Sample Calculation

During the drilling of a relatively uniform 2000-foot shale section, an API 200 continuous screen cloth was mounted on a linear shale shaker. An 11.2-ppg, freshwater, gel/lignosulfonate drilling fluid was circulated at 750 gpm while drilling. A typical set of samples will be described here.
Large pieces of shale were removed from the shaker screen and excess drilling fluid washed from the surface with distilled water. The shale pieces were ground and dried in an oven at 250F overnight. The shale was placed in a 173.91-cc pycnometer and weighed. Water was added to the pycnometer and pressurized to about 350 psi. The increase in weight of the pycnometer indicated the volume of water added to fill the pycnometer. (Room and water temperature was 68F, so the density of water was about 1.0 g/cc.) Subtracting this volume of water from the known volume of the pycnometer calculates the volume of shale sample. Once the volume of the shale sample and the weight were known, the density could be calculated. The shale drilled in this well had a density of 2.47 g/cc.
After movement of solids across the shale shaker screen appeared to be relatively uniform for more than 10 minutes, all the shaker discard was collected in a bucket. In 16.21 seconds, 3720.7 g of discard was captured. The discard rate was 13,772 g/min. The discard had a density of 1.774 g/cc or 14.8 ppg.
Calculation Procedure
A sample of the discard was placed in the pycnometer and weighed:
pycnometer+ sample weight = 869.68 g.
Since the pycnometer weighed 660.61 g dry and empty, the sample weight was 209.07 g.
The pycnometer with shaker discard sample was filled with distilled water, pressurized, and weighed:
pycnometer + sample +water =948.32 g.
The weight of water added was 948.32 g – 869.68 g=78.64 g. Volume of70°F. water added=78.64 g/0.998 g/cc.
Since the pycnometer volume was 173.91 cc, the sample volume was
173:91 cc -78:80 cc = 95:11 cc
The density of the sample was 209.07 g/95.11 cc=2.2 g/cc.
The objective of the shale shaker is to remove drilled solids, preferably without excessive quantities of drilling fluid. The fraction of the discard stream that is water, barite, and low-gravity solids can be determined by the preceding equations. These calculations indicate that the discard stream had 5.06 %vol barite, 38.38 %vol low-gravity solids, and 56.56 %vol water.
Calculation Procedure to Determine Low-Gravity Solids Discarded
The discard from the screen weighs 14.8 ppg and contains 43.44 %vol solids. We use the equation presented previously:

To determine the quantity of drilled solids discarded by the shale shaker, a sample of the discarded material was placed in a metal dish and dried in an oven overnight. The weight percentage of (wt%) dry solids was 68.11 and had a density of 2.78 g/cc.
The rate of dry solids discarded (RDSD) is calculated from the product of the wet discharge flow rate and the weight fraction of dry solids in the discharge (with the appropriate unit conversion factors):

Experimental and Calculation Procedure
A sample of discard was placed in a 40.10-g crucible and weighed:
crucible + sample weight = 114.94 g.
The wet sample weight was 74.84 g. Since the wet discard density was 1.77 g/cc, the wet sample had a volume of 74.84 g/1.77 g/cc=42.19 g/cc.
After heating overnight at 250°F, the crucible and sample weight were 91.08 g. The dry solids weight in the sample was 91.08 g- 40.10 g=50.98 g.
The wt% dry solids in the discard was the weight of dry solids divided by the wet-sample weight times 100, or
[50.98 g/74.84 g]× 100=68.12 wt%.
The volume of the dry sample was calculated by subtracting the volume of water lost from the volume of the wet sample:
The 42.19-cc wet sample lost 114.94 cc-91.08 cc=23.86 cc of water.
The volume of the dry sample was 42.19 cc-23.86 cc=18.33 cc.
The density of the dry solids was the weight of dry solids divided by the volume of dry solids, or 50.98 g/18.33 cc=2.78 g/cc.
Calculation of Barite Discarded by Shale Shaker
Assuming that all of the drilled and other low-gravity solids in the drilling fluid have a dried density of 2.47 g/cc and the barite has a density of 4.2 g/cc, the wt% barite in the dry sample may be calculated from the mass-balance equation:
Density of Dry Solids =Weight of Solids/Volume of Solids
or
Density of Dry Solids=[Weight of Barite+ Weight of Low Gravity Solids]/[Volume of Barite + Volume of Low Gravity Solids]
To determine the terms on the right side of the equation:
1. The volume of barite is the density (4.2 g/cc) divided by the weight of barite.
2. The volume of low-gravity solids is the total volume of dry solids minus the volume of barite.
3. The volume of low-gravity solids in 1 cc of solids equals 1 cc minus the volume of barite in 1 cc of solids.
Volume of low gravity solids in 1 cc of solids=1cc-[Wb/4.2 g/cc]
Weight of Low Gravity Solids in 1 cc of dry solids={1cc-[Wb/4.2 g/cc]}×(2.47 g/cc)
Density of Solids (D)={WB+ 2:47 g/cc[1 -WB/4.2 g/cc]×1 cc}/[Wb/4.2 g/cc]+{1-[Wb/4.2 g/cc]}
This equation may be reduced to the expression:
D = 0:4119WB + 2.47
or
Weight percent barite=D-2.47/0.4119
The discard density is 2.78 g/cc, so the wt% barite is 27.07. The weight of dry discard from the shaker screen is 1239 lb/hr. The quantity of barite discarded is (0.2707)(1239 lb/hr), or 377 lb/hr. The low-gravity-solids discard rate is 1239 lb/hr-377 lb/hr, or 862 lb/hr.
Calculation of Solids Discarded as Whole Drilling Fluid
A water-base drilling fluid contains 13% volume of solids in the liquid phase of the shale shaker discard, which could be associated with the whole drilling fluid.
The wt% dry solids discarded from the shaker screen is calculated to be 68.12; so 31.89% of the discard must be liquid. Assume that this liquid is composed of drilling fluid with the solids distribution of the drilling fluid in the pits. The liquid discard rate is (13,772 g/min)(0.3189), or 4391.9 g/min. This liquid should contain 13% volume of solids.
Since the drilling fluid contains 13% volume of solids, a 100 cc sample contains 87 cc of liquid. In this 100 cc sample, the water fraction wouldweigh 87 g. With an 11.2-ppg (1.343 g/cc) density drilling fluid, the 100 cc sample should weigh 134.3 g. Since the liquid weighs 87 g, the solids must weigh 47.3 g. Or, stated another way, the drilling fluid contains 47.3 g of solids for every 87 g of water. The total liquid discard rate is 4391.9 g/min. The solids discarded by the screen that are associated with the drilling fluid would be:
[47:3 g solids/87 g water][4391:9g/min]=2387.8g/min; or 315:6 lb/hr.
The wt% barite in the drilling fluid is 77.4 and the wt% low-gravity solids in the drilling fluid is 22.4. From the solids discarded from the screen associated with the whole drilling fluid, 244 lb/hr are barite and 71.2 lb/hr are low-gravity solids.
Previously, the dry solids discarded by the shaker screen were calculated to be 377 lb/hr barite and 861 lb/hr low-gravity solids. Subtracting the solids associated with the drilling fluid from the solids removed by the screen indicates the discarded solids in excess of those associated with the drilling fluid:
Barite:
377 lb/hr – 244 lb/hr = 133 lb/hr
Low-gravity solids:
861.0 lb/hr – 71.2 lb/hr = 789.8 lb/hr
This indicates that the API 200 screen is removing 133 lb/hr of barite and almost 800 lb/hr of drilled solids in addition to the quantity contained in the associated drilling fluid.
Note that the technique of using the concentration of barite in the discard does not allow an accurate measurement of the quantity of drilling fluid in the shaker discard. Some measurements even indicate that less barite is in the discard than is in the whole drilling fluid. Shaker screens can pass much of the small-size barite and remove it from the liquid before it is discarded by the shaker screen.

PROCEDURE FOR A MORE ACCURATE LOW-GRAVITY SOLIDS DETERMINATION

This procedure requires an oven, a pycnometer, and an electronic balance to weigh samples. A pycnometer can be made by removing the beam from a pressurized mud balance. Any type of balance may be used to determine weight; however, electronic balances are more convenient.
Determine the volume of the pycnometer:
1. Weigh the pycnometer (assembled).
2. Fill with distilled water.
3. Determine the water temperature.
4. Reassemble the pycnometer and pressurize it.
5. Dry the outside of the pycnometer completely.
6. Weigh the pycnometer filled with pressurized water.
7. Determine the density of water using a table of density/temperature of water. (See Appendix.)
8. Subtract the pycnometer weight from the weight of the pycnometer filled with water, to determine the weight of water in the pycnometer.
9. Divide the weight of water in the pycnometer by the density of water to determine the volume of the pycnometer.
Determine the density of drilled solids:
1. Select large pieces of drilled solids from the shale shaker and wash them with the liquid phase of the drilling fluid (water for water-base drilling fluid, oil for oil-base drilling fluid, and synthetics for synthetic drilling fluid.)
2. Grind the drilled solids and dry them in the oven or in a retort.2
3. Weigh the assembled, dry pycnometer.
4. Add dry drilled solids to the pycnometer and weigh.
5. Add water to the solids in the pycnometer, pressurize, and weigh.3
6. Determine the density of the NAFs using the procedure used to calibrate the pycnometer with water.
7. Determine the density of the water.
8. Subtract the weight of the dry pycnometer from the weight of the dry pycnometer containing the dry drilled solids. This is the weight of drilled solids.
9. Subtract the weight of the dry pycnometer containing the drilled solids from the weight of the water, drilled solids, and pycnometer. This is the weight of water added to the pycnometer.
10. From the temperature/density chart for water, determine the density of the water.
11. Divide the weight of the water (determined in step 9) by the density of the water. This is the volume of water added to the pycnometer.
12. Subtract the volume of the water added to the pycnometer (step 10) from the volume of the pycnometer. This is the volume of drilled solids contained in the pycnometer.
13. Divide the weight of the drilled solids (step 8) by the volume of the drilled solids (step 11). This is the density of the drilled solids.
14. Multiply the volume fraction of solids in the drilling fluid by 100 to obtain the %vol solids in the drilling fluid.

Waste Recycle And Disposal Guidelines

Class 1 waste is any material that, because of its concentration or physicochemical characteristics, is considered “toxic, corrosive, flammable, a strong sensitizer or irritant, a generator of sudden pressure by decomposition, heat or other means, or may pose a substantial present or potential danger to human health or the environment when improperly processed, stored, transported, disposed of, or otherwise managed,” as further defined in 30 TAC 335.505 [Texas Administrative Code].

Class 2 waste is any material that cannot be described as hazardous, as class 1, or as class 3.

Class 3 wastes are inert and essentially insoluble materials, usually including, but not limited to, “materials such as rock, brick, glass, dirt and certain plastics and rubber, etc., that are not readily decomposable.”

Table 2.4
Waste Recycle/Disposal Guidelines

M Recycle / Disposal Class
Acids (undiluted) Disposal Haz
Acids (spent, except hydrofluoric acid) Dilute and dispose of down sink drain
Barite, finished or crude Recycle
Bentonite clays and test fluids Recycle
Biocides Disposal per MSDS 1, 2, or Haz
Bleach Dilute and dispose of down sink drain
Brines, high-density, new Reclycle
Brines, high-density, used Disposal 2
Brine/oil mixtures (emulsion testing, etc.) Disposal 1
Broken glass Disposal 2
Buffer solution Dilute and dispose of down sink drain 2
Calcium carbonate Disposal 2
Calcium chloride (solid) Disposal 2
Calcium chloride (solution) Dilute and dispose of down sink drain
Chemical spill kits Disposal per kit directions 1, 2, or Haz
Cleaning service rags Disposal 2
Freshwater test fluids Recycle
Corrosion inhibitors Corrosion inhibitors 1, 2, or Haz
Culture waste (filter media, gravel, etc.) Disposal 2
Cuttings, neat Disposal 2
Cuttings, with oil Disposal 1
Empty containers, hazardous Disposal 1
Empty containers,nonhazardous Disposal 2
Enzyme solutions Dilute and dispose of down sink drain
Filter cake, disks, and paper w/chrome-free mud Recycle
Field product samples Disposal 1, 2, or Haz
Filter cake, disks, and paper w/chrome-containing mud Disposal Haz
Freshwater test fluids Recycle
Hydrofluoric acid (handle with extreme care) Disposal Haz
Hydrogen peroxide Disposal 2
Hydroxy ethyl cellulose Disposal 2
Lignosulfonate and lignite product test muds Disposal
Mercury thermometers Disposal haz
Well-cleaning chemicals Disposal per MSDS 1, 2, or Haz
Mud additives Disposal per MSDS 1, 2, or Haz
Emulsifiers
Fluid loss control
Lignosulfonates
Lubricants
Shale inhibitors
Shale stabilizers
Surfactants
Wetting agents
Mud filtrates, oil-based/synthetic-based mud Disposal 1
Mud filtrates, water-based mud Recycle
Oil, with non-OBM constituents Disposal 1
Oil, with OBM constituents required for OBM conditioning Recycle
Oil, mixed with hazardous wastes Disposal 2
Oil-based/synthetic-based mud and wash chemicals Disposal 1
Organic peroxides Disposal 2
Paper towels used to clean up brines and muds Disposal 2
Persulfates Disposal Haz
pH Buffers Dilute and dispose of down sink drain
pH test solution residuals Return to original container
Polymer slurries, mineral oil or other carrier Disposal 1
Polymers, dry Disposal 2
Potassium hydroxide (solid) Disposal Haz
Potassium hydroxide (solution) Dilute and dispose of down sink drain
Retort cooked solids (chrome-containing mud) Disposal Haz
Retort cooked solids (chrome-free mud) Disposal 2
Salt gel/attapulgite Disposal 2
Silver nitrate solution Dilute and dispose of down sink drain
Sodium carbonate (solid) Disposal Haz
Sodium carbonate (solution) Dilute and dispose of down sink drain
Sodium hydroxide (solid) Disposal Haz
Sodium hydroxide (solution) Dilute and dispose of down sink drain
Solvents, chlorinated Disposal Haz
Solvents, nonchlorinated Disposal Haz
Titration residue Dilute and dispose of down sink drain
Titration solution residue Dilute and dispose of down sink drain
Wash water, laboratory equipment and general Dilute and dispose of down sink drain
WBM spent titrations Dilute and dispose of down sink drain
WBM (Cl<20,000 ppm and oil <3%) Recycle
WBM (Cl >20,000 ppm or oil>3%) Disposal 1
WBM, chrome-free saltwater Disposal
WBM, chrome-containing Disposal
WBM, all others Disposal

OBM=oil-based mud; WBM=water-based mud; MSDS=Material Safety Data Sheet

HEALTH, SAFETY,AND ENVIRONMENT AND WASTE MANAGEMENT

  1. Handling Drilling Fluid Products and Cuttings

Working with drilling fluids can be hazardous. Some drilling-fluid products emit noxious or hazardous vapors that may reach levels that exceed the maximum recommended short-term or long-term safe exposure limits. Some shale and corrosion inhibitors and some oil-base mud emulsifiers tend to produce ammonia or other hazardous volatile amines, particularly in hot areas on a rig. Other products are flammable or combustible (flash point <140F), so that they too must be handled with caution. Thus, proper ventilation is vital in the mud pit areas and around the solids-control equipment.

Various mud products, brines, cleaning agents, solvents, and base oils commonly found on drill rigs are irritating or even hazardous to body tissues. Cuttings may be coated with these materials, too. Consequently, proper protective equipment should be worn for hands, body, and eyes when working around solids-control devices, even though the protective equipment may be inconvenient or uncomfortable.

  1. Drilling Fluid Product Compatibility and Storage Guidelines

Mud products and test reagents can be particularly hazardous when stored improperly. As in any well-run chemistry laboratory, materials on the rig that are chemically incompatible should be stored apart from each other, and preferably in separate spill trays (secondary containment vessels). Some general storage guidelines are given in Table 2.3. Mud products and test reagents are classified into six hazard groups, in decreasing order of hazard risk (priority)—reactive/oxidizer, toxic, flammable, acids and bases, unknown, and nonhazardous—and each group should be segregated from the others. There should be very little or no material on the rig that falls into the reactive/oxidizer category. Acids and bases, though grouped together, should be placed in separate spill trays.

Table 2.3

Hazard Classification of Chemical Reagents and Mud Products

Chemical Segregation Guidelines

Safe storage practices require that materials be separated according to chemical compatibility and hazard class. The following hazard classes should be used for segregating the waste of decreasing hazard potential. Each hazard class of chemicals should be stored in a separate secondary containment labeled with the hazard class name. The containment vessels for hazard classes containing primarily solids (e.g., nonhazardous materials) should be placed above all others. Priority 3 materials should be isolated from the flammables cabinet. The secondary containment vessel for the oxidizer hazard classes should be made of metal and sit on a metal shelf.

Hazard Class Definition Example
Water/air Materials that are potentially explosive, react violently, or generate toxic vapors when allowed to come in contact with air or water Acetyl chloride, sodium metal, potassium metal, phosphorus (red and white),inorganic solid peroxides
Oxidizers,inorganic salts Specific listed inorganic compounds that react vigorously with organic materials and/or reducing agents Inorganic liquid peroxides, chlorates, perchlorates, persulfates, nitrates, permanganates, bleach
Oxidizers,inorganic acids (liq) Inorganic liquids with pH<2 and strong

tendency to oxidize organics

Perchloric, pitric, concentrated sulfuric,

bromic, hypochlorous

Oxidizers, organic Specific ‘‘listed’’ organic compounds that react vigorously with organic materials and/or reducing agents Organic peroxides
Toxic materials, metals Materials that contain specific ‘‘listed’’

water-soluble or volatile, nonoxidizing/

nonreacting metallic compounds that are regulated at levels below a few mg/L

Metals and water-soluble compounds of

arsenic, barium, beryllium, cadmium, chromium, copper, lead, mercury,thallium (e.g., chrome lignosulfonate(CLS) and materials contamined with CLS.

Toxic materials, organic reagents Specific ‘‘listed’’ compounds whose concentrations in wastes are regulated at levels

of 0.1 to 200 mg/L

Phenol, biocides, cyanides, propargyl alcohol,

carbon disulfide

Flammable and combustible

liquids

Nonhalogenated, pourable, organic liquids

with flashpoint <140_F (classes I and II)

Acetone, xylene, toluene, methanol, most organic oils, oil-based mud, brine/oil mixtures, oily cuttings solvent wash,invert mud emulsifiers and wetting agents, some lubricants
Halogenated liquids Halogenated organic liquids, whether flammable or not Chloroform, methylene chloride
Acids, organic (liq) Organic liquids with pH<2 Acetic, butyric, formic
Acids, inorganic mineral (liq) and some concentrated

brines

Inorganic liquids with pH<2, generally

acids and certain salts

Hydrochloric, hydrobromic, hydrofluoric,

dilute sulfuric, phosphoric, conc. brines

(low pH, e.g., bromides and iodides)

Bases, organic (liq) Organic liquids with pH>12.5 Amines, hydrazines
Bases, inorganic (liq) Inorganic liquids with pH>12.5 Ammonia, ammonium hydroxide, sodium

hydroxide, potassium hydroxide

Unclassified materials

(hazardous and

nonhazardous)

Calorimetric ampoules (ammonia and

phosphate); mercury thermometers; salt gel (attapulgite); chemical spill kits, corrosion inhibitors, field product samples, HTCE residuals, well-cleaning chemicals, some shale inhibitors, tar

Nonhazardous materials, salts,

clays, etc.

Miscellaneous materials that do not exhibit any of the hazards identified in categories 1–10, including nonoxidizing salts with 2<pH<12.5 (if in solution) Most clays; nonflammable/noncombustible/nontoxic polymers (HEC, CMC,PAC); chrome-free lignosulfonates;most empty containers;chrome-free freshwater test fluids, filter cakes, filter media, retort solids residue; solid or aqueous chlorides, formates,carbonates,acetates, dilute bromides, and iodides

3.Waste Management and Disposal

The drilling-fluid program should address environmental issues concerned with the discharge of drilling fluid, products, and removed solids. Personnel managing the solids-separation equipment must be very familiar with this part of the drilling-fluid program and have a good

understanding of governmental regulations and operator requirements. Many drilling operations have strategies in place for drilling-fluid recovery and will have established some general guidelines for the disposal of materials classified as waste. However, situations can arise that present the engineer managing the solids-control equipment with the issue of whether to discard or recycle some types of waste and how to do it. If disposal costs are not a factor, then all waste can be disposed of and treated, if necessary, onsite or sent to a processor offsite. However, if it is possible to recycle some of the products to the mud system, it may prove economical to do so [Hollier et al]. Table 2.4 contains some general guidelines approved in the state of Texas for recycling and disposing of waste from a drilling operation. Definitions used in those guidelines for hazardous, class 1, class 2, and class 3 wastes are given below. Solid waste is classified as hazardous by the U.S. Environmental Protection Agency if it meets any of the following four conditions:

. The waste exhibits ignitability, corrosivity, reactivity, or toxicity.

. The waste is specifically listed as being hazardous in one of the four tables of 40 CFR 261: [Code of Federal Regulations]

  1. Hazardous wastes from nonspecific sources (40 CFR 261.31)
  2. Hazardous wastes from specific sources (40 CFR 261.32)
  3. Acute hazardous wastes (40 CFR 261.33(e))
  4. Toxic hazardous wastes (40 CFR 261.33(f)).

. The waste is a mixture of a listed hazardous waste and a nonhazardous waste.

. The waste has been declared to be hazardous by the generator.

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