Mud cleaner used in oilfield means the equipment processing drilling mud. It is combined with desander cone and desilter cone as well as bottom shaker. It is called 2nd and 3rd phase solids control equipments.
The first mud cleaner was a combination of two 12-inch-diameter and twenty 4-inch hydrocyclones mounted above a specially built, 5-footdiameter, stainless steel, round Sweco shaker. Even though the mud cleaner was invented for use with a weighted drilling fluid, the first application was on a well drilled using one of the first unweighted, potassium chloride drilling fluids, in a shallow, 2200-foot research well near Houston, Texas, in 1971. An API 80 screen was mounted on an unbalanced elliptical motion Linkbelt shale shaker to process the fluid as it left the well bore. The fluid was then pumped to the hydrocyclones. The well was to be used, initially, to evaluate the use of air injection into risers to reduce annular pressure at the seafloor and, subsequently, as a research test well.
The second mud cleaner was a bank of twenty 4-inch Pioneer hydrocyclones mounted above another specially built 4-foot-diameter, doubledeck, stainless steel, round Sweco shaker. The screens could be arranged in parallel or in series to process the underflow from the cones. This unit was placed on an exploration well in South Louisiana. A gas-bearing formation at about 11,000 feet contained an 11.0-ppg pore pressure. The gas-bearing formations between 11,300 feet and 16,000 feet had been depleted to pore pressures as low as 2.2 ppg. Plans were to drill through this interval with the 11.0-ppg water-base drilling fluid, set casing, and drill the exploration part of the hole. Through this interval, differential pressures, between the fluid in the well bore and the formation pressure, varied up to 6000 psi. A centrifuge was used along with the mud cleaner and dilution to keep the drilled-solids concentration very low to make a compressible filter cake. While drilling this interval, no lost circulation or stuck pipe was experienced. Torque and drag on the drill string were minimal. After reaching about 80 feet above the predicted casing depth, the mud cleaner was shut down. (Actually, the company man suggested that the research team go home for Christmas because they were having no problems and the new experimental equipment was not really needed.) As the last 80 feet was drilled, considerable drill string
drag and torque developed. The casing point was actually 120 feet below the predicted depth. The drilled-solids concentration in the drilling fluid greatly increased. Wiper trips were needed between each logging run prior to setting casing. So much drill string torque and drag were experienced that the research team was asked to return to the rig and turn on the mud cleaner. So many solids were discarded by the desilters and presented to the mud cleaner screen that an API 200 screen could not handle all of the flow. An API 150 screen was mounted on the mud cleaner to reduce the drilled solids during two circulations. Then a final cleanup was made with two circulations using an API 200 screen. The drilled-solids concentration could not be returned to the lower levels achieved during earlier drilling, but a sufficient number of drilled solids were removed to allow casing to be run without incident and cemented in the borehole.
Note that this lucky event of turning off the mud cleaner was probably the reason that mud cleaners became commercial. No drilling program schedules stuck pipe. None was programmed here. The research plan should have included a procedure to validate the mud cleaner performance. Since no problems were encountered and none were expected (although stuck pipe and lost circulation are common with 6000-psi overbalance in a well bore), no comparative data were acquired to prove that the mud cleaner was performing properly—until the machine was luckily shut off. This was also a great lesson in planning research for the drilling processes. The research team concentrated on keeping the drilling fluid in good shape and minimizing the impact of drilled solids; unfortunately, the primary function should have been to prove the machine beneficial. At that time, not all drilling personnel believed that drilled solids were detrimental or evil.
The mud cleaner’s U.S. patent—No. 3,766,997 (October 23, 1973), granted to J. K. Heilhecker and L. H. Robinson and assigned to Exxon Production Research Company—was found to be invalid because of prior art later discovered in the British Patent Office. A German inventor had been granted a patent on a similar device in the late 1800s. Although his invention had never been reduced to practice or used in the oil patch, and screens were much coarser in those days, the existence of the information in the public domain prevented collection of royalty for application of this technology. (As an interesting note, all of the companies providing mud cleaner service had offered to pay a nominal $5 a day per unit as a technology transfer fee for help in developing the product. This offer had been rejected and the service companies had been told that a much larger royalty payment would be required when the patent was issued. With an invalid patent, the service companies never had to pay a royalty and certainly did not pay a technology transfer fee.)
The first commercial application, less than a year after the initial patent was submitted, involved two wells, one production and one exploration, in the Pecan Island field in Louisiana. For the first time in that field, the intermediate long string of casing could be reciprocated during the cement job because of the lower drilled-solids concentration in the drilling fluid. The torque and drag in these wells were spectacularly lower than in previous wells.
When the mud cleaner was first introduced, many would try to decide whether to use a mud cleaner or a centrifuge. The problem with this decision is that mud cleaners do not compete with centrifuges in solids removal. In weighted drilling fluids, mud cleaners are designed to remove drilled solids larger than barite (larger than 74 microns). Centrifuges remove solids mostly smaller than most barite (less than 5 to 7 microns).