"Cleaning with a swab" and jet pump

“Swab cleaning” is called when the bottom pit pressure decreases below the forming pressure due to the pulling effects of the drilling string, which allows a flow of forming fluids into the well. When pulling the cord, there will always be some change in the bottom pit pressure. The pressure loss is caused by friction between the mud and the drilling cord. Swab cleaning can also be caused by the accumulation of full gauge pit tools (shredders, stabilizers, diggers, nuclear barrels, etc.). This can create a piston-like effect when they are pulled through the mud. This method can have drastic effects on bottom pit pressure.

Factors that affect swab cleaning and “swell” are:

“Dallgëzimi” ndodh kur presioni i gropës së poshtme rritet për shkak të efekteve të drejtimit shumë të shpejtë të shpimit në gropë. Humbjet e baltës nga gropa mund të ndodhin nëse nuk tregohet kujdes dhe presioni i thyerjes tejkalohet gjatë RIH. Monitorimi i duhur i volumit të zhvendosjes me rezervuarin e udhëtimit kërkohet në çdo kohë.

Ripple pressure during "swab cleaning"

Swab cleaning is a known hazard regardless of whether it is “low” or “high” volume. A small volume of flux can be placed in the part of the open pit. The net reduction of hydrostatics due to this low density fluid will also be small. If the flowing fluid is gaseous, it can certainly migrate and expand. Expansion can occur when there is little or no pipe left in the pit.

Withdrawal speeds

The shut-off speed should be controlled to reduce the possibility of cleaning. It is normal practice for the mud transport equipment to execute a swab and wave cleaning program and make this information available to employees. This will provide enough information to reduce the possibility of unforeseen influx occurring.

Properties of mud

Mud rheology control is important. Controlling water loss to avoid mud residues will also help.

If the well leaks or returns from the well are excessive, then you should do the following

Continuous monitoring of replacement and displacement volumes is essential when performing shutdown. A short trip of the cleaner, as well as its circulation in the well before it is completely withdrawn from the pit, will provide useful information about the cleaning speed and withdrawal.

Loss of turnover

Another cause for the occurrence of a shock is the reduction of hydrostatic pressure through the loss of drilling fluid in the formation (during lost circulation). When this happens, the height of the mud column is shortened, thus reducing the pressure at the bottom and at all other depths. The amount of shortening of the mud column can be calculated by dividing the mud gradient by the overbalance at the top of the permeable impact zone.

Insufficient weight of mud

Impact can occur if a permeable formation is pierced which has a higher pressure than that exerted by the mud column. If the overpressure formations have low permeability, then traces of the forming fluid should be detected at the returns after circulation from the bottom up. If the pressurized formations have a high permeability, then the risk is greater and the well should be closed as soon as the flow is detected.

Abnormal pressure formations

Another cause of strokes is accidental drilling in permeable areas with abnormal pressure. This comes as a result of ignoring the warning signals, which help us detect abnormal pressures. Some of these warning signals are: an increase in the rate of penetration, an increase in the cut-off of the mud gas, a decrease in the density of the clay, an increase in the size of the cut or an increase in the temperature of the flow line, etc.

Learn more about the services of our geophysical measurements and contact us for any questions.