Monthly Archives: April 2010

What is Cement Bond Log?

By | |
2 Comments

Cement Bond Log: It measures integrity of cement bond between tubing/casing and well bore. The log is typically obtained from one of a variety of sonic-type tools. The newer versions, called “cement mapping”, can give detailed, 360-degree representations of the integrity of the cement job, whereas older versions may display a single line representing the integrated integrity around the casing (see Figure below).

Concept of CBL: Transmitter sends acoustic wave to casing/cement and then receivers receive acoustic signal that transfer through casing to cement and reflects to receivers. Acoustic wave at receivers is converted to amplitude (mv). Low amplitude represents good cement bond between casing and hole; however, high amplitude represents bad cement bond. The concept likes when we knock pipe. If there is something coverage around pipe, the reflection sound will be attenuated, and vice versa (see Figure below).

Tool component for CBL currently mostly consists of following equipment:

Gamma Ray/ CCL: It is used as correlation log. Gamma ray measures formation radiation and CCL records collar depth in tubing. Correlation log is a reference for a number of cased hole jobs as perforation, set plug, set patch, etc.

CBL/VDL: CBL measures cement bond integrity between casing/tubing and well bore. It apply concept of acoustic wave transferring through media. VDL is the top view of the cut away of upper part of acoustic wave that represents how cement bond from casing to wellbore

Caliper: Caliper measures wellbore diameter.

Example of CBL is shown below.

Downhole conditions that can cause errors in acoustic CBL interpretation or reliability are as follows:

Cement sheath thickness: Cement-sheath thickness may vary, causing changes in attenuation rate. The suitable cement thickness of 3/4 in. (2 cm) or more is required to achieve full attenuation.

Microannulus: A microannulus is a very small gap between casing and cement. This gap would affect the CBL presentation. Running the CBL under pressure can help eliminate the microannulus.

Centralize tool: Tool must be centralized in order to get the accurate amplitude and time.

Ref books: Cementing Technology Books

The Deepwater Horizon Got Explosion and Fire – 12 People Missing

By | | ,
5 Comments

I just saw NEWS from the TV showing The Deepwater Horizon Got Explosion and Fire – 12 People Missing. Read news below. I wish they will find those people who are missing soon.


Photo from AP.

12 people are missing and seven injured after an explosion and fire at an an ultra-deepwater oil drilling platform off the coast of Louisiana, the Coast Guard said Wednesday.

Most of the 126 people aboard were believed to have escaped safely after the explosion rocked the rig at about 10 p.m. Tuesday, Coast Guard Chief Petty Officer Mike O’Berry said.
Continue reading →

Sensors That You Should Have Installed On The Rig

By | |
2 Comments

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

By | |
3 Comments

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

By | |
4 Comments

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.