Section 9 - Proppants

2005, Halliburton 9 1 Stimulation I

Section 9

Proppants

Table of Contents Introduction ............................................................................................................................................... 9-3

Topic Areas............................................................................................................................................ 9-3 Learning Objectives ............................................................................................................................... 9-3

Unit A: API Standards............................................................................................................................... 9-3 Roundness and Sphericity...................................................................................................................... 9-4 Specific Gravity ..................................................................................................................................... 9-4 Bulk Density .......................................................................................................................................... 9-4 Sieve Analysis........................................................................................................................................ 9-4 Acid Solubility ....................................................................................................................................... 9-4 Silt and Fine Particles ............................................................................................................................ 9-5 Crush Resistance.................................................................................................................................... 9-5 Clustering............................................................................................................................................... 9-5 Unit A Quiz............................................................................................................................................ 9-6

Unit B: Proppant Types ............................................................................................................................. 9-7 Sand........................................................................................................................................................ 9-7 Resin-Coated Sand................................................................................................................................. 9-7 Sintered Bauxite..................................................................................................................................... 9-8 Ceramics ................................................................................................................................................ 9-9 Unit B Quiz .......................................................................................................................................... 9-10

Unit C: Flow Capacity............................................................................................................................. 9-11 Unit C Quiz: Flow Capacity................................................................................................................. 9-12

Unit D: Proppant Bed Damage ................................................................................................................ 9-13 Unit D Quiz.......................................................................................................................................... 9-15

Proppants


Use for Section notes

Proppants


Introduction

Propping agents are the essential part of any fracturing treatment. Propping agents prop open the created fracture to conduct reservoir fluids to the wellbore. The selection of a propping agent requires information on the conductivity at stress of any material used. Sand is a natural material that is used as a propping agent in many hydraulic fracturing treatments.

Topic Areas

The section units are:

API Standards

Proppant Types

Flow Capacity

Proppant Bed Damage

Learning Objectives Upon completion of this section, you will be able to:

List API specifications for proppants

Distinguish between different types of proppants.

List the physical properties of the different proppants.

Compare flow capacities of different proppants under loaded conditions.

Avoid problems associated with proppant damage.

Unit A: API Standards API (American Petroleum Institute) is the major national trade association representing the entire petroleum industry: exploration and production, transportation, refining, and marketing. With headquarters in Washington, D.C., and petroleum councils in 33 states, it is a forum for all parts of the oil and natural gas industry to pursue policy objectives and advance the interests of the industry. The impetus for forming API in 1919 was the need to standardize engineering specifications for drilling and production equipment. API has developed some 500 equipment and operating standards used around the world. The API publications dealing with proppants are API RP 56 for frac sand, API RP 58 for gravel pack sand and API RP 60 for high strength frac sand. These publications set limits on certain characteristics of proppant and the procedures used for testing them.

Some characteristics of proppants used in hydraulic fracturing that need to be monitored are:

Roundness

Spericity

Specific Gravity

Bulk Density

Sieve Size

Acid Solubility

Silt and Fine Particles

Crush Resistance

Clustering These properties and their API guidelines are discussed below.

Proppants


Roundness and Sphericity

These two properties are particle factors that influence particle packing and load bearing capabilities. Roundness is the measure of the relative sharpness of grain corners or a grain curvature. Sphericity is the measure of how closely a particle approaches the shape of a sphere. The API recommended limit for sand for both roundness and sphericity is 0.6. For resin-coated sand, the API limits are 0.7. Figure 2.3 is a Krumbein chart.

Figure 9.1 Chart for visual estimates of sphericity and roundness (From Krumbein and Sieve 1963)

Several samples of a particular sand should be observed, then an average roundness factor comparison can be made. In some select cases, angularity may be advantageous because the proppant will tend to bridge in the fracture and be less likely to flow back into the wellbore. This is especially true in a formation where the fracture is slow in closing back completely.

Specific Gravity

The specific gravity of a proppant is the measure of the absolute density of individual proppant particles relative to water. The recommended API maximum limit is 2.65 for sand.

Bulk Density

Bulk density is the volume occupied by a given mass of proppant - the amount of material to fill a given volume. The units for bulk density are lb/ft3 or grams/cc. The API recommended maximum for proppants is 105 lb/ft3.

Sieve Analysis

A sieve analysis shows the size distribution of the sand within the designated size range; 90% of a sample must be within the designated size range. Not over 0. 1 % should be larger than the first sieve and not over 1.0% should be smaller than the last sieve. Table 9.2 gives U.S. standard mesh screen sizes.

U.S. Series Mesh

Sieve Opening (in.)

U.S. Series Mesh

Sieve Opening (in.)

4 0.187 25 0.0280

6 0.132 30 0.0232

8 0.0937 35 0.0197

10 0.0787 40 0.0165

12 0.0661 60 0.0098

14 0.0555 70 0.0083

16 0.0469 100 0.0059

18 0.0394 170 0.0035

20 0.0331

Table 9.1- Standard Sleeve Openings

Acid Solubility

The solubility of a proppant in 12% HCl - 3% FE acid is an indication of the amount of contaminants present and of the relative stability of the proppant in acid. It may also indicate the tendency of proppants to dissolve in hot brines. Acid solubility is measured by percentage by weight. The API recommended maximum for sand is 2%, while the limit for resin-coated sand is 7% maximum.

Proppants


Silt and Fine Particles

This measure indicates the amount of clay and silt or other fine material present. Properly washed and/or processed proppant will not have excess silt and fine particles. The API recommended maximum limit for proppant is 250 FIJI (formation turbidity units).

Crush Resistance

Crush resistance indicates the relative strength of a proppant by measuring the amount of material crushed under a given load. It is expressed in units of percentage of fines. API recommended maximum limits for sand are:

for 12/20 - 16% at 3000 psi for 20/40 - 14% at 4000 psi

API recommended maximum limits for high strength proppants are:

12/20 mesh- 25% 16/20 mesh- 25% 20/40 mesh - 10% 40/70 mesh - 8%

These tests are performed at stress levels of 7,500 psi, 10,000 psi, 12,500 psi, and 1 5,000 psi until the maximum fines limit is reached.

Clustering

Clustering is measured by percentage by weight. It indicates the degree of attachment of individual proppant grains to one another. During processing, the grains were not broken apart. The API recommended maximum is 1 %.

Proppants


Unit A Quiz

Fill in the blanks with one or more words to check your progress in Unit A. 1. List 6 characteristics of proppants used in hydraulic fracturing that need to be monitored.

a.

b.

c.

d.

e.

2. Bulk density is the _________ __________ ___ ________ of proppant

3. ______ True ______ False: The maximum API recommendation for % fines of 12/20 sand at 3000 psi is 16%.

4. The specific gravity of a proppant in the measure of the ______________ _____________ of

individual proppant particles relative to water.

Now, look up the suggested answers in the Answer Key.

Proppants


Unit B: Proppant Types

Sand

Two major sands used as proppants in hydraulic fracturing is Ottawa Sand and Brady Sand. Ottawa Sand, from the Jordan Deposit, is a high-quality sand from the northern United States. Its pure quartz composition, white color, lack of dust, high roundness and sphericity, make it an ideal sand. The grains are made up of mostly monocrystalline, which results in high individual grain strength. Brady Sand from the Hickory Deposit, near Brady Texas, is another high-quality sand used for fracturing, characterized by its slight angularity and presence of feldspars. Also known as Brown Sand because of its color, it is considered to be of lesser quality than Ottawa Sand. Although sands are available from other areas, these two provide the majority of material used in fracturing operations. The physical properties of commonly used types of sand are listed in Table 9.1

Premium Sand (Jordan/Ottawa)

Standard Sand (Hickory/Brady) Properties

12/20 20/40 12/20 20/40

Roundness 0.8 0.8 0.7 0.7 Sphericity 0.8 0.8 0.8 0.7 Specific Gravity 2.65 2.65 2.65 2.65 Bulk Density (lb/ft3) 96 102 100 102 Acid Solubility (% by Weight) 1.3 1.2 0.9 1.6

Crush Resistance (% Fines) 2.4 1.8 11.1 11.0

Clustering (% by Weight) 0.3 0.1 0.8 0.3

Table 9.2 Physical Properties of Sand

Resin-Coated Sand

Resin Coated Proppants (RCP's) have evolved over time. They are more compatible with our fracturing fluid systems compared to early generation products.

Compatibility includes the effect on fluid pH, crosslink time, breaker concentration, and foam stability. Resin coatings are available on sands, ceramics, and bauxite proppants. Pre-cured or tempered products have a hard coating or shell around the proppant grain and they are most compatible with our fracturing fluid systems. This coating will not bond grains together but it imparts a higher level of conductivity performance when compared to uncoated proppants. This is most significant with resin coated sands and less significant with resin coated ceramic or bauxite proppants. Partially curable and encapsulated materials provide proppant grains that will bond together under closure stress in a fracture. They are also more compatible with our fluid systems when compared to fully curable resin coated proppants.

Borden Chemicals, Inc. Oil Field ProductsPrecured

Product Name Description

AcFrac Black Plus Furan Resin-Coated Sand

Borden Chemicals, Inc. Oil Field ProductsPartially Curable


AcFrac SB Prime Phenolic Resin-Coated Sand AcFrac SB Excel Phenolic Resin-Coated Sand Ceramax P Phenolic Resin-Coated Bauxite

Borden Chemicals, Inc. Oil Field ProductsFully Curable


AcFrac CR 4000 Phenolic Resin-Coated Sand Santrol Tempered (precured) Proppants


Tempered LC Multiple Coat, Phenolic Resin-Coated Sand

Proppants


Santrol Curable Proppants Product Name Description

Super LC Phenolic Resin-Coated Sand Super DC Dual Coat, Phenolic Resin-

Coated Sand Super HS Multiple Coat, Phenolic Resin-

Coated Sand Super TF Phenolic Resin-Coated Sand OptiProp Encapsulated Phenolic Resin-

Coated Sand MagnaProp Encapsulated Phenolic Resin-

Coated Economy Ceramic DynaProp Encapsulated Phenolic Resin

Coated Premium Ceramic HyperProp Encapsulated Phenolic Resin-

Coated Bauxite PolarProp Encapsulated Phenolic Resin-

Coated Sand (low temperature formations)

Super HT Phenolic Resin-Coated Sand for Gravel Packs and Frac Packs

Curable resin coated proppants offer the highest bond strength and the greatest potential for interference with our fluid systems. The tables below list some of the RCP's currently available. AcFrac PR 6000 Phenolic Resin-Coated Sand AcFrac PR 4000 Phenolic Resin-Coated Sand

Ceramix I Phenolic Resin-Coated Premium Sand

Ceramix E Phenolic Resin-Coated Economy Sand

Tempered DC Dual Coat, Phenolic Resin-Coated Sand

Tempered HS Multiple Coat, Phenolic Resin-Coated Sand

Tempered TF Phenolic Resin-Coated Sand EconoFlex Phenolic Resin-Coated

Economy Ceramic Table 9.3 -

Sintered Bauxite

High-strength sintered bauxite and intermediate-strength sintered bauxite are produced by essentially the same manufacturing process. Bauxite ore is ground to a fine powder and formed into green pellets. After drying and screening, the pellets are fired in a kiln. The firing, or sintering process, fuses the edges of the individual particles of each pellet. The basic difference in the high strength and intermediate strength materials lies in the raw material used. High-strength sintered bauxite is formed from almost pure bauxite ore to create corundum, Al 2O3. This imparts the highest density (approximately 3.7 specific gravity) and strength for this proppant. Intermediate-strength sintered bauxite is formed from a less pure bauxite ore. The processing of this ore produces both corundum and mullite (Al6Si 3 O15). This mineral composition results in a less dense (approximately 3.25 specific gravity) and slightly weaker compound than the more pure sintered bauxite compound. Below is a list of some of the bauxite proppants currently available.

Norton-Alcoa Proppants Product Name Description

INTERPROP Intermediate Strength Bauxite SINTERED BAUXITE

High Strength Bauxite

Carbo Ceramics, Inc. Product Name Description

CarboProp Intermediate Strength Bauxite Carbo HSP High Strength Bauxite

Sintex Minerals and Services, Inc. Product Name Description

SinterLite Intermediate Strength Bauxite SinterProp Economy High Strength Bauxite SinterBall Premium High Strength Bauxite Table 9.4

Proppants


Ceramics

Ceramic are one of the large classes into which all useful solid materials can be divided, i.e., metals, organics, and ceramics. Generally, a ceramic is any non-organic, non-metallic solid formed by high temperature processing (above 875F). Example ceramics include glass, refractories, whiteware (dishes, pottery, etc.), structural products (brick), abrasives, and cement. Ceramic proppants are produced in a different manner than the sintered bauxite proppants using fluidizing bed processing. The composition of the ceramic-type proppants shows mostly mullite (aluminum compound) with some additional silica compounds. This produces a compound only slightly denser than sand with specific gravities of approximately 2.65 to 2.75. These ceramic proppants have greater strength than sand but less

strength than the intermediate- and high-strength sintered bauxite proppants. Below is a list of some of the ceramic proppants currently available.

Carbo Cermics, Inc. Product Name Description

CarboLite Premium Low Density Creamic EconoProp Economy Low Density Ceramic

Norton Alcoa Proppants Product Name Description

NAPLITE Premium Low Density Ceramic VALUPROP Economy Low Density Ceramic Table 9.5

Proppants


Unit B Quiz

Fill in the blanks with one or more words to check your progress in Unit B. 1. The four main types of proppant used today are:

1) 2) 3) 4)

2. The three types of resin coated proppants are: 1) 2) 3)

3. Intermediate-strength sintered bauxite is formed from a ________ _________ bauxite ore. 4. Generally, a ceramic is any ______-____________, ______-________ solid formed by

_________ ________________ processing Now, look up the suggested answers in the Answer Key at the end of this section.

Proppants


Unit C: Flow Capacity

The purpose of proppants is to help prevent the fracture from closing once pumping is stopped. Proppants are added to the fracturing fluid and are introduced into the fracture along with the fluid. A main factor affecting the outcome of a hydraulic fracturing treatment is obtaining an adequate propped fracture. The propping agent should provide and maintain a highly permeable path for fluid flow toward the wellbore. The need for a propping agent to help provide that path has been verified by numerous field experiments. When proppants are used, production is usually higher and the production decline rate is much slower. This suggests that an unpropped fracture is subjected to a combination of forces that tend to close the fracture which reduces its flow capacity. Flow capacity (or fracture flow capacity) is the ability of the fracture to convey the reservoir fluid to the wellbore. It is generally expressed as the product of fracture permeability and the fracture width: Fracture Flow Capacity = (kwf) where: k = Permeability (md) of the fracture wf = Fracture width (ft) Proppant particles must support the closure stress. In so doing, some of the particles may crush, or in a soft formation, embed into the rock. The degree of crushing or embedment depends on:

proppant strength and size

hardness of the formation being

propped closure stress being applied to the proppant bed

If the particle either crushes or embeds, the fracture flow capacity will decrease. If severe crushing or embedment occurs, the fracture flow capacity may decrease so low that not enough contrast exists between the conductivity of the proppant bed and the permeability of the reservoir rock. If this were to happen, results from the fracturing treatment may not be satisfactory because of the loss of fracture conductivity. One of the first propping agents used in fracture treatments was screened river sand. However, such angular, poorly screened sand contained some particles that were too large to enter the fracture. Also, bridges formed in the wellbore, subsurface tools, and within the fracture itself. If the proppant is too large, or if bridging occurs, screenout can result and the treatment will have to be ended prematurely. This results in a smaller propped fracture than had been designed and additional expense for cleaning out the proppant in the wellbore. Figure 9.1 is a sample fracture flow capacity curve. This data were generated using steel plates. All measurements were made with radial flow cells and nitrogen gas, and were conducted at ambient temperature.

Proppants


Figure 9.1 Fracture Flow Capacity Data 1 lb/ft2

Unit C Quiz: Flow Capacity

Fill in the blanks with one or more words to check your progress in Unit C. 1. Fracture Flow Capacity = (kwf), where:

k = ________________ ____ ______ ______________ wf = _____________ __________

2. One of the first propping agents used in fracture treatments was _____________ __________ _________.

3. If the proppant is too large, or if bridging occurs, _______________ will result and the treatment will have to be ended ________________.

Now, look up the suggested answers in the Answer Key at the end of this section.

Effect of Proppant Type20/40, 200 F, 1.0 lb/ft

0 3000 6000 9000 12000 15000

Stress (psi)

0

500

1000

1500

2000

2500

3000

Conductivity (md*ft)

Proppant Type H Brady H Ottawa

Customer: Job Date: Ticket #:Well Desc: Job Type: Fracture Job StimWinH v3.1.2 26-May-99 11:45

2

Proppants


Unit D: Proppant Bed Damage

Several factors will be discussed in this unit that may influence the flow capacity resulting from a bed of proppant under load:

The particles may embed in the rock surface if they are stronger than the rock and the closure stress is sufficient to cause embedment.

A large percentage of the grains may crush if the rock is strong and the stress is greater than the grains can withstand.

The proppant bed may become plugged because of the invasion of formation fines.

Unbroken gel and residue may remain in the proppant pack plugging pore throats.

The crushing or embedment (sinking into the fracture face) of proppant particles may cause a fast decline in productivity because of the reduction in fracture flow capacity. If there is significant embedment, the flow capacity may be partially or entirely lost because of fracture closure. In many cases, the closure may crush the formation instead of the proppant. The formation may then release debris that partially plugs the proppant bed. Sand may be crushed by the action of the formation stresses in hard rocks; however, it does not usually crush to a very fine powder. Sand may shatter into smaller grains and, eventually, produce enough small particles to give some support. The result may be a propped fracture of a slightly narrower width and a poorer range of proppant sizes than expected. Therefore, the proppant bed would have less flow capacity. Selecting the proper type and size of proppant to use in a particular formation requires the gathering of laboratory data. Of these three, only proppant crushing can easily be modeled in the laboratory. Figure 9.3 illustrates what may happen in a monolayer or partial monolayer system of rigid

particles when they are completely embedded. The flow capacity may be partially or entirely lost due to the closure.

Figure 9.3 Partial Monolayer

Propping Agent Not Crushed Propping Agent Crushed

Figure 9.4 Multilayer System

Proppants


Figure 9.5 Multilayer System

Figure 9.4 shows the crushing of rigid particles. Figure 9.5 illustrates the condition that may exist in a multilayer system as a rigid particle tends to embed into a soft formation.

The flow capacity may only be reduced due to the outer layer of grains embedding, while the inner layer of grains remains effective. The net result is to reduce the effective fracture width. The crushing of the formation due to embedment may release formation debris that could partially plug the proppant bed. Recent studies have shown that probably the greatest influence on proppant pack conductivity is our ability to break, clean up, and flow back the carrier fluid used to place the proppant. Gel residue, unbroken gel, and high gel-loading filter cake on the fracture face can reduce the flow capacity of the proppant pack by as much as 80%. The influence of gel damage became clear when studies were conducted based on gel loading, base fluid type, and crosslinker type. Figure 9.6 shows testing done through a specific proppant pack with different carrier fluids.

2400 2200 2000 1800 1600 1400 1200 1000

800 600 400 200

0

0 10 20 30 40 50 60 70 80 90 100

2128 1971

1500

1115 808

430

BORATE XLINK

30lb HPG w/ persulfate/

amine breaker

BORATE XLINK

40lb HPG w/ persulfate/

amine breaker

BORATE XLINK

40lb HPG w/ enzyme

breaker TI TANTE XLINK

40lb HPG w/ enzyme

breaker

ANTI- MONATE

XLINK 40lb HPG w/ enzyme breaker

TI TANTE XLINK

40lb HPG w/ enzyme

breaker

*Co

ndu

ctiv

ity ( m

d ft)

% C

ond

uctive

Impairm

ent

*STIM-LAB Data

20/40 Sand Con.=lb/ft 2 Closure=2000 psi

T=100F

Figure 9.6

Partial Embe dment

Proppants


Unit D Quiz

Fill in the blanks with one or more words or circle the correct answer to check your progress in Unit D. 1. Name four factors may influence the flow capacity resulting from a bed of proppant under load:

2. The crushing or embedment of proppant particles may cause a fast decline in productivity because of the reduction in ____________ _______ _____________.

3. The crushing of the formation due to embedment may release formation ________ which could partially _________ the proppant _______.

4. Gel residue, unbroken gel, and high gel-loading filter cake on the fracture face can reduce the ______ __________ of the proppant pack by as much as ______%.

Now, look up the suggested answers in the Answer Key at the end of this section.

Proppants


Self Check Test for Section 9

Mark the single best answer to the following questions. 1. Name the two properties that influence particle packing and load bearing capability.

2. Define specific gravity of a proppant.

3. Define bulk density of proppant.

4. ______% of a proppant sample must be within the designated size range.

5. The degree of crushing or embedment of proppant depends on.

6. Name four factors that may influence the flow capacity resulting from a bed of proppant under load.

Proppants


Answer Key

Items from Unit A Quiz Refer to Page

1. Roundness, Spericity, Specific Gravity, Bulk Density, Sieve Size, Acid Solubility, Silt and Fine Particles, Crush Resistance, Clustering

2. Volume / mass 3. T 4. Absolute Density

9-3 9-4 9-5 9-4

Items from Unit B Quiz Refer to Page

1. Sand, Resin Coated Sand, Ceramics, Sintered Bauxite 2. Curable, Partially cured, pre-cured 3. less pure 4. non organic / non metallic / high temperature

9-9 9-8 9-8 9-9

Items from Unit C Quiz Refer to Page

1. Permeability of the fracture / fracture width 2. Screened river sand 3. Screenout / permeability

9-11 9-11 9-11

Items from Unit D Quiz Refer to Page

1. The particle may embed in the rock surface A large percentage of the grain may crush The proppant bed may become plugged Unbroken gel and residue may remain in the proppant pack

2. Fracture flow capacity 3. Debris / plugs / bed 4. Flow capacity / 80%

9-13 9-15 9-13 9-14

Self-Check Test Refer to Page

1. Roundness Sphericity

2. The absolute density of individual proppant particle relative to water 3. The volume occupied by a given mass of proppant 4. 90% 5. Proppant size to strength

Hardness of the formation Propped closure stress being applied to the proppant bed

9-4 9-4 9-4 9-4

9-11

Proppants


6. The particle may embed in the rock surface A large percentage of the grain may crush The proppant bed may become plugged Unbroken gel and residue may remain in the proppant pack

9-13

Section 9 - Proppants

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