Horizontal Wells (why and advantages)

 

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Horizontal drilling methods(Reason and methods )

The choice of drilling method depends upon:

— Cost,

—Well spacing and

—Mechanical conditions of a vertical well bore

—In addition, reservoir consideration.

—

 BUILD RATES

—Ultra-short Radius

—Short Radius

—Medium Radius

—Long Radius

 ULTRA-SHORT RADIUS

—45 to 90 degrees per foot

—Special equipment

—Horizontal lengths of 100’ to 200’

—Used in unconsolidated, heavy oil sands and soft formation.

—Impossible to log the open hole section.

 

—An ultra-short radius drain hole is drilled using endless 1¼ inch tubing.

—Uses a jet under high pressure to cut the formation and advance the endless tubing.

— twenty-four laterals can be drilled at the same horizon.  

SHORT RADIUS

—1.5 to 3 degrees per foot.

—Needs special equipment

—Mechanical and motor systems are available.

—Typically used in sidetracking existing wells to bypass water producing or troublesome.

—Bending stress and fatigue can be a problem

—200’ to 1000’ horizontal section

—The horizontal section can be cased with a slotted liner or left open hole. 

—Open hole logging capabilities are limited for the horizontal section.

 

MEDIUM RADIUS

— The first medium radius wells were drilled in 1985

—6 to 35 degrees per 100’ build rates

—Uses conventional equipment

—Horizontal section lengths have been drilled over 7000’ but typically 2000’ to 4000’

LONG RADIUS

—2 to 6 degrees per 100’ build rates

—Uses conventional equipment

—Horizontal section lengths have been drilled over 10,000’ but typically 3000’ to 5000’

—No problem with bending stress, fatigue or completion equipment

—Build section is steerable, which means the motor can be rotated in the build section

—Offshore uses long radius almost exclusively since longer departures are required before the well gets to be horizontal

—Wells are more easily logged.

    

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Directional Drilling Applications

—Sidetracking a Stuck Bottom hole Assembly 

 

 

—Multiple Sidetracks

 

—Straighten The Hole Drilling 

 

—Multiple Wells from an Artificial Structure 

—Multilateral Wells Drilled From a Platform. 

 

—Drilling Multiple Sands from a Single Wellbore

 

—Inaccessible Location

 

—Fault Drilling

 

—Salt Dome Drilling 

 

—Relief Well Drilling 

 

—Horizontal Drilling

 

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Directional Concepts

Dogleg

an abrupt change in direction in the wellbore, frequently resulting in the formation of a key-seat.

a sharp bend permanently put in an object such as a pipe, wire rope, or a wire rope sling.

Deflection angel > 3o/100 ft

Angle of Deflection

—in directional drilling, the angle at which a well diverts from vertical

—usually expressed in degrees

—In vertical, being zero.

Azimuth

—in directional drilling, the direction of the wellbore or of the face of a deflection tool in degrees (0 -359 ) clockwise from true north.

—an arc of the horizon measured between a fixed point (such as true north) and the vertical circle passing through the center of an object.

 Steering Tool

—A directional survey instrument used in combination with a deflected downhole motor. It shows, on a rig floor monitor, the inclination and direction of a downhole sensing unit.

—MWD+LWD

 

Systems and Coordinates

Depth Reference

—Measured Depth (MD)

—True Vertical Depth (TVD)

 

Inclination (Drift)

—The angle (in degrees) between the local vertical (local gravity vector as indicated by a plumb bob) and the tangent to the well bore axis at a particular point.

—By oilfield convention, 0° is vertical and 90° is horizontal.

 

Toolface

—Rigsite use of the term “toolface” is often used as a shortening of the phrase “toolface orientation”. This can be expressed as a direction from North or topside of the wellbore.

—Toolface Orientation is the angular measurement of the toolface of a deflection tool with respect to either North or up (highside).

Highside/Magnetic Toolface

   —Highside Toolface 

—indicates whether a component is facing up, down, to the left or right 

—Magnetic Toolface 

—an angular measurement from North

Mag TFO = Azimuth + Highside

Azimuth (Hole Direction)

—the direction of the borehole on the horizontal plane, measured as a clockwise angle (0°- 360°) from the North reference.

—All magnetic tools give readings referenced to Magnetic North; however, the final calculated coordinates are referenced to True North

Quadrant Bearings

—the directions are expressed in degrees from 0°to 90° measured from North in the two Northern quadrants and from the South in the Southern quadrants, e.g., N87°E, S12°W, S90°W.

Direction Measurement

—Azimuth Reference

—Quadrant Bearings

         

  

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Properties of mud

Properties of mud

 Plastic Viscosity (PV)

•Control the magnitude of shear stress develops as one layer of fluid slides over another.

•Measure of friction between layers.

• Provides a scale of the fluid thickness.

• Decreases with increasing temperature; with liquids; the reverse with gasses .

•Effective viscosity depends on fluid velocity flow pattern, difficult to measure, but can be calculated.

• PV is the difference between readings at 600 rpm and that at 300 rpm

yield point

•A measure of the attractive forces between particles due to positive and negative charges

• Measure the forces causes mud to gel in case of motionless

•Shows a minimum level of stress must be provided before mud flows

•Expressed in lb/lOOft2

•A parameter of the Bingham plastic model. YP is the yield stress extrapolated to a shear rate of zero

•It can be increased by Bentonite .

 Gel strength

•Ability of mud to develop gel structure .

•Defines the ability of mud to held solids and measures thixotropy

• Is Determined using viscometer .

• The sample stirred at high speed and the allowed to rest for 10 sec or 10 m.

•The torque readings at 300 rpm is taken as gel strength at specified time.

• Expressed in lb/100 ft2 .

•Converted to metric by multiplying by 0.478 .

  Filtration and filter cake

• Filtrate is the liquid that passes through the porous and permeable rock medium, leaving the cake on the medium .

• A layer of solids deposited on the rock is described as filter cake

• Loss occur when mud pressure is higher than formation pressure

•Quantity of mud loss depends on volume of filtrate and thickness and strength of filter cake, and differential pressure .

•Ideal mud gives small filter loss and thin and tough mud cake

 

•Filtrate is a disadvantage due to formation damage & plugging pores by  shale swelling .

•Mud cake is an advantage due to stabilizing the well bore  but when increasing it decreases the hole diameter

•Polymers are used in mud cake .

•Drilling muds are tested to determine filtration rate and filter-cake properties.

• Cake properties such as cake thickness, toughness, slickness and permeability are important because the cake that forms on permeable zones in the wellbore can cause stuck pipe and other drilling problems.

•Reduced oil and gas production can result from reservoir

     damage when a poor filter cake allows deep filtrate invasion.

• Can be determined by filter press, called API filter press

  

pH of mud 

•Describe the acidity or alkalinity of mud

•Defined as the negative logarithm of the hydrogen ion (H)

•Measured by pH meter or strips or dyes

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Emulsion mud

Emulsion mud

•Water is a continuous (normal oil 5-10% by volume)

•Formulated by using sodium soap as emulsifier

•Oil is added to

 increase penetration rate:oil mud allows to drill faster than watermud

• reduce filter loss,

•improve lubricity,

• reduce lost circulation

•reduce torque and drag in directional well

•The stability of emulsion mud is very important to insure best performance.

 The degree of stability of a certain emulsion can be measured by several observations. The resistance of an emulsion to conduct electric current (or the breakdown voltage) is one of the important measurements which determine emulsion stability. Also filtration loss and mud viscosity are often considered measures of mud stability.

 

•The oil soluble polymers in a form of a gel, according to the instant invention, allow a good thermal stability and avoid any rheological contribution. They may be used at high temperature and high pressure conditions.

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oil base mud

oil base mud

•Water in oil emulsion

•Diesel or crude oil forms its continuous phase

•Sometimes called invert emulsion

•Water droplets are emulsified in oil

•Water is used for gel strength and barite content

•Soaps are used as emulsifiers

•Soups are made from monovalent ion (Na+) or divalent ion

•(Ca++)

•The soap molecule bridge together oil and water interfaces

•Agitation is required to break the water into small droplets

•Oil/water ratio determine the final properties

 

Oil-based muds generally use hydrocarbon oil as the main liquid component with other materials such as clays or colloidal asphalts added to provide the desired viscosity together with emulsifiers, polymers and other additives including weighting agents. Water may also be present, but in an amount not usually greater than 50 volume percent of the entire composition. If more than about 5% volume water is present, the mud is often referred to as an invert emulsion, i.e., water-in-oil emulsion

  

ADVANTAGES:

(1) performs all the functions of a water-base mud or permits an acceptable

substitute for these functions;

 (2) has most of the desirable properties of a water-base mud;

(3) does not hydrate and disperse cuttings;

(4) will not dissolve salt or other water-soluble formation deposits and can be

used to core such sections

(5)exhibits good penetration rates

 (6) protects productive horizons

 (7) does not increase the interstitial water of cores; and

 (8) is not affected by contaminants such as cement, anhydrite, salt or shale, and

can tolerate contamination with water and raw crude. 

 Higher oil water increases resistance to contamination and

temperature stability

Used to drill hole with severe stability

More stable at high temperature

An excellent to drill pay zone; reduce formation damage and

preserve original permeability

 Disadvantages:

 

• Contaminate the environment

• Flammability hazards

• Difficult removal of drilled solids due to high plastic PV 

• Difficult electric logging

        

      

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