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Part 2.1. Drilling Operations. Objectives. After reading the chapter and reviewing the materials presented the students will be able to: Understand drilling methods and operations Examine drilling contracts and drilling personnel Discuss tools and techniques of directional drilling
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Part 2.1 Drilling Operations
Objectives • After reading the chapter and reviewing the materials presented the students will be able to: • Understand drilling methods and operations • Examine drilling contracts and drilling personnel • Discuss tools and techniques of directional drilling • Analyze fishing, retrieving, and repairing pipe • Describe unconventional drilling methods
Introduction • Once the landman has secured a lease and drilling permits and other papers are in order, the company turns its attention to drilling. • Titusville, Pennsylvania is often credited as being the birthplace of the modern oil industry (1861) in the United States. • Ploiesti, Romania was the site of the first commercial refinery built in 1856. It used primitive methods of distillation to produce lamp oil to be used for street lighting.
The 1900s and Spindletop • The United States grew increasingly dependent on oil as a plentiful and inexpensive source of energy. • Spindletop in Beaumont, Texas demonstrated the effectiveness of rotary type rigs over cable-tool rigs. • One barrel of oil is equal to 42 U.S. gallons (159 liters). • Oil was used for fuel, lamp oil, and lubricants. • The United States followed Britain’s lead in converting its navy to using fuel oil (from coal).
The Power of Cable-Tool Drilling • Many of the world’s first wells were drilled using the cable tool method. • This equipment uses a drilling rope or wireline (cable) fastened to a mechanism on the surface to provide an up-and-down motion to dig a hole. • The crew lowered the drill bit into the hole with the cable. • Each time the bit dropped, it pierced the rock and deepened the hole. • Cable tool drilling is effective in hard rock formations. • The driller must frequently stop drilling and pull the bit out of the hole to bail out the rock cuttings the bit chips away. • This method is not useful in soft rock formations because the rock fragments tend to close in around the bit. • By the late 1950s, cable tool rigs were completely replaced by more efficient rotary drilling rigs.
The Success of Rotary Drilling • In rotary drilling, the teeth of the bit are forced into the rock at the bottom of the hole and rotated. • While the bit is rotating, drilling fluid – usually a mixture of clay and water referred to as drilling mud – jets out of the nozzle in the bit at high velocity. • These jets of mud fluid move cuttings away from the bit teeth to continuously expose fresh uncut rock for the bit to drill. • The mud lifts the cuttings off the bottom and carries them up the hole to the surface for disposal. • Because the drilling fluid continuously removes the cuttings from the hole, there is no need to stop drilling to remove cuttings.
Drilling Today • A rotary rig is the most common type used today. • Most mobile rigs are moved by truck. • Some offshore rigs are towed by tugboats to the drill site. • Drilling in the arctic regions has led to the development of specialized rotary rigs that can withstand extreme cold.
Oilfield Metallurgy • Metallurgy is the design, formation, and analysis of metals used in the oil and natural gas industry. • Steel has classically been the predominantly material used due to its strength, formability, and cost. • Common mechanical properties of metals are: yield (material does not return to its original shape) and tensile (material breaks) strength, toughness (resistance to cracking), and hardness (resistance to abrasion). • Testing a material’s mechanical properties helps determine safety factors and provides maximum load the material can handle.
Chemistry Considerations • Impurities that weaken mechanical properties are nitrogen, oxygen, sulfur, and phosphorous. • Cast iron is commonly used for valves, pumps, and compressors. • Low alloy steels are used for drill pipe, wellheads, and platforms and drilling rig structures.
Fundamentals of Corrosion • Corrosion is the disintegration of a material due to chemical reactions with its surroundings. • When water contacts metal, an electrochemical reaction causes corrosion. • When this occurs over time, it damages and weakens the metal. • As oilfields get older, more and more water is produced from them, and increased water production means increased corrosion problems.
Drilling Personnel and Contracts • A lease is generally owned by a group of companies with one partner designated as the operator. • The operator plans the well, obtains drilling permits, requests competitive bids for a rig, hires the expert crew, and any additional services. • Generally the operator has a person on site at all times, called the company representative. • The company representative works closely with the contractor’s manager to ensure that the contractor drills the well to specifications.
Contractors • A drilling contractor owns and operates the drilling rig. • A typical crew on a drilling rig consists of a toolpusher, driller, derrickhand, two or three rotary helpers (floorhands/roughnecks), and lease hands. • Offshore contractors also hire several roustabouts, maintenance staff, and marine crew. • The toolpusher is the contractor’s top manager on the drill site, responsible for the rig’s overall operation and performance. • The driller is subordinate to the toolpusher and operates the drilling rig. • The derrickhand has two jobs. He looks after the mud pumps, and handles the top of the pipe from a small platform high in the derrick or mast of the rig. • Rotary helpers, floorhands, or roughnecks handle the bottom of the pipe on the rig floor when pipe is removed from or put into the hole. At other times, rotary helpers help maintain and repair the tools and equipment on the rig. • Offshore, roustabouts assist in loading and unloading equipment and supplies delivered by boat to the rig. They are also responsible for keeping the entire rig painted, cleaned , and repaired.
Bid Proposal and Specifications • When the operator accepts a contractor’s bid, both parties sign the bid, and it becomes a contract. • A drilling contract is an agreement between the operator and the contractor that outlines job duties and drilling specifications. • The contact contains clauses that address items such as location of the well, the date drilling will begin, the well’s depth, timeline, amounts payable to the contractor, and other stipulation. • The contract states details such as diameter and depth of each part of the hole, the drilling mud, and the equipment and services each party will supply.
Contracts • Footage Contract: In this type of contract the operator agrees to pay the contractor a certain amount for each foot of hole drilled. These contracts are only used in areas with well known geology, where well designs are standard, and drilling conditions are predictable. • Daywork Contract: The most common contract is the daywork contract. The operator pays the contractor an amount per day to use the rig, regardless of work the rig is performing. The total cost of both the dayrate and additional costs is called spreadrate. Generally, the spreadrate is about twice the dayrate. • Turnkey Contract: A turnkey contract requires the operator to pay the drilling contractor an agreed amount when the well is finished. • Combination Agreement: A combination agreement combines payment methods.
Drilling • Drilling holes to depths of 30,000 to 40,000 feet requires a high powered rotary drilling rig. • The rig drills a hole with a rotating bit and flushes the cuttings back to the surface with the drilling mud. • Sections of drill pipe above the bit are screwed together in a drill string that connects the equipment in the hole to equipment on the surface. • The drilling crew adds more lengths of drill pipe as needed to drill a deeper hole. • Periodically drilling is stopped and steel pipes called casing are lowered into the well and cemented in place to line the borehole. • Drilling continues in the smaller size hole beneath the casing. • Drilling and casing are continued in sequence until the traget formations are reached.
The Hoisting System • The hoisting system hoists the drill pipe in and out of the hole and supports the drill pipe. • The hoisting system of a rotary drilling rig consists of a derrick or mast (the posts), the drawworks (the spool and crank), and the drilling line (the rope). • Because the loads are heavy, a block and tackle are added. • As the drill string is lowered the weight icreases. The transfer of weight must be carefully controlled, because too much weight can damage the drill bit, and too little weight can slow the drilling rate.
Derrick and Masts • The crown block and the travelling block each comprises of a set of pulleys. • The crown block sits on top of the derrick and never moves. • The travelling block moves up and down in the center of the derrick. • The drilling line is made of wound steel wire. It comes on a spool called a supply reel.
Drawworks • The drawworks is one of the largest and heaviest pieces of equipment on a drilling rig. • It houses the drum around which the drilling line is wrapped. • As the drum rotates, the drilling line spools on or off the drum. • This raises or lowers the travelling block and the drill stem hanging from it. • The driller operates the console that includes brakes, clutches, and a transmission. • By releasing the brake, the driller can use gravity to lower the drill string, and by applying power to the drum, raise the drill string. • Autodrillers and speed controllers use surface mesurements to control the drawworks and brake. • On some wells, downhole measurements are combined with the surface information and fed into computer models that calculate the optimal drilling parameters.
The Rotating System • A conventional rotating system includes all the equipment that turns the bit. • The primary element of a rotating system is the top drive or the rotary table. • The rotary table creates a strong rotating force, or torque. • The bit at the bottom of a hole can be thousands of feet deep, connected to the rotary table on the surface by a drill string. • Additional equipment helps transmit torque from the table to the bit. • Rotating equipment consists of a swivel, kelly, rotary table, drill pipe, drill collars, and bit. • On large rigs, the conventional swivel and rotary table arrangement are replaced with a power swivel called a top drive. • The top drive hangs from the travelling block and has its own heavy duty motor. • The motor turns a threaded drive shaft that connects directly to the top of the drill stem to turn it.
Drilling Assembly • The drilling assembly consists of drill pipe, drill collars, and the drill bit. • The bit is screwed onto the bottom of perhaps 15 to 30 drill collars. • The bit and drill collars are lowered to the bottom of the hole on lengths of drill pipe. • Many sections of drill pipe are added for the bit to reach the bottom of the hole. • Drill pipes and drill collars come in sections about 30 feet long. • Important pipe dimensions are the inside and outside diameter and wall thickness which affect the weight of each joint. • Drill collars are used to put weight on the bit to drill. • Drill pipe and drill collars are joined together using threaded connections on each end. • The threads are lubricated with special alloy grease called pipe dope. • At the bottom of the drill stem is the drill bit, which drills the formation rock, dislodging it so that drilling fluid can bring the fragmented material back up to the surface. • Generally the driller chooses a bit based on the hardness of the formation to be drilled.
The Circulating System • The circulating system pumps drilling fluid down the hole through a series of pipes. • Then it pumps the drilling fluid, or mud, out of the bit at the end of the pipe at the bottom of the hole, all the way back to the surface. • Large heavy duty mud pumps are the heart of the circulating system. • The driller may use two, three, or four pumps to increase pump capacity. • The pumps take mud from steel tanks or mud pits. It is pressurized before sending it down the hole. • The mud return flow line returns the mud and cuttings to the shaker where the cuttings are separated from the mud. • A desander or desilter is used to remove tiny particles of rock called solids. • If the mud contains gas, the circulating system could use a degasser to remove it.
Drilling Fluid Compensation • Drilling fluid, also called drilling mud, is a mixture of water, clay, and specific minerals and chemicals added to help perform tasks. • Drilling fluid is different from completion fluids and formation fluids. • Drilling fluid looks like dirty water in a puddle, so it is called mud. • Besides removing cuttings from the hole, the mud cools and lubricates the bit as it drills. • Mud engineers monitor the viscosity, weight, filtration rate, and solids content of the mud.
The Power System • A drilling rig needs power to run the circulating, rotating, and hoisting systems. • Most rigs need two or more engines to provide in excess of 1,000 hp (horse power). • Auxiliary power for lights and other needs may be 100 to 500 hp. • Floating rigs used in deepwater operations have 2,000 and 3,000 hp thrusters to keep the rig positioned over the well against the forces of wind, waves, and ocean currents. Total power needs of such a vessel might exceed 46,000 hp. • Today the most common source of energy is diesel engines. • Two primary transmission methods are mechanical drives or electrical drives.
Drill Site Procedures • The drill site must provide sufficient space for the drilling rig, and the collection of equipment needed to drill. • For drilling onshore, the operator or contractor may need to clear and level the land, build access roads, and dig reserve pits. • Operators must comply with federal and local government laws and regulations regarding environmental protection. • The operators line the pits with thick plastic sheeting to prevent any contaminated water or other materials from seeping into the ground. • When the well is drilled on land, the rig crew or contractor digs a rectangular pit called a cellar. The cellar provides room beneath the rig to install drilling equipment such as the well control equipment and wellhead.
Rigging Up • Once the site is prepared, the drilling contractor moves the rig and related equipment onto location. • Rigging up is installing the rig on the drill site. • Once complete the hole is ready for spudding in. • Drilling begins when all preparations are complete. • The first part of the hole is called the surface hole. • To protect zones containing fresh water the crew runs a special pipe called surface casing into the hole and cements it in place. • Pulling the drill stem and bit out to run casing, change bits, or perform some other operation is called tripping out. • Casing is large diameter steel pipe used to line or case the wellbore. • A specialized service company usually performs cementing using cement made for oil wells. • As drilling progresses deeper, formations tend to become harder. The crew usually needs to make several round trips to replace worn bits.
Controlling Formation Pressure • The drilling crew must take steps to prevent an influx of fluids into the well. • Left uncontrolled, an influx can lead to a blowout, which is an uncontrolled flow of fluids – oil, gas, water, or all three – from a formation that the hole has penetrated. • At predetermined depth, drilling stops to run another string of casing. • Intermediate casing is smaller than the surface casing because it fits inside the surface casing to the bottom of the intermediate hole. • The crew runs and cements it much the same way as surface casing. • Other reasons to run an intermediate casing are to seal off troublesome formations. • These formations could cause a blowout due to abnormal pressure or lost circulation. • Lost circulation is a condition where quantities of mud are lost to a formation that contains caverns or fissures or is coarsely permeable.
Drilling to Final Depth • The crew drills the next part of the hole using a smaller bit that fits inside the intermediate casing. • The pay zone is a formation that is capable of producing enough oil or gas to make it profitable enough for the operating company to complete the well. • To make this determination, the operator orders tests to evaluate the well. • The tests indicate conditions that help to decide whether to proceed or abandon the well.
Evaluating Formations • First, a geologist thoroughly examines the cuttings to determine whether the formation contains hydrocarbons to continue drilling. • Wireline logging: Using a mobile laboratory, well loggers lower sensitive tools to the bottom of the well or wireline, and pull them back up the hole. • As they pass up and down the hole, the special tools measure and record the formation properties and any fluid (oil, gas, and water) that might be present. • Experienced geoscientists and engineers study and interpret the logs to determine the presence and quality of oil or gas. • Geologists often take core samples of the formation hole and examine them in the laboratory.
MWD and LWD • Measurement while drilling (MWD) has become the method of choice for most current directional drilling operations worldwide. • MWD determines wellbore path in three directions: depth, north-south, and east-west. • Logging while drilling (LWD) involves measurements on the drill string to determine the volume and type of hydrocarbons present within the formation. • The operator decides whether to run either or both MWD/LWD and wireline.
Complete or Abandon • A dry hole means the well cannot produce enough oil or gas in commercial quantities. • Plugging and abandoning the well is considerably less expensive than completing it. • Completion involves running tubing, which is a string of small diameter pipe inside the casing through which the hydrocarbon flows out of the well, and setting the wellhead of steel fittings that support the tubing and contain a series of valves and pressure gauges to control oil flow. • After drilling is finished, the site must be cleaned and returned to its original condition.
Offshore Drilling • Oil companies almost always use mobile rigs for exploratory drilling. • For development drilling, the often use fixed platforms for their production and well maintenance facilities. • Bottom supported units include submersibles, and jackups. • Floating units include inland barges, drill ships and ship shaped barges, and semisubmersibles. • Submersibles can drill in water depths up to about 150 feet. • Jackups can drill in waters up to 550 feet. • Drill ships and ship shaped barges can drill wells in water as deep as 10,000 feet. • Semisubmersibles can be used in deep water are among the largest and most expensive of all MODUs (Mobile Offshore drilling Units).
Controlled Directional Drilling • Controlled directional drilling makes it possible to reach multiple underground locations, often far away, from one primary point. • Considerations in planning well trajectory include the formation to be drilled, the mechanics of bending drill string, and the limits of drilling tools being used. • Directional wells are drilled straight to a predetermined depth and then gradually curved or deviated. • The rate at which a directional well increases angle and depth is referred to as the build rate. • With directional wells, operators can drill as many as 40 or more wells from one platform. • Onshore directional wells reduce risk of harm to the environment.
Tools and Techniques • To create the side force at the bit necessary to change the well trajectory, a bend in the lower section of the bottomhole assembly is needed. • This bend can be created by using a bent sub (a short piece of pipe with the lower pin tilted) or by bending the mud motor housing. • A multilateral well is a main wellbore with attached sidetrack wells, called laterals.
Unconventional Drilling • Shale gas, produced from shale rock, is an increasingly important source of natural gas. • Production of shale gas in commercial quantities requires extensive fractures to provide enough permeability. • The size of the shale gas fields are large, offering economies of scale. • Steam assisted gravity drainage (SAGD) uses drilling technology to inject steam in a well to heat the oil and lower the viscosity, which allows the oil to drain into the producing well and be pumped to the surface.
Fishing • Fishing is a drilling term for retrieving an object, called a fish, from a wellbore. • A fish can be part or all of the drill stem stuck or lost in the hole. • Another fishing situation occurs when pipe breaks in two. • Junk in the hole can bring drilling to a standstill. Powerful magnets and special baskets capture junk and remove it from the hole.
Summary • Once the landman has secured a lease and drilling permits and other papers are in order, the company turns its attention to drilling. • One barrel of oil is equal to 42 U.S. gallons (159 liters). • In rotary drilling, the teeth of the bit are forced into the rock at the bottom of the hole and rotated. While the bit is rotating, drilling fluid – usually a mixture of clay and water referred to as drilling mud – jets out of the nozzle in the bit at high velocity. • A lease is generally owned by a group of companies with one partner designated as the operator. • The operator plans the well, obtains drilling permits, requests competitive bids for a rig, hires the expert crew, and any additional services. • A typical crew on a drilling rig consists of a toolpusher, driller, derrickhand, two or three rotary helpers (floorhands/ roughnecks), and lease hands. • The hoisting system hoists the drill pipe in and out of the hole and supports the drill pipe. • The drilling assembly consists of drill pipe, drill collars, and the drill bit. • The circulating system pumps drilling fluid down the hole through a series of pipes. • Drilling fluid, also called drilling mud, is a mixture of water, clay, and specific minerals and chemicals added to help perform tasks. • The drilling crew must take steps to prevent an influx of fluids into the well. Left uncontrolled, an influx can lead to a blowout, which is an uncontrolled flow of fluids – oil, gas, water, or all three – from a formation that the hole has penetrated. • The pay zone is a formation that is capable of producing enough oil or gas to make it profitable enough for the operating company to complete the well. • A dry hole means the well cannot produce enough oil or gas in commercial quantities. • Controlled directional drilling makes it possible to reach multiple underground locations, often far away, from one primary point. • Shale gas, produced from shale rock, is an increasingly important source of natural gas. • Fishing is a drilling term for retrieving an object, called a fish, from a wellbore.
Home Work • 1. How many U.S. gallons are in one barrel of oil? • 2. What is the job of the operator? • 3. What is a typical crew on a drilling rig? • 4. What is a blowout? • 5. What is fishing?
