Geology

MUD SENSORS

• DEPTH WHEEL
• PUMP STROKE
• ROTARY SPEED

• HOOK LOAD
• TORQUE
• STANDPIPE & CHOKE
• ROTARY SPEED
• PIT VOLUME
• FIOW OUT
• MUD TEMPERATURE
• MUD DENSITY
• MUD CONDUCTIVITY
• AMBIENT GASES

ANALOG ROTARY SPEED SENSOR

The unit consists of a small low-power D.C. generator. This generator is driven via a belt and pulley from the rotary table drive shaft. The unit produces 7 VDC per 1000 Revolution Per Minute (RPM). The Final RPM will depend upon the gearing. The DC signal is isolated through a signal conditioner electronic board .

PIT VOLUME SENSORS

The pit monitoring system uses a Delaval sensor to monitor individual pits. The computer system allows a total flexibility in defining the active and reserve pit systems. The configuration can be changed quickly through the keyboard. Alarms are computer controlled and can be set up for low

and high levels on the active system, the reserve system, or on individual pits. The system can monitor up to 16 pits. On trips the gain tank and trip tanks are also assigned through the trip monitoring programme for complete coverage of the pit system. On connections the expected flow back gain encountered at various pump rates is entered. The system can correct for

alarm if unexpected changes are seen

during the connection. Delaval sensor use a non contacting magnetic float activate discrete reed switches in reed switch resistance string inside a stainless steel pole. The position of the float determines the resistance and hence the voltage fed to the computer. The system is very robust and has been field proven for years as the simplest and most reliable of pit measurement in standard situations. If access is severely restricted or the pits are deep, we use ultrasonic  sensor. The Endures and Hawser DU 523 Z is normally specified. These have

microprocessor based filtering in the sensor to condition the signal and reject spurious echoes, temperature compensation self monitoring for faults and a simple calibration procedure.

FLOW OUT SENSOR

The flow out sensor normally specified is of the paddle type. Flow in the flowline causes a rotation of the paddle and a corresponding rotation of a 1 turn potentiometer. Various paddle sizes are available to suit the different flowlines. Nonlinear and logarithmic calibrations in the computer allow accurate calibrations to be made for most installations over a wide range of flows. The sensor is supplied with a 10 VDC excitation supply which is fed through the 10 KOhm, one turn high accuracy potentiometer. This gives a signal output of 1-10 VDC. This analogue signal is input directly to the computer. If a pressure rated flow sensor is required for installation on offshore diverted systems, a Martin-Decker MFTX05A non-contacting mud flow sensor can be supplied on request. The paddle flow sensor is a well proven and rugged instrument. However the accuracy of its measurement depends on the installation in the flowline. As the flow in the flowline is such an important measurement for the well and rig safety we recommend the installation of a magnetic flowmeters for long term contracts and where the rig’s construction allows. The magnetic flowmeter has to be mounted in a section of the flowline which is full to provide an accurate measurement. The most recent designs of meter will work in fluids with a conductivity above 1 micro mho/cm. In practice this will allow use in most field oil base muds.

MUD TEMPERATURE SENSORS

Two types of temperature sensor are in use. Either semiconductor thermistor transducers or platinum resistance elements (PRT) are used. These are mourned in a protective cage at the end of all sensor poles. The Temperature-In sensor is mounted in the suction pit andthe Temperature-Out sensor in the

shaker header box. The thermistor sensor is supplied with an 8.5 volt excitation voltage. The current output of the sensor is dependent on temperature and varies linearly between 270 and 370 microamps. This signal is converted by the signal conditioner card into a 0-10 VDC analog signal for input into the computer. The Platinum Resistance element has a 4-20 m.a. converter in the sensor head and uses a 24 VDC excitation voltage from the signal conditioner.

MUD DENSITY SENSOR

The Mud density sensor is of the differential pressure type. Two silicon oil filled diaphragms are placed one foot apart in the drilling mud and a highly accurate differential pressure transducer interrogates the readings and transmits a 4-20 m.a. signal to the computer. The sensors are mounted in the suction pit and in the shaker header box to provide the density In&Out measurements. The span can be adjusted over the desired range through calibration at the sensor head. The sensor is supplied with 24 VDC excitation supply and produces a 4-20 m.a. signal. This enters a signal conditioner card and is fed to the computer as a 0-10

VDC signal. For long term rig installations we recommend the resonant density sensors. Their superior accuracy and reliability give an on-line density reading that can be used with confidence by the customer and rig operator. These sensors can be mounted in the mud pump suction lines. This allows the sensors to pick up the density of the fluid being pumped. The sensors rapidly detect the presence of the wrong fluid being pumped and can save rig time and money by early detection of miss-aligned pits. Unlike differential pressure sensors they are unaffected by turbulence in the pits and they maintain accurate calibration over long periods.

MUD CONDUCTIVITY SENSOR

The sensor is a new 4-20 m.a. type which has all the electronics in the sensor head and gives a 4- 20 m.a. signal to the unit. This signal is then put through a density (or new conductivity) signal conditioner card (both are exactly the same) to produce a 0-10 VDC signal for the computer.

Principle of operation:

The sensor works on the principle of the toroidal coupling effect. The sensor contains two coils, known as the primary and secondary coils. AC current is fed to the primary coil by a Oscillator. The magnetic effect caused by this current is transmitted to the secondary coil by the medium surrounding the coils. This produces a current in the secondary coil, whose phase difference is

related to the resistivity of the medium. The phase difference by a demodulation unit and then amplified to a 4-20 m.a. signal. The sensor also

contains a thermistor for temperature

compensation, so that the actual value given is at it’s 20° equivalent. The 4-20 m.a. signal from the sensor is conditioned through a density/conductivity signal conditioner and then fed to the computer as a 0- 10 VDC.

DEPTH WHEEL SENSOR

Depth is monitored through an intrinsically safe encoder wheel mounted on the crown sheaves on land rigs, jackups and platforms. On semi-submersible rigs either a wire line retriever is mounted on the rig floor to provide very accurate kelly height or a combination of compensator opening sensor and crown wheel is used. The depth system provides continuous monitoring of depth, rate of penetration, running speeds, kelly, block, compensator and riser position. The system is fully operative during tripping and other rig activities and also calculates bit off-bottom depth and running speed. This allows the calculation and display of swab and surge pressures while tripping. The depth wheel sensor assembly is mounted against the slow sheave of the crown wheel. It consists of a rotating wheel, twenty four inches in circumference. Two proximity switches detect the wheel’s movement. The proximity switches produce a quadrate signal which can identify the direction of movement of the wheel. The digital pulses from the switches are converted to up or down digital signals for computer. When monitoring depth on a floating rig, a second depth wheel is mounted on either the riser tensioners or the guide base tensioners to monitor rig heave. A wireline retriever assembly and encoder are mounted on the rigfloor and a line is run to the kelly to provide heave compensated kelly movement. A compensator opening sensor utilizing a digital encoder can alternatively be used in conjunction with the crown wheel. The depth system measurements are combined to provide very accurate depth monitoring even during severe roll and heave conditions.

PUMP STROKE SENSOR

The pump rate is monitored by noncontact magnetic proximity switches, mounted over the pony rod end clamp. The BLS 2000 can monitor up to six pumps continuously. The system can assign any combination of the pumps to the active and the auxiliary pump counters, which then monitor individual pump rates and total strokes. It calculates the total volume pumped, bottoms up, well circulation times and lags. In certain installations, a whisker type limit mechanical swhich sensor may be installed if the pump configuration is unsuitable for the non-contact proximity switch. The sensor is supplied with a 24 VDC excitation voltage and feeds back a digital. This output is isolated by a signal conditioner card passed to the computer for processing.

DIGITAL ROTARY SPEED SENSOR

Rotary table revolutions are normally measured with a digital encoder mounted in the rotary drive system. The sensor is driven by a flexible belt around the rotary motor shaft. The sensor uses an encoder which gives one hundered counts per revolution of the encoder shaft. On most installations this is equivalent to 200 counts per rotary RPM giving high resolution and accuracy. Two types of encoder are used. For the North Sea sector Pepper and Fushs transformer isolated barriers is used to provide a certified L.S system. Other units use an American Optical encoder which is supplied with a 24 VDC excitation and delivers back a 24 VDC digital signal to the digital signal conditioner board then to the computer. The signal is calibrated by entering a calibration factor which converts the digital counts into RPM. A Pepper and Fuchs proximity switch can also be utilised on the drive shaft to provide a non-contacting measurement system.