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Snubbing Service

Introduction of snubbing department

Snubbing department is founded in 2012, currently owning two Hydra Rig 225k standalone snubbing units, three Caterpillar powerpacks, two sets of well control equipment with imported seals, and complete sets of auxiliary equipment. All downhole tools and core accessories are imported from America. All equipment and tools is certified and inspected by third party. The maximum pressure our units can be applied is 105MPa, highest in China at present, which fills the absence of high pressure wells snubbing operation in China. Supported workstring size ranges from 1-1/4” to 5-1/2”, and chrome tubing operation can be performed with special tools we owned.Since the day snubbing department was founded, we committed ourselves to high pressure oil and gas wells snubbing service. Cooperation with Cudd, Snubco, Topwell, Shengli was made, which contributes to the development of snubbing technology in China. Through hard effort, our service was recognized by many oil fields and gas fields. We have provided snubbing service for Jianghan oil field, Puguang oil field, Tarim oil field, Huabei oilfield, covering operations such as tripping, completion, perforation, fracturing, milling, wash over, paraffin washing etc. Our outstanding performance and efficiency was recognized and praised by customers for numerous times.(December, 2014)

Introduction of snubbing

Snubbing refers to a workover operation, by which specialized equipment are utilized to operate on live wells. During snubbing operation, wellbore pressure can be maintained, and thus eliminate the necessity of well killing (washing) and pressure release. For oil wells, the greatest advantage of snubbing operation is that, original formation pressure is preserved, which effectively protects formation pressure, avoiding pollution to oil reservoir, reducing the times of acidification, fracturing and other well stimulation, and finally providing favorable conditions for long-term development and stable production of oil and gas fields. For high-pressure oil and gas wells, the process of stopping injection and bleeding off are not required prior to operations, which shortens construction duration, saves the costs of kill fluid required for conventional operations and accessary equipment, abates pollution and finally protects the environment.For shale gas wells, well killing is avoided, which can reduce the pollution to shale gas formation, and effectively prevent gas reservoir from over-killing and formation damage.

Advantages of snubbing service

1.Snubbing operation provides a new idea for exploration and development of oil and gas fields. Traditional well killing method is adopted for oil and gas wells, intending to balance formation pressure, and prevent blowout. The operation cannot be conducted in the wells with pressure, resulting in difficulty in realization of many geological requirements and influence on geological analysis. During application of the technology in oil and gas wells, string tripping, various evaluation testing, change of working system and other processes can be completed in those wells with pressure.

2.The technology maintains original condition of formation in oil - gas layer to the maximum to accurately evaluate the reservoir. When flowing into formation, kill fluid causes pollution and has a negative effect on subsequent data acquisition, well completion, well testing and ultimately, results of reservoir description, as well as recovery efficiency. The oil and gas wells reservoir physical properties get the best protection through snubbing operation which avoids damage to newly exploited reservoirs during conventional exploration, such as blockage of new perforation, mud cake which leads to wrong stratigraphic interpretation, expansion of water-sensitive minerals which weakens the reservoir physical properties, in order to obtain accurate data during oil reservoir evaluation.

3.The technology minimizes the operation risks. During operation, kill fluid is subjected to gas or oil invading, and the density is lowered. On the one hand, the risk of blowout is larger and on the other hand, well killing is required repetitively, with complex process and expensive operation expenses.

4.The technology resolves some knotty problems during conventional well killing. For example, for the operations in gas well, when killing is conducted with kill fluid, leakage occurs upon killing; otherwise, blowout occurs; low-permeability gas wells are likely to be killed. In addition, application of non-well killing technology eliminates frequent replacement of killing mud in high-pressure oil wells, use of circulating and supporting facilities, prevents pollution to ground environment, and solves long-term discharge and overflow of injection wells.

5.The technology spares kill fluid, prevents reservoir pollution, increases production and recovery efficiency, and provides the greatest protection for yield and potentials of reservoir.

6.The technology reduces exploration and development costs, and increases production efficiency and economic benefits of oil and gas fields: since no well killing is required during operations, the costs are saved on the one hand, and operating cycle is shortened on the other hand. The harm of well killing to formation is noticeable, and costs of kill fluid are very considerable, which shall be pumped and drained after operation. However, during injection well operations, it takes a long time to stop injection and bleed off pressure, even two to three months or half a year sometimes; in order to keep balance of formation pressure field, surrounding injection wells shall stop injection, leading to oil well reduction or halt in production, greater influence on production and lower economic benefits.

7.The technology protects the environment, avoids pollution of kill fluid to the ground, meets HSE requirements for oil field, and possesses huge economic and social benefits.

Main Business Scope of Snubbing Service

Well Completion or Tubing Tripping under Pressure

Introduction to the application: the operation shall be applied to trip out the pipe string and tool string in the well out of the wellbore under pressure, and trip in new designed pipe string into the wellbore, or replace the existing pipe string in the well. Currently, Yilong snubbing department has tripped in several completion pipe strings in Jianghan Oilfield and Puguang Oilfield. The tripping operation for tubing and BHAs is achieved through controlling pressure with annular blowout preventer or stripper BOPs, and keep pressure equalized all the time. The maximum BHA allowed to go through the unit is 180mm. The maximum lift force of jack is 120 T , maximum snubbing force is 60 T, and can be applied to wells with wellhead pressure less than 105 MPa. The technology is very mature currently.

Operation description: prepare snubbing equipment; dismount the wellhead and rig up blowout preventer and snubbing equipment; trip in completion work string under pressure; land the tubing hanger; test the pressure and rig down the equipment, and recover the oil pathway, hand over to production.

Snubbing Service in Gas Storage

Introduction to the application: since the pipe strings for brine ejection in some gas storages contain high pressure gas after completion of brine ejection, and the operation cannot be realized through conventional workover, coiled tubing and other technologies, which means only snubbing operation shall be applied.

Operation description: prepare tubing plug and snubbing unit, and rig down the wellhead and install blowout preventer and snubbing unit; take out 4-1/2” pipe strings for brine ejection from 7” injection-production pipe strings; rig down snubbing equipment and BOP stacks, and put into production.

Completion Perforating for New Wells and Reperforating of Old Wells

Introduction to the application: if the well is deep, has long horizontal section or has rough dog legs, during completion perforating, it is difficult to trip the coiled tubing reaches to the target section to conduct perforating operation. Both the lifting force and snub force of equipment for operation under pressure equal to several times of those for coiled tubing. It shall be capable of tripping the perforating gun into the target section. Then the bottom layer shall be perforated through pressure perforating, so as to prepare for the subsequent perforating by cable. The equipment for operation under pressure can also be combined with the abrasive perforating technology to perforate the layers with hard rock, and several perforations can be realized in one run.

Operation description: prepare downhole tool string and equipment for operation under pressure and ground procedure; install blowout preventer and equipment for operation under pressure on large gate valve for fracturing; trip the pipe string to reserved position; conduct perforation, and trip out pipe string under pressure; close the gate valve and wait for the next command.

For example, the horizontal section of the well is too long in a certain perforating operation. Previously, the perforated pipe string could not be tripped into the target section for 5 consecutive days because of the working capacity of coiled tubing, and construction progress was affected as a result. After the discussion, it was decided to use the snubbing unit to trip the tool string into target section. With long horizontal section and large fluctuations in horizontal well section, the tripping process was blocked several times. However, the perforating gun was finally tripped into the target layer with the excellent working capacity of stand-alone equipment after hard working for two days. Pressure perforating was conducted, pipe string was tripped out after completed perforating, and equipment for operation under pressure was rigged down for standby. Party A conducted fracturing of separate layers through pumping bridge plug and coiled tubing, and 2-7/8EUE tubing was tripped in the well through the equipment for operation under pressure after completion of fracturing, as the completion pipe string. It took 6 days for tubing conveyed perforating through equipment for operation under pressure, including equipment rig up and rig down, and 5 days for pipe string tripping. New solution for well-cased perforating was proposed by tubing conveyed perforating through snubbing unit. There shall be more sections to conduct perforating and fracturing after implementation, so as to increase the production of operating well and create greater economic benefits.

Acidification and Fracturing

The tail pipe fracturing by dragging and fracturing by dragging can be realized in combination with acidification and fracturing.

Fracturing by dragging: such technical problem can be solved properly with the cup-type packer introduced by Yilong. Firstly, conduct perforating for the casing, then trip in two cup-type packers through equipment for operation under pressure, and carry out fracturing for layers requiring fracturing through pressurizing to set the packer and over pulling to release it. Since there are various selections for tubing, and their steel grade, wall thickness and intensity are stronger than those of coiled tubing, fracturing method with large discharge capacity and high pressure can be achieved during fracturing to obtain better effect. The completion pipe string can be tripped into directly after fracturing, and a lot of expenses shall be saved with fracturing, well completion and wellhead installation completed at one time.

Drilling Plug under Pressure, Sand Washover, Paraffin Removal and Fishing under Pressure

Equipment for operation under pressure will trip motor, nozzles and other tools into the well, pump the circulating liquid or chemicals into the pipe string. With the torque, yield strength, length of tubing and other advantages, if coiled tubing fails to meet the well condition requirements, it shall be solved by taking the advantages snubbing unit, especially for drilling, sand washover, paraffin removal and fishing for wells with high pressure, high production and deep wells. The torque of rotary table reaches up to 6,500 lb.ft, which can conduct drilling and milling for vertical well sections, and also can benefit slip release during blocking of pipe string. With wide coverage capacity and strong working capacity, snubbing unit is suitable for processing highly difficult wells, such as the complicated wells containing sand washover, drilling plug, milling, fishing and other procedures simultaneously.

For example, the wellhead pressure reaches up to 86 MPa. All the tubing for the well were blocked in 2012 because of serious paraffin precipitation in the tubing. Party A requested that the paraffin blockage problem must be solved in a month. Solution is shown as follows: trip 1-1/4 inches small tubing into the tubing through equipment for operation under pressure, and wash with paraffin remover under high pressure. Trip the small tubing on the top of paraffin blockage and establish circulation; pump the paraffin remover into the well, and trip in pipe string slowly; wash the paraffin, and circulate the washed paraffin outside the well at the same time.

Maintenance and Replacement of Wellhead Gate with Faults under Pressure

Generally speaking, the method of well killing shall be adopted to replace large gate valve, so as to balance the hydrostatic pressure and formation pressure. The large gate valve shall be replaced or repaired after killing well. However, on the one hand, large amount of kill fluid shall be equipped and treated for such method, and loose compaction may lead to unforeseen circumstances. On the other hand, kill fluid has a large influence on the formation. Especially for gas well and oil well with low permeability, the production may decrease greatly after well killing. According to the selection of operation under pressure, the tubing hanger and its check valve shall be tripped into the well, pressure test for tubing hanger shall be conducted after fastening the jackscrew, and the equipment for operation under pressure and wellhead shall be dismounted after passing pressure test. This method is very fast (it only takes one day for operation, excluding the time for equipment disassembly), and can protect reservoir effectively, which saves the expenses of kill fluid.

Tripping in of Chromium-Containing and Small Tubing

For the anticorrosion, chromium-containing tubing and small tubing with small wall thickness tripped in the wells with strong corrosion, high sulphur content and high carbon dioxide content, if during tripping-in, the body is scratched by the slips or hydraulic tongs, the service life of tubing will be greatly influenced, which may increase a large number of costs for future maintenance, and even induce complex working conditions, cause engineering accidents. During tubing tripping-in under pressure, both the strong jacking force in the well and dead weight of string will apply on the slips to make bite marks on the tubing body, affecting the normal operation. Therefore, Yilong has introduced advanced tool accessories from abroad, including traceless slip tooth, traceless tong teeth, traceless tubing tong, buckle tools for small tubing, slip adapter, etc., which may realize zero damage to tubing during tripping-in process, greatly save the costs for future oil and gas well maintenance, and avoid working conditions such as tubing corrosion, damage and fracture, etc. After discussion with engineers and mechanician from Hydra Rig, Yilong has creatively invented the slip adapter, making the diameter scope of standalone snubbing unit extended to 1-1/4” – 4-1/2” (which covers most small tubing), and it also is equipped with special tongs and buckle tools for small tubing, which prevents the thread of small tubing from being damaged.

Conditions of Companys Snubbing Equipment

Jack assembly

Currently, the Company owns two sets of HRS-225 snubbing rig manufactured by National Oilwell Hydra Rig Company in USA. The HRS-225K snubbing unit is a standalone work over rig that is easy to rig up and transport and capable for various snubbing operations. The basic parameters of HRS-225K snubbing unit are as follows:

Max. lift capacity: 104T

Max. snub capacity: 53.4T

Torque of rotary table: 6500 lb.ft

Stroke: 3m

Through bore: 280 mm

Working mode of hydraulic cylinders: Convertible working mode with

2 or 4 cylinders

Max. operable wellhead pressure: 105MPa

Scope of operable pipe string: 1-1/4"- 5-1/2"

Powerpack

The powerpack is located on the ground or platform deck, which provides necessary hydraulic pressure for the operations of lifting machine, BOP stack, slips, rotary tables, winches (500 kg) and power tongs.

Advantages: the powerpack is composed of 5 sets of pumps and separately provide power for each circuit, failure of one set of pump wont interfere with other pumps; besides, the built-in accumulator bottle can also provide adequate power for shutting or opening BOPs, slips, hydraulic plug valves, etc. after powerpack emergency shutdown due to equipment failures. In order to improve the operation efficiency and increase the service life expectancy, 3-level oil supply system is used in the main system to automatically adjust the volume of oil supply according to the load. Moreover, a back-up powerpack is provided, in case of failure of powerpack in the circumstances where construction schedule is tight and well condition is complex.

Work basket

Work basket sits on the top of jack, and is the working platform for operators. The control panels is located within the operating platform to control jack, traveling and stationary slips, BOP stack, CB wenches, etc.

Advantages: it is provided with 3 sets of self-contained escape devices for escaping to the ground from 3 directions in emergency circumstances, from which, each operator may choose the nearest escape device behind him to quickly escape to the ground, ensuring escaping efficiency and avoid the possibility where more than one operator share 1 set of escape device which leads to unnecessary injuries.

Hydraulic jack

The tripping of pipe string may be conducted through the 4 configured hydraulic cylinders, 2 leg mode or 4 leg mode may be chosen according to the well conditions during operation. The telescoping tubing guide is located in the through-hole of jack for providing the centralizing and guiding so as to prevent pipe buckling.

Advantages: switching between 4 legs and any 2 legs.

Control panel

Control panel is consisted of three independent parts, wherein one part is the main operation panel for controlling jack, slips, etc., the second one is auxiliary operation panel used to control strippers , equalize loop, bleed off lines and 1# safety BOP etc., and the last one is CB wench control panel used to control the dual counter balance winch.

Advantages: each panel is independent and the operation requires cooperation of three operators, making it safe through supervising one another.

Slips group

The traveling slips are located on the rotary table and runs synchronously with jack; currently, the applicable tubing size of slips ranges from 1 1/4” to 5 1/2”.The stationary slips are mounted on the lower part of jack, which are used to hold the pipe string when the traveling slips open.

Advantages: each slip is separated, whose function may be adjusted according to different working conditions; besides, we have provided the special slip dies for chrome tubing to conduct such tubing operation; when the slip gets stuck in the coupling, the normal operation may continue, without tubing flying out or falling into well or slip damages; the centralizing plate can be installed on the slips according to the working conditions to prevent the tubing from being clamped.

Rotary table

The rotary table is of hydraulic drive type, may be used for drilling and milling, Max. torque is 6,500 lb.ft and its maximum rotating speed is 46 RPM.

BOPs

The BOP stack is the core equipment for operation under pressure; currently, we have 14 BOPs in total, stripper BOPs, safety BOPs, shear / fully-sealed BOPs, slip BOPs and annular BOPs included, and can simultaneous operate on 2 wells; the BOPs now available are consisted of 10 Cameron type U single ram BOPs (7-1/16”, 105 Mpa), 2 shear ram BOPs and 2 annular BOPs (7-1/16”, 35 Mpa). Snubbing operation with dynamic sealing within 80 Mpa can be conducted.

The stripper BOP stack is composed of stripper BOPs, HCRs, manually operated plug valves, choke valves, riser or guiding BOP, etc.

Advantages: it may be flexibly assembled into different compositions according to different operation and well control requirements; the distance between 2 stripper BOPs is long enough to avoid the coupling getting stuck at the BOP ram; it suits for long BHA.

Service Status

Since 2012, our crew has successfully conducted about 110 wells in major oil fields; the service areas include the EOG Recourses, Fuling shale gas field, Puguang gas field, etc.Type of service:Replacement work string under pressure, well completion under pressure (operation of chrome tubing), cooperation with coiled tubing operation, layered fracturing operation, perforation under pressure, well workover under pressure (including sand washing, well washing, fishing, milling, etc.).(December, 2014)