How to improve the efficiency of milling tools for well repair operations?

Source of this article: China Petroleum News

[Operational difficulties]

During the construction process of underground operations in oil fields, milling tools have problems such as slow milling speed, short usage time, poor mechanical performance, and significant tool wear, resulting in long well occupation cycles, high well repair costs, and high labor intensity for employees.

[Solution]

Design and manufacture efficient grinding and milling tools for new shoe grinding. The on-site application has shown good results, with faster milling speed, higher efficiency, and better results compared to ordinary shoe grinders.

Narrator ①: Shi Kun (Oil Production Team Leader of Qinghai Oilfield Oil Production Plant)

[Cracking method] Design the structure of the shoe grinding to timely discharge the milled material and prevent secondary damage to the milled surface.

【 Application Effect 】 The design of the shoe grinding structure is reasonable, and it is safe and reliable to use underground.

In the early stage, by organizing technical personnel to dissect, survey, and consult relevant standards on several waste grinding shoes used on the underground site, combined with the on-site usage situation, important parameters that may affect the quality of grinding shoe products and underground operations were repeatedly measured. Based on the principles of "advanced performance, reasonable process, and reliable work", we can start with the design of efficient grinding and milling tools and shoe grinding structures, so that the grinding performance and manufacturing quality can reach the advanced level of similar products in China.

In the design of shoe grinding structures, it is necessary to consider channels that facilitate the export of milled materials, so that the milled materials can leave the milling surface in a timely manner and prevent damage to the milling surface caused by prolonged secondary exposure. Most shoe grinding structures are designed with symmetrical two water holes, and the grinding and milling teeth are evenly arranged at a certain angle. The water hole displacement is small, which cannot fully clean the grinding and milling interface, and the cooling effect is also not ideal. When designing efficient flat bottomed grinding shoes, a 120 degree phase angle and a 3-water eye structure design are adopted, with a displacement of not less than 30 meters per second. In the design of gear arrangement for grinding and milling, a roughly circular structure with alloy inlay arrangement of different sizes and specifications is adopted. The characteristics of this structure are that it has multiple cutting edges for grinding shoes, high cutting speed, and good cutting effect.

Narrator 2: Wang Jiancai (Welding Trainer at the Oil and Gas Storage and Transportation Equipment Technology Research Institute of CPC Pipeline Machinery Manufacturing Co., Ltd.):

[Cracking method] Three welding processes can be used to grind shoes: flame brazing, furnace brazing, and medium frequency brazing.

【 Application effect 】 The grinding speed is fast, the mechanical performance is good, and the alloy material for shoe grinding has high strength and wear resistance, reducing the frequency of drilling and tripping.

The root cause of long-term impact on milling efficiency lies in the detachment of hard alloy tungsten steel plates on the milling surface during milling operations, which cannot meet construction requirements when the milling volume is large. In response to this situation, through research on hard alloys and welding materials, it is recommended to use flame brazing welding technology to weld or brazing a layer of alloy tungsten steel sheet on the grinding shoe substrate that has been replaced with 35CrMo material, and fuse with the substrate to form a new grinding and milling surface. Before using flame brazing to weld grinding shoes, the area to be welded should be polished clean, cleaned of oil stains, rust, impurities, etc., and then uniformly preheated on the surface of the grinding shoe substrate to be welded. A grinding disc rotating fixture can be designed to ensure uniform heating temperature on the surface of the shoe body while rotating the workpiece. When the temperature of the surface to be welded reaches 500 to 600 degrees Celsius, copper brazing powder and flux can be sprinkled on it in advance to form a deoxidized protective layer on the surface to be welded. Continue preheating to around 800 degrees Celsius, and then use a clamping tool to place the tungsten steel sheet in place. Then, use high-temperature brazing material (welding wire) dipped in flux to quickly fill the area to be welded, so that the melted brazing material is completely filled around the tungsten steel sheet under the infiltration of the brazing agent. Pay attention to observing changes in the molten pool during welding to avoid situations such as porosity, false welding due to incomplete melting, and severe oxidation and overburning.

In addition to manual flame brazing process, furnace brazing and medium frequency brazing processes can also be used for welding. Furnace brazing is the process of feeding hard alloy, brazing flux, brazing material, etc. into a brazing furnace, setting a brazing temperature curve, and then welding. It should be noted that all welding processes require pre welding process evaluation and welding testing. After passing the evaluation, a welding process evaluation is formulated to guide the grinding and milling surface welding of shoes, ensuring welding quality and achieving ideal grinding and milling effects.

Narrator 3: Zhang Yong (Leader of the Drilling Site Group at Chuanqing Drilling's Western Sichuan Drilling Technology Application and Research Center)

[Cracking method] Carry out milling operations by selecting milling tools, optimizing drilling tool combinations, and selecting parameters reasonably.

【 Actual Effect 】 New concepts and designs have been obtained on the teeth and blade blades through grinding and milling tools. After on-site application, the grinding and milling efficiency has been improved. Compared with the original grinding shoes, the grinding and milling speed is faster, the usage time is longer, and the grinding and milling efficiency has been increased by more than twice. Optimize the drilling tool assembly, making milling tools safer and more reliable underground. Shorten the disposal cycle, reduce the frequency of drilling and tripping, and achieve cost reduction and efficiency improvement.

In milling operations, there are many types of milling tools used, and commonly used grinding shoes include flat bottoms, pot bottoms, sleeves, and guides (guide rods). When milling large metal objects, flat bottomed grinding shoes should be chosen, which have a large contact area and good pressure milling effect. When grinding and milling tubular fish, it is recommended to choose shoes with 3 to 5 blade blades. The blade blade should have a sharp cutting edge and a small contact area to prevent slipping; In the naked eye segment, a sleeve grinding shoe can be selected, while in the casing, a lead grinding shoe should be selected to prevent "loose skin" from sticking to the drill.

During the milling process, especially when the well is relatively deep, due to the small gap between the shoe grinding tool and the casing, the drilling tool combination should consider using downhole power drilling tools as much as possible to form high-speed, low bit pressure, and improve milling efficiency and usage time. If there is no downhole power drilling tool in combination, there should be weighted drilling tools to maintain milling and drilling pressure. The drilling tool assembly adds a fishing cup while drilling, which can be salvaged in real time according to the milling torque to prevent the risk of repeated milling and stuck drilling. If there are fewer iron chips returned from milling, they can be cleaned separately by drilling down.

The milling parameters should be adjusted in real-time according to the underground situation, and the entire milling process should have light drilling pressure, high speed, and appropriate displacement. When grinding and milling, there may be damage or unevenness on the top of the fish, so it is necessary to drill and press lightly and mill regularly and quantitatively; Grinding and milling without buttons, the fish should be milled at a variable speed or stopped from rotating. First, press repeatedly before milling. Grinding and milling displacement can reduce hydraulic erosion while meeting pump pressure and carrying iron chips. The milling torque has an increasing trend, and the milling cycle should be stopped.

Grinding and milling operators should have sufficient patience, concentrate on grinding and milling, and not slip the drill. When using an electric drilling rig, constant drilling pressure or constant speed drilling can be adopted, with less frequent drilling. Determine the milling situation underground based on torque and parameter changes, and lift at least once every 30 minutes of milling. Timely collect the returned iron filings and analyze the underground situation. If the casing suspension is not connected back to the wellhead, the drilling tool should increase the displacement circulation before drilling the horn mouth.

(Liu Lili)