Chapter 2 - Formation Damage

2. FORMATION DAMAGE

TUNIO, May' 2011,,, 2011,,, Courtesy AP Aung

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LESSON OUTCOMES

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Types of formation damage

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Pre-treatment well tests analysys fluids

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Explain when and how formation damage contributes to poor well performance Identify the major source of formation damage


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FORMATION DAMAGE CONCEPTS

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Formation damage concerns the formation of a volume of rock with a reduced permeability in the near well-bore . Formation damage means reduced current production.


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Stimulation treatments are designed to increase the well productivity,, either by: productivity –

Reduci Redu cing ng or co comp mple lete tely ly re remo movi ving ng th the e for orma mati tion on da dama mag ge by chemical matrix treatment (e.g. acidizing) OR

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Bypassing the formation damage by creation of a high permeability channel by hydraulic fracturing treatment.


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Basic causes of formation damage –

Contact with a foreign fluid is the basic cause.

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This foreign fluid may be •

Drilling mud

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Clean completion fluid or work-over fluid

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A stimulation fluid

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Well testing fluid

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Someti Some time mess ev even en th the e re rese serv rvoi oirr fl flui uid d it itse self lf if th the e or orig igin inal al characteristics charact eristics are altered TUNIO, May' 2011,,, 2011,,, Courtesy AP Aung

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FORMATION DAMAGE CONCEPTS •

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Most oil field fluids consist of two phases -liquid and solids. Either liquid or solid can cause significant damage through any one of several possible mechanisms: ,

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perforation, or in the formation. –

Solids Soli ds may be wei eig ghti ting ng ma matter eriial alss, cla lay ys, vis isccos osit ity y buil bu ilde ders rs,, fl flui uid d lo loss ss co cont ntro roll ma mate teri rial als, s, lo losst ci cirrcu cula lati tion on materials, drilled solids, cement particles, gravel pack or frac sand fines, precipitated scales, paraffin or asphaltenes. TUNIO, May' 2011,,, 2011,,, Courtesy AP Aung

FORMATION DAMAGE CONCEPTS •

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Liquid may be water containing various types and concentrations concentr ations of solids particles and surfactants. When li uid is ci When cirrcu cula latted or force ced d into or oro ous zon ones es b differential pressure, displacing or commingling with a portion of a virgin reservoir fluid, it may create blockage due to one of several mechanisms.



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Classification of Damage mechanism –

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Reduce Redu ced d ab abso solu lute te pe perm rmea eabi bili lity ty of for orma mati tion on--- re resu sult ltss fr from om plugging of pore channels by particles Increased viscosity of reservoir fluid– results from emulsions or high-viscosity high-visc osity treating fluids


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Pre-Treatment Well Tests

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Diagnosis of Formation Damage –

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It is possible to determine whether formation damage or ‘skin effect’ exists in a particular well. This can be do done ne th thrroug ugh h wel elll tes ests ts suc uch h as productivity productivi ty test.

inffec in ecti tivi vity ty or

From pr From pres essu surre bu buil ildd-up up or pr pres essu surre dr draw aw-d -dow own n te tessts ts,, th the e magnitude of damage or ‘skin effect’ can be determined. Produc Prod ucti tion on lo logg ggin ing g su surv rvey eyss ma may y sh show ow zon ones es wh whic ich h ar are e no nott contributing to the total flow stream.


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DIAGONOSIS DIAGONO SIS OF FORMA FORMATION TION DAMAGE DAMAGE

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Formation Damage during special well operations 1. Dama Damage ge du duri ring ng dr dril illi ling ng of oi oill an and d ga gass zon ones es in wi wild ldca catt or development wells

a) mud solids solids may may block block pores pores and natur natural al fractur fractures. es. b) mud filtra filtrate te inva invasion sion into into pay zones c) pore poress or fr frac actu ture ress ne near ar we well ll-b -bor ore e ma may y be se seal aled ed by the dr dril illl string.


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DIAGONOSIS DIAGONO SIS OF FORMA FORMATION TION DAMAGE DAMAGE 2. Damag Damage e durin during g Casing Casing and Cemen Cementing ting

a. Cement or mud solids may plug large pores natural fractures.

and

b. Ch Chem emic ical al flus flushe hess ma may y ca caus use e ch chan ange gess in cl cla ays in th the e producing formation. c. Filtrate from high fluid loss cement slurries may bring abou ab outt chan ch ange gess in pr prod oduc ucin ing g for orma mati tion on


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DIAGONOSIS DIAGONO SIS OF FORMA FORMATION TION DAMAGE DAMAGE 3. Damag Damage e duri during ng Compl Completio etions ns a) Duri During ng perf perforat orating ing b) Whil While e runnin running g tubing tubing and pack packer er c) Duri During ng produ productio ction n init initiati iation on


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DIAGONOSIS DIAGONO SIS OF FORMA FORMATION TION DAMAGE DAMAGE 4. Damage caused by cleaning of paraffin

a. When cleanin cleaning g paraff paraffin in from from a well with with hot oil or hot water water,, formation and perforations will be plugged unless melted paraffin . b. Wh While ile cutt cutting ing para paraff ffin in from from the tubing tubing (using (using scrape scrapers rs)an )and d circulated down the tubing and up the annulus, some particles may be pumped into perforations and into pores.


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DIAGONOSIS DIAGONO SIS OF FORMA FORMATION TION DAMAGE DAMAGE 5. Damage during well servicing and work-over

a. When killing killing or or circulati circulating ng a well, well, perfora perforations tions or or pores or fractures may be plugged. b. Filtrat Filtrate e invasion invasion by incompatible incompatible water water,, oil, or chemicals chemicals may may cause water blocks, emulsion blocks, or changes in formation clays.


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DIAGONOSIS DIAGONO SIS OF FORMA FORMATION TION DAMAGE DAMAGE 6. Damage during production phase

a. Cor Corro rosi sion on inhibit inhibitor orss or par paraf affi fin n inh inhibi ibito tors rs,, if conta contact cted ed to the formation formati on zones, may reduce permeability. permeability. . rec p a e sca es may p ug formation.

e we

ore, per ora ons, an

c. Well bor bore e opposi opposite te the the prod produci ucing ng int interv erval al in both both carb carbona onate te and sandstone wells may become plugged with silt, shale, mud or fracturi fra cturing ng sand sand.. d. Scr Screen eenss or or grav gravel el pack packss may may bec become ome pl plugg ugged ed with with sil silts, ts, mud mud,, or other debris. TUNIO, May' 2011,,, 2011,,, Courtesy AP Aung

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7. Damage during Water Injection

a. Whi While le injecti injecting ng wate waterr, emulsion emulsion may may occur occur in the forma formatio tion n adjacent to the well b. Th The e tu tubi bing ng,, ca casi sing ng,, pe perf rfor orat atio ions ns,, sc scre reen en,, grav gravel el pa pack cks, s, an and d formation fractures may be plugged with mud, silt, clay, paraffin, emulsions, and corrosi corrosion on inhibitor inhibitors. s.


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8. Damage during Gas Injection

a. Well bore, bore, perfora perforation tions, s, formatio formation n fracture fracturess and pores may may be plugged with solids scoured by injection gas. b. The injection of of corrosion corrosion inhibitors inhibitors will reduce reduce well injectivity injectivity..


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Type of Formation Damage - Skin •

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The value of the Total Well skin (Stotal) measured during a production test has many sources other than formation damage. It is very important to be able to identify the formation damag dam age e com compon ponen entt (Sd), si sinc nce e th this is can be red edu uce ced d by bett be tter er ope opera ratio tional nal pr pract actice icess or pos possib sibly ly,, be re remov moved ed or bypassed by stimulation treatment.


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Type of Formation Damage - Skin

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The total well skin is a composite parameters:


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Formation damage skin –

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Most forms of formation damage reduce the rock permeability to a certain depth away from the well Figure 1 illustrates the resulting producing pressure profile and compares it with the equivalent pres esssure profile for an undamaged well.


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–

Well geometry

which alter the skin value form due to the well design (limited entry, well not at the centre, well orientation (slanted))


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Completion skin •

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Insufficient perforation (density, penetration depth, incorrect phasing) Fractures – either naturally occurring or (artificially) created propped hydraulic fractures – will lead to increase inflow and negative skins by placing a high permeability pathway from deep in the formation to the wellbore


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Production skin •

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A rate dependent skin is often observed in high rate gas well (and very high rate oil wells). Its presen encce can be a useful indication that the wel elll is a potential stimulation candidat candidate e


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Type of Formation Damage - Skin –

The resulting extra pressure drop has to be compensated for either by a reduced pressure drop across the choke or by a smaller production rat rate e

Figure 1


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Formation Damage Concepts – Skin Components •

The total skin effect for a well, s, consists of a number of components. Generally these can be added together, and therefore

Where, –

Sd = damage skin

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Sc+θ = partial completion and slant skin

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Sp = perforation skin

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ΣSpseudo

= pseudo-skins (all phase and rate dependent effect) TUNIO, May' 2011,,, 2011,,, Courtesy AP Aung

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Formation Damage Concepts – Skin Components •

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It is alerted that once a hydraulic fracture is generated, most pretreatment skin effects (Sd, Sc+θ, Sp) are bypassed and have no impact on the post-treatment well performance Similar case in deep penetrating perforation, may bypass the near wellbore area In gen ener eral al,, it is not corr rre ect to ad add d pretr trea eatm tmen entt sk skin in effects eff ects to any post-fracture post-fracture skin eff effects ects


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Skin From Partial Completion and Slant •

These Thes e tw two o sk skiin effect ctss can be de detter ermi min ned usi sing ng th the e method of Cinco-Ley of Cinco-Ley et al. (1975) using the dimensionless parameters; hD = h/rw : zw/ h ; hw/h and  {degrees}

where; –

hw = height of the perforation interval,

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h = heigh heightt of of the the reservo reservoir ir,,

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zw = elevation of the midpoint of the perforations relative to the formation base, and

 = slant angle relative to the vertical axis TUNIO, May' 2011,,, 2011,,, Courtesy AP Aung

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Skin From Partial Completion and Slant


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Skin From Partial Completion and Slant

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Table 5-1 and 5-2 give the results for reservoir dimensionless thickness, hD= (h/rw) of 100 and 1000. The composite skin effect, Sc+θ, and the indivi individua duall parts, parts, sc and sθ, are listed


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Exercise Exerci se – Partial Partial Penetr Penetration ation and and Slant Skin Skin Effect A well with a radius, r w= 0.328 ft is completed in a 33 ft reservoir. In order to avoid severe water coning problems, only 8 ft are completed and the midpoint of the perforations is 29 ft above the base of the reservoir. (Also find the composite skin effect for a vertical section) 1.

Whatt woul Wha would d be be the the compo composit site e skin eff effect ect if θ=45o?

2.

Calcul Calc ulat ate e compo composi site te skin skin effec effectt if h=330 h=330 ft, ft, hw=80 ft and zw=290 ft.

1.

Determin Deter mine e the compo composit site e skin skin eff effect when when h= 230 230 ft, hw= 58 ft and zw=120 ft when θ=30o ,60o ,75o TUNIO, May' 2011,,, 2011,,, Courtesy AP Aung

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Exercise – Partial Penetration and Slant Skin Effect Base

h = 33ft

hw = 8ft zw = 29ft


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Exercise Exerci se – Partial Partial Penetr Penetration ation and and Slant Skin Skin Effect Answer

1. hD = 100 Sc+θ = 8.6 (vertical) Sc+θ = 6 (45o slant) 2. hD=1000 Sc+θ = 15.7 (vertical) Sc+θ = 10.4 (45o slant) 3. ???? TUNIO, May' 2011,,, 2011,,, Courtesy AP Aung

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Skin From Well Perforation

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Perforation creates a flow path for fluids from the reservoir through the cement and casing to the wellbore.


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The perforation skin (Sp) is a fu func ncti tion on of pe perf rfor orat atio ion n length (l), perforation diameter d and hasin angle (). hperf = 1/SPF


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Kar arak akas as an and d Tha Thari riq q (19 (1988) 88) per perfform ormed ed per perffor orati ation on ski skin n effect eff ect calcula calculation tion consis consisting ting of foll following owing components components;; Plane flow effect, sH Vertical converging effects, sv Wellbore effect, swb –

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Sp = sH + sv + swb


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Calculation of plane flow effect, sH

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where r’w(θ) is the effective wellbore radius and is a function of the phasing angle θ.


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The constant aθ depends on the perforation phasing and can be obtained from table by Karakas and Tariq (1988). Howeve How everr the tot total al con contribu tribution tion is usua usuall ll smal small. l.


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Skin From Well Perforation Calculation of vertical converging effect, sV

To obtain sV, two dimensionless variables (hD and rD) must be calcula calculated. ted. •

h D 

h perf

k H

l perf

k V

Where kH and kV are permeabilities, permeabiliti es, respectiv respectively ely •

the

horizontal


and

vertical 41


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And,

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The vertical pseudo-skin is then

with and TUNIO, May' 2011,,, 2011,,, Courtesy AP Aung

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Skin From Well Perforation The co The cons nsta tant nt a1, a2, b1 and b2 are als also o fun functi ction onss of the per perfor forati ation on phasing and can be obtained from the table.


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Skin From Well Perforation Calculation of wellbore effect, s wb •

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For calculation of swb, a dimension onlless quantity is calculated first

And

The constant c1 and c2 also can be obtained from the table TUNIO, May' 2011,,, 2011,,, Courtesy AP Aung

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Exercise – Perforation Skin Effect Assume that a well with rw = 0.328ft is perforated with 2 SPF, rperf = 0.25 in (0.028ft), lperf = 8 in (0.667ft), and θ = 180o. Calculate the perforation skin if the k H/kV = 10. Repeat the calculation for θ = 0o , 45o, 60o , 90o, 120o


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Exercise – Perforation Skin Effect

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Solution

r w

 . .  0.5 s H  ln

 .

0.328

0.5 s H  0.4 TUNIO, May' 2011,,, 2011,,, Courtesy AP Aung

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Exercise – Perforation Skin Effect

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Knowing that hperf = 1/SPF, h D 

0.5

0.667 h D  2.37 r D 

0.028

10

 1 20.5

h D 

0.1



r D  0.037


h perf

k H

perf

V

r perf  1  r D  2h perf 

k V 

 k H 

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Exerci Ex ercise se – Perfora Perforation tion Skin Skin Effec Effect t

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From table and equations,

Sv = 3.852 TUNIO, May' 2011,,, 2011,,, Courtesy AP Aung

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Exerci Ex ercise se – Perfora Perforation tion Skin Skin Effec Effect t

r wD 

0.328

0.667  0.328 r wD  0.33



s wb  2.6  10

2

e

4.532  0.33

s wb  0.1 s p  0.4  3.852  0.1 s p  3.552 TUNIO, May' 2011,,, 2011,,, Courtesy AP Aung

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Thank You….


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Chapter 2 - Formation Damage

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