DRILLING PROBLEM AND SOLUTIONSJefrie Ronald Muhammad rizky Peter 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 Definisi Pipe Sticking adalah keadaan dimana sebagian dari pipa bor atau stang bor (drill collar) terjepit (stuck) didalam lubang bor. Jenis dari Pipe Sticking Differential-Pressure Pipe Sticking Differential 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 supaya dapat menahan dinding lubang supaya jangan runtuh. . • Jenis aliran di annulus harus laminer.PENCEGAHAN PIPE STICKING Differential-Pressure Pipe Sticking Mechanical Pipe Sticking Mengurangi perbedaan tekanan. Mengurangi daerah kontak. • Kecepatan aliran di annulus diusahakan jangan terlalu tinggi. Menjaga rangkaian bor agar tidak statis. • Menggunakan lumpur dengan water loss yang kecil saat menembus formasi shale. Mengurangi faktor gesekan • Naikkan tekanan hidrostatik lumpur. apabila rangkaian pipa o o Supporting Fluid Operasi back off dilengkapi dengan jar.PENANGGULANGAN PIPE STICKING Differential-Pressure Pipe Mechanical Pipe Sticking Metode yang biasanya pipa yang dilakukan terjepit untuk secara Sticking o membebaskan Pengurangantekanan hidrostatik mekanis adalah dengan usaha penggerakkan pipa baik diputar ataupun ditarik atau dengan mengaktifkan jar. . biasanya disemprotkan fluida organik dan kemudian prosedur yang telah disebutkan tadi diulangi. Jika metode ini gagal. maka pipa harus dilepaskan dengan cara back off. Jika usaha tersebut belum berhasil. PIPE STICKING . .LOSS OF CIRCULATION Definisi: Tidak terkontrolnya aliran lumpur pengeboran sehingga terperangkap ke dalam sebuah formasi yang seringkali disebut sebagai thief zone. sehingga formasi tidak kuat untuk menahannya. . Tekanan pada downhole yang terjadi terlalu besar. mempunyai permeabilitas tinggi.PENYEBABNYA Karakteristik formasi yang mudah hancur. Pengaturan intermediate casing yang yang terlalu tinggi pada zona transisi. ZONA DARI LOSS OF CIRCULATION . untuk mengantisipasi terjadinya loss of circulation. -Meminimalisir terjadinya friksi anular sehingga terjadi loss pressures. -Melakukan pemantauan secara berkala terhadap karakteristik formasi zona pengeboran.PREVENTION BEFORE LOC -Melakukan pemilihan pada berat lumpur secara tepat. pada saat terjadinya proses pengeboran. . -Pembersihan lubang pengeboran dengan benar. HOLE DEVIATION . kelonggaran) Tidak tepatnya proses pembersihan hole.PENYEBABNYA Terjadinya ketidakseragaman pada formasi dan sudut pengeboran. jumlah. . Karakteristik dari drillstring. Stabilizers (lokasi. Sudut inklinasi vertikal pengeboran yang tidak sesuai. khususnya pada BHA Makeup. DRILLPIPE FAILURES Jenis-jenis Drillpipe Failures -Twistoff -Parting -Collapse and Burst -Fatigue . -Melaksanakan inspeksi secara teratur pada drillstring. -Menggunakan material anti korosi pada peralatan pengeboran.PREVENTION -Meminimalisasi tegangan siklik dengan mengontrol dogleg dan getaran pada mata bor. . . yang menyebabkan terjadinya perubahan pada gauge size dan struktur mekanis dari lubang tersebut.BOREHOLE INSTABILITY Definisi: Kondisi yang terjadi akibat tidak stabilnya interval dari lubang pengeboran. TIPE DARI HOLE INSTABILITY -Hole Closure -Hole Enlargement -Fracturing -Collapse . Mechanical Instability 2. Pressure Diffusion 6.CAUSES -Mechanical Rock Failure Mechanisms -Shale Instability 1. Capillary Pressure 4. Osmotic Pressure 5. Chemical Instability 3. Borehole-Fluid Invasion Into Shale . PREVENTION -Pemilihan berat dan maintenance lumpur yang baik. -Pemilihan yang sesuai pada hole-trajectory. . -Terjadinya kecocokan antara jenis fluida pengeboran dengan formasi yang sedang dibor. -Pemilihan sistem hidrolik yang sesuai dengan kontrol ECD. Borehole-Fluid Invasion Into Shale Pada pengeboran konvensional. . perbedaan tekanan positif (perbedaan antara tekanan fluida borehole dan tekanan fluida sumur) selalu dipertahankan.Pressure Diffusion Pressure diffusion merupakan fenomena perubahan tekanan didekat dinding borehole yang terjadi setiap saat. tekanan fluida sumur dan kandungannya. nonlinear. Tergantung dari model. purely mechanical. Beberapa model dalam literatur Several models in the literature membahas mengenai analisis stabilitas wellbore. elastoplastic.10. Model tersebut termasuk yang sangat sederhana hingga model yang sangat kompleks seperti linear elastic. modulus of elasticity). data yang dibutuhkan termasuk data batuan(Poisson ratio. in-situ stresses(overburden. horizontal). and physicochemical. serta data lumpur(mud) dan kandungannya.6 WELLBORE-STABILITY ANALYSIS.6. strength. . pemilihan lintasan lubang pengeboran.7 BOREHOLE-INSTABILITY PREVENTION Total pencegahan dari ketidakstabilan borehole tidaklah realistis karena mengembalikan kondisi fisik dan kimia dari batuan sangatlah tidak mungkin. Bagaimanapun. Latihan ini termasuk pemlihan berat lumpur dan pemeliharaan.10. drilling engineer dapat megurangi problem ketidakstabilan borehole instabilities dengan latihan yang baik.6. penggunaan hidrolik yang sesuai untuk mengontrol ECD. . dan penggunaan fluida borehole yang sesuai dengan kondisi formasi yang dibor. 10.7 MUD CONTAMINATION . 7. Lumpur disebut terkontaminasi ketika material asing masuk kedalam sistem lumpur dan menyebabkan perubahan sifat lumpur yang tidak diinginkan. seperti density. .10. Biasanya. sistem lumpur water-based sangat rentan terkontaminasi. and filtration. viscosity.1 DEFINITION. dan garam/ aliran air bergaram(Na+.10. cement/lime (Ca++). soluble bicarbonates and carbonates (HCO3−. Zat yang paling banyak mengkontaminasi sistem lumpur water-based yakni berbentuk solid. makeup water (Ca++. gypsum/anhydrite (Ca++). Mg++). S−−). Cl−).7.CO3−−). SOURCES. AND TREATMENTS.2 COMMON CONTAMINANTS. . soluble sulfides (HS−. and pH decrease. or over treatment with soda ash and bicarbonate. The contaminant ions (HS−. The ions. Calcium-Ions Contamination. HCO3−) are from drilling a CO2-bearing formation. Solids are materials that are added to make up a mud system (bentonite. cement. The sources of calcium ions are gypsum. Salt/Saltwater Flows. anhydrite. Solids Contamination. Bicarbonate and Carbonate Contamination. thermal degradation of organics in mud. lime. high fluid loss. seawater. and hard/brackish makeup water. Hydrogen Sulfide Contamination. S−−) generally are from drilling an H2S-bearing formation.barite) and materials that are drilled. . 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. The contaminant ions (CO3−−. Na+Cl−. 10.8 PRODUCING FORMATION DAMAGE . 1 INTRODUCTION. Producing formation damage has been defined as the impairment of the unseen by the inevitable.10.8. causing an unknown reduction in the unquantifiable . completion fluids. . oil). gas. There are two types of mud: water-based (pure polymer. or gasified mud. Drilling fluids are categorized as mud. pure bentonite.8. or workover fluids.2 BOREHOLE FLUIDS. Borehole fluids are classified as drilling fluids. bentonite/polymer) and oilbased (invert emulsion.10. emulsion blockage. Formation damage is a combination of several mechanisms including solids plugging. saturation changes. wettability reversal.8.3 DAMAGE MECHANISMS. clay-particle swelling or dispersion.10. and mutual precipitation of soluble salts in wellbore-fluid filtrate and formation water. aqueousfiltrate blockage. . .FIG. 10.8—FORMATION SKIN DAMAGE. 10. .9—FORMATION DAMAGE CAUSED BY SOLIDS PLUGGING.FIG. When a fresh-water filtrate invades the reservoir rock. therefore. . Production is predicated on the amount of saturation within the reservoir rock. Fig. Wettability Reversal. minimize the amount of fine solids in the mud system and fluid loss. it will cause the clay to swell and thus reduce or totally block the throat areas. Clay-Particle Swelling. it will cause some change in water saturation and. Reservoir rocks are water-wet in nature. To minimize this form of damage. Saturation Change. When a mud-system filtrate enters the reservoir. Solids Plugging.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. 10. This is an inherent problem in sandstone that contains water-sensitive clays. potential reduction in production. FIG.10—FORMATION DAMAGE CAUSED BY SATURATION. . 10. can cause solids blockage and hinder production. Precipitation of Soluble Salts. the aqueous filtrate that enters the reservoir can cause some blockage that will reduce the production potential of the reservoir. which hinders production through emulsion blockage. These surfactants enter the rock and can form an emulsion within the pore spaces. Any precipitation of soluble salts. whether from the use of salt mud systems or from formation water or both. Emulsion Blockage. Aqueous-Filtrate Blockage. . While drilling with water-based mud. Inherent in oil-based mud systems is the use of excess surfactants. 10.9 HOLE CLEANING . . Throughout the last decade. 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. many studies have been conducted to gain understanding on hole cleaning in directional-well drilling.9.10.1 INTRODUCTION. .FIG. 10.11—CUTTINGS-BED BUILDUP IN DIRECTIONAL WELLS. flow-rate requirement increases. In the inclined section of the hole. shape. Hole Inclination Angle.10. and therefore. Hole/Pipe Eccentricity. Laboratory work has demonstrated that when hole angle increases from zero to approximately 67° from vertical. Drillstring Rotation. Mud Properties. and specific gravity of cuttings affect their dynamic behavior in a flowing media. Under similar conditions. Flow rate is the dominant factor in cuttings removal while drilling directional wells. Laboratory studies have shown and field cases have reported that drillstring rotation has moderate to significant effects in enhancing hole cleaning. The functions of drilling fluids are many and can have unique competing influences. distribution. Rate of Penetration. . The size. Cuttings Characteristics. an increase in the drilling rate always results in an increase in the amount of cuttings in the annulus. An increase in flow rate will result in more efficient cuttings removal under all conditions. Annular-Fluid Velocity. hole cleaning becomes more difficult.2 FACTORS IN HOLE CLEANING. the pipe has the tendency to rest on the low side of the borehole because of gravity.9. The danger is that if the well is shut in. which will result in the most severe blowout problem. underground blow.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. there are very specific requirements to abide by in accordance with Intl.10. 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. . formation fracturing is more likely to occur. of Drilling Contractors rules and regulations. Assn. If it is known or anticipated. divert the gas flow through a diverter system instead. .FIG.3).12—FLUID VELOCITY PROFILE IN ECCENTRIC ANNULUS (AFTER HZOUZ ET AL. 10. 11 EQUIPMENT AND PERSONNELRELATED PROBLEMS .10. proper hoisting power for efficient tripping out. The integrity of drilling equipment and its maintenance are major factors in minimizing drilling problems. proper derrick design loads and drilling line tension load to allow safe overpull in case of a sticking problem. annular preventers. internal preventers) that allow kick control under any kick situation are all necessary for reducing drilling problems. and wellcontrol systems (ram preventers. .1 EQUIPMENT.11. Proper rig hydraulics (pump power) for efficient bottom and annular hole cleaning.10. therefore. Given equal conditions during drilling/completion operations. personnel are the key to the success or failure of those operations. continuing education and training for personnel directly or indirectly involved is essential to successful drilling/completion practices. . Overall well costs as a result of any drilling/ completion problem can be extremely high.11.10.2 PERSONNEL.