(I) Mud-while-drilling method
Mud-while-drilling method is generally suitable for low-pressure seepage formation with leakage less than 3m3/h, that is to say, small particle fiber plugging materials, rigid particle plugging materials and variable particle plugging materials added into mud will penetrate into formation pores or micro-cracks under the action of mud pressure difference, thus playing the role of bridging, filling and plugging, and achieving the purpose of plugging while drilling. Compared with stopping drilling and plugging, mud while drilling can save more time and is suitable for plugging micro-fractured formations such as high permeability sand layer, gravel layer and broken coal seam. Polymer chemical treatment agent, high viscosity mud or plugging material while drilling (80 1 plugging agent while drilling), etc. ) is often added to mud.
(2) casing isolation method
For Quaternary loose strata or strata with serious leakage such as collapsed oversize, old caves, karst caves and underground rivers, steel casing is often used for isolation. Casing isolation is generally used in shallow hole section of 1000m, but the cost is high in deep hole section, which affects the overall benefit of drilling engineering.
(3) Cement pouring method
For the formation with small fractures and medium leakage, good plugging effect can be achieved by injecting cement. Different hole wall maintenance methods should be selected according to the specific leakage situation during construction.
1. Pure cement slurry plugging
Pure cement slurry plugging is suitable for small formation cracks and small underground confined water and groundwater flow. Triethanolamine, salt and other accelerators can be added to the pure cement slurry, and the common formula is cement ∶ triethanolamine ∶ salt = 100∶0.5∶ 1, or the quick-setting early-strength cement slurry can be directly selected (surface test should be done before grouting to determine the initial setting time and other parameters of the cement slurry). Deep hole grouting must be pumped by mud pump, and the water cement ratio should be controlled between 0.5 and 0.6. This method has been successfully applied to the plugging of φ9 1mm and φ 1 10 mm in the broken leakage sections of Huoqiuji mining area in Anhui and Langyashan copper mining area in Chuzhou.
2. Cement mortar plugging
Cement mortar plugging is suitable for large formation fractures, large drilling diameter and large leakage. Cement mortar is composed of cement, yellow sand (or quartz sand), crushed stone (average particle size is 5 ~ 10 mm), quick-setting early strength agent, cement expansion agent, etc. Firstly, the location of water leakage (or water gushing), the size of cracks and the over-diameter of drilling holes are judged, and then stones and sand are placed in the leaking hole section to fill the cracks; Prepare cement slurry with water cement ratio of 0.5 ~ 0.6, add 0.5% ~ 1% quick-setting early strength agent and 5% cement expansion agent, drill to the bottom of gravel hole section, and pump the prepared cement slurry, the dosage of which is 2 ~ 3 times of the volume of the lost hole section, so that the cement slurry can penetrate into the gravel filled in the formation fracture to form a new hole wall cemented by concrete, thus achieving the purpose of plugging. After pouring, you must wait 72 hours before drilling. This method has been applied in three geological exploration boreholes (the hole depth is 600 ~ 700 m, and the final aperture is φ 1 10 mm) in shaft engineering of Lujiang Iron Mine in Anhui Province. The cement sand formed after grouting has high strength and good filling and sealing effect for large cracks.
(4) jelly slurry and chemical flocculation method
This method, also called elastic-plastic plugging method, is to fill the fractured stratum with glue, instead of forming a rigid hole wall with high consolidation strength, only an elastic-plastic hole wall with glue is formed. Suitable for heavy WOB, large pore water, water gushing, water leakage and dissolved strata, and it is difficult to cast stones with cement slurry.
1. Frozen mud is blocked
Gel slurry consists of cement (or hydrated lime), sawdust, clay powder, water glass (or calcium chloride) and so on. The proportion is: 50kg cement, 15kg water glass and proper amount of sawdust are added into the mud with viscosity of 1m3 and 50 ~ 60s; Or add 100kg hydrated lime and 25kg water glass (40kg calcium chloride can also be added) to the above slurry.
In the process of plugging, sawdust is filtered with a 40-mesh sieve, then mixed with cement (or lime) and pumped to the leaking position. When pumping water, slowly add sodium silicate into the water-absorbing shower. Mud mixes in the holes to form low-strength colloidal cement to fill the cracks. Under normal circumstances, after grouting, stop drilling for 5 ~ 6h before drilling through holes. After successful plugging, low solid mud must be used for wall protection drilling. This method has been applied in the exploration hole (hole depth 850m, final hole diameter φ 1 10 mm) of Dangtu Yangzhuang Iron Mine in Maanshan, Anhui Province, and achieved good plugging effect.
2. Chemical flocculation plugging
Chemical flocculation method mainly uses clay, polymer chemical flocculant (polymer polyacrylamide PHP, PAM) and other materials. When plugging by flocculation, mud with viscosity of 50 ~ 60s is pumped into the leaking hole section, and PAM solution with molecular weight of 8 million ~ 100000 and hydrolysis degree of 5% ~ 10% is slowly added to the water suction nozzle, and the addition amount is controlled at 2% of the mud volume (dry powder amount). In case of water gushing formation, the water gushing pressure can be balanced with weighted mud first, then mud balls are thrown into the leakage and water gushing holes, and then drilling tools are lowered to pressurize and tamp. PAM dry powder is put into the center of clay ball, so that the clay ball swells with water and mixes with PAM, resulting in cross-linking and flocculation of polymer and clay, which is filled and adsorbed in the cracks of rock stratum and plays the role of stopping surge and plugging. This method has been successfully applied to the anomaly verification hole of Zhengyangguan Iron Mine in Shouxian County, Anhui Province, the ZK 1725 test hole for deep prospecting in Huoqiu Zhou Ji, the NLSD- 1 hole for scientific drilling site selection in Du Yu-Ganxian ore concentration area in South China, and the LZSD- 1 hole for scientific drilling site selection in Luzong Basin in East China, which not only saves plugging time, but also saves plugging time.
During the construction of exploration and mining holes in Gui Long Salt Mine, Guangdong Province, serious layer leakage was encountered, and the mud did not return to the whole hole. A survey brigade of PetroChina spent nearly half a year plugging, but failed to solve the problem by using more than 100 tons of cement, and then handed it over to the 3 13 geological team of Anhui Bureau of Geology and Mineral Resources. 3 13 Geological Team, through analysis, realized that the failure of predecessors was due to grouting salt rock cracks with ordinary cement slurry. Because the cement slurry stones become rigid cementation in the cracks, the crystalline salt is also dissolved after entering the cement in the salt rock cracks. Even if the cement slurry stones are good, they will peel off from the cracks in a short time, and then the cracks will continue to dissolve and expand. Every time cement is injected, formation cracks expand and leakage increases. Therefore, it is decided to adopt polymer flocculation elastic-plastic plugging scheme. That is, saturated salt water (or dry salt powder) is mixed with clay powder to make clay balls, which are wrapped with PAM dry powder and put into holes, and then tamped with drilling tools to form polymer flocs with certain strength after hydration in the holes, thus plugging the cracks in salt rocks. This method of plugging is very successful. When the last well was cemented with cement, the pump pressure reached 16MPa, but no leakage was found.
The example shows that the flocculated elastic-plastic body produced by mixing clay and polymer can be closely crosslinked and adsorbed with salt rock cracks under the action of polymer chains, and the flocculated body has certain expansibility and firm filling, and at the same time, it can form a protective layer of salt water crystallized mud skin to prevent salt rock from dissolving in cracks.
(5) inert material filling method
This method uses inert materials to form "bridge" body, "suspension" body and "plug" body in fractured interval to plug formation fractures, which is suitable for drilling with large formation fractures and collapse oversize. Inert plugging materials mainly include:
1) granular materials: such as walnut shell, perlite, limestone, sandstone, asphalt, etc. , play a bridge role.
2) Fibrous substances: such as sawdust, paper fibers, peanut shells, cottonseed shells, etc. , play a role in suspension.
3) Plate: such as mica, rice husk, etc. , play the role of filling.
When plugging, the above three materials should be used in a certain proportion and gradation according to the leakage situation of the formation. Inert materials are easy to float on the water surface because of their low density, so it is necessary to add some high molecular polymers or clay to play a bonding role to facilitate feeding into the holes. At the same time, it is better to use it with other plugging methods.
(6) Composite plugging method
In the process of drilling construction, a single plugging method is often difficult to be effective when encountering extremely complex strata with the phenomena of breakage, collapse, leakage, surge and surge at the same time, and various methods must be adopted to solve it. The principle of dealing with this complex formation is "to deal with gushing first, then to stop plugging, and then to protect the wall". First, use weighted mud to balance the formation pressure, then use inert materials to bridge the fracture channel, and then use polymer flocculation to plug or use cement wall to plug. The working process of composite plugging and wall protection is shown in Figure 5- 14.
Fig. 5- 14 plugging operation flow of composite retaining wall
For example, the core of the deep prospecting 1050 ~ 1~2m m test hole in Huoqiu Zhou Ji iron mine area is severely broken, with serious over-diameter, water inrush and water leakage. Mud does not return to the hole when the pump is started, and water gushes in the hole when the pump is stopped, and the water head is 1 ~ 2 m higher than the surface, so it is impossible to drill. After that, the composite plugging method was used to successfully plug the leakage. After crossing the complex stratum, cement is used to solidify the hole wall, and after drilling to the hole depth of 1230m, the 89mm casing is lowered to protect the wall, so that the hole can be successfully drilled to the final hole of 2706.68m.