Plug Technology Research Articles

Optimization of degradable temporary plugging material and experimental study on stability of temporary plugging layer

Temporary plugging technology is an important drilling technique for maintaining wellbore stability and resolving lost circulation problems. The key to its success lies in the use of materials that can form a tight and stable “temporary plugging layer” with certain pressure bearing capacity and a permeability close to zero in the loss channel near the wellbore. Experimental studies have been conducted to develop adhesion formulations for optimal temporary plugging materials, as the matching relationship between particle size and fracture width is critical [(0.5−1)/1]. By measuring the permeability of the temporary plugging layer under varying confining pressure with a soap foam flowmeter, researchers have been able to evaluate the effectiveness, degradation, and dosages of temporary plugging agents. It has been shown that a single-particle material, such as a walnut shell, has a smaller permeability than a hyperfine CaCO3 coated temporary plug layer. The latter, however, is less capable of bearing pressure. By combining different materials, such as walnut shells and hyperfine CaCO3 particles, the researchers were able to create a temporary plug layer that had the lowest permeability and did not change much at variable confining pressures. Its pressure-bearing capacity is strong and the temporary plug works well. Experiments have shown that a ratio of 2:1–3:1 of hyperfine CaCO3 and walnut shell particles work well for plugging a fracture system with particles of size 2–3 times the fracture width. It developed an evaluation method for temporary plugging agents, studied their plugging capability and degradation performance for reservoir conversion, and evaluated degradation performance after successful temporary plugging. The temporary plugging rate of the temporary plugging agent increased from 98.10% to 99.81%, and the maximum temporary plugging pressure is 50.39 MPa, which can be completely reduced at 150°C for 4 h, meeting the technical requirements of “dense temporary plugging, two-way pressure bearing” to some extent.

Application of Grouting Water Plugging Technology in Enriched Water Mountain Tunnel

In the expressway built in Chongqing northeast region, the tunnel occupies a large proportion in the total mileage. Long mountain tunnels with large buried depth and complex geological conditions are common in this area, which are prone to water gusher disasters during construction, which seriously threaten the construction quality and affect the operation of the expressway after it is completed and opened to traffic. In this paper, Jixinling Tunnel under construction in Wuzhen Expressway is taken as an example. Combined with advanced geological forecast data and site conditions, appropriate grouting materials and reasonable and feasible construction technology are selected for the surrounding advanced curtain grouting reinforcement and water plugging treatment, which effectively controls the water gushing disaster of the tunnel and ensures the safety of the construction process. It can provide some reference for the treatment of water gushing disease in mountain tunnel under similar geological conditions.

Research and Application of Fast Plugging Method for Fault Zone Formation in Tarim Basin, China

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.

New Research of Borehole Wall Protection Technology in Ocean Scientific Drilling

Abstract In the process of ocean scientific drilling, borehole accidents (e.g., borehole collapse, burying of drill tools, and sticking of drill tools) are often caused by borehole wall instability in loose and broken strata. It is very difficult to deal with such accidents, and the drill pipe in the borehole has to be discarded in serious cases. Therefore, the stability of the borehole wall seriously affects the drilling quality and efficiency. At present, there are three effective methods of ensuring wellbore stability: casing, drilling fluid, and agent plugging technology. Casing can effectively prevent instability of all types of unstable formations and can isolate different pressure zones. Using the proper drilling fluid can control drilling fluid loss, reduce free water infiltration into the borehole wall, and form a thin and dense mud skin, which is conducive to the stability of the borehole wall. Agent plugging technology, especially chemical gels, is mainly aimed at the broken zone. After entering the formation, it makes the entire broken zone form a single high strength unit, improves the cementation ability of the lost formation, and improves the sealing and bearing capacity in order to achieve the purpose of sealing and plugging of leaks. In this paper, the present situation, technical principles, and technological processes of wall protection technology in ocean scientific drilling are summarized, and the different types of wall protection technology were researched and tested. The results of this study provide a reference for international ocean scientific drilling in the future.

Research Progress of Dike Leak Rescue Technology

Leaks refer to seepage holes running through a dike body or foundation, the formation of which may pose dire threats to dike safety and cause dike breaching due to a large flow rate and strong scouring force. Once the water inlet of a leak is detected, sealing and rescue measures should be taken in accordance with the principle of “inlet plugging and outlet anti-filtration”. The key is the quick filling and stability of the plugging materials. Herein, the rescue technology of dike leaks is systematically laid out; the formation causes and development mechanism of the leaks are analyzed; the dike leak detection, plugging, and sealing technology is summarized; and the future research direction is clarified. Existing plugging technology and equipment are complicated and time-consuming. Hence, plugging methods should be innovated and improved to effectively improve the efficiency and success rate of emergency rescues. A new concept of “grade-by-grade plugging and sealing” is correspondingly proposed for dike leaks, changing leak rescues from “single-level plugging and sealing at the leak inlet” to “grade-by-grade plugging and sealing at the portal and inside the leak”. A tandem closed space is formed in the leak. The hydrodynamic pressure is changed from the independent bearing of the portal to the gradual bearing of the plugging materials at the portal and inside the leak.

Numerical Simulation of Bridging Ball Plugging Mechanism in Fractured-Vuggy Carbonate Reservoirs

Pores, fractures, caves, and other storage spaces are commonly distributed in fractured-vuggy carbonate reservoirs. During the drilling process, more than half of all drill-in fluid loss issues are caused by developed caves. Cave scales range from centimeters to meters, making leak prevention increasingly difficult through the use of traditional technologies. Currently, there is still high demand for the understanding of feasible loss control techniques, especially in fractured-vuggy carbonate reservoirs. Multistage Bridge Plugging (MBP) technology has facilitated pioneering experiments in many oilfields, but the success rate of plugging is less than 50%, and the effects of plugging are uncontrollable and difficult to predict. This is due to a lack of clarity regarding the plugging mechanism and the key controlling factors. In this study, we used the Discrete Element Method (DEM) simulation method to investigate the controlling factors of MBP technology, and analyzed its applicable conditions. We found that the prerequisite for the success of MBP is the presence of a constricted throat near the wellbore when drilling the well hole; the first-stage bridging ball is the key to the success of MBP. Larger ball radius, cave inclination and initial flow rate, and lower ball velocity are beneficial to the first-stage bridging. All discussion in this research is based on the ideal situation. However, the cave pattern is difficult to describe using several models, let alone by one ideal model. With the progress of seismic fine description technology and mud logging, more accurate characterization of caves in carbonate reservoirs will help to accurately formulate the plugging scheme and greatly improve the success rate of plugging technology. Additionally, the engineering risks of this technology, such as plugging the coiled tubing, need to be further studied.

Control Model and Optimization Study of Temperature Distribution Applied in Thermite Plugging and Abandonment Technology

Abstract With the continuous exploration and development of oil wells, we must pay attention to the risk of leakage from abandoned wells. Therefore, it is necessary to plug and abandon the abandoned well. However, there are many limitations in the traditional plugging and abandonment (P&A) operation, for example, cement's bearing capacity, the cement's corrosion resistance, the problem of the extended operation time, and high cost. To overcome the aforementioned issues, a thermite plugging and abandonment (TP&A) technology is proposed in this field. The technology uses the aluminothermic reaction to melt the original or set materials for P&A operation. To promote the phase transformation of more materials in the well to form a plug with good plugging performance, the temperature distribution in the TP&A system was optimized. Based on the heat conduction theory and successive overrelaxation iterative method, a heat conduction model based on the temperature release law of aluminothermic reaction is established and solved. The temperature change law under different combinations of the downhole environment is studied. The optimized model can maintain the high-efficiency transfer of energy, fluid–structure interaction, and the interaction between fluids. The material after the phase change can be cooled to form a plug with good plugging performance.

A composite temporary plugging technology for hydraulic fracture diverting treatment in gas shales: Using degradable particle/powder gels (DPGs) and proppants as temporary plugging agents

Temporary plugging and diverting fracturing is one kind of technology for efficiency-enhancing the productivity of oil and gas wells, which is widely used in hydraulic fracturing treatments in shale gas reservoirs. However, the closure of unpropped fractures at the temporary plugging zone under the high closure stress post fracturing treatment may influence the efficiency of shale gas well productivity-enhancing. The unpropped temporary plugging zone plays the role of a “closed valve” that would intercept the connection of the old fractures to the flowable fracture system. Thus, a composite temporary plugging technology for hydraulic fracture diverting treatment in gas shales is proposed for solving this problem by using degradable particle/powder gels (DPGs) and proppants as temporary plugging agents. This study examined the adaptability of the DPGs, as well as the proper combinations for composite temporary plugging technology. Moreover, the temporary plugging mechanism and behavior of the composite temporary plugging zone are discussed. Experimental investigation results show that the DPGs have good adaptability for composite temporary plugging technology, and meet the requirements of diverting fracturing within the hydraulic fractures. The optimum experimental combinations are determined, the mass ratio of DPGs to proppants for temporary plugging is 16%, which can ensure the temporary plugging efficiency, as well as the timely removal of plugging. Temporary plugging mechanism and behavior of composite temporary plugging zone are closely related to the internal structure evolution of composite temporary plugging zone, the plugging processes can be divided into bridging and plugging, deformation, adhesiveness, and degradation of DPGs. This study provides the understanding and mechanism of the composite temporary plugging behavior during hydraulic fracture diverting treatment. This technology is of great significance to achieve enhanced and stable production in shale gas reservoirs.

Research on Plug and Play Implementation Technology for Distribution Network Equipment

From the point of view of primary diagram, secondary equipment and Model Association of distribution network, this paper studies Plug and Play technology of distribution network equipment from access to application, describes the advantages and disadvantages of different technologies, and provides development ideas for future construction of distribution automation.

Performance Analysis of Soluble Bridge Plug Materials for Fracturing in Unconventional Oilfields

With the continuous in-depth development of oil and gas resources, unconventional oil and gas resources show great potential. In recent years, 70% of the proven oil and gas resources in China are unconventional oil and gas resources. Therefore, the development of unconventional oil and gas resources has a huge impact on the increase in the production capacity of the oil and gas resources in China. Staged fracturing of horizontal wells is the main technical measure to improve unconventional oil and gas production stimulation. In the fracturing process, the soluble bridge plug technology can not only effectively solve the problems of large investment in drilling and grinding of composite bridge plugs, high risks, self-locking of oil, casing deformation, etc., causing the bridge plug to be unable to be drilled and remove and affect subsequent production but also can successfully make up for the problems of subsequent production. The large-diameter bridge plug cannot achieve the full diameter of the wellbore and cannot carry out operations such as postproduction logging and refracturing, which can ensure the integrity of the wellbore to the greatest extent. In this paper, HNBR was used to modify MPU to prepare HNBR/MPU soluble rubber, and the effect of blending ratio on the vulcanization characteristics, mechanical properties, compatibility, thermal stability, and degradation behavior of composites was studied. The results showed that with the increase in the amount of HNBR, the degree of cross-linking of the composite material decreased gradually, and the mechanical properties decreased slightly. With the increase in the amount of HNBR, the thermal stability of the material decreases. The use of HNBR greatly reduced the degradation rate of MPU. When the amount of HNBR was changed from 20 phr to 40 phr, the tensile strength retention rate of the composite after soaking increased from 14.73% to 39.72%.

Research on Coiled Tubing Drill Plug Technology and Matching Tools

Research on Coiled Tubing Drill Plug Technology and Matching Tools

Fracture Interference and Refracturing of Horizontal Wells

Due to fracture interference, not all perforations can be fractured, resulting in 20% of fractures contributing to 80% of the total production. The extraction of oil and gas also reduces production, necessitating refracturing. In this study, the finite element method was used to simulate multiple fractures fracturing simultaneously and the stress field distribution was then extracted and applied to a new geological model. This paper explains the effect of stress around the horizontal wellbore on new fractures during the refracturing of old wells using a temporary plugging technique. The results show that initial breaking pressures are the same, but as fractures extend, inter-fracture interference increases, resulting in different fracture extension pressures and widths. The fracturing fluid is filtered into the reservoir matrix after fracturing, reducing formation stress. Compared with fracturing at the initial fracture site, reperforating fracturing has a lower fracture extension pressure and a longer fracture length. According to this study, hydraulic fractures have a 15 m effective influence radius on the external formation. Stress relief is beneficial for fracture initiation prior to refracturing. Reperforating and fracturing, in combination with temporary plugging technology, can assist in increasing the effective stimulated reservoir volume and achieving high and stable production.

Lost circulation materials for deep and ultra-deep wells: A review

The number of deep wells and ultra-deep wells drilled worldwide is gradually increasing, and the problem of deep well leakage has become one of the challenges in drilling. The high-temperature and high-pressure environment in deep formations severely test the drilling leakage control. The lost circulation material and its nature largely determine the success rate of deep well leakage control. The paper discusses the failure and instability mechanism of the lost circulation materials in deep wells and the plugging zone formed by them. The lost circulation materials are classified as physical and chemical lost circulation materials. It includes bridge plugging materials, high filtration loss plugging materials, organic gel plugging materials, expansion plugging materials, resin plugging materials, and inorganic gel plugging materials. According to the published evaluation and analysis of temperature and pressure resistance of leakage lost circulation materials, the characteristics of different types of temperature and pressure resistance leakage lost circulation materials are summarized. Based on a large number of existing researches and the practice of the team on high temperature and high-pressure leakage plugging, the research on the theory of high temperature and high-pressure leakage plugging and the research adaptability of high temperature and high-pressure resistant materials, the research on new physical and chemical temperature and pressure-resistant materials, the composite leakage plugging method and its suitability Prospects are put forward in terms of temperature and pressure plugging technology and strive to improve the success rate of loss control in deep wells.

Application of Temporary Plugging Technology in Liaohe Oilfield

Application of Temporary Plugging Technology in Liaohe Oilfield

Experimental Research of Compound Monitoring on Multiple Temporary Blocking Refracturing for Long-Section Horizontal Wells

As an important energy replacement block in China, the tight conglomerate oilfields in the Mahu area are difficult to develop and are characterized by strong heterogeneity, large horizontal stress differences, and undeveloped natural fractures. However, new development processes including temporary blocking diversion and large section-multiple clusters have been implemented on the oilfields in the past few years. In 2020, two adjacent horizontal wells in the MD well area experienced a poor fracturing development effect compared with the earlier wells in this area. Analysis suggests that the main reasons are water sensitivity of the reservoir, insufficient fracturing scale, and/or interference from the adjacent old wells. To ameliorate the problem, this study presents an experimental study of multiple temporary plugging and refracturing technology in long horizontal well sections, in combination with electromagnetic and microseismic monitoring. Results from the study show a great difference between the two monitoring techniques, which is attributed to their different detection principles. Interestingly, the combination of the two approaches provides a greater performance than either approach alone. As the fracturing fluid flow diversion is based on temporary plugging diversion and electromagnetic monitoring of fracturing fluid is advantageous in temporary plugging diversion monitoring, both approaches require further research and development to address complex situations such as multiple temporary plugging and refracturing in long intervals of adjacent older wells.

Research on temperature propagation law based on thermite plugging and abandonment technology

The continuous exploration and development of oil wells increases the risk of leakage from abandoned wells and brings challenges to the traditional plugging and abandonment technology. In order to overcome the above problems, a thermite plugging and abandonment technology is proposed in this field. The technology uses the aluminothermic reaction to melt the original or set material for sealing. The natural convection under different confinement conditions directly affects the heat flux transfer in the heat transfer process. In order to study the melting effect of the thermite reaction on sandstone, based on the heat conduction theory, a heat conduction model based on the temperature release law of the thermite reaction was established. The numerical simulation results show that the surrounding heat transfer conditions are the key factors affecting the heat transfer effect in the axial and radial directions without considering the particle size and dosage of the thermite itself. This work is of great significance for studying the temperature law of thermite reaction release and the future research of thermite plugging and abandonment technology.

Study on Plugging Technology in Oil Test

In view of the shortcomings of poor temperature resistance, poor pumpability and poor pressure-bearing capacity of commonly used gel plugging materials, polyacrylamide (HPAM) and N,N-methylene bisacrylamide (BIS) were selected for crosslinking and compounding to make a new type of gel plugging material with high temperature and pressure resistance. The compressive strength and yield stress were measured by inverted observation method to evaluate the gel strength. The anti-temperature, anti-pressure, anti-dilution and gel-breaking properties of the gel were evaluated. Finally, 71 type high temperature and high pressure water loss instrument and high temperature and high pressure filter with slit plate were used to evaluate the plugging capacity of gel plugging agent. The experimental results show that the new gel plugging system between 100°C - 120°C, gelation time can be controlled at about 5 h; it has strong temperature resistance, compression resistance, dilution resistance and gel breaking performance. In the face of permeability and fracture leakage simulation experiments, when the ambient temperature below 120°C, pressure within 5 MPa, the filter loss of gel plugging agent is far less than the market two conventional plugging agent, has excellent plugging performance.

Application of flexible colloid-fiber compound plugging technology in oil and gas wells with large differential pressure in the East China Sea

In order to solve the contradiction between the safety requirements of well control in the upper reservoir and the loss of kill fluid in the lower reservoir, the idea of “compound plugging technology” was proposed to solve the abnormal pressure inversion phenomenon of “the co-existence of blowout and lost circulation” with large interlayer pressure difference. Flexible colloidal particle-fiber composite temporary plugging fluid was developed. The plugging layer formed by the temporary plugging fluid of flexible rubber fiber can withstand the positive pressure difference of more than 40 MPa, and there is no overflow and leakage. The advantages of compound temporary plugging fluid under large differential pressure are verified and it has a good application prospect.

Research and application of composite plugging technology with organic gel and inorganic gel for malignant leakage

Research and application of composite plugging technology with organic gel and inorganic gel for malignant leakage

Multistage circuitous-temporary plugging fracturing technology for deep oil-gas reservoirs

China is rich in deep oil and gas resources with buried depth of more than 3 500 m. To overcome the technical difficulties in the implementation of conventional temporary plugging technology for the staged fracturing of horizontal well of deep oil-gas reservoirs, such as the small net pressure of fractures and the limited pressure window, we propse a technical idea of multi-level circuitous temporary plugging of fracturing and then build a mathematical model and solve this model by Newton iterative method. On this basis, we conduct the substantive research work on the simulation and optimization of technical parameters, such as the timing of circuitous temporary plugging, the decrease of pump rates, etc. The research results show that circuitous temporary plugging can significantly improve the pressure window of fracturing construction and the net pressure of the main fracture, which is helpful to realize the diversion of the fractures of deep and ultra-deep oil-gas reservoir and greatly increase the reformed volume; multistage circuitous temporary plugging fracturing can further increase the fracturing pressure window and the net pressure of the main fracture based on single-level circuitous temporary plugging, which is conducive to achieving the complexity of the fractures of deep and ultra-deep oil-gas reservoir and the maximization of the reformed volume. And meanwhile remaining the cost of fracturing vehicles and other processes basically unchanged. The application results of test wells show that the production after fracturing can be increased by more than 30% compared with adjacent wells. Therefore, the multi-level circuitous temporary plugging technology provides important guiding significance and reference for improving the fracturing effect, exploitation level and economic benefits of deep-ultra-deep oil-gas reservoir.