Category Archives: Oil Field Knowledge

Sensors That You Should Have Installed On The Rig

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Sensors that you should have on the rig are as follows


Anchor tension (Heave sensor) : Use for towing and rig move operation.
Bit depth: Use for tracking bit depth
Bit rotating hours: Use for tracking rotating hours. The rotating hours will be used for drill pipe management, preventive maintenance program, etc.
Block height: Use for knowing where the block is in derrick.
Block speed: Use for knowing how fast of block while pulling up or lowering down.
Bulk sensor: Use for knowing how much bulk on the rig.
Choke pressure: Use for knowing how much casing pressure in case of well control situation
Fire Alarm: In case of emergency, fire alram will notify regarding fire on the rig.
Flow In: Flow in from mud pumps.
Flow out sensor (paddle): Flow out at flowline. It will indicate how the well bore is doting.
Gas detector and gas alarm: For detecting gas such as CO2, H2S, etc.
Gas sensor (while drilling): For detecting formation gas coming from wellbore. It’s normally installed at flowline after bell nipple.
Global Positioning System (GPS): It’s used for dectecting where the rig is and it’s very useful for remote area.
Hole depth sensor: For tracking how depth of the well we drill.
Hook load: Know how much drilling line tension.
Leg depth (Jack up rig): Know how depth of the legs are.
Pit volume sensor: Know pit volume on the rig.
Pump stroke: Know how fast we pump.
Rig air pressure: Know air pressure used to supply rig equipment.
Rig water pressure: Know rig water pressure to supply water to all area of the rig.
Stand Pipe Pressure: Know how much pressure at stand pipe.
Torque sensor: How much torque we apply to make up drill pipe or torque while drilling and reaming.
Total stroke count: Track how many strokes the rig has pumped from certain period.
Trip tank sensor: Track how much mud in trip tank. This is very important while we flow check the well, pull out of hole, trip in hole, etc. Due to ability to detect small changes in trip tank, trip tank can tell us how the well dictate to us.
Voltage for jacking system: For leg jacking operation.
Weather condition: Know how current weather condition on the rig and adjacent area.
Weight on Bit: Know how much weight applied to the bit.
Wind direction sensor: Know where the wind direction is and how fast wind blows.

Since I’ve not been working on drill ship or semi rig, please fell free to add your know ledge. This will help share knowledge to other people.

Surge Pressure, Swab Pressure and Trip Margin

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You may have heard about Surge Pressure, Swab Pressure and Trip margin in the drilling business. Today, I would like to share my knowledge about these terminologies.

What is surge pressure?
Surge Pressure: When pipe moves downward with mud circulation through drill string, additional bottom hole pressure called “Surge Pressure” is created. If surge pressure is too much, many problems will occur as formation brake down, partial mud loss and lost circulation.

What is swab pressure?
Swab Pressure: If a drill string , casing string or logging tool is being pulled out of hole too fast, due to bigger diameter almost same hole size, BHA/ bit, casing or logging tool will possibly swab mud out of hole, like pulling small a piston of syringe. For this reason, hydrostatic pressure of bottom hole will be reduced. Pressure reduction created by this situation is called “Swab Pressure”. If swab pressure is too much, kick (wellbore influx) may be into the hole and well control must be conducted in order to secure well.

What is Trip Margin?
Trip Margin: It is an increase in the hydrostatic pressure of mud that compensates for the reduction of bottom pressure due to stop pumping and/or swabbing effect while pulling pipe out of hole. Trip Margin is calculated by following equation:

How do we calculate trim margin?

The formula used to calculate trip margin is listed below;

Trip Margin (PPG) = (Margin needed (Psi) – Present Margin (Psi))/ (0.052xTVD (ft))

 

Ref book: Formulas and Calculations for Drilling, Production and Workover, Second Edition

 

Frictional Pressure Loss Components in the Rig Circulating System

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Frictional Pressure Loss: Frictional Pressure Loss is pressure loss created by fluid flowing through the flow path. It is a function of fluid property (density, viscosity, gel strength), velocity of fluid, characteristic of flow path (hole size/drill string size). Frictional pressure loss affects on pump pressure because higher frictional pressure loss, higher pump pressure is required to maintain the pump rate.

In order to clearly demonstrate the pressure loss component in the drilling rig system, the diagram below describes pressure loss each flow path of drilling fluid in the total rig circulation system.

The Diagram of Frictional Pressure Loss in Circulation System

Parameters, which affect pump pressure, are as follows:

1. Fluid properties especially mud weight, viscosity, gel strength and yield point affects directly on pump pressure. Higher mud weight, viscosity, gel strength and yield point, higher pump pressure requires to maintain pump rate.

2. Pump rate is another factor that affects directly on pump pressure. This is a basic concept when higher pump rate is needed; higher pump pressure is required.

3. Hole size/drill string size: Smaller internal diameter of both hole and drill string, higher velocity of fluid flow is created at same pump rate. Higher velocity creates more frictional pressure loss. High pump pressure is required in order to maintain pump rate because there is additional pressure loss due to smaller hole size and drill string.

4. BHA and Bit: Due to small inner area, BHA and bit can cause majority of pressure loss.  Hence, BHA design/selection and bit nozzle selection are critical for hydraulic design.

5. Well Depth: The deeper of the well is, the more pressure loss will occur . It means we need more pump capacity to achieve the drilling goal.  Depth of the well is based on geological targets underneath the earth by geologists. This part will influence on how to select the proper rig capacity in order to meet hydraulic proposes of the wells.

I hope this post will help you understand more about pressure loss in the drilling rig : )

Any comments are always welcome.

What are Magnetic Toolface and Gravity Toolface?

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Magnetic Toolface: It is the direction, in the horizontal plane, the bent sub scribe line is pointing with regard to the north reference (Grid, Mag, or True). 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 in azimuth or quadrant form, referenced to magnetic north. The magnetic toolface reading is whatever magnetic direction the toolface is pointed. If the orientation lug on the survey instrument is pointed towards S 20 E, then the magnetic toolface would be 160°.

Gravity Toolface : It is the angular distance that a bent sub scribe line is turned, about the tool axis, relative to the high side of the hole. If the inclination of the wellbore is above 5° to 8°, then the gravity toolface can be used. The toolface will be referenced to the highside of the survey instrument, no matter what the hole direction of the survey instrument is at the time. The toolface will be presented in a number of degrees either right or left of the highside. For example, a toolface pointed to the highside of the survey instrument would have a gravity toolface of 0°. A toolface pointed to the lowside of the survey instrument would have a gravity toolface of 180°. If the orientation lug was rotated to the right of highside, the gravity toolface would be 70° to the right.

Reference books: Directional Drilling Books

What are gas show, connection gas and trip gas?

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You may have heard about gas show, connection gas and trip gas. What are differences of those term?

Gas show: It is gas that appears in drilling mud and it indicates the presence of gas zones or soluble gas in oil.

Connection gas: It is relatively small amount of gas that enters well when mud pump is stopped because ECD (equivalent circulating density) decreases when stop pumping. Connection gas indicates that mud weight in hole is less than formation pressure.

The difference of gas show and connection gas:If there is connection gas, gas shown in a mud logger screen increases and decreases sharply like small gas peak; however, gas show demonstrates the smoother curve than connection gas. Lag stroke, lag time are used to  find where the location of connection gas or gas show comes from. Especially, when the connection gas presents, lag time of gas peak will be relative to the time when pumps are off.

Trip gas: It is gas entering to well bore when tripping out of hole. There are several factors as balled-up bit,  fast pulling out rate, bigger diameter BHA, etc can create swab effect that can reduce hydrostatic pressure while tripping out of hole. If too much reduction in hydrostatic pressure is present, formation gas can influx into the well bore, called “Trip gas”.

Reference book: Well Control Books