application claims the benefit of U.S. provisional application Ser. No. 61/649,966, filed on May 22, 2012, the entire content of which is incorporated herein by reference.


BACKGROUND
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
This application relates in general to well treatment such as stimulation of wells penetrating subterranean formations, and more specifically to fracture stimulation by injection of fluid into a fracture to form regions of low resistance to flow through the fracture for the production of hydrocarbons.
Various methods are known for fracturing a subterranean formation to enhance the production of fluids therefrom. In the typical application, a pressurized fracturing fluid hydraulically creates and propagates a fracture. The fracturing fluid carries proppant particulates into the extending fracture. When the fracturing fluid is removed, the fracture does not completely close from the loss of hydraulic pressure; instead, the fracture remains propped open by the packed proppant, allowing fluids to flow from the formation through the proppant pack to the production wellbore.
SUMMARY
Embodiments relate to methods, comprising adding cement and a source of divalent ions to a treatment fluid containing a polymer and water thereby increasing the viscosity of the treatment fluid.
Embodiments pertain to compositions comprising a polymer, a source of divalent ions, water and cement.
Further embodiments aim at methods of treating a well, comprising adding cement and a source of divalent ions to a treatment fluid containing a polymer and water to form a thickened composition; then, pumping the thickened composition down the well.



BRIEF DESCRIPTION OF THE DRAWINGS
These and other features and advantages will be better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings.
FIG. 1 shows the experimental setup used to measure the force exerted on a probe inserted into a gel.
FIG. 2 illustrates the force recorded for a mixture of 100 g of 5 particles per thousand (ppt) of diutan polymer at various concentrations of calcium carbonate.
FIG. 3 shows the effect of adding cement and calcium carbonate to 100 g of 5 ppt of diutan solution.
FIG. 4 shows the effect of adding higher concentration of cement to a calcium carbonate and 100 g of 5 ppt of diutan solution.
FIG. 5 shows the force measurement with time.
FIG. 6 illustrates the effects of varying the nature of the polymers.



DETAILED DESCRIPTION OF SOME ILLUSTRATIVE EMBODIMENTS
For the purposes of promoting an understanding of the principles of the disclosure, reference will now be made to some illustrative embodiments of the current application. Like reference numerals used herein refer to like parts in the various drawings. Reference numerals without suffixed letters refer to the part(s) in general; reference numerals with suffixed letters refer to a specific one of the parts.
As used herein, “embodiments” refers to non-limiting examples of the application disclosed herein, whether claimed or not, which may be employed or present alone or in any combination or permutation with one or more other embodiments. Each embodiment disclosed herein should be regarded both as an added feature to be used with one or more other embodiments, as well as an alternative to be used separately or in lieu of one or more other embodiments. It should be understood that no limitation of the scope of the claimed subject matter is thereby intended, any alterations and further modifications in the illustrated embodiments, and any further applications of the principles of the application as illustrated therein as would normally occur to one skilled in the art to which the disclosure relates are contemplated herein.
Moreover, the schematic illustrations and descriptions provided herein are understood to be examples only, and components and operations may be combined or divided, and added or removed, as well as re-ordered in whole or part, unless stated explicitly to the contrary herein. Certain operations illustrated may be implemented by a computer executing a computer program product on a computer readable medium, where the computer program product comprises instructions causing the computer to execute one or more of the operations, or to issue commands to other devices to execute one or more of the operations.
At the outset, it should be noted that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system related and business related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. In addition, the composition used/disclosed herein can also comprise some components other than those cited. In the summary of the invention and this detailed description, each numerical value should be read once as modified by the term “about” (unless already expressly so modified), and then read again as not so modified unless otherwise indicated in context. Also, in the summary of the invention and this detailed description, it should be understood that a concentration range listed or described as being useful, suitable, or the like, is intended that any and every concentration within the range, including the end points, is to be considered as having been stated. 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. Thus, even if specific data points within the range, or even no data points within the range, are explicitly identified or refer to only a few specific, it is to be understood that inventors appreciate and understand that any and all data points within the range are to be considered to have been specified, and that inventors possessed knowledge of the entire range and all points within the range.
As used herein, the terms “treatment fluid” or “wellbore treatment fluid” are inclusive of “fracturing fluid” or “treatment slurry” and should be understood broadly. These may be or include a liquid, a solid, a gas, and combinations thereof, as will be appreciated by those skilled in the art. A treatment fluid may take the form of a solution, an emulsion, slurry, or any other form as will be appreciated by those skilled in the art.
As used herein, “slurry” refers to an optionally flowable mixture of particles dispersed in a fluid carrier. The terms “flowable” or “pumpable” or “mixable” are used interchangeably herein and refer to a fluid or slurry that has either a yield stress or low-shear (5.11 s−1) viscosity less than 1000 Pa and a dynamic apparent viscosity of less than 10 Pa·s (10,000 cP) at a shear rate 170 s−1, where yield stress, low-shear viscosity and dynamic apparent viscosity are measured at a temperature of 25° C. unless another temperature is specified explicitly or in context of use.
In some embodiments, the treatment fluid may include a continuous fluid phase, also referred to as an external phase, and a discontinuous phase(s), also referred to as an internal phase(s), which may be a fluid (liquid or gas) in the case of an emulsion, foam or energized fluid, or which may be a solid in the case of a slurry. The continuous fluid phase may be any matter that is substantially continuous under a given condition. Examples of the continuous fluid phase include, but are not limited to, water, hydrocarbon, gas, liquefied gas, etc., which may include solutes, e.g. the fluid phase may be a brine, and/or may include a brine or other solution(s). In some embodiments, the fluid phase(s) may optionally include a viscosifying and/or yield point agent and/or a portion of the total amount of viscosifying and/or yield point agent present. The slurry may also be an energized fluid (e.g., an N2 or CO2 based foam), a viscoelastic surfactant (VES) viscosified fluid, and an oil-based fluid including a gelled, foamed, or otherwise viscosified oil.
The discontinuous phase if present in the treatment fluid may be any particles (including fluid droplets) that are suspended or otherwise dispersed in the continuous phase in a disjointed manner. In this respect, the discontinuous phase can also be referred to, collectively, as “particle” or “particulate” which may be used interchangeably. As used herein, the term “particle” should be construed broadly. For example, in some embodiments, the particle(s) of the current application are solid such as proppant, sands, ceramics, crystals, salts, etc.; however, in some other embodiments, the particle(s) can be liquid, gas, foam, emulsified droplets, etc. Moreover, in some embodiments, the particle(s) of the current application are substantially stable and do not change shape or form over an extended period of time, temperature, or pressure; in some other embodiments, the particle(s) of the current application are degradable, dissolvable, deformable, meltable, sublimeable, or otherwise capable of being changed in shape, state, or structure.
The particles in the slurry in various embodiments may be multimodal. As used herein multimodal refers to a plurality of particle sizes or modes which each has a distinct size or particle size distribution, e.g., proppant and fines. As used herein, the terms distinct particle sizes, distinct particle size distribution, or multi-modes or multimodal, mean that each of the plurality of particles has a unique volume-averaged particle size distribution (PSD) mode. That is, statistically, the particle size distributions of different particles appear as distinct peaks (or “modes”) in a continuous probability distribution function. For example, a mixture of two particles having normal distribution of particle sizes with similar variability is considered a bimodal particle mixture if their respective means differ by more than the sum of their respective standard deviations, and/or if their respective means differ by a statistically significant amount. In certain embodiments, the particles contain a bimodal mixture of two particles; in certain other embodiments, the particles contain a trimodal mixture of three particles; in certain additional embodiments, the particles contain a tetramodal mixture of four particles; in certain further embodiments, the particles contain a pentamodal mixture of five particles, and so on. Representative references disclosing multimodal particle mixtures include U.S. Pat. No. 5,518,996, U.S. Pat. No. 7,784,541, U.S. Pat. No. 7,789,146, U.S. Pat. No. 8,008,234, U.S. Pat. No. 8,119,574, U.S. Pat. No. 8,210,249, US 2010/0300688, US 2012/0000641, US 2012/0138296, US 2012/0132421, US 2012/0111563, WO 2012/054456, US 2012/0305245, US 2012/0305254, US 2012/0132421, PCT/RU2011/000971 and U.S. Ser. No. 13/415,025, each of which are hereby incorporated herein by reference.
In some embodiments, there is disclosed a method comprising adding cement and a source of divalent ions to a treatment fluid containing a polymer; thereby increasing the viscosity of the treatment fluid. The polymer may be a polysaccharide such as gellan gum and gellan gum derivatives, diutan gum and diutan gum derivatives, ramsan gum and ramsan gum derivatives. The divalent source may be calcium, magnesium, and other divalent ions. In some embodiments, the divalent source is calcium and the source of calcium may be a calcium containing inorganic material selected from the group consisting of calcium oxide, calcium hydroxide, or calcium carbonate, and mixtures thereof. The source of cement may be a Portland cement, either hydrated or unhydrated. Other types of cement such as calcium-aluminate cement or Sorel cements may also be used in the current application.
In some embodiments of the current application, a small amount of cement is utilized in conjunction with calcium carbonate and a bio-polymer to produce significant improvement in fluid properties. In particular the gel strength of the fluid may be enhanced. The fluid composition may also include different types of additives including sand, proppants, fibers and the like. Further polymers may also be present such as guar gum, xanthan, polyacrylamide, karaya, gum tragacanth, gum ghatti, gum, acacia, gum konjak, shariz, locus, psyllium, tamarind, gum tara, carrageenin, gum kauri, hydroxypropyl guar, hydroxyethyl guar, carboxymethyl hydroxypropyl guar and carboxymethyl hydroxy-ethyl guar. The concentration of cement may be from 0.1% to 10% by weight of composition; or it may be from 0.1 to 5%, or it may be from 0.2 to 3%.
The proppant, when present, can be naturally occurring materials, such as sand grains. The proppant, may also be man-made or specially engineered, such as coated (including resin-coated) sand, modulus of various nuts, high-strength ceramic materials like sintered bauxite, etc. In some embodiments, the proppant of the current application, when present, has a density greater than 2.45 g/mL, e.g., 2.5-2.8 g/mL, such as sand, ceramic, sintered bauxite or resin coated proppant. In some embodiments, the proppant of the current application, when present, has a density less than or equal to 2.45 g/mL, such as less than about 1.60 g/mL, less than about 1.50 g/mL, less than about 1.40 g/mL, less than about 1.30 g/mL, less than about 1.20 g/mL, less than 1.10 g/mL, or less than 1.00 g/mL, such as light/ultralight proppant from various manufacturers, e.g., hollow proppant.
In some embodiments, the current application discloses a composition for treating a subterranean formation, said composition comprising a polysaccharide, a source of calcium, and a source of cement. The polysaccharide may be a heteropolysaccharide. In some embodiments, the polysaccharide is selected from a group consisting of gellan gum and gellan gum derivatives, diutan gum and diutan gum derivatives, ramsan gum and ramsan gum derivatives. Specifically, the polysaccharide may be a diutan gum having a tetrasaccharide repeating unit in the polymer backbone. The concentration of polymer may be from 0.02% to 1.5% by weight of composition; or it may be from 0.05 to 1%.
In some embodiments, the source of calcium is a calcium containing inorganic material, such as calcium oxide, calcium hydroxide and calcium carbonate. The concentration of calcium may be from 4% to 40% by weight of composition; or it may be from 5% to 30%.
The combination of cement, polymer and calcium may be present in an aqueous fluid. Any type of water may be used in the present fluid such as sea water, buffered water or water produced from a well.
The composition may further comprise particulates of silicates, sand, or proppants. The composition may further comprise heavy brines such calcium bromide, zinc bromide, potassium chloride, sodium chloride, or magnesium chloride. In some embodiment, the composition may further comprise a weighting agent such as barite or hematite; the composition may also comprise clay.
Without being bound by any theory, it is believed that the addition of low cement concentration together with calcium carbonate have a viscosifying effect on the polymer, enabling the fluid to suspend particulate solids with varying densities including proppants. The viscosity and gel strength of the composition may be increased by adding small amounts of cement before or after the addition of calcium containing material.
The kinetics of gel formation of the composition may be controlled by the size of the Portland cement and calcium containing inorganic solids and/or by encapsulation. Using a low amount of cement and divalent ions enables a reduction of polymer concentration is the treatment fluid while achieving the same viscosity. Moreover, the composition of the current application may further enhance the conductivity of the treatment fluid compared to conventional treatment fluid, such as high solid content formulation. The composition of the current application may also provide beneficial environmental impact due to the usage of less material volume and polymer concentration compared with conventional treatment fluid.
In further embodiments, the composition of the current application may be used to strengthen pillars formed by the treatment fluid such as when using a high solid content fluid. An overflush fluid comprising cement filtrate or formulated synthetically may be used to create efficient channels into the high solids content fluid placed inside the fracture.
Cement may be used either as cured cement particulates or unhydrated cement particles or encapsulated cement particulates to create localized gelled areas within the high solids content fluid placed inside a fracture. Accordingly, cement can be used in high solids content formulation to promote segregation and/or channelization. Cement may also be used in the formulation to create controlled rate of gelation and channelization.
A high solid content fluid may be a fluid as defined in U.S. Pat. No. 7,833,947, incorporated herein by reference in its entirety.
In some embodiments, the composition may also be used as a spacer fluid between treatment fluid and overflush fluid or any other sequential fluid to minimize mixing down the pipe. Such composition may also be used as a scavenger.
Embodiments of the current application may be used to create gels of specific strengths, isolate zones, conduct clean-out operation by coiled tubing, create gels such that any fluids containing solid particles may be suspended, plug formation, create temporary plugs, conduct water shut off applications.
In some embodiments, fibers may be added for example to improve lost circulation properties.
The following examples show development of varying gel strengths based mainly on three additives including a polymer, cement and calcium carbonate. The amount of cement required is relatively small that has pronounced effect on the gel strength. The composition is not limited to the three components mentioned here but may also include other polymeric and particulate additives and their combinations.
EXAMPLES
Example 1
Two gels were formed in order to compare qualitatively the gel formed without cement and with 5 wt % cement added to a mixture of calcium carbonate and a diutan polymer. The Diutan polymer concentration was 30 ppt (pounds per thousand) in water and the calcium carbonate concentration was 80 grams added to 100 ml polymer solution. In the presence of cement a much stronger and cohesive gel was formed compared with a formulation without cement where the gel was exhibiting syneresis.
Example 2
Table 1 shows the full formulation of the base fluid used in the experiment which includes 11.39 wt % of calcium carbonate and, 0.036 wt % of a Diutan polymer and 0 g of cement. This formulation was modified in two ways as given in Table 1 to demonstrate that a stable rheology may still be maintained by including cement in the formulation and reducing the calcium carbonate and polymer concentration. The first modification reduced the amount of small particle size calcium carbonate (2 microns) and Diutan, and included small amount of cement. The second modification used reduced amount of calcium carbonate of larger particles size (35 microns), reduced amount of Diutan and small amount of cement.







TABLE 1







Formulation of the base fluid and its two modified versions


Diutan was GEOVIS ® XT from Kelco Oil field Group. The dispersant was


Sodium-Polynaphtalene Sulfonate from BASF Corp.












Modified Fluid




Base Fluid
No. 1
Modified Fluid No. 2



Wt %
Wt %
Wt %













Proppant sand
51.72
55.83
55.87


(40/70 mesh)





Sand
8.75
9.45
9.44


(100 Mesh)





Silica flour
7.95
8.59
8.59


CaCO3
11.39
4.39 (2 μm)
4.39 (35 μm)


Diutan
0.036
0.026
0.026


Dispersant
0.097
0.105
0.105


Portland Class G
0
0.081
0.026


Cement





Water
19.94
21.52
21.64


Solid Volume
60
54.7
54.7


Fraction (%)





Specific Gravity
2
1.85
1.85


PPA
14.1
15.5
15.5









The rheology of the second modified fluid measured using Fann 35 viscometer is given in Table 2. Both modified formulations resulted in stable formulations over a period of at least 5 days at room temperature and gave rheology that was similar to the base fluid.







TABLE 2







Fann rheology (Rotor 1 Bob 5) at room temperature of the two modified versions


of the base fluid











Base Fluid
Modification No. 1
Modification No. 2















Dial

Dial

Dial



Dial readings
Readings
Dial readings
Readings
Dial readings
Readings


RPM
after mixing
15 min later
after mixing
15 min later
after mixing
15 min later
















300
>300
>300
181
186
178
180


200
238
239
140
144
139
140


100
144
145
90
92.5
90
90.5


60
103
104
69
71.5
70
71


30
71
78
49
51.5
50
51


20
58
65
41.5
44
42.5
43


10
44
49
32
34
32.5
33


6
36
40
27
28.5
28
27.5


3
30
33
21.5
23.5
22.5
22.5









Example 3
FIG. 1 shows the experimental setup used to measure the force exerted on a cylindrical probe driven at a constant rate of 2 mm/s into a gel. A texture analyzer, TA HD plus (From Texture Technology Corp.) was used to characterize the gel quality and acquire force with distance driven into the gel data.
FIG. 2 show a graph of force recorded for a mixture of 100 g of 5 ppt Diutan polymer and various concentrations of CaCO3. This was the baseline data in the absence of cement. FIG. 3 shows the effect of adding 0.5 g of cement to varying concentrations of CaCO3 in a 100 g, 5 ppt Diutan polymer solution. The presence of cement increased the gel strength by almost 10 times at higher concentration of CaCO3. The strength of the gel may be increased by more than 30 times by increasing the amount of cement added to the mixture as shown in FIG. 4.
Example 4
FIG. 5 shows that including cement in a mixture of polymer solution and calcium carbonate increases it gel strength with time. A more pronounced increased in gel strength was observed after one day and thereafter the increase was somewhat smaller. The kinetics of the gel strength development may therefore be tuned through varying cement, CaCO3 and polymer concentration.
Example 5
The use of different polymers in conjunction with cement and calcium carbonate on the gel strength gave different magnitude of gel strength. The order of increasing gel strength was found to be Diutan<Guar<Xanthan<10% partially polyacrylamide as shown in FIG. 6. The polymer concentration was 10 ppt in water to which 20 g of CaCO3 and 2 g of cement was added. The 10% partially polyacrylamide gave the strongest gel followed by Xanthan, Guar and Diutan.
The preceding description has been presented with reference to some embodiments. Persons skilled in the art and technology to which this disclosure pertains will appreciate that alterations and changes in the described structures and methods of operation can be practiced without meaningfully departing from the principle, and scope of this application. Accordingly, the foregoing description should not be read as pertaining only to the precise structures described and shown in the accompanying drawings, but rather should be read as consistent with and as support for the following claims, which are to have their fullest and fairest scope.

## Claims

1. A method, comprising:
adding from 0.1% to 10% by weight cement, and from 4% to 40% by weight of a source of calcium ions selected from the group consisting of calcium oxide, calcium hydroxide and calcium carbonate, to an aqueous treatment fluid containing a polymer, proppant and water, based on the weight of the resulting composition;
increasing the viscosity of the aqueous treatment fluid.

2. The method of claim 1, wherein the polymer is a polysaccharide.

3. The method of claim 1, wherein the polymer is present in a concentration of from 0.02% to 1.5% by weight of the composition.

4. The method of claim 1, wherein the source of cement is a Portland cement, calcium aluminate cement or Sorel cement.

5. The method of claim 2, wherein the polysaccharide is selected from the group consisting of gellan gum, diutan gum, ramsan gum and derivatives thereof.

6. The method of claim 1, wherein the polymer is selected from the group consisting of guar gum, xanthan, polyacrylamide, karaya, gum tragacanth, gum ghatti, gum, acacia, gum konjak, hydroxyethyl guar, carboxymethyl hydroxypropyl guar, or carboxymethyl hydroxyl-ethyl guar and mixtures thereof.

7. The method of claim 1, further comprising:
pumping the aqueous treatment fluid down a well to treat the well.

8. The method of claim 7, wherein the treatment is hydraulic fracturing.

9. The method of claim 7, wherein the treatment is a fluid separation.

10. The method of claim 7, wherein the viscosified treatment fluid comprises diutan, calcium carbonate, the cement and water.

11. The method of claim 10, wherein the cement is Portland cement.