DRILLING PROBLEM AND SOLUTIONS

Jefrie RonaldMuhammad rizkyPeter lewis h

INTRODUCTION

Pada pengeboran, banyak sekali masalah yang dapat terjadi terutama pada sumur pengeboran. Dalam perencanaan sumur, yang perlu diperhatikan adalah mendesain pengeboran dengan antisipasi terjadi masalah pada lubang sumur.

Pada umumnya masalah yang dihadapi adalah pipe sticking, lost circulation, hole deviation, kegagalan pipa, borehole instability, kontaminasi lumpur, kerusakan formasi, hole cleaning dan lainnya. Hal ini berkaitan dengan penyebab masalah pengeboran hingga solusinya.

PIPE STICKING

Pipe Sticking adalah keadaan dimana sebagian dari pipa bor atau

stang bor (drill collar) terjepit (stuck) didalam lubang bor.

Jenis dari Pipe Sticking

Definisi

Differential-Pressure Pipe StickingDifferential pipe sticking terjadi jika perbedaan antara tekanan hidrostatik lumpur pemboran dan tekanan formasi menjadi sangat besar. Mechanical Pipe Sticking

Pipa terjepit secara mekanis ini dapat dibedakan menjadi dua, yaitu pipa terjepit karena runtuhan dan pipa terjepit karena lubang bor mengecil.

PIPE STICKING DESCRIPTION

PENCEGAHAN PIPE STICKING

Differential-Pressure Pipe Sticking

Mengurangi perbedaan tekanan.

Mengurangi daerah kontak.

Menjaga rangkaian bor agar tidak statis.

Mengurangi faktor gesekan

Mechanical Pipe Sticking

• Naikkan tekanan hidrostatik lumpur, supaya dapat menahan dinding lubang supaya jangan runtuh.

• Kecepatan aliran di annulus diusahakan jangan terlalu tinggi.

• Jenis aliran di annulus harus laminer.

• Menggunakan lumpur dengan water loss yang kecil saat menembus formasi shale.

PENANGGULANGAN PIPE STICKING

Differential-Pressure

Pipe Sticking

o Pengurangantekanan

hidrostatik

o Supporting Fluid

o Operasi back off

Mechanical Pipe Sticking

Metode yang biasanya dilakukan untuk

membebaskan pipa yang terjepit secara

mekanis adalah dengan usaha

penggerakkan pipa baik diputar ataupun

ditarik atau dengan mengaktifkan jar,

apabila rangkaian pipa dilengkapi

dengan jar. Jika metode ini gagal, biasanya

disemprotkan fluida organik dan kemudian

prosedur yang telah disebutkan tadi

diulangi. Jika usaha tersebut belum

berhasil, maka pipa harus dilepaskan

dengan cara back off.

PIPE STICKING

Pipa terjepit karena key seat terjadi

pada saat mencabut rangkaian. Tool

jointdrill pipe akan menyangkut

pada lubang key seat sehingga

rangkaian tidak bisa dicabut

• Definisi

LOSS OF CIRCULATION

Definisi: Tidak terkontrolnya aliran lumpur pengeboran sehingga terperangkap ke dalam sebuah formasi yang seringkali disebut sebagai thief zone.

PENYEBABNYA

Karakteristik formasi yang mudah hancur, mempunyai permeabilitas tinggi.

Tekanan pada downhole yang terjadi terlalu besar, sehingga formasi tidak kuat untuk menahannya.

Pengaturan intermediate casing yang yang terlalu tinggi pada zona transisi.

ZONA DARI LOSS OF CIRCULATION

Gambar kiri adalah zona sebagian dari Loss of Circulation, sedangkan gambar kanan adalah zona totalnya.

PREVENTION BEFORE LOC

-Melakukan pemilihan pada berat lumpur secara tepat, untuk mengantisipasi terjadinya loss of circulation.

-Meminimalisir terjadinya friksi anular sehingga terjadi loss pressures, pada saat terjadinya proses pengeboran.

-Pembersihan lubang pengeboran dengan benar.

-Melakukan pemantauan secara berkala terhadap karakteristik formasi zona pengeboran.

HOLE DEVIATION

Contoh Dari Hole Deviation

PENYEBABNYA

Terjadinya ketidakseragaman pada formasi dan sudut pengeboran.

Karakteristik dari drillstring, khususnya pada BHA Makeup.

Stabilizers (lokasi, jumlah, kelonggaran) Tidak tepatnya proses pembersihan hole. Sudut inklinasi vertikal pengeboran yang

tidak sesuai.

DRILLPIPE FAILURES

Jenis-jenis Drillpipe Failures -Twistoff -Parting -Collapse and Burst -Fatigue

PREVENTION

-Meminimalisasi tegangan siklik dengan mengontrol dogleg dan getaran pada mata bor.

-Menggunakan material anti korosi pada peralatan pengeboran.

-Melaksanakan inspeksi secara teratur pada drillstring.

BOREHOLE INSTABILITY

Definisi: Kondisi yang terjadi akibat tidak stabilnya interval dari lubang pengeboran, yang menyebabkan terjadinya perubahan pada gauge size dan struktur mekanis dari lubang tersebut.

TIPE DARI HOLE INSTABILITY

-Hole Closure -Hole Enlargement -Fracturing -Collapse

CAUSES

-Mechanical Rock Failure Mechanisms-Shale Instability

1. Mechanical Instability2. Chemical Instability3. Capillary Pressure4. Osmotic Pressure5. Pressure Diffusion6. Borehole-Fluid Invasion Into Shale

PREVENTION

-Pemilihan berat dan maintenance lumpur yang baik.

-Pemilihan sistem hidrolik yang sesuai dengan kontrol ECD.

-Pemilihan yang sesuai pada hole-trajectory. -Terjadinya kecocokan antara jenis fluida

pengeboran dengan formasi yang sedang dibor.

Pressure DiffusionPressure diffusion merupakan fenomena perubahan tekanan didekat dinding borehole yang terjadi setiap saat.

Borehole-Fluid Invasion Into ShalePada pengeboran konvensional, perbedaan tekanan positif (perbedaan antara tekanan fluida borehole dan tekanan fluida sumur) selalu dipertahankan.

10.6.6 WELLBORE-STABILITY ANALYSIS.

Beberapa model dalam literatur Several models in the literature membahas mengenai analisis stabilitas wellbore. Model tersebut termasuk yang sangat sederhana hingga model yang sangat kompleks seperti linear elastic, nonlinear, elastoplastic, purely mechanical, and physicochemical.

Tergantung dari model, data yang dibutuhkan termasuk data batuan(Poisson ratio, strength, modulus of elasticity); in-situ stresses(overburden, horizontal); tekanan fluida sumur dan kandungannya; serta data lumpur(mud) dan kandungannya.

10.6.7 BOREHOLE-INSTABILITY PREVENTION

Total pencegahan dari ketidakstabilan borehole tidaklah realistis karena mengembalikan kondisi fisik dan kimia dari batuan sangatlah tidak mungkin.

Bagaimanapun, drilling engineer dapat megurangi problem ketidakstabilan borehole instabilities dengan latihan yang baik. Latihan ini termasuk pemlihan berat lumpur dan pemeliharaan, penggunaan hidrolik yang sesuai untuk mengontrol ECD, pemilihan lintasan lubang pengeboran, dan penggunaan fluida borehole yang sesuai dengan kondisi formasi yang dibor.

10.7 MUD CONTAMINATION

10.7.1 DEFINITION.

Lumpur disebut terkontaminasi ketika material asing masuk kedalam sistem lumpur dan menyebabkan perubahan sifat lumpur yang tidak diinginkan, seperti density, viscosity, and filtration.

Biasanya, sistem lumpur water-based sangat rentan terkontaminasi.

10.7.2 COMMON CONTAMINANTS, SOURCES, AND TREATMENTS.

Zat yang paling banyak mengkontaminasi sistem lumpur water-based yakni berbentuk solid; gypsum/anhydrite (Ca++); cement/lime (Ca++); makeup water (Ca++, Mg++); soluble bicarbonates and carbonates (HCO3−,CO3−−); soluble sulfides (HS−, S−−); dan garam/ aliran air bergaram(Na+, Cl−).

Solids Contamination.Solids are materials that are added to make up a mud system (bentonite,barite) and materials that are drilled.

Calcium-Ions Contamination. The sources of calcium ions are gypsum, anhydrite, cement, lime, seawater, and hard/brackish makeup water.

Bicarbonate and Carbonate Contamination. The contaminant ions (CO3−−, HCO3−) are from drilling a CO2-bearing formation, thermal degradation of organics in mud, or over treatment with soda ash and bicarbonate.

Hydrogen Sulfide Contamination. The contaminant ions (HS−, S−−) generally are from drilling an H2S-bearing formation.

Salt/Saltwater Flows. The ions, Na+Cl−, that enter the mud system as a result of drilling salt sections or from formation saltwater flow cause a mud to have high yield strength, high fluid loss, and pH decrease.

10.8 PRODUCING FORMATION DAMAGE

10.8.1 INTRODUCTION.

Producing formation damage has been defined as the impairment of the unseen by the inevitable, causing an unknown reduction in the unquantifiable

10.8.2 BOREHOLE FLUIDS.

Borehole fluids are classified as drilling fluids, completion fluids, or workover fluids. Drilling fluids are categorized as mud, gas, or gasified mud.

There are two types of mud: water-based (pure polymer, pure bentonite, bentonite/polymer) and oil-based (invert emulsion, oil).

10.8.3 DAMAGE MECHANISMS.

Formation damage is a combination of several mechanisms including solids plugging, clay-particle swelling or dispersion, saturation changes, wettability reversal, emulsion blockage, aqueous-filtrate blockage, and mutual precipitation of soluble salts in wellbore-fluid filtrate and formation water.

FIG. 10.8—FORMATION SKIN DAMAGE.

FIG. 10.9—FORMATION DAMAGE CAUSED BY SOLIDS PLUGGING.

Solids Plugging. Fig. 10.9 shows that the plugging of the reservoir-rock pore spaces can be caused by the fine solids in the mud filtrate or solids dislodged by the filtrate within the rock matrix. To minimize this form of damage, minimize the amount of fine solids in the mud system and fluid loss.

Clay-Particle Swelling. This is an inherent problem in sandstone that contains water-sensitive clays. When a fresh-water filtrate invades the reservoir rock, it will cause the clay to swell and thus reduce or totally block the throat areas.

Saturation Change. Production is predicated on the amount of saturation within the reservoir rock. When a mud-system filtrate enters the reservoir, it will cause some change in water saturation and, therefore, potential reduction in production.

Wettability Reversal. Reservoir rocks are water-wet in nature.

FIG. 10.10—FORMATION DAMAGE CAUSED BY SATURATION.

Emulsion Blockage. Inherent in oil-based mud systems is the use of excess surfactants. These surfactants enter the rock and can form an emulsion within the pore spaces, which hinders production through emulsion blockage.

Aqueous-Filtrate Blockage. While drilling with water-based mud, the aqueous filtrate that enters the reservoir can cause some blockage that will reduce the production potential of the reservoir.

Precipitation of Soluble Salts. Any precipitation of soluble salts, whether from the use of salt mud systems or from formation water or both, can cause solids blockage and hinder production.

10.9 HOLE CLEANING

10.9.1 INTRODUCTION.

Throughout the last decade, many studies have been conducted to gain understanding on hole cleaning in directional-well drilling. Laboratory work has demonstrated that drilling at an inclination angle greater than approximately 30° from vertical poses problems in cuttings removal that are not encountered in vertical wells.

FIG. 10.11—CUTTINGS-BED BUILDUP IN DIRECTIONAL WELLS.

10.9.2 FACTORS IN HOLE CLEANING. Annular-Fluid Velocity. Flow rate is the dominant factor in cuttings

removal while drilling directional wells. An increase in flow rate will result in more efficient cuttings removal under all conditions.

Hole Inclination Angle. Laboratory work has demonstrated that when hole angle increases from zero to approximately 67° from vertical, hole cleaning becomes more difficult, and therefore, flow-rate requirement increases.

Drillstring Rotation. Laboratory studies have shown and field cases have reported that drillstring rotation has moderate to significant effects in enhancing hole cleaning.

Hole/Pipe Eccentricity. In the inclined section of the hole, the pipe has the tendency to rest on the low side of the borehole because of gravity.

Rate of Penetration. Under similar conditions, an increase in the drilling rate always results in an increase in the amount of cuttings in the annulus.

Mud Properties. The functions of drilling fluids are many and can have unique competing influences.

Cuttings Characteristics. The size, distribution, shape, and specific gravity of cuttings affect their dynamic behavior in a flowing media.

10.10 HYDROGEN-SULFIDE-BEARING ZONES AND SHALLOW GAS

Drilling H2S-bearing formations poses one of the most difficult and dangerous problems to humans and equipment.

If it is known or anticipated, there are very specific requirements to abide by in accordance with Intl. Assn. of Drilling Contractors rules and regulations.

Shallow gas may be encountered at any time in any region of the world. The only way to combat this problem is to never shut in the well; divert the gas flow through a diverter system instead.

The danger is that if the well is shut in, formation fracturing is more likely to occur, which will result in the most severe blowout problem, underground blow.

FIG. 10.12—FLUID VELOCITY PROFILE IN ECCENTRIC ANNULUS (AFTER HZOUZ ET AL.3).

10.11 EQUIPMENT AND PERSONNEL-RELATED PROBLEMS

10.11.1 EQUIPMENT.

The integrity of drilling equipment and its maintenance are major factors in minimizing drilling problems.

Proper rig hydraulics (pump power) for efficient bottom and annular hole cleaning, proper hoisting power for efficient tripping out, proper derrick design loads and drilling line tension load to allow safe overpull in case of a sticking problem, and wellcontrol systems (ram preventers, annular preventers, internal preventers) that allow kick control under any kick situation are all necessary for reducing drilling problems.

10.11.2 PERSONNEL.

Given equal conditions during drilling/completion operations, personnel are the key to the success or failure of those operations.

Overall well costs as a result of any drilling/ completion problem can be extremely high; therefore, continuing education and training for personnel directly or indirectly involved is essential to successful drilling/completion practices.