Sonatrach Hole Problems

8/8/2019 Sonatrach Hole Problems

1/14

Development Phase

September October 2005abalt solutions limited - 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION

Introduction to Hydrocarbon Exploitation

2005 Abalt Solutions Limited. All rights reserved

Development Phase

Hole Problems

DrillingTechnology-HoleProb

lems


Any Event which causes drilling operations tostop can be described as Non Productive Time

(NPT).

Events such as Pipe sticking, lost circulation orwell kicks can lead to the hauling of operations

resulting in considerable NPT

NPT


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Development Phase



DrillingTechnology-HoleProblems


The sticking of drill pipe inside the borehole is oneof the main Hole problems associated withDrilling Operations.

Mechanisms:

Differential Pipe Sticking Mechanical Pipe Sticking

Pipe Sticking


lems


Causes

Differential Pipe Sticking

Drill String comes in contact with filter cakeof a permeable zone subjected to a lowerpressure.

The pressure differential across the filtercake enables the drill string to beembedded.

Drill string further differentially stuck if sideload and over balance is higher on otherside.

Pipe is differentially stuck if it cannot bemoved up, down or sideward.


3/14

Development Phase





Differential Sticking Force = (Mud Hydrostatic-FormationPressure) x effective area of contact x friction factor



lems


Example:

Determine the magnitude of differential force across a permeable

zone of 50 ft in thickness using the following:

Differential pressure-500 psi

Area of contact-20% of drill pipe perimeter,

filter cake =1/2 inch,

friction factor=0.1

Drill pipe OD =5



4/14

Development Phase





Solution

Perimeter of Drill Pipe= x OD =15.71 in

Differential force =(Hs-Pf) x h x 20% x 15.71

=500 x(50 ft x 12in) x 20% x15.71

=942,600 lb



lems


Reduction of Hydrostatic Pressure

Spotting Pipe Release Agents

Freeing Differential Pipe Sticking


5/14

Development Phase






Reducing the Hydrostatic pressure will enablethe freeing of the pipe. The lowering of

hydrostatic pressure reduces the side loadingforces on the pipe and frees the pipe.

Considerations:

Are there pressurised zones in the open hole.

Will exposed zones kick if hydrostatic pressure

is reduced. Mechanical stability of formation

Confidence level in pore pressure estimates

Volumes of fluids required to carry out

operations.


lems


Methods

Circulation & reducing mud weight

Displacing choke

U-Tube Method.



6/14


7/14

Development Phase





U-Tube Method

Hydrostatic pressure of mud reduced to levelequal to or slightly higher than formation

pressure of zone under consideration.

Pipe freeing agent needs to spotted prior tomethod.

To free differential pipe sticking without loss in

well control


lems


Spotting Pipe Release Agents

Blend of Surfactants + emulsifiers + diesel oil

+ water.

Penetrate filter cake and reduce surface tensionbetween pipe and filter cake.


8/14

Development Phase





Mechanical Sticking

Pipe is completely stuck with little or no

circulation unlike differential sticking wherecirculation takes place.

Causes-

Bridging or Hole Packing off

Formation and BHA (Wellbore Geometry)

Understanding the problem is the key to solution.Cause

determines the Action required..


lems


Causes of Mechanical Sticking

Hole Pack off (bridging)

Shale Instability

Unconsolidated formations

Settled cuttings due to inadequate hole cleaning

Junk in well

Cement blocks

Fractured or faulted formations

Formation & BHA

Key Seating

Under gauge hole

Ledges & Micro doglegs

Mobile formations


9/14

Development Phase





Hole Pack Off-Settled Cuttings

Cuttings settle as a result of inadequate hole cleaning .

In horizontal and highly deviated wells ,good hole cleaning isusually around the larger Drill collar OD,however cuttings cansettle on smaller OD Drill pipe higher up.

Cutting beds develop on the lower side of boreholes with 30degree or greater inclinations depending upon suspension andflow rates of drilling mud.

Settled Cuttings can also result in slow ROP,excessive overpull,increased torque and formation break down due to increaseECD.

Hole cleaning can be controlled by :

Mud rheology modifications

Flow rate Hole angle

Mud weight

ROP

Drill pipe rotation

Hole diameter


lems


Brittle Shale Caused by tangential stresses around the wellbore. Tends to break free and sloughing into hole.

Swelling Shale Caused by hydrational processes or osmotic potential

between pore fluid of shale and drilling fluid salinity.

Degree of clay hydration depends upon clay type andcat ion exchange capacity of clay.

Prevention Use inhibited mud or displace to OBM. Addition of various salts will reduce chemical

attraction between shale and water. Reduce exposure time. Good hole cleaning.

Hole Pack Off- Shale Instability


10/14

Development Phase





Unconsolidated formations have low cohesivestrength and therefore collapse easily.

Usually occur near the top hole where there isloose sand, gravel and silts.

Indicated by increasing pump pressure, torqueand drag.

Remedy

Use mud system with an impermeable filter cake Reduction of flow rate.

Hole Pack Off- Unconsolidated Formations


lems


Common problem in limestone and chalk.

Caused when stresses holding are released.

Drill string whipping can dislodge rockfragments when drilling fractured zones.

If Drill string is stuck and cannot be freed byjarring, then inhibited HCL Pill may be spottedaround the stuck neck.

Hole Pack Off- Fractured & Faulted formations


11/14

Development Phase





Stuck pipe caused by cement blocks fallingfrom rat hole beneath casing shoe or fromcement plugs.

Cement not properly set in a cement pluginside the casing or open hole can flash setaround drill pipe, causing pipe to bepermanently stuck.

Remedies

Minimize rat hole to maximum 5ft ensuring goodtail cement is placed around shoe.

Recommended to start circulation 2 or 3 standsabove expected top of cement.

WOB should be kept to absolute minimum.

Hole Pack Off- Cement Blocks


lems


Pipe sticking can be as a result of Junk falling

from upper parts of the hole or surface duringdrilling operations.

Typical junks from surface include pipe

wrenches, spanners, broken materials, hard

hats etc. Junks can also fall from broken packer

elements, liner hanger slips and metal piecesfrom milling operations.

Remedies

Hole covered on surface when no tools are rundown hole.

Hole Pack Off- Junk


12/14

Development Phase





Caused by rotational drill string coming in contact withsoft formations. Erodes a narrow groove in the formationequal to the diameter of drill pipe tool joint.

Groove created is smaller in size than BHA componentsbelow. When POH, the BHA may be pulled into narrowsized key seat and getting stuck.

Often seen in soft formations and in wells with doglegs.

Doglegs and ledges provide points of contact betweentool joints and walls of hole.

Key seats can be easily recognised by :

Hole tight when tripping out. Circulation is free when pipe is stuck.

Remedies

Jarring downwards with minimum tension and slowrotation.

Formation and BHA (Well Geometry)-Key

Seating


lems


Halites(salt) & Claystone formations posses

plastic properties enabling them to deformunder applied stresses.

Salt Wash Out-WBM dissolve salt sections

during drilling operations causing a large washout. Wash outs usually lead to poor cement

jobs and casing collapse. OBM is the bestdrilling fluid to prevent wash outs.

Salt Movement (Creep)-Salt behaves as a super

viscous fluid and depending upon temperature,earth stresses and water content move around

the well bore causing stuck pipe and casingcollapse.

Formation and BHA (Well Geometry)-Mobile

Formations


13/14

Development Phase





Other Hole Problems

Other problems also arise which may not causethe pipe to stick but are important, such as:

Bit balling

Tight Hole

Hole Wash out and erosion

Hole collapse and Hole Fracture


lems


Bit Balling

Occurs while drilling reactive shales exhibiting

plastic properties and in poorly inhibited WBMwhen shale particles adhere to the BHA.

Can be recognised by reduced ROP as Bit

cutting face is covered with cake, blocked

shaker screens with clay and Overpull on trips.

Remedies

Using inhibited mud systems which preventdispersion of clay particles.

Small percentages of glycol.

Using OBM and increasing salinity.


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Development Phase





Tight Hole

The upward pulling force (drag) is greater thanthe buoyant weight of drill string.

Increase in drag is a clear indication of a tighthole.

Tight holes are usually be observed in reactiveclays or salt.

Remedies

Symptoms

Increased torque

High pump pressures.

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Sonatrach Hole Problems

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