Arctic Casing Packs
Casing packs perform a special function in arctic areas. They are applied between strings of casing which penetrate the permafrost layer in these areas. They have an added function of reducing the heat flow from the well to the surrounding environment. Arctic packs are highly gelled to limit the formation of convection currents which increase heat transfer. They should also be non-freezing, which effectively limits them to being oil-based fluids. The freezing restriction is necessary to protect...
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Alumina has an octahedral structure consisting of an aluminum atom with six oxygen atoms arranged in an octahedron around it. These alumina octahedra are then joined in a structure which is replicated to form a sheet or layer. The structure is the same as the mineral gibbsite AL2 OH 6 see Figure 4 . These sheets of alumina and silica alternate to form the various clays. The clays we are most concerned with are either two-layer or three-layer clays. Structural Diagram of a Single Alumina...
Shear Rate RPM
Plastic Viscosity PV - Drilling muds are usually composed of a continuous fluid phase in which solids are dispersed. Plastic viscosity is that part of the resistance to flow caused by mechanical friction. The friction is caused by Viscosity of the fluid phase. For practical field applications, plastic viscosity is regarded as a guide to solids control. Plastic viscosity increases if the volume percent of solids increases, or if the volume percent remains constant, and the size of the particle...
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Viscosity of Bentonite Slurry vs. Calcium Concentration Dry Bentonite Added to Electrolyte Solution Dry Bentonite Added to Electrolyte Solution We use several terms for describing the specific behavior of clay-water interactions. These are aggregation, dispersion, flocculation and deflocculation see Figure 14 . Figure 14 Types of Clay Associations Figure 14 Types of Clay Associations The clay in its dry state has platelets stacked in face-to-face association, like a deck of cards. This is...
Chemical Analysis Mud Check
Table 6 pH of 10 Solution approximate Soda Ash Sodium Hydroxide Potassium Hydroxide Calcium Hydroxide Barium Carbonate Gypsum Alkalinity of the whole mud, or PM, is a measure of both the soluble and insoluble materials in a mud. Soluble ions, such as hydroxyls, carbonates and bicarbonates, and insoluble compounds, such as lime and magnesium hydroxide, have an affect on the PM. The PM is expressed as the volume in cm3 of 0.02N sulfuric acid required to lower the pH of 1 cm3 of the mud to 8.3....
Plug Choices and Techniques
When a loss zone cannot be stabilized with sealing materials it may be desirable to try a plug. Several choices and techniques are available however, in all cases a reasonably accurate estimate of depth of the loss is required prior to setting the plug. Spinner surveys, radioactive traces, and temperature surveys are most commonly used for this purpose. The following is a typical list of plug choices. These are generally classified as soft, medium or hard plugs Bentonite-diesel oil squeeze gunk...
Clear Brine Fluids SolidsFree Brine Fluid Systems
These fluids are made from fresh water or are solutions made with water and the addition of one or more electrolytes. These fluids do not contain either suspended particles or viscosifiers, which means neither filtration control nor viscosity control are provided. Some brines are corrosive and when corrosion inhibitors are required, compatibility studies should be performed. Some brines are toxic and precautions should be taken to prevent contact with unprotected skin. Brine solutions can be...
Marsh Funnel Viscosity
Marsh Funnel viscosity is used to indicate relative mud consistency or thickness. Marsh Funnel viscosity is the time required seconds for a quart of mud to flow through a 2-in. long, 3 16-in. diameter tube at the bottom of the Marsh Funnel. This viscosity measurement is used to periodically report mud consistency. One quart of water should flow through a Marsh Funnel in 26 1. Hold one finger over the orifice at the tip of the funnel. Pour the mud sample through the funnel screen until mud...
Typical Properties of Saturated Salt Muds
Saturated Salt Muds typically exhibit high yield point values and gel strengths. Gel strengths, although high, are generally fragile. Table 21 lists typical properties for unweighted 10.5 lb gal and weighted saturated salt muds. Typical Properties of Saturated Salt Muds
Saturated Salt Muds
common practice to maintain the pH of the mud from 11-11.5 with additions of caustic soda. Saturated salt muds require larger additions of caustic soda to maintain a higher pH than do freshwater muds. Maintaining an 11 to 11.5 pH offers several advantages Deflocculants are more effective Lower concentrations of filtration control additives are required when Ca and Mg solubility is reduced Foaming tendency is lessened Mud is generally more stable Saturated salt muds will normally contain soluble...
Shear Rate
Non-Newtonian fluids are classified into four major categories Those with properties independent of time, Those with properties dependent on time, The first two categories are of principal concern to drilling fluids. There is a further subdividing of these Time Independent, Non-Newtonian Fluids Time Dependent, Non-Newtonian Fluids
Principal Additives for HighTemperature Deflocculated DURATHERM Muds
Principal Additives of DURATHERM Mud Systems Bentonite - Bentonite is used for fluid loss control and suspension. The bentonite content at mud densities greater than 14.0 lb gal should not exceed 10 lb bbl. MELANEX-T - MELANEX-T is a melanin polymer derivative deflocculant used to reduce viscosity and high temperature gelation. RESINEX - RESINEX is a resin polymer fluid loss control additive that can be used to replace some of the XP-20 especially in salty environments. XP- 20 - XP-20 is a...
Sodium Polyacrylates SPA
SPAs are polymers that are available in various ranges of molecular weight and offer high temperature stability. SPAs of low molecular weight are deflocculants for clays and are used to improve fluid loss control by that mechanism. SPAs of very high molecular weight are effective for fluid loss control by increasing the viscosity of the filtrate and by plugging in the cake. They are sensitive to calcium ions, especially at high molecular weight. Derivatives of SPA which are less sensitive to...
Mud Test Data for Solids Calculations
In order for solids calculations to be reliable, all input data must be as accurate as possible. Small errors in input data can become magnified in the calculated concentrations. For example, the calculated concentration of low-gravity solids MLGS will be larger than they should be if retort water is under-estimated or if the mud density used in the calculations is higher than actual. A major consideration in the quality of input data for solids calculations is accurate mud test results. To...
SHALE STABILITY Introduction
Wellbore instability encountered while drilling shale formations is a worldwide problem. Despite much experience and considerable research, drilling and completion operations continue to be plagued by various hole problems attributed directly to shale formations. Studies and solutions to shale problems are not a simple matter because of the wide variations in clay chemistry. Shales are sedimentary rocks which were generally deposited in marine basins. They are composed of compacted beds of...
Nitrogen Application
Nitrogen can be used to solve loss of circulation in areas which have an abnormally low pressure gradient. Nitrogen can be injected into the mud system at the standpipe in order to accurately control annular hydrostatic pressures and thus regain mud returns. Nitrogen has advantages over other aerated systems because pressure, volume, and temperature of the gas from a tank of liquid N2 can be better controlled and temperature is lower than air from a compressor. Temperature is a major factor to...
PotassiumBased Muds
Potassium-based muds are used in areas where inhibition is required to limit chemical alteration of shales. Potassium performance is based on cationic exchange of potassium for sodium or calcium ions on smectites and interlayered clays. The potassium ion compared to calcium ion or other inhibi-tive ions, fits more closely into the clay lattice structure, thereby greatly reducing hydration of clays. Potassium-based muds perform best on shales containing large quantities of smectite or...
AdvantagesDisadvantages of KOHLime Muds
KOH-Lime Muds offer many of the same advantages as Lime Muds. Both KOH-Lime Muds and conventional lime muds have low viscosities and low gel strengths and are solids tolerant. Advantages Disadvantages of KOH-Lime Muds Decreased penetration rates in hard formations Resistant to contaminants such as anhydrite, cement, carbonates, and salt.
Contamination Due to Bacteria
Bacteria are widely distributed in nature a typical soil sample may contain 1,000,000,000 g, which in terms of weight may only represent about 10 mg of the total weight. Bacteria may be divided into two general groups aerobic bacteria, which require oxygen, and anaerobic bacteria, which flourish in oxygen-free environments. The presence of bacteria in a drilling fluid does not, in itself, present a problem. However, there are two general situations where bacteria may become problematic. Aerobic...
Magnesium Contamination
Magnesium is encountered when seawater is used as makeup water. It has also been encountered as magnesium water flows. Magnesium has similar effects as calcium on mud properties such as increased flow properties and fluid loss. Treatment - Magnesium can be precipitated with caustic soda as insoluble magnesium hydroxide Mg OH 2. One-half pound of caustic per barrel of mud will precipitate approximately 430 mg L of magnesium. Most of the magnesium ion will be precipitated when pH is increased to...
Principal Additives of Saturated Salt Muds
Saturated Salt Muds are generally inexpensive to maintain and contain few additives. System complexities are greatly reduced due to the limited selection of additives that will function effectively in a saturated salt mud. Table 20 lists typical additives, function, and concentration for Saturated Salt Muds. Principal Additives of Saturated Muds Bentonite - Viscosity can be controlled to a limited degree with the addition of prehydrated bentonite. The positive sodium ion from the salt acting on...
Commercial Bentonite
Commercial bentonites used in drilling muds are naturally occurring clays and are mined in many areas of the world. They contain the clay mineral smectite and may contain accessory minerals such as quartz, mica, feldspar and calcite. Smectites are three-layer swelling clays of which the most predominant form is calcium, but also sodium. Because smectites have the ability to swell hydrate in the presence of water, these bento-nites are used to viscosify drilling fluids. Sodium bentonite, found...
Unweighted Freshwater Muds No Retort Data Needed
For water-based muds which are unweighted containing only low-density solids , the material balance equation is A simplified form of the equation which assumes 2.6 density for all solids and 8.33 lb gal for fresh water, is Note The calculated values for VSOL for fresh water muds should agree with the measured retort solids, VS, within experimental error.
Principal Additives of Lime Muds
Lime or lime-treated muds generally contain native or commercial clays, caustic soda, organic defloc-culants, lime as a source of calcium , and a fluid loss control agent. Principal additives of lime muds are listed in Table 6. Bentonite - Bentonite is added for viscosity and filtration control. Because sodium is replaced by calcium when the mud is broken over to a lime mud, the bentonite must be prehydrated in fresh water before adding it to the active system. Lignosulfonate - Lignosulfonate...
INHIBITIVE FLUIDS Introduction
Inhibitive fluids are fluids which do not cause appreciable formation alteration. These fluids are primarily used for drilling shale and clay formations however, they are also used in areas where contamination is a problem. Even in large quantities salt, anhydrite, and cement can be handled successfully with the proper inhibitive fluid. Inhibitive salt-based muds use sodium chloride NaCl to achieve inhibition. Calcium-based muds use lime Ca OH 2 or gyp CaSO4 2H2O , and potassium-based muds use...
OilBased Mud
For oil-based muds which are composed of two liquid phases oil and brine and a solid phase having high- and low-densities, even more information is needed to calculate salinity and solids composition. These calculations are covered in Section 3, and will not be discussed here. Note 50 cc retorts are recommended for accuracy over smaller models. Methylene Blue Capacity, Mud lb bbl Methylene Blue Capacity, Drill Solids lb bbl Methylene Blue Capacity, Bentonite lb bbl Volume solids calculated -...
Mud Pit Capacity
What is the total mud pit capacity Mud Pitcap for three rectangular pits, each one 30 ft x 12 ft x 9 ft The general equation for calculating the capacity of the surface mud system or pit capacity is as follows Rectangular Mud Pits, bbl - L W D a. 30ft 12 fp 9 ft- 577 bbl pit 5.6146 ft3 bbl Mud Pitcap 577 bbl pit 3 pits 1731 bbl Total b. 577 4btbl 64.1 bbl ft per pit c. 12 in ft 5.3 bbl inch per pit
Tectonically Stressed Shales
Stressed shales occur in areas where diastrophic movement has occurred. This is the process by which the earth's crust is reshaped, producing continents, oceans, mountains, etc. The shales may incline considerably from the horizontal, having steeply dipping bedding planes. Forces may be acting upon the formation which, when relieved, cause the shale to fall into the hole see Figure 2 . Figure 2 Tectonically Stressed Shales Figure 2 Tectonically Stressed Shales The problem may be further...
Flow Regimes
The mud flow in various parts of the circulating system will be either laminar, transition, or turbulent, depending on the magnitude of the Reynolds number. Reynolds number is a dimensionless number which indicates the type of fluid flow. The Reynolds number can be expressed Figure 13 Hysteresis Loops of Rheogram Figure 13 Hysteresis Loops of Rheogram D Dimension of flow channel V Average velocity in flow channel MW Fluid density, lb gal Typically, for power law fluids the flow regime can be...
Bottoms Up Time
What is the bottoms-up time with one pump operating at 110 SPM a. _min Bottoms up time with one pump operating at 110 SPM is equal to the total annular capacity drill string in the hole divided by the pump output in barrels per minute. In Problem 7, the total annular capacity was calculated to be 802 bbl. .A n n c a p , b b l Q, bb. min
Drill String Capacity
What is the capacity of the drill string DScap when the bit is on bottom at 15,000 ft a. _bbl The general equation for calculating the capacity of the drill string is as follows DScap Drill Pipe DPcap Drill Collar Capacity DCcap DPcap 0.01422 bbl ft 14, 290 ft 203.2 bbl ID 2 L 2.5 2 710 ft 4 3 DScap 203.2 bbl 4.3 bbl 207.5 bbl
PreDisplacement Steps
1. Run bit and dual or tandem scrapers. 2. Circulate and condition mud. Reduce funnel viscosity as much as possible while maintaining adequate rheological properties to clean hole and prevent settling of solids. Maintain critical annular velocity to assure that liner tops are thoroughly cleaned prior to displacement. 3. Rig up equipment for displacement of completion fluid. All tanks, circulating lines, and pumps to be used in the displacement should be cleared of residual mud. 4. Insure...
Solids Removal Region
The devices and associated tank arrangement in the removal region are 1 Mud Gas Separator, 2 Shale Shaker, 3 Sand Trap, 4 Degasser, 5 Hydrocyclones, 6 Mud Cleaner, and 1. Mud Gas Separator - Ahead of the entire sequence of solids removal equipment on most rigs is the Gas Buster. This is a large volume mud gas separator vessel that allows gross amounts of gas to escape from the mud prior to going on to the shale shaker. It has a gas line laid far from the rig where gas can be flared however, it...
NonNewtonian Fluids
Non-Newtonian fluids most drilling fluids fit this general classification do not show a direct proportionality between shear stress and shear rate. The ratio of shear stress to shear rate viscosity varies with shear rate and the ratio is called effective viscosity, but this shear rate must be identified for each effective viscosity value. An example of a non-Newtonian shear stress shear rate slope of the dashed lines shear rate relationship is shown in Figure 4. Note that the ratio of shear...
Mechanics of keyseat sticking are
The number and severity of dog-legs. Length of time that the uncased section of the wellbore is left exposed, especially in terms of rotating hours and number of trips. The drillability of the formation. The relative size between the drill pipe tool joints and the drill collars. Very large collars are less likely to pull into a key-seat and become stuck than are collars that are just slightly larger than the tool joint outside diameter. Rapid transition from a formation that is prone to wash...
POLYMER FLUIDS Introduction
Polymer fluids contain polymers which greatly diversify their application. These fluids contain polymers to viscosify, polymers to control filtration, polymers to deflocculate, polymers to provide high-temperature stabilization, etc. Polymer fluids generally contain only minor amounts of bentonite to build viscosity. Primary viscosification is provided by high molecular weight polymers such as PHPA, PAC, XC polymer, etc. Because these fluids contain only small quantities of bentonite or clay...
HighTemperature Deflocculated Polymer Muds
High-Temperature Deflocculated Polymer Muds were developed to extend the temperature stability of conventional polymer muds. They are designed to tolerate, in addition to contaminants the inclusion of inhibiting ions such as KCl or NaCl. These muds are required to provide stability along the same lines as an oil mud yet still be economical. If the high-temperature deflocculated polymer mud can be used in place of an oil-base mud, then it becomes very attractive for reasons of environmental and...
Total Circulating Volume
What is the total circulating mud volume with pipe on bottom Total Circulating Volume HoleVo OE Mud PitVo Hole Volume and Total Circulating Volume Intermediate J set 4 amp 0Q Ft. Pump MakK.j fiTfOnqt Model J -P-13 Production or Liner Set lt Ft.
Introduction Ckw
Pneumatic drilling fluids are used to drill in areas where loss of circulation and low reservoir pressures restrict the use of conventional drilling fluids. Pneumatic fluids also find application to minimize formation damage caused by 1 invasion of mud filtrate and solid particulates into reservoir pore spaces, 2 flushing of hydrocarbons, 3 hydration of clays within the reservoir, 4 emulsion blocking, or 5 formation of chemical precipitates within the reservoir. These damage problems are all...
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1. Measure 1.0 cm3 of mud into a titration vessel using a 2.5 or 3.0-cm3 syringe. 2. Add 50 cm3 of distilled water to the mud sample and stir with stirring rod. 3. Add 5 drops of phenolphthalein indicator solution. A pink color will appear if alkalinity is present. 4. While stirring, rapidly titrate with 0.02 normal N 50 sulfuric acid until the pink color disappears. Note If endpoint color change is masked, a pH meter can be used to determine when the endpoint of pH8.3 is reached. 5. Report the...
Oil Mud Formulations
Product requirements are listed for each company over the temperature ranges noted. These formulations are based on lab conditions and will be lower in actual field usage. The field requirement is lower because of the incorporation of drill solids, particle size of the weighting material, and longer periods of shear experienced while drilling. The formulations listed can be formulated in diesel or mineral oils with only small modifications. BAKER-HUGHES INTEQ - CONCENTRATION OF PRODUCT, LB BBL...
CalciumBased Muds
Calcium-based muds are primarily used to drill intervals of highly reactive shales. They exhibit greater inhibition than sodium-based muds by reducing hydration of clays. Calcium-based muds are highly resistant to contamination. They tolerate solids well, but a high concentration of low-gravity solids will cause unstable rheological properties. In a calcium-based mud, calcium ion and magnesium ion contamination do not have adverse effects on fluid performance. Chloride ions, however, do...
Volume Capacity and Displacement
1. Mud System Volume - The total mud system volume may be calculated with the drill string either in or out of the hole. Total Mud Volume Pit Volume Hole Volume 2. Pump Output Volume - Pump output tables must be adjusted for estimated or measured pump efficiencies. Triplex pumps usually have an efficiency between 90-98 . Double action duplex pumps usually have an efficiency between 85-95 . The following two equations calculate pump output at 100 volumetric efficiency. The constant, K, may be...
System ConversionMaintenance
Conversion - Lignite Lignosulfonate Deflocculated Muds are quite flexible in their makeup, conversion, and maintenance. Care should always be taken so that conversion to a lignite lignosulfonate mud is not initiated before hole and mud conditions dictate. When converting to a lignite lignosulfonate mud, the volume of solids should be lowered by dilution with water or by mechanical removal prior to the conversion. Calcium ion hardness should not exceed 200 mg L. If hardness is greater than 200...
Metallurgy
To understand corrosion, it is necessary to have some knowledge of metallurgy. Metals and alloys are granular in structure. Variations in this microstructure determine steel properties. Generally, the finer the structure, the harder and stronger the steel. The microstructure and final properties of the steel are determined by type of alloying constituents, temperature, and by the rate and procedure of cooling. Tensile strength and hardness are major factors in the corrosiveness of oil-field...
Packer Fluids
A packer fluid is a fluid left in the casing tubing annulus when completing a well. The purpose of the fluid is to help balance pressures on the tubing and casing strings by providing a hydrostatic pressure on the static side of the tubular goods. The fluid may be either water-based or oil-based. Regardless of the type of fluid used, there are several common properties required for adequate performance. The principal requirement of a packer fluid is stability. A packer fluid will be left static...
Clear Water
Clear water is a nearly ideal drilling fluid however, when drilled solids are incorporated they remain in suspension and thus, reduce the drilling efficiency. An effective means of removing solids from clear water is settling. The settling area should be large enough to allow sufficient time for small particles to settle. Treatment with polymers designed to flocculate drill solids or lime treatments may be used to accelerate settling. Clear water varies in salinity from fresh to saturated...
Introduction Tft
In general, a contaminant is any material that causes undesirable changes in drilling fluid properties. Solids are by far the most prevalent contaminant. Excessive solids, whether commercial or from the formation, lead to high rheological properties and slow the drilling rate. Most other contaminants are chemical in nature and require chemical treatment to restore fluid properties. While there are specific treatments for each contaminant, it is not always possible to remove the contaminant from...
Rheology
Rheological properties measured with a rotational viscometer are commonly used to indicate solids buildups flocculation or deflocculation of solids, lifting and suspension capabilities, and to calculate hydraulics of a drilling fluid. A rotational viscometer is used to measure shear rate shear stress of a drilling fluid - from which the Bingham Plastic parameters, PV and YP, are calculated directly. Other rheological models can be applied using the same data. The instrument is also used to...
Polymer
Those which do not significantly suppress clay swelling, are generally comprised of native clays or commercial bentonites with some caustic soda or lime. They may also contain deflocculants and or dispersants such as lignites, lignosulfonates, or phosphates. Non-inhibitive fluids are generally used as spud muds. Native solids are allowed to disperse into the system until rheological properties can no longer be controlled by water dilution. Those which appreciably retard clay swelling and,...