snubbing unit vs workover rig for sale

Snubbing units have evolved into one of the most capable and efficient well servicing tools in the oil & gas industry. In the 1920"s, the need for a rig to work with pressures at surface drove the invention of the snubbing unit. The first snubbing unit was primarily designed to work in well control situations to "snub" drill pipe and or casing into, or out of, a well bore when conventional well killing methods could not be used. The first snubbing unit relied on the draw works of the companion rig to supply its" power. A series of sheaves, cables and counter weights were rigged up so that as the rig"s traveling blocks hoisted up, the snubbing unit would snub in the hole. Conversely, when the traveling blocks on the rig were lowered, the snubbing unit would snub out of the hole. As you can imagine, this required close communication with several different contractors in order to perform the work safely and efficiently.

One of the main components of a snubbing unit is the slip. Stationary and travelling slips are operated in sequence to grip the pipe as it is snubbed into the well. Typically, a minimum of four slip bowls are used in snubbing operations. Two slip bowls are designated for "pipe light" operations. Pipe light is when the well bore forces are greater than the tubular weight in the well bore. The other two slip bowls are designated for "pipe heavy" operations. Pipe heavy occurs when either enough pipe has been snubbed into the well bore and fluid weight inside of the pipe is greater than the snub forces acting against the pipe in the well bore.

While snubbing into the hole, there is a transition point the tubular goes through from being pipe light, to pipe heavy. This transition is an equilibrium typically referred to as the "balance point". The balance point occurs when there is enough pipe weight in the wellbore to equal the snub forces generated against the pipe. In certain instances, thousands of feet of pipe can be moved with minimal effort since the pipe weight is at an equal state with the snub forces. Snubbing contractors calculate this snub force and add in a friction factor from the BOP and wall contact on either a casing or tubing string. If done correctly, the snubbing contractor can predict when this balance point will take place and can properly prepare for it.

Modern snubbing units are powered by sophisticated hydraulic systems. These hydraulic units typically supply all power required by the components of a snubbing operation. With a better understanding of hydraulics and modern advances, companies have been able to harness this hydraulic energy to develop precision controlled snubbing units. These units move tubulars into and out of a well bore by use of a "multi cylinder jack"; a snubbing jack comes in many sizes depending on the task at hand. They are usually denoted in size by the snubbing unit description (i.e. 460K, 340K, 200K, etc). The 460K snubbing unit has the ability to lift 460,000 LBS and a snubbing capacity of 230,000 LBS. Most snubbing units can typically snub half of their lift rating. Assume you had a well with 10,000 PSI at surface and wished to snub in a string of 2 3/8" tubing. The snubbing contractor can calculate the snub force, add in their respective friction calculations and project the snub force to overcome will be approximately 51,000 LBS. This would put a 120K snubbing unit to close to its maximum capacity of 60,000 LBS snub loading. The safest bet would be a 150K or 235K snubbing unit.

Well control is taken very seriously by snubbing contractors. The BOP is the only barrier between the well bore and personnel. Depending upon well conditions, pressures and work performed, the BOP stack configuration varies greatly; there can be a minimum of three BOP"s and in some cases, up to ten. All of this is determined in the pre-job phase of the operation.

Pipe handling is performed by the snubbing units "gin pole" and "pipe winches". The gin pole is typically telescoped out in excess of 40ft above the snubbing unit. With the use of dual tubing winches, multiple joints of pipe can be handled simultaneously, speeding up the operation.

The snubbing "basket" is the platform where the snubbing personnel work. The basket contains all of the necessary hydraulic controls to operate all the features of the snubbing unit, as well as a large bank of BOP"s and hydraulic valve controls.

Today"s snubbing units can be employed to provide a wide range of services. In essence, a snubbing unit is a hydraulic rig that can do everything a rig can do, plus it can perform under pressure in an under balanced live well state. This is especially critical to the operators in the Haynesville Shale, which is known for HPHT wells. With the use of the snubbing units" hydraulic rotary, the unit can be employed for fishing, milling, drilling, side tracking or any task needed to remove bridge plugs, cement or deepen wells.

The industry has become more aware of damages caused by heavy kill weight fluids and mud. This has helped make snubbing units more popular in a completion and workover role, versus its" traditional use as a well control response tool. With the advances in drilling technologies in the unconventional shale market, the benefits of snubbing units have become very apparent. These types of completions often have laterals extending out thousands of feet. With costly stimulations used to help extract the gas more efficiently, operators often times do not wish to turn around and load the well with heavy fluids to complete the well dead.

Coiled tubing has its limitations in reach, due to wall to wall mechanical friction in horizontal wells. Often times the coiled tubing units cannot reach TD or supply the needed weight on bit to mill up composite plugs typically used in completions.

Another clear advantage to using a snubbing unit is its" small footprint, which is critical on the tight locations in the unconventional shale"s. Moreover, the small size and ease of mobilizing is especially useful and cost effective with offshore wells.

In conclusion, with the snubbing unit"s size, ability to handle pressure, rotary capabilities, rigidity of jointed tubing and minimal wall contact, snubbing units have become the chosen resource for these types of completions.

Pumping services tend to get more expensive offshore, because of the degree to which the equipment must be assembled on location. Wire based services still require assembly, but because the parts are smaller can usually be mobilized in larger ‘chunks’ thus requiring less assembly on location. On land, fluid pumping equipment is much more readily portable on trucks or trailers. Workover rigs on land are incredibly cheap in most places as measured on a per diem basis. Part of their advantage is that they arrive to location with most of their key components already assembled in/on one truck. This advantage disappears offshore where the rig must be assembled on site first.

Paying for a drilling rig or intervention vessel is the price of gaining physical access to the well. Everything else must be added to it to get physical access to the general area and then gain access to the well. There is no need for various forms of standalone pumping services because the vessel or rig will already have a cementing unit and/or the mud pumps available for that sort of work.

Performing the same operation over and over again has significant cost savings attached to it. Once the correct housing and supply arrangements are in place, and all the necessary people and equipment have been assembled, continuing to use it altogether ‘as is’ can save an enormous amount of money compared to dispersing it all and starting over again later. For land operations, this is most pronounced in areas where reservoir, surface, and operational practices allow for grouping wells together in relatively small areas, and for clustering well pads. Depending on what work is being done to the wells and how close together they are it may be possible to ‘hop’ from one well to the other without ever moving the equipment on a road or doing a complete rig-down.

Deepwater operations can benefit from this too, but not as much as ‘traditional’ fixed or surface access facilities, because the overall day rate of the rig or intervention vessel is often much higher, and the process of switching between wells is often much lengthier.

On land, you hire the unit and crew, and a small diem fee is added to the cost of employing them so they can stay in a hotel and get food when they are not working. The crews will transport themselves to and from the well and move the equipment to and from the well also.

The costs of conducting business in each of these 3 areas tend to scale very roughly in factors of 10. 100 wells making 50 bbls of oil each on land is a cash cow. Offshore that is a disaster, because the cost of servicing those wells is prohibitive. A more reasonable scenario is 10 wells making 500 bbls of oil each. In deepwater, a well making 500 bbls of oil a day is an abandonment candidate, if indeed it got that far along before abandonment. One well making 5,000 bbls a day is more. The direct cost of hiring (for example) a snubbing unit do not scale by factors of 10, but the overall cost of employing a snubbing unit do. As a result, different types of well servicing make sense in one area which may not make sense in another. On land in areas with ordinary access to infrastructure (not the Sahara or Alaska) operations like slickline are often so cheap that they are a routine procedure, with preventative or predictive maintenance schedules to scrape away paraffin or remove small amounts of scale. By contrast, it is completely cost prohibitive to try and attempt to perform similar work in deepwater – you either design and operate the well in such a way that paraffin and scale do not build up in the wellbore at appreciable rates, or you P&A the well. The cost of routine mitigation is simply too high. The relative cheapness of most workover rigs on land is another major factor. Many types of operations which could in theory be carried out in some other way are done with a workover rig simply because it is the most cost-effective technique, even if other methods might be faster, or involve fewer people. The relatively high cost of a rig for offshore facilities means that in most cases every effort short of getting a rig is tried first. Then a catalogue or list of operations to be conducted by a rig at a given facility will be gradually built up over time until they reach a critical level. At that point, a rig will be sent out to conduct all the operations which only it can perform, moving from one well another to save costs by making the work repeatable.

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Snubbing is a process that controls the pressure of oil or gas in order to run or pull tubing, drill pipe, or casing. These applications use the standard snubbing unit to complete or re-complete wells in a “live well” condition. Any type of workover application can be performed utilizing quick jacks.

Snubbing units are often used in place of workover units for offshore applications. Snubbing can offer the same services at a greatly reduced cost to the customer. Snubbing can be performed on live and dean wells. Milling operations can be faster and more precise with snubbing units due to infinite control of torque and speed of the rotary mounted on the snubbing jack.   Snubbing is versatile alternative that can overcome the limitations of other workover systems - wireline, coiled tubing and conventional workover rigs.  It eliminates the use of kill fluids that can damage the producing formation and require costly disposal. Snubbing is also a faster solution.  Snubbing units can often have the task completed before a conventional workover operation is even rigged up.

Snubbing is your best choice when conventional draw works are absent.  The self-contained equipment requires little space and can finish the job quickly.  The hydraulic system"s precise control over force protects against overload and allows responsive tool manipulation.

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Jereh truck/trailer mounted workover rig is mechanically and hydraulically driven. The power system, drawworks, mast, travelling system and transmission mechanism of the workover rig are mounted on the self-propelled chassis, which improves the moving efficiency greatly. Now, Jereh truck mounted workover rig series cover the workover depth from 2500m to 7000m and drawworks power from 250HP to 1000HP, featuring high operation load, reliable performance, excellent off-road performance, convenient movement and low operation/moving cost. Besides, workover rigs for arctic, desert and highland applications are available.