Search

The Silurian strata in the Shunbei No. 5 fault zone have the characteristics of long open holes, easy leakage and complex leakage. In the early stages, plugging technologies and methods such as bridging plugging, cement, chemical consolidation and high-water-loss plugging have poor effects and low plugging efficiency. Plugging slurry directly prepared with drilling fluid has low filtration characteristics, and the main reason is that the plugging material cannot filter quickly after the fluid enters the fracture. Based on the basic principle of fast filtration, the main plugging fluid M-Fluid, the micro-elastic high-strength main plugging agent M-Block and the filling agent Filling-Seal have been developed. In combination with the water-loss and wall-building properties of the circulating drilling fluid after plugging, a fast plugging technology for fractured volcanic rock formation has been established. The laboratory evaluation experiment showed that the filtration rate increased rapidly with the increase of temperature, and the filtration rate was about 0.31~0.79 mL/s, while the filtration rate of the drilling fluid was 0.0067 mL/s under the same conditions. The pressure-bearing capacity of various plugging evaluation methods, such as the simulated fracture of a large-grain sand bed, artificial fracture of small core and full-size core and multi-form fracture of double core, all exceed 5 MPa, and the system has a good plugging effect for complex fractures. [ABSTRACT FROM AUTHOR]

With the development of oil exploration, the number of complex situations encountered in the drilling process is continuously increasing. During the operation of large displacement and horizontal wells, the safe density window of drilling fluid is narrow in complex formations and the lost circulation problem is becoming increasingly prominent. This can easily cause the drilling fluid to enter the formation from inside the well through lost circulation channels, which will prolong the drilling cycle, increase drilling costs, affect geological logging, and could cause a series of malignant accidents (such as blowout, sticking of a drilling tool, borehole collapse, and well abandoned). According to the severity, common lost circulation can be classified into three types: fractured lost circulation, karst cave lost circulation, and permeability lost circulation. Currently, researchers are developing different types of lost circulation materials (LCMs) for various lost circulation situations. Compared with conventional lost circulation control methods, the polymer gel lost circulation control technique applies a three-dimensional cage-like viscoelastic body formed via the crosslinking reaction of polymer gels. These materials have strong deformability and can enter fractures and holes through extrusion and deformation without being restricted by lost circulation channels. They then settle in the lost circulation formation and form a plugging layer through a curing reaction or swelling effect. Among the polymer gel LCMs, high-temperature resistant polymer gels can either be used alone or in combination with other LCMs, bringing the advantages of adjustable gelation time, strong lost circulation control ability, and strong filtration ability of the plugging slurry. Moreover, they are suitable for the lost circulation control of microporous leaky layer and have limited influence on the performance of drilling fluids. Therefore, the high-temperature resistant polymer gel lost circulation control technique is increasingly becoming a hot spot in the research of LCMs nowadays. This paper summarizes the research progress into high-temperature resistant functional gels for profile control and water shutoff, lost circulation prevention and control, and hydraulic fracturing. Furthermore, the current application status of high-temperature resistant gels and high-temperature resistant gel temporary plugging agents is demonstrated, followed by a detailed overview of the gel-breaking methods. Overall, this research lays the theoretical foundation for the application and promotion of high-temperature resistant gels. [ABSTRACT FROM AUTHOR]

Nanoplugging materials are used in drilling fluid systems to seal nanopores and cracks in the shale formation, which is a focus for developing shale gas. In this work, nanoparticles of the St-NaSS copolymer were synthesized by emulsion polymerization of styrene and styrene sulfonic acid sodium salt as monomers. The St-NaSS copolymer was characterized by FT-IR, TGA, and light scanning phase analysis. The results show that the grain size of the St-NaSS copolymer nanoparticles ranges from 37 to 50 nm, and the average diameter is about 43.2 nm. The decomposition temperature of the St-NaSS copolymer is 410.7°C, indicating that the material has good temperature resistance. The St-NaSS nanoparticles have little effect on the rheological properties of the water-based drilling fluid. The plugging performance of the St-NaSS nanoparticles was evaluated by the mud cake simulation method. The permeability of the mud cake is 3.32×10-5 μm2 which is close in value to that of the shale. When the drilling fluid contains 0.5 wt.% of St-NaSS nanoparticles, the plugging rate is 88.93%. The plugging rate of the mud cake increases with increase in the concentration of the St-NaSS nanoparticles. When the amount of rho St-NaSS nanoparticles is 1.0% the plugging effect of the drilling fluid is excellent. Therefore, St-NaSS copolymer nanoparticles can be successfully applied as a plugging agent to provide borehole stability in the shale formation. [ABSTRACT FROM AUTHOR]

In the development of shale gas, it is important to ensure the stability of the borehole wall. The stability of the borehole wall depends on the plugging ability of the drilling fluid, while the stabilizing ability of the drilling fluid is provided by adding the plugging agent to the fluid. Conventional plugging agents are characterized by a relatively high volume and do not allow one to effectively plug micropores and microcracks in shale rock. In this work, the PMMA-St copolymer was synthesized by emulsion polymerization of methyl methacrylate and styrene. The characteristics of the PMMA-St copolymer were studied by FT-IR, TGA, and phase analysis optical scanning methods. The results show that the size of PMMA-St nanoparticles ranges from 34 to 58 nm, and the average diameter is about 40.6 nm. The decomposition temperature of PMMA-St nanoparticles is 374.8°C, which indicates the good thermal stability of the copolymer. The PMMA-St nanoparticles have little affect on the rheological properties of water-based drilling fluids. The mud cake simulation method was used to evaluate the plugging performance of PMMA-St nanoparticles. The permeability of mud cake is 2.24 × 10-5 m2, which is close to the permeability of shale formation. When 0.5 wt % of the PMMA-St copolymer is added to the solution, the blocking rate is 70.27%. With increase in PMMA-St concentration, the blocking rate of the mud cake increases. The best stabilizing effect is achieved when the PMMA-St copolymer concentration is 1.0%. The results of the core experiments are consistent with the mud cake simulation, which indicates the excellent sealing ability of the PMMA-St copolymer. Therefore, PMMA-St nanoparticles can be effectively used as a plugging agent to ensure borehole stability in the shale formation. [ABSTRACT FROM AUTHOR]

The reservoir in the Central Tarim Basin is a typical high-pressure fracture-vuggy carbonate reservoir with high temperatures, which easily leads to drilling fluid losses and the high-temperature carbonate. The conventional lost circulation materials (LCMs) cannot meet the reservoir. To resolve this problem, a rigid particle with high-temperature resistance, high acid solubility, and high rigidity was developed, tested, and evaluated. According to bridge rules of 1/2–2/3 opening degree of formation fracture, the formulation experiments of GZD and other lost circulation materials were conducted and a novel composite lost circulation material (LCM) was completed. Lastly, we investigated the compatibility of LCM and mud in site though compatibility experiment, analyzed the plugging effect of the system for fracture and vuggy by laboratory static lost circulation simulation and evaluation and sand-bed plugging experiments, respectively. The results show that compared with the conventional rigid lost material, the value of high-temperature resistance is more and acid solubility is over 98%. Also, it can work well with other fiber materials (E), variable filling particles (F and G), and superfine filling particles (H) and form a novel plugging material, named MGY-I, whose temperature resistance value is more than 473.15 K, the bearing strength is over than 9 MPa, the mud filtrate invasion depth of sand bed made from coarse particles (10∼20 mesh) is only 3.0 cm within 30 minutes, and the invasion depth is less than 1 cm within 30 minutes when the sand bed is made from 80∼100 mesh. The optimal concentrations of rigid granule, lignin fiber, elastic particle, and superfine calcium carbonate are 8% (A : B : CD = 2 : 1 : 1), 0.5%, 6%, and 1%, respectively. And, the plugging function of "GZD-rigidity bridge and filling, fiber network and deformable filing" is better exerted on the formation fracture with a high loading capacity and a high-temperature resistance. [ABSTRACT FROM AUTHOR]