Slide 1

Mazhar Ali Soomro (K13PG43)

Presentation Topic: Air, Natural Gas and Foam used as Drilling Fluid

Drilling Engineering-I

ContentsFoam mudIts properties and applicationsFoam DrillingAdvantages and Disadvantages of Foam DrillingAir, Its composition, function and applications Air drilling Advantages and disadvantages of Air Drilling

Stiff Foam mud

Foam is created by combining water, surfactants and air.Foam (stiff; like shaving cream) is circulated as the drilling fluid.

Stiff foam applications include areas of severe lost circulation, large diameter holes and unconsolidated formations. Stiff foam can be prepared by injecting a base slurry of 35 45 seconds per liter viscosity fluid prepared.

It acts in the manner of a drilling fluid, cleaning the hole by suspending and carrying the cuttings out of the wellbore. When properly formulated to produce an apropos liquid volume fraction, stable foam exhibits superior hole cutting carrying capabilities to that of a drilling liquid

Super Foam Mud

Super-foam is a biodegradable mixture of anionic surfactants which has been formulated for use in the mineral and water well drilling industries. Typical PropertiesAppearance: Thin liquid, fluorescent yellowpH: 7.5 9.5

ApplicationSuper-foam may be used in a variety of air drilling operations, ranging from simple air drilling to stiff foam drilling where the foam is extended by the use of polymers such as Liqui-pol or Aus-trol, Ezee-pac R and Trol or Bio-vis.

AdvantagesEnvironmentally friendly and biodegradable, it does not pollute.Generates instant high foam quality of exceptional stability.Economical, produces stable foam at low concentrations.Reduces erosion when drilling poorly consolidated formations. Reduces air requirements and allows deeper drilling.Reduces the tendency of softer clays to stick together.Improves hole cleaning and increases penetration ratesEffective in suppressing dust.Cuttings carrying capacity is 6-7 times grater than Air / Dust. Required annular velocity for optimum hole cleaning is significantly lower Air / Mist Drilling. AV = 1000 1500 ft/ min.

Foam DrillingFoam Drillingis especially suitable for drilling large holes in formations that are prone to lost circulation. Foam is generated at the surface by mixing the air from the compressors with a foaming solution from the mist pump. The consistency of this fluid is much like shaving cream with an interlocking bubble structure of encapsulated air providing a lifting capacity superior to that to any drilling fluid. The adjustment of the Foam Quality (gas/fluid ratio) in conjunction with a back pressure valve allows the operator to produce a bottom hole pressure equivalent to a circulating fluid weight in the range 0.2 to 0.8 s.g.

Foam Drilling

In foam drilling, water, surfactants, and air are combined to create a stiff foam. The foam is then circulated as a drilling fluid. The cuttings carrying capacity is 6-7 times greater than dust drilling, and the required annular velocity for optimum hole cleaning is significantly lower. The lower air volume equals less air equipment is required than in dust or mist drilling. Holding back pressure on the annulus can reduce water influx and/or maintain hole wall stability. But foam drilling has its drawbacks: surface requirements, or pits, for foam can become a problem; large pits must be built to contain foam and allow time for the foam to settle; the cost of chemicals to break down foam can be high; a large influx of fluids can break down the foam, reducing hole cleaning.

Foam drilling

AirPure air is a mixture of several gases that are invisible and odorless. It consists of about 78% nitrogen, 21% oxygen, and less than 1% of argon, carbon dioxide, and other gases as well as varying amounts of water vapour. Adults breathe in about 10-20 cubic metres of air every day. Thats about 20,000 breaths. Children breathe almost twice that amount because they are smaller, and their respiratory systems are still maturing.

Air DrillingAir Rotary Drilling is a method used to drill deep boreholes in rock formations. Most water wells and environmental monitoring wells drilled into bedrock are constructed using air rotary. It is used for the drilling in all rock types, igneous, metamorphic, and sedimentary rock. Deep drilling for the recovery of crude oil and natural gas are almost exclusively carried out in sedimentary rock. Boreholes for the recovery of geothermal steam and water are constructed in all three rock types. This method is also called Dust drilling due to the clouds of dust (finely ground formation cuttings) that are expelled away from the well bore by way of a return line usually called a Blooie Line.

The rotary drilling method requires the use of a rock cutting or crushing drill bit, typically a mill tooth tri-cone roller cone bit. This type of drill bit uses more of a crushing action to advance the bit in the rock. Impact energy is supplied to the drill bit from either an above ground impact or down hole impact hammer. This impact force aids in the drilling. Depending on the competency of the substrate, drill casing is advanced as the hole is cut to keep the hole open during drilling. Competent rock may be drilled "open hole" not requiring the use casing.

Milled tooth tri-cone bit

Drill Cuttings

In Air Rotary, all drill cuttings are lifted from the bit face to the ground surface using high pressure compressed air. Compressed air laden cuttings are typically routed into a device called a cyclone where the air is slowed and exits out the top while the rock chips drop out the bottom into a pile or soil bin. If drilling below the water table, copious amounts of water are also ejected with the rock chips requiring water management. Depending on the depth of the hole, one or more additional air compressors called "tag on air" may be required to lift drill cuttings. Driven split spoon samples are not typically feasible due to the hardness of the drilled materials.

Air DrillingDust drilling is another term for air drilling; compressed air is the sole circulating medium. Because no fluid is injected, the annular returns are dust. Dust drilling provides an ideal environment for use with air hammers, is the least expensive type of air drilling, requires no fluid system for cleanup, provides maximum penetration rates, and extends drill bit life. However, dust drilling cannot effectively handle wellbore fluid influxes, those influxes will wet cuttings and result in mud rings in the annulus, and there is a risk of a down-hole fire if mud rings are not eliminated. Switching to mist or foam drilling would allow continued air drilling in the presence of water.

Air drilling layoutDry Air is compressed and boosted to the required circulation pressure to remove cuttings from the hole with high annular air velocities from 2500 to 3500 feet per minute.

Advantages

air is the ideal low density drilling medium, air drilling provides many advantages. To achieve the best results and greatest economy, several factors must be considered for air drilling. The best conditions for air drilling involve hard, dry formations that produce relatively few formation liquids. Once the formation is completely dry, or the influx of liquids is small enough to be absorbed in the air stream, the drill cuttings return to the surface as dust. The process allows for the immediate and sustained evaluation of hydrocarbons.Other advantages of air drilling are low cost, increased rate of penetration, extended bit life, superior control in cavernous and lost circulation areas, and minimal damage to liquid-sensitive pay zones.Increased rate of penetration occurs because the low density of air or gas used minimizes hydrostatic pressure and aids with fracturing. The rate of penetration in air drilling has been recorded at up to 200 ft/hr compared to 30 ft/hr in conventional drilling.

Advantages of Air Drilling-:The main advantages of Air Drilling are as follows: Increased Penetration Rates over conventional drilling fluid systems, in many cases 2 - 3 times higher Ability to drill Lost Circulation zones and low-pressured formations, and maintain returnsFormation Damage is minimized since to the lack of hydrostatic pressure. Extended Bit Life since the compressed air cools the bit and transports the cuttings more quickly away from the drill bits cutting structureFaster R.O.P. (2-5 times faster than on Mud)Improved Deviation Control (light WOB) Minimal Formation Damage in Production sectionEffective Pressure Control thru Lost Circulation Zones Detection of Low Pressure ZonesFaster return of drilled cuttings (formation evaluation)Overall Lower Cost per Foot

Most Common Air Drilling Applications

Hard Rock Drilling where ROP is less than15 ft/hr using mud. Areas that have Deviation Problems with conventional BHAs and use light WOB.

Lost Circulation Problems

Pay-Zones that are sensitive to Formation Damage

Functions

The most common air drilling applications include: hard rock drilling where rate of penetration is less than 15 ft./hr. using mud, areas that have deviation problems with conventional BHA's and use light WOB, lost circulation issues, and pay zones that are sensitive to formation damage.Disadvantages of Air Drilling

Large amount of Air Volume usedHigh Annular Velocity is required to carry cuttings up the hole;3000 ft/min.5000 ft/min Annular Velocity suggested for Optimum Hole Cleaning Formation Pressure Control is minimal Can Not drill when H2 S zones are presentDanger of Down-hole fires: Use Nitrogen membraneUse Fire Float / StopUse Mist

Disadvantages

Large water-bearing formations are the biggest enemies of air drilling, and the rate of formation water influx that can be handled is not defined. However, when water is encountered, mist, foam, aerated, or slug drilling can be used. Other disadvantages to air drilling include: possible down hole fires and explosions, sloughing of formations (when dry or wet), and soft formations. Such disadvantages reduce air drilling's efficiency, but modern air equipment can handle the challenges. Another detriment of air drilling is bits going out of gauge, which is prevalent when hard, abrasive quartzite sands are drilled.

How to overcome down hole fires in borehole?Nitrogen MembraneLike mist drilling, Nitrogen membrane drilling minimizes chance of down hole fire. Membrane units usually reduce operating costs when compared to cryogenic (liquid) nitrogen drilling and transportation problems related to liquid nitrogen are eliminated. The US patent for nitrogen membrane drilling is held by Weatherford, which owns the largest fleet of on-site generated membrane Nitrogen Production Units in the world.AdvantagesMinimizes chance of Down hole FireMembrane Units typically will reduce operating costs.

NitrogenA colorless, odorless gas, Nitrogen is a non-hydrocarbon inert gas used for a variety of functions in the drilling, work over and completion phases of oil and gas wells, as well as in pigging and purging pipelines.Additionally, nitrogen is used to maintain pressure in reservoirs that have either been depleted of hydrocarbons or experienced natural pressure reduction. Because nitrogen is immiscible (or does not mix) with oil and water, a nitrogen injection program or nitrogen flood can be used to move missed pockets of hydrocarbons from an injection well to a production well.

Thanks for your kind attention

ANY QUESTION??