Tripping

Prior to tripping out when drilling with conventional mud, it is recommended that the fluid be circulated for at least one bottoms-up' time to ensure that the wellbore has been cleaned thoroughly. The tripping out procedures for a drilling motor is basically the same as those for tripping in. Taking care when pulling the drilling motor through tight spots, liner hangers, casing, casing shoes, and the B.O.P. is necessary to minimize possible damage to both the drilling motor and the wellhead...

Tangential

At one time the tangential method was the most widely used because it was the easiest. The equations are relatively simple, and the calculations can be performed easily in the field. Unfortunately, the tangential method is the least accurate method and results in errors greater than all the other methods. The tangential method should not be used to calculate directional surveys. It is only presented here to prove a point. The tangential method assumes the wellbore course is tangential to the...

Mwd Surface System

The MWD surface system consists of an interface display for data reception, a rig floor display for remote display of data, a PC which logs the data and a printer. The mud signal is digitally filtered within the interface display and five integrity checks are completed on all data. These checks enable the system to recognize pulses of 9 psi amplitude in a system operating at 4300 psi. these filters are programmable for various applications. The data can be plotted on screen or on the plotter on...

Components

A gyroscope is a spinning wheel whose spin axis can move relative to some reference mount. For the sake of simplicity, the major components of the gyro are comprised of The Spin Motor, the main characteristic of which is angular momentum. The Gyro Case which is the outer enclosure. The Gimballing System which is the structure carrying the spin motor. The gimballing system isolates the spinning rotor from the gyro-case if the gyro-case turns around the outer gimbal axis or if the gyro-case turns...

Drilling Services Fundamentals

Sedimentary Transport & Depositional Sedimentary Rock Origin of Hydrocarbon Hydrocarbon Igneous rocks are formed from magma. Two principal types of igneous rock Intrusive (plutonic), those that have solidified below Extrusive (volcanic), those that have formed on the surface Exposed surface rock is subject to weathering Weathering breaks down the structure Erosion is the removal of weathered rock Sedimentary rocks cover 75 of the land surface. Because sedimentary rocks are capable of...

Applied Drilling Engineering

Even though the gyroscope is not influenced by magnetic interference, its very design introduces unique problems associated with obtaining accurate survey information. If the gyroscope could be supported exactly at its center of gravity, it would be free of influences by external forces. However, such accuracy is practically impossible to achieve. Consequently, a slightly off-center gyroscope will tend to show a force, caused by gravity, to drift. The gyroscope compensates for the gravitational...

Magnetic Fields

Our understanding of earth magnetism is based on ideas about how magnets interact with one another and about how magnetism is produced. The eighteenth century French physicist Charles Coulomb described the interaction of magnets in terms of forces acting at points called magnetic poles. Every magnet possesses a positive pole and a negative pole, so named because of their opposite effects on the poles of another magnet. As the like poles of two magnets exert a repelling force on one another, the...

Magnetic Single Shot

The magnetic single shot instrument is used to simultaneously record the magnetic direction of the course of an uncased well bore and its inclination from vertical. It is also used, in some cases, to determine the tool-face of a deflection device when deviating the well (usually a gyro is used). The instruments consist of four basic units 1) a power pack or battery tube 2) a timing device or sensor 3) a camera unit and 4) a compass - inclinometer unit. These four elements are assembled together...

Gyroscopic Measurement

A gyroscopic compass is used when magnetic surveying instruments cannot be used because of the magnetic interference of nearby casing or when a borehole with casing already set is being surveyed. There are various kinds of gyroscopic instruments single- and multishot gyroscopes, the surface-recording gyroscope, the rate or north-seeking gyroscope, and the Ferranti tool (a highly precise, inertial guidance tool similar to that used on modern commercial aircraft). Of the gyroscopic instruments...

Angle Unit or Compass

The inclinometer measures the inclination of the wellbore, and the compass measures the direction or azimuth of the well. These devices are normally designed for a specific application and vary in design and principle. They may measure inclination only, high side (for use with mud motors), a combination of inclination and direction, they may use pendulums, weighted floats or air bubbles. Perhaps the simplest inclinometer is one which that is used for measuring...

Directional Sensors

The Directional Sensor is made up of electronic printed circuit boards, a Tensor Tri-Axial Magnetometer and a Tensor Tri-Axial Accelerometers, and Temperature sensor. These modules are configured into a directional probe and are run in the field mounted in a nonmagnetic drill collar. The Directional Sensor provides measurements which are used to determine the orientation of the drill string at the location of the sensor assembly. The Directional Sensor measures three orthogonal axis of magnetic...

Survey Accuracy And Quality Control

To achieve a high range of accuracy and devise a means of assuring it, is a significant, difficult, and expensive task. For simplicity's sake, let's say the accuracy goal is one foot per 1,000 feet of hole. This means that in a 10,000 foot wellbore survey, the operator is to be assured of bottom-hole location by plus or minus 10 feet. Although other survey technologies (magnetic and free-gyro) may achieve this range of accuracy some percentage of the time, they have no available means of...

Origin Of Hydrocarbons

For most of their history, oil and natural gas were thought of as minerals, substances formed out of nonliving rock, just as gold, sulfur, and salt were part of the rock. There was little reason to assume otherwise. Although petroleum smelled like something that had died, and although natural gas burned like swamp gas, most of the gas and oil escaping from the ground seemed to come from solid rock deep beneath the surface, where, as everyone knew, nothing lived. Beginning two centuries ago,...

Biological Factors

Petroleum contains solar energy stored as chemical energy. Many steps are involved in the conversion from the simple radiant energy of the sun to the complex molecules of hydrocarbons. Coastal waters, rich with nutrients brought in by rivers and upwelling deep-sea currents, support an elaborate community of organisms ranging from microscopic, single-celled plants and animals to large predatory fish and mammals. Some of the smallest and simplest of these organisms perform the first capture and...

Source Rocks

Rock in which organic material has been converted into petroleum is called source rock. (Rock in which petroleum accumulates is called reservoir rock). Generally, the best source rocks are shales rich in organic matter deposited in an anaerobic marine environment. Often these are dark shales, although the dark color can be caused by other substances. However, limestone, evaporites, and rocks formed from freshwater sedimentary deposition also become source beds. Some petroleum geologists think...

Introduction to Directional Well Profiles

In the early days of drilling, no one worried about hole deviation. The objective was to get the well drilled down, completed and producing as quickly as possible. Many drilling personnel assumed the wells were straight - others simply did not care. Subsequently, wells were deliberately drilled in some unknown direction. This began as a remedial operation to solve a drilling problem - usually a fish or junk left in the hole. Today, with the advent of tighter legal spacing requirements, better...

Hydrodynamic Traps

Movement of water through reservoir rock affects not only the amount but also the distribution of oil. An oil-water contact is usually tilted downward in the direction of flow. The pool can be displaced so far that a well drilled into the crest of an anticline might produce only water. The slope of the oil-water interface, and therefore the location of the pool, is related in a predictable way to the slope of the potentiometric surface (which is always in the direction of flow) and to the...

Disconformity

An unconformity along which the layers above and below are parallel is called a disconformity. The disconformity may be parallel to the layers, representing a period during which deposition simply ceased or it may be irregular, indicating an episode of erosion. In the former case, the disconformity may be difficult or impossible to distinguish from an ordinary bedding plane. Unless revealed by correlation with nearby strata, a gap of thousands or millions of years of deposition may go...

Unconformities

A major subcategory of stratigraphic traps includes those associated with unconformities. Permeable outcrops overlain by impermeable layers can accumulate hydrocarbons from sources both above and below the unconformity. A buried anticlinal outcrop may trap petroleum in both flanks, downdip from the eroded crest. Locations that would have seeps on the former landscape surface become traps beneath an unconformity. A porous, permeable formation lapping out on an unconformity can also become a...

Permeability changes

Diagenetic changes can create traps within formerly permeable rocks or can create reservoir areas within formerly impermeable rocks. Minerals crystallizing out of circulating water between the grains of a porous sandstone may reduce local permeability enough to form a barrier to hydrocarbon migration. Alternatively, circulating water may increase permeability by leaching out cement or by enlarging fissures and vugs in limestone, thereby increasing the potential for hydrocarbon accumulation....

Evaporites

Rocks formed by the precipitation of chemicals from solution are called evaporites. Deposits of evaporites can form as the result of either the drying up of a body of water, such as a desert playa lake, or continuous evaporation from a confined body of water that is continually replenished by inflowing water. In the latter case, dissolved minerals become supersaturated (so concentrated that they can no longer stay in solution) and precipitate out to form deposits on the bottom. Evaporites...

Specfic Features Of The Computalog Mwd System

The Computalog MWD system consists of s Secondary Acquisition Module (SAM) which controls downhole data transmission, a Computalog Interface Display (CID), a Rig Floor Display (RFD) for remote display of data, and a pulser which generates the signal. A personal computer is used by the operator for configuration, displaying and logging of data. The standard system provides drill string orientation and temperature information as measured downhole by the SAM. The SAM is initially programmed...

External Magnetic Interference

When magnetic interference from external sources is encountered (such as from a fish in the hole or from nearby casing), all three axis of the directional sensor package will be affected. Therefore, the total magnetic field will vary. The total H value will also vary when the sensor package is close to casing joints. If a hot spot occurs on a non-magnetic collar, the total H value will change with varying tool face settings, but will be repeatable when the BHA is placed in the same orientation....

Drilling Motor Stall

Stalling usually occurs when the application of excessive weight on bit or hole sloughing stops the bit from rotating and the power section of the drilling motor is not capable of providing enough torque to power through. This is indicated by a sudden sharp increase in pump pressure. This pressure increase is developed because the rotor is no longer able to rotate inside the stator, forming a long seal between the two. If circulation is continued, the drilling fluid forces it's way through the...

Lithification

Rivers flow in only one direction - down to the sea. Unless the land subsides or sea level rises, sediments deposited in fluvial environments above sea level are eventually carried away by the unrelenting erosive force of the river. However, sediments that reach the sea eventually come to rest in a relatively stable environment, beyond the influence of most wind, weather, and current, and become buried beneath other sediments. For this reason most sedimentary rocks originate in marine...

Petroleum Geology

What comes into your mind when you hear the word geology If you're like most of us, chances are you get a vivid picture - such as the May 1980 eruption of Mount St. Helens. We tend to think of geology in terms of landscapes too vast to fully comprehend - volcanoes, mountain ranges, and canyons - created by forces beyond our comprehension. Perhaps, then, you will be surprised to learn that most geological changes occur so slowly that you cannot see them happening that our understanding of those...

Tripping In Hole

Generally, a drill string with a drilling motor can be run into the hole like a standard bottom hole assembly. The drilling motor is rugged, but care should be taken to control travel speed while tripping into the hole. The drill string should be tripped with the blocks unlocked and special care must be taken when passing the B.O.P., casing shoe, liner hanger, bridges and nearing bottom. Tight spots should be traversed by starting the pumps and slowly reaming the drilling motor through them....

Compass Grid Corrections

Magnetic survey tools do not reference to geographic north but to the earth's north magnetic pole. Since geographic and magnetic north differ an error is introduced in the survey called magnetic declination. However these values are well known at most places on earth and are easily added to survey calculations. The grid correction is a survey error caused by differences in map orientation. Most maps are drafted to have true north be vertical. Because the maps are on rectangular coordinates and...

Gamma

All MWD tools are capable of providing this service and this tool is frequently used while drilling horizontal wells. The term commonly referred to is geosteering. The probe measures natural gamma radiation and has a depth of investigation between 8 to 15 inches depending upon your trust in the technology. Recently two variations in this tool have been made available to the industry. One type is called focussed gamma ray and the other is called dynamic oriented gamma ray and both are used to...

Directional Sensor Components

Contained inside the assembly is a Single Port MPU, Triple Power Supply and a Digital Orientation Module. The Single Port MPU is a modular micro-controller assembly based on the Motorola MC68HCll microprocessor implementing Honeywell's qMIXTM communications protocol qMIX ll TM . The Triple Power Supply provides regulated power for the complete assembly. The microprocessor provides the control and timing to interface the logic circuit controls the analog power switch. With the analog power...

Types Of Traps

The basic requirements for a petroleum reservoir are a source of hydrocarbons, a porous and permeable rock formation through which hydrocarbons can migrate, and something to arrest the migration and cause an accumulation. Although most of the known reservoirs are anticlinal, many other geologic situations can cause hydrocarbons to accumulate. Petroleum geologists have, for convenience, lumped hydrocarbon traps into two major groups structural, in which the trap is primarily the result of...

Hydrocarbon Migration

Secondary Hydrocarbon Migration

Like other formation fluids, oil and gas migrate. In some situations, they accumulate near where they originate, sometimes within a few inches or feet of the source bed. In other places, the migration covers many miles. Because it is lighter than water and does not readily stay mixed with it, oil tends to separate from water and float on top. Usually it moves as a diffuse scattering of suspended droplets, but it may reach higher concentrations when its movement is impeded. Gas is usually...

Physical Factors

Petroleum Window

The clay that settles out of suspension in quiet waters is buried and transformed into shale. Organic matter trapped within is subjected to pressure that increases at slightly less than the geostatic pressure gradient, which is about 1 pound per square inch psi per foot of depth. The temperature increases gradually, both from compression and by heating from the earth's interior. Below a thin zone that is affected by climate, the temperature rises about 1.5 F for every 100 feet of depth. At 120...

Building Assemblies

As previously stated, the building assembly uses a stabilizer acting as a fulcrum to apply side forces to the bit. The magnitude of that force is a function of the distance from the bit to the tangency point. An increase in bit weight and or decrease in drill collar stiffness will increase the side force at the bit increasing the rate of build. The strongest building assembly consists of one stabilizer placed 3 to 6 feet above the bit face with drill collars and drill pipe above the stabilizer....

Rocks and Minerals

Drilling Rocks For Minerals

A mineral is a naturally occurring inorganic crystalline element or compound. Although some rocks, such as rock salt, are made up of grains of a single mineral, most rocks are assemblages of different minerals. A mineral has a definite chemical composition and gt characteristic physical properties such as crystal shape, melting point, color, and hardness. However, most minerals, as found in rocks, are not pure. Quartz, a form of silica, has a definite chemical formula SiO2 , but usually...

Chemical Factors

Unsaturated Hydrocarbon

Petroleum is both simple and complex. It is composed almost entirely of carbon and hydrogen but the number of ways that carbon and hydrogen can combine is astronomical, and most petroleum contains hundreds of different kinds of hydrocarbons. It occurs in forms as diverse as thick black asphalt or pitch, oily black heavy crude, clear yellow light crude, and petroleum gas. These variations are due mainly to differences in molecular weight - that is, the sizes of the molecules - and the types of...

Data Transmission Formats

MWD tool data are sent to the surface as a series of 0's and 1's. The pulse tools are programmed to begin a data sequence with a distinct marker recognizable by the surface decoder. EM MWD tools have a data on demand format. Data are then transmitted in order, with a certain number of 0's and 1's representing a 'word or frame of information. Transmission formats are programmable at the surface to send data in different styles. For example, toolface becomes very important while slide drilling...

Shelf Environments

Capitan Reef

A typical continental shelf is an underwater plain sloping 10 feet per horizontal mile seaward. It extends from the transition zone beach or delta to the edge of the continental mass. Most of the energy in this zone comes from shallow ocean currents and tides. Sediments are mostly silt and clay mixed with fecal pellets, skeletal debris, and shell fragments, with local deposits of coarser sediments brought in by infrequent tidal and flood cur rents. In warm tropical oceans, the clay of the shelf...

Stream Transport

Most sediments, even those involved in mass movement, are at some time transported by flowing water. The distance a sedimentary particle is carried depends both upon the size, shape, and density of the particle and upon the available stream energy. The steeper a stream, the more gravitational energy it has - and the faster it flows. If the water flows smoothly, like a formation of marching soldiers, the flow is said to be laminar. However, if this orderly, parallel movement is disrupted, the...

Timer or Sensor

The timing device is used to operate the camera at a predetermined time. The Surveyor must estimate the time it will take for the instrument to fall to bottom, whether lowered on wire line or dropped go devilled . The timers available today are either mechanical, or electronic. In the past, mechanical timers have been considered more robust, although less accurate than the electronic timers. With modern solid state electronics this is no longer true and mechanical timers are now rarely used....

Vertical Comp Onentz nT

Igrf Inclination 2010

iEM 2000 ,0 HDE EL E3RF2000 Contour mterval 5000 E0 ISO iEM 2000 ,0 HDE EL E3RF2000 Contour mterval 5000 E0 ISO E0 180 E0 180 The angle of the magnetic field relative to the level ground tangent to the earth is the inclination, or dip, which is 90 at the magnetic north pole and 0 at the magnetic equator. YEAfc 2000.0 IIQE ED IGEF20 00 Contour Interval 5 -ISO -150 YEAfc 2000.0 IIQE ED IGEF20 00 Contour Interval 5 -ISO -150 Finally, the angle of the horizontal intensity with respect to the true...

Metamorphic Rock

Any rock that has been changed by pressure and heat while in the solid phase is termed metamorphic. When shale, a common sedimentary rock, undergoes deep burial, heat and pressure fuse individual mineral grains into a metamorphic rock known as slate more intense metamorphism produces schist. Similarly, limestone becomes marble. One type of low-grade metamorphism, the alteration of limestone to dolomite, involves chemical replacement of calcium by magnesium in solution. Metamorphism always...

Beach sand

The linear zone of sediments marking a former coastline may form a series of sandstone reservoirs. Unlike river sandbars, grain orientation and direction of maximum permeability are across the trend. Information on facies changes is especially useful in locating this type of reservoir. Knowing that limestone and shale usually form some distance offshore, the geologist can determine the direction in which the sediments become coarser and more permeable. The coarsest, best-sorted, most permeable...

Minimizing Errors

One way to minimize the error caused by the drill string is to eliminate as much of the magnetism as possible. This is done by isolating the magnetometer package with as many non-magnetic drill collars as possible. The length of the non-magnetic collars implies a uniform and non-interrupted nonmagnetic environment. This, however, is not true in practice. Each connection in a drill string, whether magnetic or not, is magnetic due to the effects of the mechanical torque of the pin in the box....

Timing And Preservation Of Traps

The Bed Anticline

The accumulation of oil underground is a dynamic phenomenon. It is a function not only of the location and configuration of source and reservoir beds but also of timing - the formation of the trap and the arrival of the resource. A potential trap may form but remain barren because all the petroleum has migrated out of the area or it may form and be destroyed before hydrocarbons are generated. An accumulation of hydrocarbons in a perfectly suitable reservoir may eventually be lost either because...

Applications Of Steerable Assemblies

A steerable assembly is defined as a bottomhole assembly whose directional behavior can be modified by adjustment of surface controllable drilling parameters including rotary speed and weight on bit. The ability to modify behavior in this way enables the assembly to be steered toward a desired objective without its removal from the wellbore. To some extent, rotary assemblies are steerable if the build or drop tendency is weight sensitive. However, the ability to control a rotary assembly is...

Reasons for Using Stabilizers

The placement and gauge of stabilizers are used as the fundamental method of controlling the directional behavior of most bottom hole assemblies. 2. Stabilizers help concentrate the weight of the BHA on the drill bit. 3. Stabilizers resist loading the bit in any direction other than the hole axis. 4. Stabilizers minimize bending and vibrations, which cause tool joint wear and damage to BHA components such as, MWD tools. 5. Stabilizers reduce drilling torque by preventing collar contact with...

Aeolian deposits

Aeolian Deposits

Sediments deposited by wind aeolian deposits range from loess thick beds of silt carried by winds from the outwash plains of glaciers to sand dunes. Large desert dunes that migrate downwind because of prevailing winds develop a pattern of cross-bedding that may be preserved beneath younger sediments. Examples of cross-bedded dune structure can be seen in canyons of the southwestern United States. Erosion, Transportation, and Depositional Environments Erosion, Transportation, and Depositional...

Controlling Vertical Wells

Controlling Vertical Wells

Directional techniques are used to straighten crooked holes. In other words, when deviation occurs in a well which is supposed to be vertical, various techniques are used to bring the well back to vertical. This was one of the earliest applications of directional drilling. Sidetracking out of an existing wellbore is another application of directional drilling. This sidetracking may be done to bypass an obstruction a fish in the original wellbore or to explore the extent of the producing zone in...

Mass Movement

Huascaran Peru Avalanche 1970

In high mountains, severe weathering and the instability of steep slopes often result in the sudden movement of large masses of rock and sediment. A large block of bedrock may separate along deep fractures or bedding planes, causing a rockslide or avalanche. In seconds, a single rock mass weighing millions of tons can come crashing down, shattering itself and everything it hits into boulders and dust. Even though gravity is the principal agent in mass movement, water plays a key part. Besides...

Sealed or Mud Lubricated Bearing Section

The bearing section contains the radial and thrust bearings and bushings. They transmit the axial and radial loads from the bit to the drill string while providing a driveline that allows the power section to rotate the bit. The bearing section may utilize sealed, oil filled, and pressure compensated or mud lubricated assemblies. With a sealed assembly the bearings are not subjected to drilling fluid and should provide extended, reliable operation with minimal wear. As no drilling fluid is used...

Rotary Bottomhole Assemblies

Tangency Point Drilling

There are three basic types of rotary bottomhole assemblies used in directional drilling Building Assemblies, Dropping Assemblies, and Holding Assemblies A building assembly is intended to increase hole inclination, a dropping assembly is intended to decrease hole inclination, and a holding assembly is intended to maintain hole inclination. It should be noted that a building assembly might not always build angle. Formation tendencies may cause the assembly to drop or hold angle. The building...

Fluvial Deposits

Different Types Fluvial Deposit

Sediments deposited by flowing water are called fluvial deposits. Local variations in flow determine where particular types of sediments accumulate. Stream velocity is greatest on the outside of a bend, where the stream under- cuts the bank and increases its sedimentary load. On the inside of the bend, where the water slows and eddies, the stream has less energy. Here is left much of the suspended sediment - first the sand, which takes the most energy to move then higher on the sloping bar,...

Marine deltas

Foreset Layer

The mouths of rivers fall into two general categories. A river with a low sediment load may reach the sea in an estuary, where the effect of current, waves, and tides keeps sediment from accumulating. A heavily laden river, however, usually creates a marine delta, a seaward extension of land at or near sea level caused by the accumulation of sediments at the river's mouth. A delta is composed mostly of sediments brought down by the river, but mixed with them are fine wave-borne sediments...

Aspects Of The Transitory Field

Earth Magnetosphere

The transitory field is responsible for the following variations of the magnetic field. Secular variations of approximately 15 gammas per year - a minor effect. Diurnal solar variation on the order of 30 to 40 gammas per day a minor effect. The cyclical Eleven Years variation - a minor effect. Magnetic storms which may reach several hundreds of gammas - a major effect. The Earth's own magnetic field extends out to approximately 8 times the radius of the planet. Beyond this prevails the Magneto...

Faults

Overthrust Fault Geology

Many structural traps, especially those near the surface, can be located by careful study of the surface geology. Stratigraphic traps, however, are usually unrelated to surface features. Their elusiveness has stimulated the development of more and more sophisticated exploration techniques and devices. Many stratigraphic traps have been discovered accidentally while drilling structural traps. A good example of why stratigraphic traps are hard to find is the shoestring sand. This type of...

Anticlines

Salt Anticlines

A short anticline plunging in both directions along its strike is classified as a dome. A dome is distinguished on structural maps by its nearly circular shape. Many domes are the result of diapirism, the penetration of overlying layers by a rising column of salt or other light, mineral. Salt domes are common along the U.S. Gulf Coast and in the Middle East, northern Germany, and the Caspian Volga area of Russia. When deformational forces exceed the breaking strength of rock, the result is a...

Secondary Migration

Why Clay Impermeable

Hydrocarbons are moved through permeable rock by gravity. This force works in several ways by compressing pore spaces containing fluid, by causing water containing hydrocarbons to flow, and by causing water to displace less dense petroleum fluids upward. Saying that water flows through formations does not mean that it flows in underground rivers. Flow can mean movement of a few inches a year, which can add up to many miles in a geologically short time. What causes water to flow is a difference...

Directional Sensor Package Spacing

In order to avoid magnetic interference, non-magnetic drill collars must be used and empirical charts are used to estimate the length of non-magnetic material needed. Experiments have shown that mud motors can produce a magnetic field from 3 to 10 times greater than components such as steel stabilizers and short drill collars. As a rule of thumb, anytime a mud motor is run, a non-magnetic short drill collar of 3m to 5m should be placed between the motor and sensor package. It may even be...

Magnetic Declination

Magnetics Total Field Intensity

Many people are surprised to learn that a magnetic compass does not normally point to true north. In fact, over most of the Earth it points at some angle east or west of true geographic north. The direction in which the compass needle points is referred to as magnetic north, and the angle between magnetic north and the true north direction is called magnetic declination. You will often hear the terms variation, magnetic variation, or compass variation used in place of magnetic declination,...

Average Angle

When using the average angle method, the inclination and azimuth at the lower and upper survey stations are mathematically averaged, and then the wellbore course is assumed to be tangential to the average inclination and azimuth. The calculations are very similar to the tangential method and the results are as accurate as the balanced tangential method. Since the average angle method is both fairly accurate and easy to calculate, it is the method that can be used in the field if a programmable...

Sedimentary Rock

Sedimentary Shale Rock Pictures

When any type of rock is exposed at the surface, it becomes subject to weathering and erosion. Weathering processes are those that break down the structure of the rock by chemical and physical attack. Erosion is the removal of weathered rock or soil particles by flowing water, wind, moving ice, or other agents. When weathering has proceeded far enough, the erosion process may complete the job of separating the particles from the parent rock. The rock and soil particles carried away by erosion...

Combination Traps

Reservoir Formation

Many petroleum traps have both stratigraphic and structural features. Some, in which both types of characteristics are essential in trapping petroleum, are difficult to classify as either primarily structural or primarily stratigraphic. For instance, originally horizontal formations that now pinch out updip can trap hydrocarbons that might not otherwise have accumulated. Secondary porosity in a shattered brecciated fault zone or anticlinal crest is a stratigraphic trapping mechanism caused by...

Drilling Fluids

Most drilling motors are designed to operate effectively with practically all types of drilling fluids. In fact, the stator or power-section of most PDM's are supplied by the same one or two manufacturers with the same general elastomer type. Successful runs have been achieved with fresh or salt water, oil based fluids, fluids with additives for viscosity control or lost circulation, and with nitrogen gas. However, some consideration should be taken when selecting a drilling fluid, as elastomer...

Kick Pads

Most drilling motors can incorporate wear pads directly above and below the adjustable bend for improved wear resistance. Eccentric kick pads can also be used on most motors ranging from 121 mm 4 3 4' to 245 mm 9 5 8 in size. This kick pad is adjustable to match the low side of the motor to increase build rate capabilities. It will also allow lower adjustable settings for similar build rates, thereby reducing radial stresses applied to the bearing assembly, and permit safer rotation of the...

Trapping

Updip Downdip

The permeability of the formation that seals off a petroleum reservoir is never absolutely zero, but just low enough to reduce the flow rate effectively to zero under reservoir conditions. Given enough pressure and fluidity as opposed to viscosity , hydrocarbons may seep into a tight formation that under less extreme conditions would totally exclude them. Effective permeability is the rock's permeability to a given fluid when another fluid is also present. Water has seven times the ability of...

Balanced Tangential

The balanced tangential method is similar to the tangential method in that the tangent to the angle determines the wellbore course. The difference between the two methods is the balanced tangential uses both the upper and lower surveys stations. The top half of the wellbore course is approximated by the upper inclination line I1A in the figure below and the lower half of the wellbore course is approximated by the lower inclination line AI2. The azimuth is approximated in the same manner. Both...

Tool Face

Tool face TF is an angular measurement of the orientation of the BHA versus the top of the hole gravity tool face or magnetic north magnetic tool face . Reference for tool face is usually the Scribe mark on the non-magnetic drill collar. Computation for tool face angles are made from magnetometers. Accuracy requirement for tool face typically - 1 to 2 degrees is not at all the same as the one for Azimuth typically 1- 0.5 degrees . None of the directional sensors in common use have any moving...

Conglomerates

Rounded Conglomerate

Conglomerates are rocks most of whose volume consists of particles more than 2 mm in diameter. They are formed from the sediments found in alluvial fans, debris flows, glacial out- wash, and other high-energy depositional environments. Most conglomerates occur in thin, isolated layers they are not very abundant. In common usage, the term conglomerate is restricted to coarse sedimentary rock with rounded grains conglomerates made up of sharp, angular fragments are called breccia. The rounding of...

Azimuth References

Half Convergence Meridians

Azimuth, AZ used in directional drilling, may be defined as the direction of the wellbore at a given point projected into the horizontal plane measured in a clockwise direction from Magnetic North, True North or Grid North after applying a North Reference system. Azimuth should be expressed as a value on a 0 -360 compass system. Quadrant or bearing systems i.e. N45 20'E may be easier to visualize, but make the probability of convergence mistakes higher than in an azimuth system. It is therefore...

Radius of Curvature

How Calculate Radius Curvature

The radius of curvature method is currently considered to be one of the most accurate methods available. The method assumes the wellbore course is a smooth curve between the upper and lower survey stations. The curvature of the arc is determined by the survey inclinations and azimuths at the upper and lower survey stations as shown below. The length of the arc between I and I2 is the measured depth between surveys. In the previous methods, the wellbore course was assumed to be one or two...

Power Section

The drilling motor power section is an adaptation of the Moineau type positive displacement hydraulic pump in a reversed application. It essentially converts hydraulic power from the drilling fluid into mechanical power to drive the bit. The power section is comprised of two components the stator and the rotor. The stator consists of a steel tube that contains a bonded elastomer insert with a lobed, helical pattern bore through the center. The rotor is a lobed, helical steel rod. When the rotor...

Directional Drilling Limitations

Any drilling limit described in a textbook written today would be simply broken tomorrow by some operator. We have drilled horizontal wells with laterals over 6,100m long extended reach wells with over 10,000m of horizontal reach horizontal to vertical ratio of 6 or 7 to 1 multi-lateral horizontal wells with 10 legs purposefully turned horizontal wells 180 in bearing drilled 27 wells off a single land based pad location re-entered just about every wellbore configuration to drill to a new target...

Electromagnetic

Directional surveying with the EM MWD tool has become a reliable and cost effective means for surveying both directional and horizontal wells. Advances made over the past years have significantly improved tool reliability when drilling in harsh underbalanced air mist environments, and have also overcome some of the earlier obstacles associated with operational depth. Additionally since the rig pumps do not have to be cycled to receive a survey, the overall survey cycle time can be reduced and...

Jetting

Dog Leg Severity Drilling

The jet bit method of deflecting a well was, at one time, the most common method used in soft formations. Jetting has been successfully used to depths of 8,000 feet 2,400m however the economics of this method and the availability of other directional drilling tools limit its use. Geology is the most important influence on where jetting can be used next in importance is the amount of hydraulic energy available for jetting. Sandstones and oolitic limestones that are weakly cemented are the best...

Differentiation

Oil Saturation

With few exceptions, petroleum reservoirs are water-wet - that is, the oil is not in contact with the rock grains because they are coated with a film of water. Most oil fields have 50 to 80 maximum oil saturation. Above 80 oil saturation, the oil can be produced with very little water mixed in below 10 , the oil is not recoverable. A hydrocarbon reservoir is divided into two or more zones. If only oil and water are present, the oil occupies the upper zone. Although water still lines the pores,...

Cross Hair Pendulum Compass

One of the most common types of angle units, for inclination and direction up to twenty degrees. The compass card is free to rotate inside the housing and maintain a reference to magnetic north. The inclinometer is an independent and free swinging pendulum cross-hair. The compass card is printed in reverse in order for the pendulum, which naturally falls to the low side, to depict the direction as it should be on the high side. The survey disk is read as correct. Care should be taken when...

Directional Sensor Package

The directional sensor package of any MWD tool consists of a set of triaxial inclinometers and triaxial magnetometers to measure respectively hole inclination drift and hole direction azimuth . The triaxial inclinometer measures the 3 orthogonal axes components of the earth gravity vector 'G'. The triaxial magnetometer measures the three orthogonal axes components of the earth magnetic field vector 'H'. The reference axes for measurements are usually as follows but each vendor's tools can have...

Openhole Whipstock

Drilling Whipstock

The whipstock was the first widely used deflection tool for changing the wellbore trajectory, and is seldom used in open-hole deflections today. A whipstock is selected according to the wedge needed to effect the desired deflection. A bit that is small enough to fit in the hole with the whipstock is then chosen at the start of the running mode, the bit is locked to the top of the whipstock. When the whipstock is positioned at the kickoff depth, whether it is the total depth of the wellbore or...

Optional Topics

Most commercial MWD Systems use mud pulse or electromagnetic telemetry to transmit survey data during tool operation. In Mud Pulse the mud pressure in the drill string is modulated to carry information in digital form. Pressure pulses are converted to electric voltages by a transducer installed in the pump discharge circuit standpipe . Then this information is decoded by the surface equipment. Tool measurements toolface, inclination, azimuth etc. are digitized downhole and then the measured...

How do I determine the Declination diagrams on maps

Most topographic maps include a small diagram with three arrows magnetic north, true north and Universal Transverse Mercator grid north. The given value of declination, corresponding to the center of the map, does not take local anomalies into account. The value is usually out of date, since it may have drifted several degrees due to secular change, especially on maps of remote regions with several decades between updates. Some maps, such as the 1 50,000 scale topographic maps by the Canadian...

What factors Influence Declination Location

Geomagnetic Storm Pipeline Effects

Each position on the Earth has a particular declination. The change in its value as one travels is a complex function. If a navigator happens to be traveling along a rather straight line of equal declination, called an isogonic line, it can vary very little over thousands of kilometers. However for one crossing isogonic lines at high latitudes, or near magnetic anomalies, the declination can change at over a degree per kilometer 6 10 mile . Predictive geomagnetic models such as the World...

Igneous Rock

When Magma Cools What Does Form

Igneous rocks are those formed directly from molten rock material, or magma. When the planet was formed, the original crust was entirely igneous today the percentage is 65 . Two principal types of igneous rock are intrusive plutonic , those that have solidified below the surface, and extrusive volcanic , those that have formed on the surface. Granite, the most common intrusive igneous rock, has crystals that are easily seen by the unaided eye. Magma that reaches the surface is called lava...

Motor Selection

Positive Displacement Motor Mud Drilling

Four configurations of drilling motors provide the broad range of bit speeds and torque outputs required satisfying a multitude of drilling applications. These configurations include 4. Low Speed High Torque -Gear Reduced The high speed drilling motor utilizes a 1 2 lobe power section to produce high speeds and low torque outputs. They are popular choices when drilling with a diamond bit, tri-cone bit drilling in soft formations and directional applications where single shot orientations are...

Magnetic Field Strength

The total magnetic field strength may be referred to as the H value, HFH, magnetic field strength or TTL field. The Geological Society Electromagnetic Units are used for measuring the strength of the Earth's magnetic field and are called Gammas. Some useful conversions 1 gamma 1 microtesla 1 tesla 1 gauss 1 gauss 1 gauss 1 tesla 1 x 10 Tesla 1000 gammas 1 x 109 gammas 1 x 105 gammas 1 x 10-4 Tesla 1 oersted The magnetic field intensity recorded at ground level is of a much smaller magnitude...

Methods of Deflecting a Wellbore

There are several methods of deflecting a wellbore. Deflecting means changing the inclination and or direction of a wellbore. Three common methods of accurately kicking off a well are whipstock operations, jetting, and downhole motors. The mud motor techniques are most commonly used because they are fast and accurate, however the whipstock is still used. Jetting is rarely used today, but it is still a valid and inexpensive technique. Rotary bottomhole assemblies are the least expensive method...

Dump Sub Assembly

As a result of the power section described below , the drilling motor will seal off the drill string ID from the annulus. In order to prevent wet trips and pressure problems, a dump sub assembly is utilized. The dump sub assembly is a hydraulically actuated valve located at the top of the drilling motor that allows the drill string to fill when running in hole, and drain when tripping out of hole. When the pumps are engaged, the valve automatically closes and directs all drilling fluid flow...

Scale Inclinometer Compass

Similar in principle to the pendulum cross-hair, this angle unit has an independent weighted inclinometer which appears as a scale superimposed onto the compass card on the survey photo disc. This type of angle unit is normally used for higher inclinations above twenty degrees . Depending on the manufacturer, gravity toolface is interpreted either as read or is reversed. Care should be taken to establish the correct method of determining gravity toolface, before using the single shot for...

Bioherm

Another type of stratigraphic trap is the reef. A wave-resistant accumulation of coral or shells serves as an anchor for calcareous debris that forms limestone. If deeply submerged faster than it can accrete it may become buried beneath marine shales. Such an isolated reef is called a bioherm. It may be porous enough to hold large accumulations of hydrocarbons, especially if it has been dolomitized. Limestone is especially vulnerable to dissolution by groundwater, particularly if raised above...

Drill String Magnetic Interference

Drillstring

The drill string can be compared to a long slender magnet with its lower end comprising one of the magnetic poles. Even if the components of a drilling assembly have been demagnetized after inspection, the steel section of the drill string will become magnetized by the presence of the Earth's field. Drill string magnetism can be a source of error in calculations made from the supplied magnetometer data. This may happen as the angle builds from vertical Figure 5-4 or as the azimuth moves away...

Magnetic Declination Angle

Magnetic Declination

The Earth can be thought of as having a magnetic dipole running through its center with north and south poles at either end. This dipole does not correspond with the Earth's rotational axis tilted approximately 12o relative to earth's axis of rotation . The angle between magnetic north and geographic north True North is defined as the magnetic declination or the angle of declination refer to illustration . The magnetic declination is dependent upon the location latitude and longitude and may...

Analog Circuit

The Analog Circuit provides an interface with the inclinometer, magnetometer, and pressure transducer sensors. The 16 channel multiplexer on the analog circuit takes input from various sensor outputs and sends the data to the logic circuit for transmission. A sensor power switch takes power from the 12 volt regulator and selectively powers up the accelerometers and magnetometers. A 5 volt excitation supply from the 12 volt regulator is used to power the pressure transducer. The status voltages...

Directional Surveying Measurements And Sensors

In order to guide a wellbore to a desired target, the position and direction of the wellbore at any particular depth must be known. Since the early days of drilling, various tools have been developed to measure the inclination and azimuth of the wellbore. To calculate the 3D path of the wellbore, it is necessary to take measurements along the wellbore at known depths of the inclination angle from vertical and azimuth direction normally relative to true north . These measurements are called...

Cementation

As compaction brings individual particles into closer contact, the process of lithification is completed by cementation. Minerals in solution - mainly calcite CaCO3 , the basic constituent of limestone -crystallize out of solution to coat the grains. Other common cementing agents include silica SiO2 , which is less soluble and therefore less abundant in groundwater and iron oxide Fe2O3 , which colors the rock yellow or red. These coatings grow together and may eventually fill the pore spaces....

Grid Systems

Latitude And Longitude Point Globe

One of the oldest systematic methods of location is based upon the geographic coordinate system. While this information is basic, a short review is included for reference. By drawing a set of east-west rings around the globe parallel to the equator , and a set of north- south rings crossing the equator at right angles and converging at the poles, a network of reference lines is formed from which any point on the earth's surface can be located. The distance of a point north or south of the...

Planning

Once the information has been collected from the various departments, a directional plan is prepared that meets all the requirements if possible . A good well planner also tries to incorporate operational issues that contribute to the success of the well and can have a dramatic impact on the length of time required for directional equipment. This can be very important on pad layouts for multiple directional wells and can save the operator considerable expenses if properly utilized. Anyone can...

Magnetic Interference

There are two types of magnetic interference drill string and external magnetic interference which can include 1 interference from a fish left in the hole 2 nearby casing 3 a magnetic hot spot in the drill collar 4 fluctuation in the Earth's magnetic field and 5 certain formations iron pyrite, hematite and possibly hematite mud . Any deviation from the expected magnetic field value can indicate magnetic interference. External magnetic interference can occur as the drill string moves away from...

Applications of Magnetics and Gravity

In the MWD sensor package, two sets of sensors are used. One set magnetometers uses an XYZ system to measure orientation with respect to the earth's magnetic field Hx, Hy, Hz . The other set accelerometers uses an XY or XYZ system to measure orientation with respect to the earth's gravitational field Gx, Gy, Gz . From the magnetic sensors we can learn inclination, azimuth, and tool face angles. From the gravity sensors we can learn inclination and tool face angle. For hole inclinations of 0 to...

Reactive Torque

Drilling motors drive the bit with a right-hand clockwise rotation. As weight is added to the bit, reactive torque acting on the drilling motor housing is developed. This left-hand counter-clockwise torque is transferred to the drill string and may cause the joints above the motor to tighten. Reactions of this type increase with larger weight on bit values and reach a maximum when the motor stalls. This reactive torque also affects the orientation of the motor when it is used in directional...

Directional Drilling Azimuth Reference Systems

Magnetic Declination

This section discusses the primary azimuth reference systems currently used in directional drilling. This will include True North and Magnetic references with particular detail given to Grid Coordinate systems i.e. UTM, Lambert, Geographic, and Local . A simple field-proven method is also presented to help avoid confusion when converting from one system to another. More than one multi-million dollar directional drilling project has missed its intended target s due to errors and or...