What is a Pad Type Weight Indicator
Weight indicators are essential to oilfield drilling operations in that they help drillers determine the weight on the surface and downhole. From initial drilling to production to maintenance, every time tools are downhole, the operator needs to know the hook load’s weight. When hook load is not properly maintained and monitored, a variety of problems on the rig can occur. In order to maintain bit life, to control hook load, and to maintain drilling operations it is best to use the right weight indicator for the right application.
Two Kinds of Weight Indicators
Two kinds of weight indicators exist: diaphragm and pad type. Both use a closed-loop hydraulic system and bourdon tube dial gauge that detects weight changes on the drill string. These weight indicators have changeable load dials to sense a range of rigging system pressures. Diaphragm type weight indicator systems are often used for workover and small drilling operations; whereas, pad type are often used to gin pole applications and workover rigs. Diaphragm weight indicators sense deadline tension in order to determine hook load; on the other hand, pad type indicators determine absolute hook load by factoring out the weight of the guy wires and mast.
Pad Type Weight Indicators
Pad type weight indicators consist of two load cells, hydraulic hoses, and pressure gauges that provide the operator with the hook load’s absolute value. The two load cells are located under the rig’s jack screws of the mast’s legs and range in size from 6 to 8 inches in diameter, depending on the load to be measured. When a load is applied to the cell, the hydraulic fluid travels from the cell through the hoses to the bourdon tube gauge. The pressure travels through the bourdon tube, causing it to move the pointer indicator and recording the weight of the load. Each load cell is connected to its own gauge, and the pressure integrator adds the two pressures together. Each gauge comes with customizable dials that measure the capacity needed, based on the size of the load cells. The dials can be zeroed out so that the operator has the ability to compensate for the mast’s and the guy wires’ weight.
Advantages of Pad Type Weight Indicators
Pad type weight indicators offer a number of advantages for the drilling operation.
- With pads under mast legs, the load is not skewed by friction in the rigging.
- Having gauges for each load cell offers the operator the option of reading each cell’s load.
- The rotating dial allows the operator to determine absolute weight of downhole equipment.
- The operator is able to track load changes on the pressure integrator without any possible mathematical error, since it determines total load weight.
Pad type weight indicators have proven to be a very versatile, reliable hydraulic system for weighing hook load. With capacity of up to 360,000 lbs., the system will detect the slightest weight changes accurately and efficiently. As with all hydraulic systems, pad type weight indicators stand up to the harshest working conditions and provide accurate readings during a long service life.