Dull Bit Analysis

When soft, sticky shales and limestones are being drilled with low hydraulic energy levels, diamond bits tend to clog. The fluid courses may clog and the fluid that normally would flow through is diverted elsewhere. The impacted formation tends to build up and pack tighter. In low horsepower applications, it is not uncommon to pull a bit that has as much as one-third of the fluid courses clogged, with the matrix around these areas showing heat cracks. The shale acts as a bearing at these...

LOT Errors

When measured from the surface, hydrostatic pressure is added to the surface pressure readings to obtain the actual pressure exerted on the formation. Hydrostatic pressure calculations use the surface mud weight. Cuttings in the annulus or poorly conditioned mud can introduce errors into this hydrostatic measurement. This is why it is standard practice to circulate uniform mud for 1 to 2 hours before performing the LOT or FIT. There are also pressure transmission losses associated with surface...

Accuracy

The accuracy of the Resistivity measurements varies with the formation Resistivity. Like wireline induction tools, propagation Resistivity sensors are most accurate at low Resistivity, where small changes in Resistivity correspond to large, easily-measured changes in phase shift and or attenuation. The measurements become less accurate at higher Resistivity where small changes in phase shift and or attenuation correspond to large changes in Resistivity. Since phase shift-derived Resistivity...

Logging Speed and Sampling Interval

There are restrictions on logging speeds when using the Gamma Ray sensor because gamma rays are counted over a fixed time period, called the sampling interval. Practically speaking, the gamma ray sensor should not travel more than 30 cm during the sampling interval. The goals in any type of nuclear logging are mutually exclusive. That is, we know that the longest sampling interval possible is best for precise statistics, but that the shortest sampling interval provides for the maximum log data...

Logging Source Spectrum

When the 2-3 curie logging source is installed in the tool, gamma rays, in addition to those from the reference source, are detected. In each detector, these additional gamma rays have their own characteristic spectrum, which we will call the logging source spectrum. The shape of this spectrum depends on the path these gamma rays take en route to the detectors, and on the materials through which they pass. It is from the logging source spectrum that the in formation about the formation density...

Diamond Bits

Diamond bits are used in conventional rotary, turbine, and coring operations. Like any other product, their design and applications must be understood to obtain optimum results at economical rates. Diamond bits are typically used to achieve a lower cost per foot. The bit also can achieve greater drilling rates than roller cone bits, resulting in a reduction in trips to change bits, under certain conditions. Structurally speaking, diamond bits are different from roller cone and PDC bits. A...

Cesium Reference Source Spectrum

The Density tool contains two scintillator PMT detection packages, one placed near the source and the other farther away. Because the response of both the crystal and the PMT of each package are affected by temperature, it is necessary to monitor and control, or stabilize, each detector system. For this purpose, a small cesium reference source is placed adjacent to each NaI detector inside the Density sensor pressure housing. Gamma rays from this source continuously enter the scintillator,...

Torsional Stick Slip Vibration

Stick-slip motion is the most well-known of the self-sustained torsional vibrations. Stick-slip motion is known to create a fluctuating downhole RPM. Therefore, measurements of changing downhole RPM can be used to detect and characterize torsional motion. The accelerometers are DC coupled, and use an rpm sensor that will be used as the primary indicator of stick-slip. The signal from each axis is conditioned using four different methods shock count, peak, rms and waveform capture. The shock...

Section IV

The pipe in this section must be able to resist buckling and withstand the bending stresses imposed by rotation in the build up section. Buckling is more of a concern in this section since the pipe does not benefit from sidewall support available at the higher angles of hole inclination. The pipe weight in this section can contribute significantly to bit weight. Heavyweight drillpipe is usually used here. However, drillpipe can be used if there is a tangent...

Formation Fluid Influx in a Weighted Mud System

Formation Mud Holes

When drilling with weighted mud, the formation fluid is less dense than the mud weight. Therefore, an influx dilutes the mud and lowers the EMW. However, if the formation fluid carries a lot of solids, the reduction in EMW may not be apparent. A kick in a weighted mud is detected on the EMW log by a decrease in EMW that cannot be explained by a change in operating conditions. The rate of change in EMW depends on the amount of the influx and the relative difference in the weight of the mud and...

EMW Response to Axial Movement of Drill Pipe while Tripping In the Well

Movement of the drillstring in or out of the well causes a movement of fluid displaced by the pipe (surge) or a movement of fluid to fill the space vacated by the pipe (swab). In a surge, the fluid is moving up the annulus with increased velocity. The pressure for this increased velocity comes from the pipe acting like a piston in the annulus. This shows up as an increase in EMW. In a swab, the fluid flows down the annulus. This subtracts from the pressure felt at the sensor and lowers the EMW...

Invasion Process Verification of R t

This S-shaped well, located in the Gulf of Mexico, was drilled with a 9.875-inch diameter drill bit using a bentonite-based fresh water drilling mud. Mud weight in these intervals was 9.7 pounds gallon, API fluid loss was 4.8 cc 30 minutes, and mud resistivity was 0.26 ohm-m at reservoir temperature. Formation water resistivity was 0.025 ohm-m at reservoir temperature, and the mud filtrate resistivity was 0.17 ohm-m at reservoir temperature. Log ex. 1 displays a gas sand with a porosity of 31 ,...

Effect of Rotation on

The rib for a given formation density does not change with mud weight or formation density for standoffs less than about 1 inch. One might conclude then that the correction is accurate under all situations for this much standoff. However, when hole enlargement and rotation are both present there is an additional source of error. This error results from the combination of multiple values of standoff in one sample measurement as the tool is rotated. This error grows as the range of standoffs...

Stand Off Correction

Consider the specific operational issues for the Density sensor. The first is the sign of the SOC, which may be either positive or negative, depending on the mud and formation density contrasts. The appropriate sign of the correction will come from the SOC formula. The reasons are as follows When the mud is very light, more of the gamma rays will travel through the volume occupied by the mud than would have had this volume been occupied by formation material. Thus the apparent density readings...

Downhole Porosity with Hole Size Correction

As the hole size increases, relative to the calibration hole size, so does the quantity of drilling fluid surrounding the tool, and consequently the amount of hydrogen surrounding the tool. This increase in hydrogen content will cause lower count rates, appearing to the tool as an increase in porosity. Hence, an increase in hole size requires a negative correction to the porosity. Because the porosity calculation is dependent on hole size, a suitable transform equation is required (linear fit)...

Geiger Mueller Tubes

The G-M tube has a crude detection capability. The tube consists of a metal cylinder, which functions electrically as a cathode and a single anode wire down its center. The tube contains inert gases (e.g., bromine, neon) in which ionization takes place. A high voltage (usually > 1000 volts) is placed between the wire and the cylinder, with the wire functioning as the (positive) anode. Operationally, a gamma ray is detected when it interacts with an electron in the wall of the tube (either...

Real Time Swab and Surge Measurement

If there is circulation while the pipe is moving, swab and surge show up in the real-time data. However, the sampling frequency of real-time data does not accurately define the short duration pressure changes caused by surge and swab. The plotted trace may show the presence of pressure spikes, but the values are seldom accurate measures of the maximum pressure experienced. When the pumps are off while moving the drillstring, the pump cycle data catches the maximum and minimum value during each...

Mud Weight Correction

As the mud weight increases, the suspended solid material displaces the liquid component of the mud. This results in a reduction in the amount of hydrogen in the borehole surrounding the tool. This decrease in hydrogen content will cause higher count rates, appearing to the tool as a decrease in porosity. Hence, an increase in mud weight requires a positive correction to the porosity. To some extent the density of the suspended solids also determines the volume of liquid displaced. If you...

Oil Drilling Bibliography

Knoll, Radiation Detection and Measurement Darwin V. Ellis, Well Logging for Earth Scientists A Cs-137 source emits gamma radiation that is focused into the formation at an energy of 0.662 MeV Gamma rays collide with electrons in the formation and are scattered, losing energy, not speed, in the process (Compton Scattering) Eventually, when the gamma ray is at very low energy (< 100 keV) it is absorbed by an electron-atom system (Photoelectric Effect) and completely disappears The...

Detecting Mud Weight Variations

Poorly conditioned mud or out of specification mud shows up as a variation from the expected EMW. This difference from expected can be from viscosity or weight differences. Mud that is out of specification on weight shows up in two ways. A consistent static EMW that is different than expected A drift away from expected, with no operational changes, in both static and circulating If the Static weight is correct but the ECD is different than expected, the viscosity may be out of specification....

Factors Effecting EMW

Equivalent mud weight includes all factors that affect the pressure exerted on the formation. These may be long term or very short duration. Breaking a Gel Mud sets up in a thixotropic time-dependent gel when it is not flowing. The force needed to break the gel and return the mud to a fluid state adds to the annulus pressure losses until the mud is again fluid. Cuttings Load Suspended solids in the mud increase the mud weight. This increases the hydrostatic pressure of the mud column. Downhole...

Detecting Loss Gain with the Formation

The phenomenon variously called borehole ballooning, breathing, or loss gain is the result of slow mud losses to the formation while drilling, followed by mud returns after the pumps have been turned off. Any flow when the pumps are off is cause for concern as it may be due to an influx of formation water, liquid hydrocarbons, or gas. However, if the flow is due to mud returns, well control is not an issue. The loss is into fractures that are contained within a limited fracture network and with...

Formation Water Salinity Correction

Chlorine is very efficient at capturing thermal neutrons. Chlorine's thermal neutron capture cross-section (33.3 Barns) is 100 times that of hydrogen (0.33 Barns). Thus, increasing formation water salinity causes a reduction in thermal neutron population. This decrease in thermal neutrons will cause lower count rates, appearing to the tool as an increase in porosity. There is also a competing effect in that the increase in chlorine causes a reduction in the hydrogen content of the formation...

Hole Cleaning

Circulating cuttings out of the hole decreases the mud density. As the cuttings are removed, the density of the annular fluid drops and the EMW reflects this decrease (see Figure 7). the cuttings settle Lit of suspension. JI JnClTl + I-1 h.'.l IO ICjJ. 1 ne biwv croppea ircm 1.276 to 1.209 after 140 minutes of drc ation.

Controlling Gel Strength Pressure Spikes

The gel strength of drilling mud prevents cuttings and barite from dropping out of suspension when the mud is static. However, this gellation produces an initial resistance to circulation when pressure is applied to the mud. This gellation may require significant force or pressure to break the gel and start fluid movement. In Figure 15 the sharp spikes are a measure of the extra pressure necessary to break a gel each time the pumps come on. This increase pressure of up to 0.06 sg is greater...

Transmitterto Receiver Spacing

The depth of investigation of Resistivity measurements increases with increasing transmitter-to-receiver spacing. This principle is illustrated by the generalized diagrams below, which show the lines of constant phase of the shallow and medium-spaced transmitters in an isotropic medium. The shaded area indicates the region that will influence the phase shift measured between the near and far receivers. Note that for a longer transmitter-receiver spacing, this area of investigation extends...

Y Plan E

Its relationship to the X - Y plane and the gravity vector, along with the components of gravity in the X - Y plane and on the Z-axis. Gxy is the vector sum of the X and Y components of the gravity vector measured by the tool. On the right is a diagram of the X - Y plane showing the X and Y components of the gravity vector and the sum Gxy. Highside toolface is the angle between the X axis and the highside of the hole and is calculated as follows HSTF ATAN ( Gy -Gx ) or HSTF ATAN2 ( Gy, -Gx)...

Roller Cone Bits

The grading and evaluation of dull roller cone bits in an accurate and consistent manner is critical in today's market because of the need to maximize all of the resources used in the process of drilling. Dull bit gradings are essential to all of the people responsible for drilling wells in an efficient and cost effective manner. The information available from dull grading and evaluation is invaluable to bit manufacturers in providing information on which to base improvements and advancements....

Tensor Magnetometer

The Tensor Tri-axial Magnetometer measures three orthogonal axes of magnetic bearing (Bx, By, and Bz) as well as temperature. The Tensor Model 7002MK Magnetometer has an output operating range of plus and minus 100,000 Nanotesla (the earth's field is about 50,000 Nanotesla) and operates within these parameters 1. Input voltage + - 12 - 18 vdc 3. Flux Gate Output 1 mv 20 Nanotesla 4. Temperature Output Voltage 10 mv oK The Tensor magnetometer is a saturable core device. It consists of two coils...

Bz msrd

7QQQQ 65QQQ 6QQQQ 55QQQ 5QQQQ 45QQQ 4QQQQ 35QQQ 3QQQQ 25QQQ 2QQQQ 15QQQ 1QQQQ 5QQQ Q 6QQQQ 59QQQ 58QQQ 57QQQ 56QQQ 55QQQ 54QQQ 53QQQ Inc Plot example of acceptable data t Drilling Fluid + Cuttings + Reservoir Fluids ( Drilling Fluid + Gas + Cuttings + Reservoir Fluids t Drilling Fluid + Cuttings + Reservoir Fluids ( Drilling Fluid + Gas + Cuttings + Reservoir Fluids Sour oil and gas wells Conventional connections Mud pulse directional Continuous UBD Single phase fluid in horz. Hole size...

Resistivity Frequencies KHz and MHz

The Resistivity tool operates at frequencies of 2 MHz (shallow, and medium spacing measurements) and 400 KHz (deep spacing measurement). 400 KHz is in the medium wave or AM radio band, and 2 MHz lies between the AM and FM radio wave frequency bands. The choice of this frequency range is dictated by two physical phenomena. First, at frequencies above about 10 MHz, the dielectric permittivity dominates the wave propagation, and the measured phase shift and attenuation values are more dependent on...

Influx of Gas into the Annular Fluid

When the volume is sufficient to create gas bubbles, the drop in EMW is rapid and easily detected on the real-time EMW log. When drilling near gas-bearing formations, carefully monitor the Pressure data to provide early detection of a gas kick. Figure 29 illustrates a gas kick. Circulate Lit cuttings. Reduced now morn 1 . i ie ti< 'i i h i ui'v . 1 Circulating out cuttings Reduced flow from 450 to 3 00 g rn ECD drops from 1 G.B to 14.5 in 25 minutes Shut in...

Vibration Measurement

Directional Drilling Measurements

The Environmental Severity Monitor (ESM) is a single axis sensor mounted in the Pulser Driver, Resistivity and Netron Density inserts to provide multiple parts of the tool string with lateral shock measurements. Quantitative Environmental Severity Measurement (QESM) features a full three axis device with a rpm measurement. Three mutually orthogonal accelerometers are used to measure three axes of accelerations X, Y and Z. The X-axis is used to measure both lateral and radial accelerations. The...

Pressure Evidence for Loss Gain

When loss gain occurs, the recorded pressure response during the pump shut down and startup provides a definitive shape in the EMW trace. The normal shape of the EMW trace is a sharp square drop to the static EMW when the pumps are turned off. The pump-on increase in EMW is equally square. Figure 23 shows these pressure changes with no loss gain during a normal connection. The mud in use was a 15.90 lb gal synthetic oil-based. During the pumps-off interval, the pit gained approximately 30 bbl....

Washout

The Gamma Ray log is relatively unaffected by small borehole irregularities, but is greatly affected by large washouts. This is due to the increase in drilling fluid between the formation and the detector which causes increased Compton scattering and a decrease in the gamma ray log value. As the hole gets larger relative to the tool size, fewer gamma counts are detected. Turbulent flow of mud occurs when annular velocity exceeds critical velocity. Turbulent mud flow causes a washout to occur...

Short Trips Backreaming

Periodic short trips and or backreaming is used to remove cuttings beds by mechanical agitation. This is very effective when top drive is available as the short trip pumping out is enhanced hydraulically and rotationally. If necessary, use riser booster pumps while drilling the 311 mm (12-1 4 in) and 216 mm (8-1 2 in) hole sections. Any indication of a failure to clean the hole adequately should be countered by increasing the frequency of wiper trips, increasing circulation time on connections...

CPA Resistivity

Because the measured values of both phase shift and attenuation are inversely proportional to Resistivity, a formation Resistivity measurement can be computed from any one of the following 3. a combination of the phase shift and attenuation measurements The Resistivity service provides Resistivity values computed from the phase shift measurement, and from a mathematical combination of phase shift and attenuation measurements the latter is known as the combined phase and attenuation (CPA)...

Attenuation Measurement

An EM wave will decay exponentially as it propagates through a conductive formation. The rate of decay, or attenuation, is directly proportional to the formation conductivity. Attenuation (sometimes referred to as amplitude ratio) is calculated from the ratio of the amplitudes of the signals detected at the two receivers, which are at different distances from the transmitter. A root-mean-squared (RMS) circuit in the receiver electronics is used to measure these signal amplitudes. This circuit...

Indications of Poor Hole Cleaning

Pressure data provides these indicators of poor hole cleaning Cuttings settling while sliding in high angle holes A rapid increase in EMW after starting rotation Short term variations in EMW Cuttings Settling while Sliding in High Angle Wells The effect of sliding on hole cleaning depends on the inclination of the hole. In vertical sections the effect of cuttings settling out of the mud is minimal. However, as the angle increases, so does the tendency of cuttings to settle on the low side of...

Surface vs Downhole Measurement

EMW measured downhole can differ by more than 0.5 ppg from that predicted by hydraulic modeling or surface measurements. The many possible causes for the surface-to-downhole difference include Uncertainties in the hydraulic model (pipe rotation, drillstring eccentricity) Changes in the mud at downhole temperature Fluid compression due to confining pressure The presence of solids in the mud (cuttings, sand, cavings, etc.) These significantly increase the EMW. Error in surface measurements....

Validating Sensor Response

This document describes how to use the excel spreadsheet INC MAG QC Plots to validate the sensor response of the OM (Orientation Module) and IDS (Inclination and Direction Sensor) from a field operations prospective. The following items (Gx, Gy, Gz, Bx, By, Bz, Temperature) calculated from the OM and IDS (with scale, bias and misalignment applied) must be scrutinized to assess the validity of the calibration and software interaction. Enter the calculated and measured data from a 24 or 72 point...

Worn Teeth

This is a normal dulling characteristic for steel tooth bits as well as for the tungsten carbide insert bits. When WT is noted for steel tooth bits, it is also often appropriate to note self sharpening (SS) or flat crested (FC) wear. NO (No Dull Characteristics) - This code is used to indicate that the dull shows no sign of the other dulling characteristics described. This is often used when a bit is pulled after a short run for a reason not related to the bit, such as a drill string washout.

Introduction to Neutron Physics

Neutrons are subatomic particles, and along with protons, are most often found in nature as the constituents of atomic nuclei. Having almost exactly the same mass (the neutron is a fraction of a percent heavier), the proton and neutron differ primarily in that the proton carries a positive electric charge, equal but opposite in character from the charge on the much less massive electron. The neutron is electrically neutral. Protons seem to be stable (there is a theoretical possibility that...

Toolstring Vibration

Destructive downhole vibration has been the culprit of many drill bit and drillstring failures. The most effective way to control vibration has proven to be modifying the operating parameters (RPM WOB) based on feedback from the real-time downhole vibration measurements. The main purpose of this guideline is to provide operators with a method to Diagnose the condition using real-time Vibration data, and Take corrective actions based on the condition. However, in very hard and abrasive...

Class Exercise

The following example will illustrate the principles of drillstring design for a horizontal well. The design process usually begins with the following variables already established the bottom hole assemblies, the mud program, the available pipe, and the well profile. The drillstring design process can be used to select between several proposed well profiles to minimize torque and drag. Only one well profile will be analyzed in this example. You will need API Recommended Practice 7G to complete...

Self Sharpening Wear

This is a dulling characteristic that occurs when teeth wear in a manner such that they retain a sharp crest shape. Figure 26 Cone with Wear from Tracking Figure 26 Cone with Wear from Tracking This dulling characteristic occurs when the teeth mesh like a gear into the bottomhole pattern. The tooth wear on a bit that has been tracking will be on the leading and trailing flanks. The cone shell wear will be between the teeth in a row. Tracking can sometimes be alleviated by using a softer bit to...

Lost Circulation Evaluation

Pressure does not provide a direct indication of lost circulation unless the lost circulation is severe enough to cause a loss of hydrostatic head see Figure 16 . However, the Pressure data is often useful in determining how the lost circulation occurred and what the EMW was when it occurred. This helps prevent it in the future. In Figure 21, the recorded data shows a large reaming down surge in the EMW that immediately preceded a lost circulation incident. Figure 21 EMW During a Lost...

Inertial Navigation System

The only supplier of an Inertial Navigation System is the Ferranti Inertial Navigation System FINDS This is the British Inertial Guidance System that is presently used in the Harrier jet This system uses three single, degree-of-freedom gyros and three accelerometers This system can survey continuously without stopping at survey stations. The FINDS differs from the other gyrocompasses in the fact that instead of recording survey data, the FINDS tracks its course and gives the displacement from...

Rig Heave

When the bit is off bottom and there is no active heave compensation, rig heave causes a short frequency reciprocal surge swab variation in EMW. These variations are shorter frequency than the real-time data frequency and show up as scatter in the real-time data and a very noisy trace in the recorded data see Figure 6 . The severity of this effect depends more on the speed of the rig movement than on the height of the heave. Ri nnrrtprl Fnv M iH mit RT F n M11H wt In this example from the North...

Applying Declination

To convert from Magnetic North to True North, Declination must be added True Direction Magnetic Direction Declination East Declination is Positive amp West Declination is Negative in both the northern and southern hemispheres The formula for calculating a true north direction is True Direction Magnetic Direction Declination Where East Declination is Positive West Declination is Negative For example, the magnetic direction is 75 and the declination is 5 east The true direction would be...

Grid Zones

Central Meridian bisects each 6 grid zone To correct for the curvature of the earth projected onto a flat plane we apply CONVERGENCE If directly on the central meridian or on the equator, the grid correction is ZERO Convergence correction increases as location moves away from the equator and central meridian Convergence should not be more than 3 , otherwise the incorrect grid zone has been chosen For rectangular coordinates, arbitrary values have been established within each grid To convert...

Density Sensor Theory of Operation

Directional Pulse Material Detector

The current Density sensor uses a basic stabilizer design to displace drilling fluid from the volume between the collar and the formation in order to reduce the influence of materials other than the formation on the density measurement. Radioactive cesium Csm , mounted in the mandrel of the Density sensor, is the source of the gamma radiation used in the measurement. Gamma rays are emitted in all directions, but shielding and collimating material in the tool and the stabilizer blade are...

Phase Shift Measurement

Conductivity Principle Measurement

Although the propagation velocity for electromagnetic waves is normally thought of as a constant 300,000 km second, commonly referred to as the speed of light , this is actually the case only for an electromagnetic EM wave traveling through a vacuum or free space. In an electrically conductive material, the velocity of a propagating EM wave slows in proportion to the conductivity of the material. The wavelength, frequency, and velocity of a propagating wave are related by the following...

Survey Accuracy Quality Control Issues

Students will differentiate between mechanical sensor failures, unstable gravity values, and magnetic interference effects by analyzing survey data and quality control plots. Accuracy Limitations electronic vs. mechanical Sensor Failure Mechanisms Hardware Failure Hard Failure saturation, no response Soft Failure sticking, calibration drift, wrong compass, film, batteries Gravity Values Unstable Rotational Movement During Survey Axial Movement During Quality Control Check Goxy vs. Gz vs. Gtotal...

Ringout Failure

A ring-out failure appears like an o-ring groove anywhere on the drilling face, often just inside the nose. A ring-out is recognizable on the surface by the rapid increase of the standpipe pressure accompanied by a decrease in ROP. Improper stabilization is the most frequent culprit in ring-out failure. Broken formations, junk, erosion, and too few diamonds also aid in the development of ring-out failures. A modified design, smaller diamonds, increased density, and judicious use of carbonado...

Dip Angle vs Latitude

Lines of magnetic flux lie perpendicular 90 to the earth's surface at the magnetic poles Lines of magnetic flux lie parallel 0 to the earth's surface at the magnetic equator Dip Angle increases as Latitude increases As dip angle increases the intensity of the horizontal component of the earth's magnetic field decreases The components vary with geographic locati on The components vary with geographic locati on At the magnetic equator, Bh Btotal, Bv 0 At the magnetic poles, Bh 0, Bv Btotal Bh is...

BHA Backward WhirlA Lateral Motion

Similar to bit whirl, the BHA gears around the borehole and results in severe lateral shocks between the BHA and the wellbore. BHA whirl has been proven as the major cause of many drillstring and MWD component failures. BHA whirl can occur while rotating reaming off-bottom and is also very difficult to be detected on the surface. Typical Environment. Vertical or near vertical wells, pendulum or unstabilized BHA. Consequences. MWD component failures motor, MWD tool, etc. , localized...

Tensor Inclinometer

The TENSOR Tri-axial Accelerometer measures three orthogonal axes of inclination Gx, Gy, and Gz and also includes a temperature sensor. The inclinometer has a 1g full scale output in survey mode and a 7 g full scale output in steering mode. The sensor operates within the following parameters 1. Input Voltage - 12.5 to 15.5 volts 3. Accelerometer Output 3.0 ma g The inclinometer is made up of three accelerometers. The operation of the accelerometer is based on the movement of a quartz proof mass...

Fluid Pills

For wells deviated below 30 , use conventional high viscosity high weight slugs to help remove cuttings from the annulus. For wells deviated beyond 30 , the best method to remove cuttings from settled bed is by pumping thin fluids e.g., base oil, water in turbulent flow. These pills should be followed immediately by high viscosity high weight pills which increase their effectiveness by carrying the cuttings raised from the cuttings bed out of the hole. The base oil weighted pill size must be...

Calibration Theory

The Resistivity tool measures basic physical parameters phase shift and attenuation of electromagnetic waves. Thus, it is not necessary to calibrate each tool in a simulated formation or calibration pit. The fundamental mathematical transforms between Resistivity and the measured values of phase shift and attenuation are based on well-established electromagnetic principles that are described by Maxwell's equations, and have been experimentally verified by logging large bodies of water of known...

Gravity Toolface

Gravity toolface is a function of Gx, Gy, scale, bias, and temperature Gravity toolface data is typically used in angled holes greater than 5 to orient the motor scribeline to achieve the desired build and turn in the hole The reference point for 0 gravity toolface is the X-axis accelerometer reading a full scale positive value i.e., the highside of the probe is facing straight up, or towards the highside of the hole 44

Rotation

The presence of rotation of the drill pipe increases the EMW in several ways. When steering in a non vertical well, the drill pipe lays against the low side of the annulus. With rotation, the drill pipe is more centralized in the annulus but it constantly moves about laterally. This change in eccentricity changes the flow path and flow regime of the fluid. This adds turbulence that requires more pressure to move the fluid. These changes increase the pressure drop in the annulus. This effect is...

Hole Cleaning Practices

Use Hole Cleaning Curve to determine optimum flow rate for cleaning. Flow rates in the 300 - 500 gpm range will generally be adequate for cleaning 216 mm 8-1 2 in horizontal sections. Select mud properties which provide turbulent flow, if possible. To achieve turbulence, maintain maximum mud YP close to 10 lb 100 ft2. ECD increases when drilling horizontally, but formation strength remains fixed. Ensure that ECD does not cause formation breakdown when drilling horizontal section. Select MWD...

Magnetic Declination

The Earth's magnetic field varies by location on the Earth and by time The magnetic north pole is constantly moving, although very slowly. Because of this, a survey referenced to magnetic north today will not be accurate at some time in the future However, we are able to compensate for this variable by applying a correction to a magnetic survey which references it to true north Tue north can also be thought of as geographic north or the spin axis of the Earth. The true north pole does not move...

Monitoring Hole Cleaning

The cuttings transport efficiency must be maximized by optimizing the mud system carrying capacity, annular mud velocities, drill cuttings size, maximum allowable ROP, etc. A reliable hole cleaning monitoring system should also be followed to flag cuttings transport inefficiencies before they become a problem. These include Correlate the total volume of drilled cuttings being generated to the total volume being processed by the solids control equipment and the amount of solids retained in the...

Definitions for Dull Characteristics Space

Space 3 is used to characterize the predominant failure mode for a bit. These selections will appear as a pull down menu when this form is on computer. If the primary dull characterization is not a PDC type characterization, erosion, broken blade, ring out, etc. , then enter in the type when filling out the rest of the IADC code. If the dull characterization is PDC related, spalling, chipped, broken cutters, etc. , then wait until the PDC failure characterization table is completed before...

Basic Gyroscope Principle

A rotor gyroscope is composed of a spinning wheel mounted on a shaft. It is powered by an electric motor and is capable of reaching speeds of over 40,000 revolutions per minute rpm The spinning wheel rotor can be oriented or pointed in a known direction. The direction in which the gyro is spinning is maintained by its own inertia. Therefore, it can be used as a reference for measuring azimuth An outer and inner gimbal arrangement allows the gyroscope to maintain its pre-determined direction...

Psi X ppg X psi

Directional Drilling Motor

Annular velocity must be 32 ft min AP GPM, MW, VIS, Pipe I.D., TFA, Pipe, Length, SPP Using Reed hydraulic slide rule, index 172. AP gt drell 17is1 X15,340' 2,685psi APdrill 710psi X 200' _ 140ps collars 1000' X200 _ l40psi APmotor from look up table 4 5 LOBE configuration _ 520psi Annular velocity must be 32 ft min AP GPM, MW, VIS, Pipe I.D., TFA, Pipe, Length, SPP Using Reed hydraulic slide rule, index 172. APmotor from look up table 4 5 LOBE configuration 520psi

Survey Quality

The following items will be used to validate a MWD survey G total - this value is equal to Gx2 Gy2 Gz2 1 2, and should be within 0.003 g of the local gravity, which is 1.000 g in most locations. A Gtotal value outside of these limits may indicate that the Directional Sensor did not achieve stability during accelerometer polling, there was a hardware failure, BHA movement or improper misalignment and or scale bias values were used. B total is equal to Bx2 By2 Bz2 1 2, and should trend...

Toof Face

Dip Angle Earth

Azimuth is the direction of the wellbore relative to true or grid north in the horizontal plane. We measure this angle by measuring the direction of the earth's magnetic field relative to the tool. Magnetic Declination is the difference in degrees between magnetic north and true north or grid north for a particular location on the earth. This value changes with time and location and must be determined using the software program. On a directional well it is important that the value for magnetic...

Circulation Prior to Tripping

Tripping Drilling

Hole size and inclination will influence the minimum off-bottom circulation time prior to tripping. The figures in the table below are guidelines based on simple slip velocity considerations and field experience. In practice, some of the section back to surface will not be deviated at the same angle. The overall minimum circulation time prior to tripping should be apportioned in direct relation to the relative lengths of section at each angle. This is shown in Figure 25 for tripping out of 445...

Applying a West Declination

If the magnetic direction is 120 and the declination is 5 west , the true direction would be calculated as True Direction Magnetic Direction Declination Implications of an Incorrect Declination Since declination is a addition of degrees of correction to the magnetic hole direction, any mistakes made to the declination have serious consequences. For example, if you intend to apply a 18 declination but instead input a -18 declination, your reported hole direction will be wrong by 36 This can...

Degree Gyro Compass

Read from the 0 vernier line horizontally to the intersection of the inclination to determine the inclination to a precision of 0.5 30 always round down Use the 30' vernier scale to increase the precision of the reading to 5'. To use the vernier, look for an alignment of the division markings on both the vernier and inclination scales, read the value on the vernier scale at this intersection point. This is then added to the previous reading Determine the hole direction of the chart as follows...

Magnetic Toolface

Magnetic toolface is the direction, in the horizontal plane, the bent sub scribe line is pointing with regard to the north reference Grid, Magnetic, or True Magnetic Toolface Dir Probe Mag Toolface Total Correction Toolface Offset Magnetic orientation is used when the inclination of the wellbore is less than 5 to 8 When the inclination is below this amount, the survey instrument cannot accurately determine the highside of the instrument for orientation purposes The toolface will be presented...

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...

Density Borehole Compensation Standoff Correction

Spine And Ribs Density Correction

Figure 10 - Spine and Ribs Standoff Correction Crossplot Figure 10 - Spine and Ribs Standoff Correction Crossplot In the downhole logging situation, environmental corrections must often be made. In LWD density logging, the most common is a correction for the effect of standoff from the borehole wall. The correction that must be made is dependent on both the amount of standoff and on the density of the drilling fluid that occupies the standoff space between the tool and wall. The spine and rib...

Factors Contributing to Swab and Surge

Swab and surge pressures are principally related to the wellbore geometry, mud properties, pipe running speed and circulation. The wellbore geometry and the size of the drill pipe determine the size of the annulus. A larger annulus allows a slower movement of displaced fluid past the moving drill pipe. This reduces the swab or surge pressure effect. Any restrictions such as packoff or swelling of the well bore reduces the annulus size and increases the swab or surge effect. See Figure 11. The...

Compton Scattering

Collision Scattering

Compton scattering refers to the particle-like interaction between a gamma ray and a free electron. The outcome of scattering between a gamma ray and an electron is governed by the laws of conservation of energy and momentum. Basically, these laws establish limits on the possible outcomes of the interaction. The best analogy to Compton scattering is that of a collision between two billiard balls. In such a collision, a ball moving at some velocity collides with a second ball that can be...

Lithology Correction

Corrections are required for lithologies other than limestone. In addition to limestone the main lithologies that are encountered in logging are sandstone and dolomite. Although the presence of hydrogen in the pore space of the rock is the primary variable in neutron porosity measurements, the moderating effects of the rock type can be significant, amounting to several porosity units above or below the porosity that would be computed were the rock a limestone. The sandstone correction is...

Pdc Cutter Technology

Pdc Heat Checking

Description Characterized by a worn ring or worn region of the bit which especially occurs but is not limited to the nose and shoulder region. Ring out can occur over the entire bit with the entire nose, shoulder, and gauge becoming massively worn. It is often accompanied by heat checking due to the extreme heat builduopo which occurred. Cause Usually cause by the loss of a cutting structure at a pinpointed area. Description Characterized by a section of the blade which has chipped or broken...

Equivalent Circulating Density ECD Calculations using Annulus Pressure

The ECD is the effective mud density resulting from the circulating pressure and mud weight. It is defined by the equation ECD Annulus Pressure Loss psi 0.052 TVD ft MW lb gal In Metric Units ECD Annulus pressure loss Kpa 9.81 TVD m MW gm cc or sg MW mud weight ECD is the annulus pressure loss plus the hydrostatic pressure. ECDs normally range from 0.2 to about 1.0 ppg above the original mud weight. They may be as high as 3.0 ppg above the original mud weight under some conditions.

Packoff Pressure Spikes

Crown Mounted Compensdator Designs

Packoff occurs when enough settled cuttings are present in the well to cause a restriction partial or total in the annulus. This plug restricts the circulation and causes a sudden increase in pressure that washes away the restriction. Recorded Pressure data displays this as a spike in the EMW. Figure 19 illustrates packoff spikes. Packoff spikes can be large enough to cause formation damage. A packoff can result from hole collapse or from allowing cuttings to accumulate in the annulus. Pulling...

Directional Sensor Calibration

The accuracy of borehole azimuth and inclination measurements are largely dependent on our ability to identify and correct constituent errors in the individual sensors that are used to calculate the directional parameters of the well bore. These sensors include the three orthogonal accelerometers and three orthogonal magnetometers. The calibration process is based upon the known value of the total field intensity of both the gravity and magnetic fields at the location of the calibration. Each...

Influx of Water During Riserless Drilling

Riserless Pressure

When drilling with sea water and no riser, an influx of water into the annulus may not change the EMW enough to register on the Pressure sensor. This problem may not be detected until other symptoms develop. If the fluid influx from the formation carries solids, which is normally the case in deepwater drilling, it can be heavier than the annulus fluid and cause a detectable increase in the EMW. Figure 27 shows the recorded data for an influx of unconsolidated sand and water into a salt water...

Recorded Surge and Swab Measurement

Swab And Surge

The recorded data can be plotted with a number of other surface parameters to give an accurate picture of the cause and effects of downhole pressure variations. Figure 10 is an example of measured surge and swab pressures. In this case, an EMW variance between 1.57 sg and 1.73 sg is generated. In some situations, this is sufficient to damage the formation. Recorded surge and swab data must be time synchronized before it is used. Figure 10 Recorded Swab and Surge Pressures Figure 10 Recorded...

Fluxgate Magnetometer

Horizontal Well Torque Drag Worksheet

Fluxgate magnetometers measure components of the Earth's magnetic field orthogonally, i.e., in the same three axes as the accelerometers. From this measurement, the vector components can be summed up to determine hole direction The magnetometer contains two oppositely wound coils around two Mu-metal rods As AC is applied to the coils, an alternating magnetic field is created, which magnetizes the Mu-metal rods Any external magnetic field parallel with the coil will cause one of the coils to...

Leak Off Test LOT and Formation Integrity Test FIT

Fit Formation Integrity Test

Both LOT and FIT are designed to verify that the casing, cement, and formation below the casing shoe can withstand the pressure required to drill to the next casing point or next section of the well. The data has application in planning the next casing point selection, well control planning, and preventing lost circulation. Pressure downhole pressure is a definitive measurement for the LOT FIT. This removes many uncertainties in the hydrostatic density of the mud column and the pressure to...

Formation Resistivity Effects

The factor having the greatest effect on depth of investigation is the formation Resistivity itself. As previously mentioned under the discussion of the principles of the attenuation measurement, a radio-frequency electromagnetic wave suffers greater attenuation in a low-Resistivity medium than in a high-Resistivity medium. This increased attenuation at low Resistivity means that the transmitted field will not extend as deep into the formation at low Resistivity as it will at higher...

Factors Affecting Downhole Vibration

The amount and form of toolstring vibration is influenced by a number of factors. Operating Parameters RPM WOB The main source of excitation in drilling is the rotation of the drillstring and the drill bit. Thus, the primary method to control the downhole vibrations is to find an optimum RPM that will create a safe vibration level. It is well known that centrifugal force is proportional to the rotary speed squared. The higher the RPM, the higher the imbalance force to the bit and drillstring,...

Anisotropy Effects

Horizontal Anisotropy Figure

Because of their layered nature, many sedimentary formations are electrically anisotropic. This means that the electrical resistivity measured parallel to the bedding planes is different from the resistivity measured perpendicular to the bedding plane. This phenomenon can be caused by either of two distinctly different geologic situations. However, to the Resistivity tool, these two different geologic settings appear the same. One type of anisotropy is commonly called microscopic anisotropy....

Inertial Navigation Systems

The most accurate method of surveying is with the use of an Inertial Navigation System. This system uses groups of gyros to orient the system to north It can measure movement in the X, Y, and Z axis of the wellbore with the use of the gyros and gravity accelerometers Because of the sensor design, this instrument does not have attitude limitations for accurate surveying The instrument can survey in all attitudes without sacrificing accuracy

Scintillation Detectors

Detection of gamma rays using Scintillators represents a significant improvement over both the efficiency and spectral deficiencies of G-M tubes. The most common scintillation detector, and the one used in MLW LWD sensors, is the sodium iodide NaI crystal. Again, the detection occurs as the gamma ray interacts with the electrons in the NaI crystal, either through Compton scattering or the photoelectric event. However, the effective volume of the detector is that of the crystal to be compared...

Gtotal Btotal

As a general guideline, MDIP should not vary by more than - 0.3 degrees from the local magnetic dip angle or from survey to survey during a bit run. The local magnetic dip angle is determined by using magnetic modeling software or directly measuring it through infield referencing. Surveys which do not conform to this guideline should alert the field engineer that some magnetic interference or pipe movement is probable, or that there was a hardware failure. MDIP may also change abruptly from bit...

Gamma Ray Applications

Clay Volume Gamma Ray Log Calculation

Determining shale volume - By using the relative response of the gamma curve compared with a 100 shale reading, the shale volume Vsh in the formation can be estimated from the following equation To calculate the shale volume Vsh of any zone, determine the denominator of the equation by subtracting the clean sand reading GRclean from the shale baseline reading GRsh . Then, determine the numerator of the equation by subtracting the reading in the zone of interest GRzone from the shale baseline...

Survey Accuracy As A Function Of Inclination

Well Inclination

Berror IS A LARGER PERCENTAGE OF Bref AT HIGHER INCLINATIONS For systematic uncertainty, the uncertainty is along the Z-axis. This will result in decreased survey accuracy when drilling east or west as opposed to drilling north or south. This is due to the fact that Berror will tend to pull Bref in the direction of the Z-axis, away from Bn. This relationship is shown in the figure below.

Cuttings Bed Suppression

Cuttings beds formation in deviated holes can be suppressed by using muds with exceptionally good suspension characteristics. However, high flow rates are still necessary since the beds can never be totally eliminated. For water based mud, the best conventional additive for this purpose is XC polymer. All the major service companies now offer low shear enhancers sometimes referred to as rheology modifiers for oil based muds. A simple force balance approach can be used to determine the minimum...

Pump Rate

The single most crucial factor for successful hole cleaning is mud flow rate, especially for deviated holes. As a rough guide, the annular velocity needed for cleaning wells deviated 50 - 60 is approximately twice that required for the vertical case. Take all reasonable steps to reduce frictional pressure. Doing so will extend the range of available flowrate. In critical cases, careful consideration should be given to BHA design, nozzle selection, and additional losses due to mud motors MWD...

What Are Gamma Rays

Gamma rays are a form of high energy electromagnetic EM radiation. Other examples of EM radiation are visible light, radio and microwaves, infrared and ultraviolet light, and x-rays. Each of these forms is distinguished in the EM spectrum by their frequency f and wavelength A, . In free space that is, a vacuum all EM waves travel at the speed of light, c, which is 3 108 meters second, or 186,000 miles second The frequency and wavelength are related to the speed by the equation While the...

Principles of Neutron Logging

Neutrons are emitted from the source at a high energy, usually between 1 and 10 MeV. However, they are not detected until their energy has been reduced to a fraction of an eV through collisions with atomic nuclei in the formation. The rate at which energy is lost by the neutrons is a function of the elements in formation. Hydrogen is the most efficient element in slowing down, or moderating, neutrons. Porosity is inferred from the detection of these low energy, or thermal, neutrons because...

Broken Diamonds

Gaskick Curves

Broken diamonds result from excessive tangential force. When the diamond's strength is exceeded, a fracture along a cleavage plane s occurs on most bits, and all or most of the exposed stone separates. This is recognizable on the used bit by the generally flat, highly reflective surface. Causes are stones too large, broken formation, junk, too few stones, excessive WOB, improper stabilization, and erosion. Downhole pressure sensors are drilling performance tools that provide continuous and...