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Article

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

by
Zhong He
1,
Sheng Fan
1,*,
Junwei Fang
1,
Yang Yu
1,
Jun Zhang
1,
Shuanggui Li
1 and
Peng Xu
2
1
Engineering Technology Research Institute of Sinopec Northwest Oil Field Branch, Urumqi 830000, China
2
School of Petroleum Engineering, Yangtze University, Wuhan 430100, China
*
Author to whom correspondence should be addressed.
Energies 2023, 16(11), 4330; https://doi.org/10.3390/en16114330
Submission received: 3 March 2023 / Revised: 28 April 2023 / Accepted: 16 May 2023 / Published: 25 May 2023
(This article belongs to the Section H1: Petroleum Engineering)
Browse Figures
Versions Notes

Abstract

:
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.

1. Introduction

The low recovery efficiency of a reservoir can be attributed to the fact that the reservoir is generally heterogeneous, and the available formation energy is not sufficient to fully cover the thermoelectric threshold potential (activation energy) of the displacement process. While lowering the thermodynamic potential is a general requirement, several factors are reasons for the application of such IOR/EOR methods (polymer flooding, gel treatment, etc.), which increase the threshold potential in porous systems. This obvious fact makes a new theoretical approach timely if we want to move towards more efficient technical solutions. Therefore, an attempt was made to classify basic chemical and non-chemical recovery procedures by comparing different IOR/EOR methods using thermodynamic flow characteristics. One of the main conclusions of this new approach is that there is convergence and divergence between reservoir engineering and thermodynamic preconditions. Despite these contradictions, we can predict that these chemical methods will completely move forward with higher recovery efficiency and thus be able to reduce the viscous flow activation energy, interface deformation, wettability changes, adsorption/desorption, etc. [1].
The Shunbei oil and gas field in Tarim Basin, China, belongs to a fault solution reservoir, with 13 fault zones as interpreted by geology [2,3,4]. Currently, drilling is mainly conducted in the No. 1 and No. 5 fault zones. The Shunbei No. 5 fault zone is characterized by a low penetration rate and a long drilling cycle. According to the statistics of the drilling situation in this area, leakage in the block is frequent, the average number of leakages per well is 14, and the leakage density is mainly 1.36~1.38 g/cm3. The block leakage is characterized by frequent leakage and repeated leakage. The success rate of one-time plugging is low, and a large amount of time is lost. The average time of plugging construction is more than 40 days, and the drilling cost is high, which cannot meet the strategic requirements of low-cost development [5,6].
Many experts and scholars have carried out research on the leakage problem in Shunbei, mainly focusing on the leakage problem of the Permian igneous rock in Shunbei; their research targets include the problems of the development of fractures in the Permian igneous rock, the poor cementation of the formation, the fragility, the weak pressure-bearing capacity, etc., and they have engaged in some discussions on bridging plugging, cement slurry plugging and other technologies [7,8,9,10]. Fang et al. (2017) [11] applied a pressure test of 5 MPa and an equivalent density of 1.55 g/cm3 in the field to meet the pressure-bearing requirements of the Permian system by taking advantage of the multiple synergistic plugging effect of a chemical gel plugging agent on the leakage of the Permian igneous rock in the Shunbei 3 Well; Luo et al. (2017) [12] described a method of using 12% medium-fine particle plugging slurry to drill through the Permian rock in the whole of Well Shunbei 1-1H to solve the leakage problem; Niu et al. (2016) [13] discussed the use of bamboo fiber, ultra-fine calcium carbonate and the polymer gel plugging agent PSD along with other plugging materials while drilling in the leakage-prone formation of Well Shunbei 1-6H to avoid the occurrence of lost circulation and formed an optimized drilling fluid with a good application effect; Guo et al. (2019) [14] described the successful application of high-temperature-resistant chemical gel plugging technology in Well Shunbei 52X. At the same time, Xiao Xuyu, Pan Jun, Gao Wei, He Chunming and other scholars [15,16,17,18,19] have also carried out research on similar issues.
According to the application status of plugging technology in the Shunbei No. 5 fault zone, the existing leakage-plugging technology mainly includes bridge plugging, cement slurry, chemical consolidation, high filtration, gel and other systems, and there are problems such as inconsistent effects, instability and leakage recovery in the application process of the systems [20,21]. Based on an analysis of plugging effects, these five types of plugging systems have their own advantages, but they all have defects, mainly including the following problems: (1) bridging plugging: using drilling fluid to prepare the plugging slurry, the requirements of water loss and wall building of the drilling fluid and the rapid accumulation of plugging particles to form a plugging barrier contradict each other, resulting in elongation and low strength of the plugging belt and easy occurrence of backflow [22,23]; (2) cement slurry plugging: cement slurry is an important method to solve malignant leakage, but on the premise of ensuring wellbore safety, cement slurry needs to ensure a certain waiting time, and it is easy to spit back and transmit wellbore pressure to connect fractures when cement slurry is not cemented [24]; (3) high-filtration plugging and chemical consolidation: under many conditions, these two kinds of plugging are used in combination, but porous or fibrous materials with high filtration make it easy to seal the door at the joint, resulting in false plugging [25,26]; and (4) gel plugging: gel plugging has solved many malignant leakage problems on sites, but its own strength has certain defects, which mean it cannot be used alone to solve the plugging problem [27,28].
According to the field plugging situation and the research of different scholars aiming at problems such as the open hole length and repeated leakage of the Silurian system in the Shunbei No. 5 fault zone, it is proposed to establish a plugging system with strong universality, form a special plugging system suitable for the fault zone strata, construct and optimize the existing technology system, improve the plugging success rate and reduce the probability of re-leakage [29,30].

2. Silurian Leakage Characteristics of Shunbei No. 5 Fault Zone

The Silurian strata in the Shunbei No. 5 fault zone are weak, with micro-fractures developed and possible faults (see Figure 1). Therefore, the vulnerable well sections are mostly in the Permian igneous rock section and the Silurian strata. Due to the undercompaction of the upper stratum of Neogene rock, the Silurian mudstone is prone to collapse, sand–mudstone interbedding is developed, the mudstone section is long, and the mudstone section is prone to water absorption and expansion, resulting in denudation and collapse [31]. Complex downhole problems such as leakage and overflow occur easily. At the same time, there is high-pressure saline water at the bottom of the Keping Tage Formation, and the density of the pressure-stabilized water layer needs to be increased (≥1.40 g/cm3), resulting in the reopening of the upper lost well section fractures or inducing new fractures. However, the thin layer distribution of Silurian formation intrusions is irregular and difficult to predict, the collapse stress is high (≥1.37), and the leakage pressure of the Tataertag Formation is low, which increases the difficulty of plugging [32].
Due to the type of wells distributed in the Shunbei block of the fault zone, the compression and deformation of geological structures led to the development of a fracture network near the Silurian fault zone, which is characterized by low pressure and random multi-point leakage throughout the well interval. There are a large number of open and closed fractures in the Silurian lost circulation formation, and the structure of the fracture network is complex. Therefore, the lost circulation characteristics in this layer are mainly the characteristics of the fracture network. In the lost circulation construction, repeated plugging will lead to the existing fracture network structure being placed under pressure, leading to fracture-induced connection, causing the original fragile formation to be more fragmented and full of holes, as well as wellbore instability, which makes it difficult for the lost circulation measures to achieve a successful plugging. At present, the plugging technology and supporting process still continue leakage prevention and plugging measures in the Permian system, and the plugging is not targeted.

3. Results

3.1. Principle and Method of Rapid Plugging Slurry

3.1.1. Defects of Current Plugging Slurry System

According to the application status of plugging technology in the Shunbei No. 5 fault zone, the existing leakage plugging technology mainly includes bridge plugging, cement slurry, chemical consolidation, high filtration, gel and other systems, and there are problems such as inconsistent effects, instability and leakage recovery in the application process of the systems. Based on an analysis of plugging effects, these five types of plugging systems have their own advantages, but they all have fatal defects, mainly including the following problems [33,34,35]: bridge plugging can easily cause the plugging area to be elongated, has low strength and is vulnerable to backflow; cement slurry plugging can easily cause backflow when unconsolidated, and the wellbore pressure is transferred to the connecting crack; high-filtration plugging and chemical consolidation in porous or fibrous materials with high filtration can easily seal a door at the joint, causing false plugging; and gel plugging’s strength has certain defects, meaning it cannot be used alone to solve the problem of plugging.

3.1.2. Proposed Solution

The traditional plugging system mainly focuses on bridging and plugging and uses drilling fluid to add plugging materials to form plugging slurry, but there are two problems (as shown in Figure 2):
(1)
After the plugging slurry prepared by the drilling fluid enters the fracture, the drilling fluid acting as the carrier fluid needs to be drained as quickly as possible under the premise of ensuring the safety of the fracture. However, the nature of the drilling fluid itself determines that it is easy to drain the relatively dense plugging layer or mud cake on the two walls of the fracture, which directly leads to the rapid loss of the drilling fluid.
(2)
The drilling fluid flows to the crack tip intensively, further inducing the crack to continue to extend and causing more serious leakage problems. At the same time, the drilling fluid and plugging materials in the plugging slurry cannot be separated, and the plugging slurry is in the slurry state, which cannot achieve the plugging effect.
Based on the problem of difficult accumulation of plugging materials caused by the preparation of plugging slurry with conventional drilling fluid and the adaptability of current plugging materials, the concept of rapid filtration of traditional high-filtration plugging methods is used for reference, and a series of plugging materials are designed and formed indoors to realize the rapid plugging scheme of high filtration. The core of the scheme is as follows: (1) On the premise of ensuring pumpability and pumping convenience, the plugging material is carried into the formation through a special plugging fluid, and the fluid is quickly filtered after the appropriate clamping position is established in the fracture, so as to quickly realize the local concentration of the plugging material and establish a high-shear-resistance plugging area, and some materials supplement the high-shear-resistance plugging area through continuous filling and aggregation. (2) After the drilling fluid re-enters circulation, use the low-filtration property of the drilling fluid to further plug the plugging area that still has a certain filtration property, so as to establish a high-strength solid plugging barrier area with less sealing and no backflow.

3.2. Development of Plugging Materials

Based on the idea of a plugging solution, it is necessary to form a plugging agent and its composition system that are suitable for the Silurian formation in the Shunbei No. 5 fault zone. The system must meet the requirements of rapid pumping and rapid establishment of a plugging barrier under the conditions of existing tools, while taking into account the need for efficient plugging ability of multiple forms and types of fracture conditions in fracture formations. According to the above requirements for the rapid plugging system, the main plugging body, micro-elastic high-strength main plugging agent and filling agent were developed in a laboratory; the composition of different treatment agents was adjusted appropriately according to the fracture type and size, supplemented by some conventional plugging agents; and the basic composition and filtration characteristics of the current drilling fluid were fully considered. On this basis, a special plugging system for the Silurian formation in the Shunbei No. 5 fault zone was established.
(1)
Plugging mainstream: M-Fluid
Traditional plugging slurry uses the drilling fluid to carry the plugging materials. The drilling fluid itself has a good carrying capacity and the ability to suspend the plugging materials, which can better carry the plugging materials into the fractures. However, under the conditions of complex fracture morphology, the particle matching degree is poor, and the plugging material can easily gather at the fracture mouth, resulting in failure to enter the fracture well. On the other hand, the drilling fluid cannot be filtered into the formation quickly. Under the condition that the plugging time is not long, a drilling fluid that is not well filtered in the fracture will easily lead to backflow.
In order to solve the problems of drilling fluid, existing alkyl glycosides, xanthan gum, guar gum, polyanionic cellulose, etc., are compounded in a certain proportion indoors, and the advantages of each treatment agent in the construction of the mainstream body are integrated to ensure the good flow of the mainstream body and the ability to carry plugging materials. There are two kinds of aggregation forms of alkyl glycoside micelles: spherical and cylindrical structures. When they are used in wellbore fluid, it may become wormlike and take other forms due to the influence of dosage and temperature. After the length and density reach a certain degree, it will wind and overlap to form a three-dimensional network structure (as shown in Figure 3). In the process of high-speed pumping in the wellbore, the high shear rate will break the network structure formed by the micelles and reduce the viscosity of the main stream, which is conducive to rapid pumping. When the main flow is lifted into the fracture, the spatial network structure is properly restored, the viscosity rises, and the plugging material is carried into the fracture. The cost of using alkyl glycosides alone is too high, and the structure formed by alkyl glycosides is not completely suitable for the requirements of plugging slurry. Therefore, water and alkyl glycosides are used in combination to optimize the performance of the plugging slurry and further reduce the cost of the plugging slurry base fluid.
(2)
Micro-elastic high-strength main plugging agent: M-Block
The core treatment agent of traditional plugging materials is mainly rigid particles, fibers, etc. Rigid particles play a role in supporting and bridging the cracks, and they are the key factors in establishing the plugging barrier in the cracks. However, there is a significant problem with rigid particles. The particle shape is irregular, and the rigid structure has no deformation. In the process of entering the crack, they are easily affected by many factors. The length of the deep crack cannot be controlled, and it is easy to cause door sealing, resulting in a very short crack-sealing area. On the other hand, most of the existing non-deformable rigid materials have obvious brittleness and are easy to break under high pressure. Even if a long plugging area is formed, the structure of the plugging area under high pressure will still be easily damaged.
According to traditional rigid material and bridging plugging theory, indoor elastic resin and elastic graphite are used as the main body, and other strengthening materials are added to form a high-strength plugging agent with micro-elastic properties. The particle size distribution is mainly 0.2–1 mm, 1–2 mm, 2–3 mm, 3–5 mm, etc. (see Figure 4), which can be adjusted. The material can have a certain degree of micro-elastic ability at a safe temperature and can produce a certain degree of micro-deformation in the fracture under the appropriate wellbore pumping pressure; it enters a relatively stable position in the fracture, which solves the problem that rigid materials cannot be deformed. While maintaining its micro-deformation ability, the micro-elastic high-strength main plugging agent also has high overall structural strength, which can produce certain micro-deformations under the action of high pressure but will not cause great changes in the strengthening of the material and will not cause brittle failure. The micro-elastic high-strength main plugging agent can rapidly form a high-strength framework plugging area with high filtration performance in the fracture, providing a basis for the subsequent filling agent to enter.
(3)
Filling agent: Filling-Seal
The filling agent (see Figure 5) is mainly used to fill the pores in the high-strength plugging area formed by the micro-elastic high-strength main plugging agent to form the sealing structure area. The filling agent mainly includes rigid particles, flexible particles, deformable particles and other mixed inert plugging materials which can plug the remaining pore structure in the frame plugging area, forming a dense plugging area with higher strength closer to the fracture opening; the particle size distribution is mainly 200 μm in the interval with a fine grain.
In using the developed main plugging agent M-Fluid, micro-elastic high-strength main plugging agent M-Block and filling agent Filling-Seal, under certain conditions, a conventional plugging agent can be added to reduce the cost and plugging effect for a certain degree of composite treatment, and the particle size of the main plugging agent can be adjusted according to the change of fractures. This can allow the formation of a better high-strength structure plugging area and establish a loss-plugging system suitable for the Silurian formation of the Shunbei No. 5 fault zone and carry out corresponding plugging and fracture adaptability evaluation.

4. Discussion

4.1. Construction of Fast Plugging Slurry System and Evaluation of Plugging Effect

4.1.1. Construction of Plugging Slurry System

According to the construction principle of the rapid plugging system, the plugging system is established with the main body M-Fluid, the micro-elastic high-strength main plugging agent M-Block, the filling agent Filling-Seal and ultra-fine calcium carbonate as the main body. According to the characteristics of the Silurian strata in the Shunbei No. 5 fault zone, the formation fracture widths are mainly concentrated below 5 mm. Considering the characteristics of multiple fracture types, the micro-elastic high-strength main plugging agent M-Block is further optimized to be 1–2 mm (M-Block1), 2–3 mm (M-Block2) and 3–5 mm (M-Block3). The particle size distribution of barite for weighting is considered to be 10~40 μm in order to optimize the grading of the filling agent Filling-Seal, cover the particle size area susceptible to external forces and achieve the best plugging effect after plugging in combination with the low filtration of the drilling fluid.
According to the formed plugging treatment agent and the density of the formation drilling fluid, the plugging slurry base fluid is formed: drilling water + 30% mainstream M-Fluid + barite is weighted to the density of the drilling fluid. According to the needs of formation fracture properties, the main plugging agent and filling agent are added to establish a plugging slurry system matching with the fracture: base fluid + 5~8% micro-elastic high-strength main plugging agent M-Block1 + 3~5% micro-elastic high-strength main plugging agent M-Block2 + 2~4% micro-elastic high-strength main plugging agent M-Block3 + 5~15% filling agent Filling-Seal.

4.1.2. Evaluation of Plugging Action Time

The main plugging agent and filling agent are added into the plugging base fluid to form a plugging system. According to the principles of rapid plugging technology, a plugging barrier with high strength (pressure greater than 3.5~7.0 MPa) is formed in the most appropriate length of time. However, while considering the action time of fast plugging, it is necessary to consider the sudden force that the crack tip can bear, slow down the speed of crack expansion and effectively protect the formation of the sealing plugging zone in the appropriate range. A high-temperature and high-pressure loss instrument is used to evaluate the plugging action time indoors. The main purpose of using the high-temperature and high-pressure evaluation device is to simulate the leakage rate of the plugging slurry under a certain filtration aperture and pressure of 3.5~7.0 MPa, which can reflect the filtration time of the plugging slurry to a certain extent. According to the distribution of the formation, the leakage times under the conditions of normal temperature, 40 °C, 80 °C, 120 °C and 160 °C are evaluated respectively and compared with the formation of the drilling fluid on site. The plugging slurry system used in the experiment is: base fluid + 6% M-Block1 + 4% M-Block2 + 2% M-Block3 + 10% Filling-Seal, with a density of 1.40 g/cm3. The experimental results are shown in Table 1.
The experimental data in Table 1 show that the filtration rate increases rapidly and the filtration time decreases rapidly as the temperature increases. The filtration rate is about 0.31~0.79 mL/s, while the filtration rate of the drilling fluid is 0.0067 mL/s under the same conditions. Compared with the plugging action time, the rapid plugging slurry formed is greatly reduced in terms of action time, ensuring that the plugging material is concentrated in the crack in a very short time and quickly forms the plugging barrier. From the perspective of the properties of polymer drilling fluid, the low-filtration property of its drilling fluid will further plug the pores formed by the rapid plugging slurry and achieve the effect of high-strength plugging.

4.1.3. Large-Particle Sand Bed Simulation Fracture Plugging

Previous studies have shown that the surface of most fractures in the formation is rough, and there are a large number of micro-convex bodies. The two walls of the fractures show a discontinuous contact state, which can also be regarded as a highly connected layer with a network structure. Conventional flat fracture simulation plugging is not suitable. Outcrop rock is used indoors to break and screen out 5–10 mm stones and fill them into the high-pressure plugging evaluation device to evaluate the pressure-bearing capacity under different conditions. Under the condition of compaction, 5–10 mm particles can roughly simulate 2–3 pores. The mutual extrusion of scattered stones can simulate the structure of micro-convex bodies on the crack surface to a certain extent, and the formed scattered pores can also be regarded as a highly connected network structure to a certain extent. From this point of view, it is appropriate to use a large-particle sand bed to simulate cracks. In the experiment, a high-pressure device was used to change the conventional sand bed plastic pipe into a steel structure to solve the problem of plastic non-pressure. In the experiment, 500 mL of 5–10 mm stones is used to form the sand bed, 500 mL of plugging slurry (the same as 4.2 plugging slurry) is prepared, the pressurized plugging slurry is quickly filtered, and the drilling fluid is added again. In the experiment, the pressure is increased by 1 MPa every 10 min, the action process of plugging slurry in the sand bed is observed, and the plugging effect is observed after being pressurized to 5 Mpa for 60 min. The experimental results are shown in Table 2.
The experimental process in Table 2 shows that the plugging slurry can be quickly lost. After the drilling fluid is added, during the continuous pressurization stage, the drilling fluid continues to have filtration. This filtration shows a continuous downward trend with the continuous strengthening of the structure of the plugging area, and the filtration stops within 10 min. The filtration-reducing materials in the drilling fluid play a role one after another to plug some small pores formed after rapid plugging. After stopping, the plugging barrier can remain stable without re-leakage. However, in the 5 Mpa long pressure-bearing stage of 60 min, the plugging barrier is stable without damage, the pressure bearing of 5 Mpa also meets the demands of on-site pressure bearing, and the loss reduction rate of the plugging slurry reaches 100% (see Figure 6). This shows that the plugging slurry can better block a sand bed simulated by large particles, and it is also proved from the side that in the cracks with contact points, the rapid plugging technology studied can meet the plugging requirements.

4.1.4. Dynamic Plugging Evaluation of Small Core

The standard small core with a diameter of 2.5 cm and a length of about 5 mm is an important evaluation tool for conventional simulation plugging. It is a plugging method that can be quickly realized indoors in addition to the standard experimental device in the natural gas industry. However, the dynamic plugging evaluation of a small core is relatively rare. The multi-functional core dynamic displacement device is used indoors to realize the dynamic plugging evaluation of a small core. The dynamic evaluation device has a simulated wellbore. Two sets of core holders are installed on the wellbore wall to ensure that one end of the core can be in direct contact with the fracture, which ensures that the device can install two cores at the same time to simulate the plugging process of two fractured cores near the wellbore formation. In the laboratory, a natural core is used to squeeze the core into two parts along the radial and axial directions to form a relatively real artificial crack, and a gasket is used on both sides of the axial direction to make the crack width reach 2–3 mm, which is consistent with the field. Firstly, 1000 mL of plugging slurry is added to the simulated wellbore. After the slurry at the upper part of the open end of the wellbore core is pressurized and filtered, the remaining plugging slurry in the wellbore is removed, 1000 mL of field drilling fluid is added, the wellbore rotation cycle is started, and the plugging effect is simulated by pressurizing to 5 Mpa. The experimental results are shown in Table 3.
The experimental data in Table 3 show that the two cores have good plugging effects under the same wellbore. The drilling fluid stops filtering after a short period of filtration. The low-filtration characteristics of the drilling fluid quickly play a role, blocking the pores formed by the rapid filtration of the plugging slurry and forming a high-strength and dense plugging layer in combination with the shear-resistant plugging area formed by the materials in the plugging slurry. Compared with the fracture simulated by the large-particle sand bed, the filtration of the small core decreases greatly, which is due to the small core itself and the fracture opening length being less than 2.5 cm. Compared with 10 cm in the sand bed experiment, the pressure concentration of the core fracture is higher, the filtration channel is greatly reduced, and the corresponding extension length is longer, which objectively reduces the filtration of the drilling fluid and improves the plugging effect.

4.1.5. Full-Size Core Fracture Plugging Evaluation

The evaluation of the full-size core has a better effect on the evaluation of the fracture plugging effect. The full-size core obtained in the field is used indoors, and an artificial fracture is used to split the core into two parts along the fracture direction as far as possible to form a more real fracture. In view of the fact that the full-size core is easy to break under the action of confining pressure, the arc surface of the core is wrapped with metal to form a stable full-size core. An indoor high-temperature and high-pressure simulation plugging device is used to simulate the full-scale core plugging effect under the same temperature and drilling differential pressure as in the field. Furthermore, 1500 mL of plugging slurry and 1500 mL of drilling fluid were used in the experiment, and the simulated temperature was 80 °C. Firstly, plugging slurry was added for rapid filtration, and then 1500 mL of drilling fluid was added. The method of sequential pressurization was adopted, and 1 Mpa was pressurized every 10 min. After 5 Mpa, the pressure was held for 60 min. The plugging effect was observed. The experimental results are shown in Table 4.
The experiment carried out in Table 4 is the same as the experimental device used in the simulation evaluation of the large-particle sand bed. The difference is the difference of the plugging objects. The plugging effects of the two pluggings show little difference, and the filtration of drilling fluid decreases rapidly with the continuation of the pressurization process. There are two main reasons for this phenomenon. First, the original fracture-sealing area is formed at 1 Mpa. With the increase of the pressure exerted by the drilling fluid, the sealing area becomes denser after extrusion, and some high-permeability pores are reduced, reducing the filtration rate. Second, when the applied pressure continues to increase, the pressure makes the drilling fluid enter the pores more deeply, and the filtrate reducer and other treatment agents further reduce the filtration capacity of the plugging area. These two effects objectively reduce the filtration rate of the drilling fluid. After the plugging barrier continues to strengthen to form a high-strength plugging area, the impact of re-pressurization on it is reduced. The fracture pressure of 5 Mpa can meet the needs of most drilling tasks (as shown in Figure 7).

4.1.6. Evaluation of Dual-Core Multi-form Fracture Plugging

The Silurian strata in the Shunbei No. 5 fault zone have many fracture types and forms. It is necessary to evaluate the plugging effects of different types of fractures under the condition of simultaneous existence. In the laboratory, a multi-functional core dynamic displacement evaluation device is used for evaluation, and steel fracture cores with a variety of shapes and widths of 4 mm are made, including Z-shaped, cross-shaped and parallel double fractures, 90° angle double fractures and 45° angle double fractures. The plugging evaluation of double-core multi-angle fractures is evaluated by the same method as in Section 4.1.4 through the combination of multiple cores. In order to more truly simulate the characteristics of formation rocks, steel cores are pasted with 400 mesh sandpaper on the fracture wall to simulate the roughness of fracture walls and control the fracture width to 2–3 mm. The formed steel cores have a certain similarity to the effect of small cores. The experimental results are shown in Table 5. The plugging slurry is quickly filtered out under a pressure of 1 MPa and is no longer shown in the table.
In Table 5, the system’s plugging ability regarding Z-shaped fractures, cross-shaped fractures, parallel double fractures, 90° angle double fractures and 45° angle double fractures is evaluated in pairs, and 5 of the 10 combinations are selected for evaluation. The experimental results show that the plugging of different forms of fractures is completed within 10 min, and the overall plugging effect is good. For different forms of fractures, there are certain differences in plugging time, which has a great relationship with the experimental conditions and the randomness of the plugging particles. However, the fracture morphology basically involves random combinations on the site. In the later stage, if conditions permit, we will try to inspect more fracture morphologies and evaluate the plugging effect for existing conditions, so as to have better representativeness. However, in general, considering various combinations of fracture forms, the plugging system cooperates with the drilling fluid to form a plugging barrier with high strength and shear resistance which can better meet existing plugging requirements.

4.2. Application

Based on the project research, the rapid plugging materials and technology in the Shunbei No. 5 fault zone have been applied in the Shunbei HD1 well. Well HD1 is a horizontal well with a deviation point of 6347 m. During drilling, a pressure-lifting operation was carried out for the well section of 5096–6347 m of the Kepingtag Formation. The open hole section is 1251 m long, and the volume is about 50 m3. The maximum density is 1.58 g/cm3. After the pressure reaches 3.5 Mpa, it is difficult to raise it further. It is required to increase the pressure to more than 17 Mpa, and the equivalent density is increased from 1.51 g/cm3 to 1.8 g/cm3. According to the particle size analysis of the materials used for plugging the previous four times, the first time involved mainly 0.5–1 mm particles, the second time involved mainly 3–5 mm particles, and the maximum-size particles are 10 mm mica sheet particles. According to the plugging situation, it can be inferred that particles more than 5 mm in size entered the leakage joint. During the third plugging construction, it is judged that the leakage layer is near 5720 m, and the existing data indicate that the leakage joint is 5–10 mm in size.
Compared with the plugging slurry used in other fracture formations in Shunbei, such as the chemical gel plugging slurry used in Well 3, according to the situation of cement plug cleaning and pressure testing, the pressure effect of the chemical gel plugging agent is good, and the vertical pressure of the pump is 5 MPa. The result is still different from the sealing pressure capacity of the rapid plugging slurry [11,36].
According to the needs of formation fracture properties, the main plugging agent and filling agent are added to establish a plugging slurry system matching with the fracture: base fluid + 8% micro-elastic high-strength main plugging agent M-Block1 + 4% micro elastic high-strength main plugging agent M-Block2 + 3% micro-elastic high-strength main plugging agent M-Block3 + 10% Filling-Seal. We prepare 100 m3 of plugging slurry and cover the leakage layer from bottom to top (50 m3 in the first stage, covering the 5096–6347 m well section). Intermittent squeeze injection is adopted for shut-in squeezing. The squeeze target pressure value (15 MPa) is calculated according to the required maximum equivalent density, and the squeeze displacement, interval time and pressure increment are controlled. Based on the field plugging slurry effect, after the squeezing reaches the target pressure stabilizing value of 17 MPa, we continue to shut in and hold the pressure for 4~6 h, start the pump for circulation, verify that the plugging pressure reaches 17 Mpa, screen the plugging agent and resume drilling. The plugging is successful, which verifies that the established system has a good plugging effect.

5. Conclusions

(1)
Based on the low-filtration characteristics of the drilling fluid, the plugging slurry prepared with the drilling fluid cannot be quickly filtered after entering the fracture, resulting in a low plugging success rate. The rapid plugging technology uses a special plugging slurry to quickly filter the carrier fluid, and the materials are quickly concentrated to form a high-shear-resistance plugging barrier.
(2)
The main plugging body M-Fluid, micro-elastic high-strength main plugging agent M-Block and Filling-Seal are developed to form a special plugging slurry for the Silurian formation in the Shunbei No. 5 fault zone. With the increase of temperature, the filtration rate of the plugging slurry increases rapidly, and the filtration time decreases rapidly. The filtration rate is approximately 0.31~0.79 mL/s. Combined with the low-filtration property of the drilling fluid, an efficient plugging technology is constructed.
(3)
Various plugging evaluation experiments such as plugging action time, a large-particle sand bed-simulated fracture, small core and full-size core artificial fractures, a dual-core multi-form fracture and so on have been carried out in the laboratory. The experiments show that the pressure-bearing capacity of the plugging barrier exceeds 5 MPa, the pressure-bearing effect is good in field application, and the special plugging technology has a good plugging effect. Finally, the plugging ability for Z-shaped fractures, cross-shaped fractures, parallel double fractures, 90° angle double fractures and 45° angle double fractures was evaluated. The results showed that the plugging system cooperated with the drilling fluid to form a plugging barrier with high strength and shear resistance, which could better meet the plugging requirements.

Author Contributions

The authors confirm contribution to the paper as follows: study conception and design: S.F. and J.F.; data collection: J.F. and Z.H.; analysis and interpretation of results: Y.Y., J.Z. and S.L.; draft manuscript preparation: P.X. and S.F. All authors have read and agreed to the published version of the manuscript.

Funding

The research is supported by the National Natural Science Foundation of China (No. 51804044).

Acknowledgments

The successful completion of the research of the thesis benefited from cooperation between the Sinopec Northwest Oilfield Company and Yangtze University, and the authors are thankful for the support of the two research institutions.

Conflicts of Interest

No conflict of interest exists in the submission of this manuscript, and all authors approve the manuscript for publication. I want to declare on behalf of my co-authors that the work described was original research that has not been published previously and is not under consideration for publication elsewhere, in whole or in part. All the authors listed have approved the manuscript that is enclosed.

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Figure 1. Types and characteristics of leakage layers in the Shunbei No. 5 fault zone.
Figure 1. Types and characteristics of leakage layers in the Shunbei No. 5 fault zone.
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Figure 2. Schematic diagram of different plugging methods. (a) Drilling fluid plugging; (b) Plugging with special plugging agent.
Figure 2. Schematic diagram of different plugging methods. (a) Drilling fluid plugging; (b) Plugging with special plugging agent.
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Figure 3. Structure and function diagram of alkyl glycoside.
Figure 3. Structure and function diagram of alkyl glycoside.
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Figure 4. Micro-elastic high-strength main plugging agent: M-Block.
Figure 4. Micro-elastic high-strength main plugging agent: M-Block.
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Figure 5. Filling agent: Filling-Seal.
Figure 5. Filling agent: Filling-Seal.
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Figure 6. Change of loss reduction rate of plugging slurry with increasing pressure.
Figure 6. Change of loss reduction rate of plugging slurry with increasing pressure.
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Figure 7. Change of loss reduction rate of plugging slurry with increasing pressure.
Figure 7. Change of loss reduction rate of plugging slurry with increasing pressure.
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Table
Table 1. Filtration time of quick plugging slurry and drilling fluid.
Table 1. Filtration time of quick plugging slurry and drilling fluid.
Liquid TypeTemperature (°C)Filtration Time (s)Filtration Loss (mL)Filtration Rate (mL/s)
Quick plugging slurry15784850.11
40487850.17
80273850.31
120124850.69
160107850.79
Drilling fluid1201800120.0067
Table
Table 2. Evaluation of sand bed-simulated fracture plugging.
Table 2. Evaluation of sand bed-simulated fracture plugging.
Compression (Mpa)Action ProcessLoss of Plugging Slurry or Drilling Fluid (mL)
1The plugging slurry is pressurized at 1 Mpa to quickly filter out.The plugging slurry is filtered
1The drilling fluid is pressurized at 1 Mpa, and the filtration is stopped for 6 min.36
2The drilling fluid is pressurized at 2 Mpa, and the filtration is stopped for 4 min.14
3The drilling fluid is pressurized at 3 Mpa, and the filtration is stopped for 2 min.7
4The drilling fluid is pressurized at 4 Mpa, and the filtration is only a very slow drop.≈1
5The drilling fluid is pressurized at 5 Mpa, only a small amount of droplets are suspended at the outlet, the pressure is stable for 60 min, and there is no re-filtration.≈0
Table
Table 3. Core dynamic plugging evaluation.
Table 3. Core dynamic plugging evaluation.
CoreCompression (Mpa)Plugging EffectCumulative Drilling Fluid Filtration (mL)
C23-11Rapid loss of plugging slurryThe plugging slurry is filtered
5184 s drilling fluid filtrate stopped flowing out14
C23-21Rapid loss of plugging slurryThe plugging slurry is filtered
5215 s drilling fluid filtrate stopped flowing out17
Table
Table 4. Fracture plugging evaluation of full-size core.
Table 4. Fracture plugging evaluation of full-size core.
Compression (Mpa)Action ProcessLoss of Plugging Slurry or Drilling Fluid (mL)
1The plugging slurry is pressurized at 1 Mpa to quickly filter out.The plugging slurry is filtered
1The drilling fluid is pressurized at 1 Mpa, and the filtration is stopped for 8 min.114
2The drilling fluid is pressurized at 2 Mpa, and the filtration is stopped for 6 min.46
3The drilling fluid is pressurized at 3 Mpa, and the filtration is stopped for 6 min.18
4The drilling fluid is pressurized at 4 Mpa, and the filtration is stopped for 92 s.3
5The drilling fluid is pressurized at 5 Mpa, only a small amount of droplets are suspended at the outlet, the pressure is stable for 60 min, and there is no re-filtration.≈0
Table
Table 5. Fracture plugging evaluation of full-size core.
Table 5. Fracture plugging evaluation of full-size core.
Experiment NoFracture MorphologyCompression (MPa)Plugging EffectCumulative Drilling Fluid Filtration (ML)
1Zigzag5353 s drilling fluid filtrate stops flowing out64
Cross-bonding5281 s drilling fluid filtrate stops flowing out32
2Parallel double crack5215 s drilling fluid filtrate stops flowing out20
Cross-bonding5267 s drilling fluid filtrate stops flowing out29
3Zigzag5367 s drilling fluid filtrate stops flowing out78
45° angle double crack5248 s drilling fluid filtrate stops flowing out35
4Parallel double crack5169 s drilling fluid filtrate stops flowing out15
90° angle double crack5227 s drilling fluid filtrate stops flowing out23
545° angle double crack5221 s drilling fluid filtrate stops flowing out27
90° angle double crack5194 s drilling fluid filtrate stopped flowing out24
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He, Z.; Fan, S.; Fang, J.; Yu, Y.; Zhang, J.; Li, S.; Xu, P. Research and Application of Fast Plugging Method for Fault Zone Formation in Tarim Basin, China. Energies 2023, 16, 4330. https://doi.org/10.3390/en16114330

AMA Style

He Z, Fan S, Fang J, Yu Y, Zhang J, Li S, Xu P. Research and Application of Fast Plugging Method for Fault Zone Formation in Tarim Basin, China. Energies. 2023; 16(11):4330. https://doi.org/10.3390/en16114330

Chicago/Turabian Style

He, Zhong, Sheng Fan, Junwei Fang, Yang Yu, Jun Zhang, Shuanggui Li, and Peng Xu. 2023. "Research and Application of Fast Plugging Method for Fault Zone Formation in Tarim Basin, China" Energies 16, no. 11: 4330. https://doi.org/10.3390/en16114330

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