MUD CONDITIONING TESTS

These tests are used to determine the shaker mesh size required to provide protection against screen impairment and quantify the mud plugging index (MPI) to be used on the rig to control mud quality prior to running the screen in the hole.

Equipment:

  • HPHT cell with 2.5’’ screen media disks
  • Sieves of various size (200, 230, 270, 325 mesh)
  • Constant air pressure source (100 psi)
  • Graduated cylinder
  • Stopwatch

Mud Conditioning Qualification Test

scope: to select the shale shaker size to remove mud and drill solids damaging to the screen.

Objective: to remove mud solids coarse enough to damage the screen. In order to protect the screen, 3 ‘lab barrel’, ie 1050 mL of mud must flow through a 2 ½” inch screen disk sample.

Procedure:

  1. The mud should be a representative field sample, but if one is not available, a simulated field mud can be made from a fresh batch of mud with material added to simulate insoluble drill solids.
  2. Install the screen samples at the bottom of the cell with the downstream valve closed;
  3. Fill the container with unconditioned mud (approximately 500 mL) and pressurized the reservoir to 100 psi;
  4. Flow 350 mL of fluid through the screen and relieve the pressure inside the cell;
  5. Repeat step 2-3 a total of three times (to get a total mud throughput of 1050 mL) or record the total volume of mud throughput;
  6. Change the shale shaker screen sample;
  7. Repeat step 1-5 with mud conditioned through 200 mesh sieve, mud conditioned through 230 mesh sieve, etc. down to 325 mesh sieve if necessary, until the required volume of mud (1050 mL) passes through the screen sample without plugging it.
Bottom shaker screen in desilter
Bottom shaker screen in desilter

MPI Index

Scope: To qualify a field test procedure for the monitor of mud
conditioning on the rig.

Objective: When plugging occurs, the leak off rate through the screen medium decreases. By comparing the leak off time, T1, of a first batch of mud (1 lab barrel), with that of a second, T2, through the same screen sample, one can evaluate the plugging tendency of the screen and monitor mud quality. This test is designed to require very little equipment and expertise so that it can easily be run on the rig.

Water-Based Mud (WBM)
Water-Based Mud (WBM)

Procedure:

  1. Close the valve underneath the screen sample and fill the mud cell with 350 mL of unconditioned mud;
  2. Open the valve and measure the time taken by the mud volume to flow through the medium, T1 (note: in this test, no pressure is applied. The mud flows by gravity only);
  3. Close the valve again and fill the mud cell with another lab barrel;
  4. Open the valve and measure the time taken by the second lab barrel to go through the same screen sample, T2;
  5. Calculate the MPI: MPI = T2/T1
  6. Note: When there is no plugging, MPI = 1. As plugging increases, MPI increases.
  7. Change the screen sample and repeat the test with mud conditioned through the sieve selected from the Mud Conditioning Qualification test.