Fuzzy-Ball Fluids Enhance the Production of Oil and Gas Wells: A Historical Review

Abstract

Advancements in drilling technology are pivotal to optimizing the production and sustainability of oil and gas wells. One of the emerging innovations is the application of a specialized fluid known as “Fuzzy-ball” fluid. This paper comprehensively reviews the historical evolution and advancements in the utilization of fuzzy-ball fluid in drilling and well-repair processes. Fuzzy-ball fluid has been discovered to bolster a formation’s pressure-bearing capabilities and systematically augment resistance against oil, gas, and water flow. These attributes have been instrumental in the phased integration of fuzzy-ball fluid into procedures aiming to enhance production in oil and gas wells. This paper bridges the knowledge gap in the industry regarding the application of fuzzy-ball fluid, thereby circumventing the challenges of inadequate understanding and suboptimal designs. However, the study acknowledges the potential limitation of information loss despite the extensive data collection from diverse sources, such as articles, patents, and reports. As a future direction, this paper emphasizes the need for a more encompassing and critical evaluation of fuzzy-ball fluid’s performance and applications. This will enable a more informed decision-making process, fostering the expanded use and understanding of this fluid’s mechanism within the industry.

1. Introduction

In 2006, a study on reservoir damage mechanisms in the Wenchang oilfield revealed that one of the critical factors causing damage to reservoirs during extraction was the loss of drilling fluids in the well-repair process [1]. At that time, it was widely believed that reducing the density of drilling fluids could decrease fluid loss, consequently minimizing reservoir damage and mitigating production losses. However, due to the nature of offshore operations, the repair process could not employ the use of fluids that required ancillary equipment, such as inflatable devices or foams. The pressure-bearing capacity of recyclable foam was found to be suitable for wells deeper than 2000 m [2]. As a result, the concept of developing foams with higher pressure resistance was proposed. However, it was discovered through experimentation that simply enhancing pressure resistance was not sufficient. Integrating aspects such as density and stability to create a functional working fluid proved to be considerably challenging [3].

Numerous experiments were conducted, many of which failed. A casual discussion about cells and why they do not rupture led to a breakthrough. The structure of cells suggested the possibility of achieving a balance between fluidity and stability requirements. After three years of diligent efforts, foams with enhanced pressure resistance were developed. The bubbles in these foams had a polyhedral structure with plateau borders between the air pockets, with sizes ranging from 1 to 10 mm. Micro-foams, on the other hand, did not have plateau borders and had sizes ranging from 10 to 100 µm. The newly developed bubbles also lacked plateau borders, and their sizes ranged from 10 to 100 µm, rendering them visibly different from conventional drilling fluids.

Figure 1 shows the developed bubble structure and fluid system. As can be seen, the new fluid consists of a polymer colloid formed by macromolecules dissolved in water and the bubbles dispersed therein. The bubble that is developed is encapsulated so thickly that it resembles a ball, which is referred to here as a “ball” bubble. These balls have fuzzy extensions dispersed in the polymer colloid and conform to the Fuzzy Sealaplug Law. This law states that balls of a certain size range can block the flow channels of a specific range. As a result, these balls were named fuzzy-balls, and the fluid was named fuzzy-ball fluid [4]. Further research indicated that fuzzy-balls possess a structure with a “single core, dual layers, and triple membranes” at the microscopic level. Furthermore, these fuzzy-balls are sealing materials formed naturally through the physicochemical processes of foam surfactants and stabilizing polymers dissolved in the base fluid of fuzzy-balls. They come into existence due to interfacial tension, hydrophobic associative forces, intermolecular forces, and other forces [5].

On 8 June 2009, fuzzy-ball fluids were successfully employed in a horizontal well at a depth of 2500 m to achieve leak prevention and plugging. The pressure-bearing capacity was validated using downhole pressure gauges. Patents were applied for the treatment agents and formulation methods, and the technology was subsequently promoted for use in coalbed methane extraction [6].

Field applications have demonstrated that fuzzy-ball drilling fluids maintain stable downhole density [7] and effectively prevent cave-ins and leakage using adhesive technology. Moreover, due to their low density [8], substantial preparatory work was undertaken for field applications. This enabled the completion of various coalbed methane drilling projects and oil and gas well repairs, and both indoor and outdoor reservoir damage tests showed lower damage rates [9,10]. The fluids also exhibited excellent thermal resistance, resistance to high mineralization levels, and stability under exposure to hydrogen sulfide [11]. Additionally, fuzzy-ball fluids were environmentally friendly [12]. These impressive attributes indicated promising prospects for the development of biomimetic technology [13]. Consequently, the fluids were also used in the subsequent combined extraction of three gases and were evaluated for reservoir damage levels [14].

Due to the breakthrough in pressure-bearing capacity, in 2009, two wells in the Jidong oilfield were chosen for testing. After temporary plugging with fuzzy-ball fluids, Well A’s pressure-bearing capacity increased by 6 MPa, allowing for successful fracturing and well completion. Well B underwent secondary well completion with cement squeezing as a pre-flush. Post-operation, Well A showed a reduction in water content compared to adjacent wells, and Well B demonstrated excellent quality in cement sheath integrity after the plugging. This marked the beginning of fuzzy-ball fluids’ journey in enhancing oil and gas production rates and reducing water production through fluid loss control [15].

The Main works studying fuzzy-ball drilling fluid in the last 20 years are shown in

Table 1. Main works studying fuzzy-ball drilling fluid in the last 20 years.

No.	Year	Main Works	Remark
1	2010	Conducted static plugging test for coalbed methane rock cores using KCl and fuzzy-ball drilling fluids	Fuzzy-ball drilling fluid achieved better results than KCl solution on plugging behavior
2	2010	Tested the plugging ability of fuzzy-ball fluid on multiple permeable cores and packed sand	Demonstrated the wide applicability of fuzzy-ball fluid for plugging pore spaces with various pore sizes and permeabilities
3	2012	Applied fuzzy-ball fluid in a multilateral horizontal well for coalbed methane	Successful application in a complicated horizontal well for coalbed formation and efficient prevention of fluid loss in circulation
4	2013	Applied fuzzy-ball fluid for U-type drilling wells	Proved the excellent working properties of fuzzy-ball fluid for solving problems in U-type coalbed methane wells
5	2016	Performed field pollution assessment	Demonstrated fuzzy-ball drilling fluids
6	2018	Conducted rock mechanism test and core plugging test using various drilling fluids	Gave the systematic geo-mechanism of applying fuzzy-ball fluid in drilling
7	2020	Performed laboratory test for heterogeneous rock samples	Proved that fuzzy-ball fluid displays higher oil recovery than conventional polymer and surfactant fluids
8	2023	Core flooding test for studying damage control mechanism and formation damage of fuzzy-ball fluid	Discovered that fuzzy-ball fluid has good performance in damage control in single- and double-layer tight reservoirs

.

Lihui, Shangzhi, and Zhongfeng studied the plugging performance of fuzzy-ball drilling fluid on coalbed methane cores in a laboratory and found that it had a stronger ability to control formation damage compared to 3% KCl solution. They displayed the micro structures of a single fuzzy-ball bubble and explained the plugging mechanisms for various porous media. Zixuan investigated the plugging ability of fuzzy-ball fluid in packed sands and reservoir rock cores with various pore sizes and permeabilities, such as 0.5, 80, 300 mD. Meanwhile, they changed the density of the fluid from 0.85 to more than 1.0 g/cm³. So that it was able to be applied to different formation pressures for preventing circulation loss and formation damage. Meng, Dou, Liu, and Sun adopted the fuzzy-ball drilling fluid to solve the issue of severe circulation loss during well drilling and completion for coalbed formations. The multilateral horizontal well had five branch holes where it was easy to encounter coal formation collapse and drilling fluid loss in the well. After using fuzzy-ball drilling fluid, the rate of circulation loss was well controlled to 2 m³/h, and the five branch holes were successfully completed. Guo, Zheng, Meng, and Zhang extended the field application of fuzzy-ball fluid to U-type drilling wells and claimed that after applying the fuzzy-ball drilling fluids, the rate of penetration was increased by 10% and the problems of well-bore stability and cutting carrying were efficiently tackled.

Xuanqing, Lihui, Yuwei, and Siwen tested six pollution indexes in drilling fluid waste from field wells, including pH, chrominance, total suspended matter, biochemical oxygen demand, chemical oxygen demand, total chromium, and hexavalent chrome, and found that fuzzy-ball fluid showed excellent performance in solidifying technology and was friendly to the environment. Zheng, Su, Li, Peng, Wang, Wei, and Han conducted uniaxial and triaxial compressive tests for coal rock samples after using fuzzy-ball fluid to plug the samples and compared the results with KCl and polymer fluids. They realized that the fuzzy-ball fluid could increase the core strength from 2.6 to 3.6 MPa, which KCl and polymer fluids could not reach. Meanwhile, they demonstrated the high plugging properties of fuzzy-ball fluid via in situ applications in a coalbed methane reservoir. Therefore, they proposed a systematic explanation of fuzzy-balls in wellbore stability via the bonding formation of fuzzy-balls in the pore space. Wei, Zheng, Yang, Wang, Chang, and Zhang investigated the effect of rock heterogeneity on the plugging behavior of fuzzy-ball fluid. They injected the fuzzy-ball fluid into four artificial cores with a permeability range of 200~1200 mD and into two cores with parallel heterogeneous permeabilities. The results showed that fuzzy-ball fluid filled high-permeable pore space first and then the low-permeable pore region due to its variable ball size and vesicle structure, which led to a higher oil displacement efficiency than the conventional polymer and surfactant fluids. Okere, Sheng, Fan, Huang, Zheng, and Wei evaluated the permeability and flow-rate index for single- and double-layer rock samples after using fuzzy-ball flooding. They noticed that fuzzy-ball fluid could be used for efficiently preventing or controlling the formation damage in the near-wellbore area. Furthermore, they established the formation damage mechanism for tight gas reservoirs with multiple formation layers in China.

We observed the effective blocking and seepage behavior of fuzzy-ball fluid at the pore scale using glass microfluidics and explained the microscopic blocking mechanism for water-based fuzzy-ball fluid. The blockage of fuzzy-balls was because of the wide average range of fuzzy-ball sizes, from 100 to 200 µm, and their deformable structure to fit various pore and throat diameters, which provided their capability for enhanced oil recovery compared with polymer flooding. Wang et al. [16] gave a further microscopic investigation of the enhanced oil recovery induced by fuzzy-ball fluid. They proposed a mechanism in three aspects: emulsification during fuzzy-ball flooding, a squeezing–carrying mechanism for columnar oil, and specific entanglement due to the floss structure of the fuzzy-ball. We discussed the anti-collapse mechanism of using fuzzy-ball working fluid for coalbed methane reservoirs. Based on the uniaxial geo-mechanism test for the coalbed samples, the fuzzy-ball increased rock strength by 38.46% and demonstrated an outstanding capacity for stretch and blockage. From the in-situ application, the fuzzy-ball fluid successfully prevented circulation loss and strengthened the wellbore stability. Further, the density of the fuzzy-ball fluid was easily changed from 0.5 to 1.5 g/cm³, which efficiently equaled the circulation density to avoid formation fracture.

The outline of this paper is summarized as follows: Section 2 introduces the functions of fuzzy-ball working fluid and its applications in the wide aspects of reservoirs; Section 3 provides the gap of using fuzzy-ball fluid in field application and our solutions to tackle these issues; Section 4 lists the conclusions and recommendations.

2. Enhancing Oil-Well Production through the Utilization of Fuzzy-Ball Fluid

Increasing the production of oil and gas wells requires extensive in-lab research before field application. Zheng et al., based on numerous experiments, posited that there are three possible mechanisms through which fuzzy-ball fluid can plug leakage pathways, namely the diversion-pressure, pressure-consumption, and supporting-pressure mechanisms [17]. These insights have provided answers as to why the fluid has proven to be effective in leak prevention and plugging. After well-repair operations, Zhang Yuan noted that the use of fuzzy-ball fluid not only addressed the issues of severe leakage in the well adjustment and repair stages at the offshore SZ36-1 oilfield but also resulted in an increase in oil production and a decrease in fluid production [18].

Similarly, in the Ordos Basin, during well repairs of the Lower Paleozoic carbonate rock low-pressure gas wells that faced severe formation leakage, the use of fuzzy-ball fluid in four wells demonstrated comparable gas production levels and a significant reduction in water production as compared to the pre-operation phase. This suggests that fuzzy-ball fluid can stabilize gas and control water during well-repair operations.

The success stories in addressing operational challenges have led to the discovery of new effects, leading to further applications. The pressure-bearing and water-plugging properties of fuzzy-ball fluid have hinted at its potential application in fracturing for water control.

2.1. Example of Fuzzy-Ball Plugging Enhancing Fracturing Effects

The low density of fuzzy-ball fluid is believed to address leak prevention and plugging in coalbed methane drilling. Experimental attempts were made to control leakage during the coalbed methane drilling process using fuzzy-ball fluid [19]. Subsequent research in the Qinshui Basin found that fuzzy-ball fluid, despite its low density, prevented collapse during coalbed methane drilling and was attributed to an increase in rock strength [20]. This led to the proposal of its use in directional fracturing and the introduction of the concept of steering angle [21].

Zheng Lihui and colleagues conducted non-damaging fracturing of the original seams in well LH-1 using fuzzy-ball fluid. The downhole production string of well LH-1 is presented in Figure 2. Well LH-1 is a vertical well with an original artificial well-bottom depth of 1667 m and a borehole diameter of 177.8 mm. The estimated bottom-hole temperature was 76.678 °C, proving that fuzzy-ball fluid was capable of temperature resistance. The plugging operation using fuzzy-ball fluid without changing the existing downhole production string and fluid consumption were calculated to be 14 m³ according to the plugging radius, which met the economic requirements.

Figure 3 shows the production dynamics before and after non-damaging fracturing. Compared to the 30 days before fracturing, the average daily oil production and fluid production increased by 119.2% and 48.7%, respectively, and the average water content decreased by 7.5% in the 60 days following the fracturing, demonstrating that the fuzzy-ball fluid could control the water cut and increasing oil production, and the non-damaging fracturing operation was successful.

Additionally, it was noted that the injection pressure at the wellhead was not high, indicating that the plugging was not too extensive and, thus, not overburdening the wellhead. The fluid’s performance led to the hypothesis that it could plug water without affecting gas production. After continuous testing in ten wells in the Liaohe oilfield, it was found that some wells did not experience a gas reduction, which raised questions regarding the fluid’s selectivity in plugging water but not gas [22].

In 2016, a fracturing technique based on fuzzy-ball temporary plugging fluid was successfully tested in well Zheng X, where a new fracture with a steering angle of 55° was monitored, providing the first field verification of the feasibility of fuzzy-ball temporary plugging and steering [23].

2.2. Acidization/Fracturing to Enhance Well Productivity

To increase the production of carbonate rock gas wells, Wen Zhehao and colleagues utilized fuzzy-ball fluid for repetitive acidization of well GX-3. The wellbore structure and downhole string of well GX-3 are shown in Figure 4. As can be seen, well GX-3 is a vertical well with a total depth of 3557 m and a casing depth of 3574.29 m. It can be inferred that the temperature at the artificial well bottom was 127.31 ℃, which in turn suggests that the fuzzy-ball fluid was well-tolerant to that temperature. During the operation, fuzzy-ball fluid preferentially entered and sealed the original fracture’s high-conductivity wormholes, allowing subsequent acid to flow into the un-acidized formation. The site-specific process involved injecting 110 m³ of fuzzy-ball fluid in a recirculating manner to seal the hypertonic channel, followed by 6.5 m³ of hydrochloric acid solution, which was left in place for 7 h, drained, and production resumed.

Figure 5 shows the gas production index before and after the temporary acidizing operation of well GX-3. As can be seen, upon resuming production, the daily gas production increased from 5 to 7 × 10⁴ m³, an increase of 40%; the cumulative gas production in 100 days increased from 465.28 to 612.15 × 10⁴ m³, an increase of 31.57%. Therefore, fuzzy-ball fluids offer an effective method for repetitive acidization in carbonate rock reservoirs.

Fuzzy-ball fluid, a non-solid-phase fluid developed for oil and gas wells under the guidance of fuzzy plugging theory, operates through diversion-pressure, pressure-consumption, or supporting-pressure mechanisms to plug the leakage zones. With the introduction of fuzzy-ball technology to fracturing operations, fuzzy-ball-diverting agents were developed for temporary plugging of the original fractures. With a pressure-bearing capacity of 25 MPa and a permeability recovery rate exceeding 85%, the diverting agent has proven to have a strong plugging ability and low reservoir damage, which has been well-received in field applications.

Jiang Jianfang and colleagues studied the temporary plugging and steering effects of fuzzy-ball fluid in deep wells within carbonate rocks [24]. The results showed that after injection into the formation, fuzzy-ball fluid altered the mechanical properties of the rocks, increasing their toughness and deformability. Moreover, the fluid sealed the fractures, and once the net pressure exceeded the differential horizontal stress, the fracture was diverted. This clearly defines the adaptability of fuzzy-ball temporary plugging agents in deep carbonate rock reservoirs for steering fracturing. The THX well underwent acid fracturing using the fuzzy-ball temporary plugging and acid-pressuring technique, creating high-flow-capacity artificial fractures to communicate between oil and gas accumulation spaces, thereby improving underground oil and gas recovery. After the implementation of fuzzy-ball temporary plugging and steering fracturing in 2017, the daily average oil production increased from 4.02 to 14.10 tons, and the daily average gas production increased from 9.56 to 63.1 m³, increases of 3.5 times and 6.6 times, respectively, in oil and gas production [25].

2.3. Stabilizing Oil Production and Controlling Water Influx in Oil and Gas Wells Using Fuzzy-Ball Fluids

Fuzzy-balls have the function of stabilizing oil production and controlling water, which is derived from the detection of blocking effects in practical applications. In order to further clarify this function, the researchers verified this function of fuzzy-balls through laboratory experiments, theoretical mechanism inference, and field application and analyzed and summarized the effects of these three parts. Recent research has examined the feasibility of using fuzzy-ball fluids in oil and gas wells for stabilizing oil production and controlling water influx.

Laboratory simulation trials indicated that in on-site wells with mineralization degrees of 80,000 mg/L and 40,000 mg/L, the fuzzy-ball fluids remarkably augmented daily oil production by 6200% and 180%, respectively [26].

Zheng proposed three conceivable mechanisms by which fuzzy-ball fluids could obstruct leakage pathways, all grounded in thorough experimentation: the pressure -differential mechanism, the pressure-consumption mechanism, and the pressure-support mechanism. When fuzzy-ball fluid encounters a leakage pathway larger than its own size, the fluid, due to its Bingham plastic characteristics at lower shear rates, accumulates and dissipates the displacement pressure. Concurrently, the reservoir temperature triggers the expansion of the fuzzy-ball, consequently filling the flow channels and forming a robust sealing structure. Should the fuzzy-ball enter leakage channels of similar size, it gravitates towards the low-pressure zone due to the pressure differential. As it approaches the leakage pathway, it elongates and is drawn into the pathway by the low pressure, subsequently filling it and augmenting the flow resistance for the following fuzzy-ball fluid. Formation temperature ensures a sturdier solid filling by the fuzzy-ball. When fuzzy-ball fluid navigates channels smaller than its size, the fluid velocity diminishes, displaying a higher apparent viscosity at lower shear rates and, hence, elevating the flow resistance [27].

The application of fuzzy-ball fluid was first tested during the workover of well C22 in the SZ36-1 oilfield. The wellbore structure and downhole string of well C22, as depicted in Figure 6, reaches a depth of 7707 m, with an estimated bottomhole temperature of 237.756 ℃, presenting a significant challenge to the temperature resistance of the fuzzy-ball fluid. In accordance with the plugging radius, 50 m³ of fuzzy-ball fluid was prepared on site. The operation witnessed no fluid loss, and the well was successfully repaired, thereby corroborating its exceptional temperature resistance.

Figure 7 presents the production item for well C22 before and after well repair. After the well-repair operation, the liquid production decreased from 251 to 217 m³/d, a decrease of 13%; the crude oil production increased from 49 to 67 m³/d, an increase of 37%; the water cut decreased by 12%, from 80% to 68%; and the gas production decreased from 105 to 102 m³/d, remaining almost unchanged. Therefore, synthesizing all the above production items, fuzzy-ball fluid demonstrates an excellent capability of descending liquid, increasing oil, controlling water, and stabilizing gas.

Zhao Zhihui [28] implemented the use of fuzzy-ball fluid in a water shutoff operation addressing the issue of severe heterogeneity and low displacement efficiency during water flooding in the Gao Sheng oilfield. After the operation with fuzzy-ball fluids, the comprehensive water cut was reduced by approximately 24%, and cumulative incremental oil production reached 794.6 tons.

In response to the serious water production problem in deep coalbed methane wells in the Linxing area, fuzzy-ball fluid was used in water shutoff operations. Following the operations, the daily water production declined from 82.97 m³ to 42.03 m³, while daily gas production increased from 300 m³/d to 394 m³/d, demonstrating the effectiveness of fuzzy-ball fluid in stabilizing gas production and controlling water [29].

Given the specific reservoir characteristics of the Linxing gas field, termed as “four lows, two highs, one strong”, fuzzy-ball fluid was utilized for water-control fracturing. After injection of the fuzzy-ball fluid, the breakthrough pressure gradients of gas and water in fractures and the matrix were 0.02 MPa/cm and 0.03 MPa/cm, respectively, while for water, they were 0.04 MPa/cm and 0.2 MPa/cm. This suggests that after injecting fuzzy-ball fluid, the breakthrough pressure gradient of water in fractures and matrices surpasses that of gas, thus facilitating water shutoff without impeding gas flow.

2.4. Enhancing Oil and Gas Production through Deep Displacement Control

In 2020, Wei Panfeng conducted experiments with artificial homogenous sandstone as the test material. Through single-core flooding experiments, they investigated the efficacy of surfactants, polymers, and fuzzy-ball fluids in enhancing oil recovery after water flooding. The results showed that after water flooding, injection of a 0.6 pore volume of surfactant increased oil recovery by 7.27–8.41% and polymers by 10.03–11.25%, while fuzzy-ball fluid boosted the recovery by 22.16–28.13%. Compared to surfactants and polymers, fuzzy-ball fluids demonstrated superior performance.

In the Qi Dong 1 area of the Karamay oilfield in Xinjiang, field tests with fuzzy-ball fluids were conducted. Fuzzy-ball fluids exhibited remarkable profile control and enhanced oil recovery effects. After the displacement of fuzzy-ball fluids in the four affected wells of well TX, the daily fluid production in high-permeability layers declined within the range of 11.24–88.25%, while that in the low-permeability layers increased by over 200%. In the four affected wells of well TY, the daily fluid production in high-permeability layers declined within the range of 67.88–73.70%, while in the low-permeability layers, it increased by over 300%. This implies that the injection of fuzzy-ball fluids effectively sealed high-permeability layers, causing a subsequent fluid flow to divert more towards the low-permeability layers, thereby increasing the average daily oil production of the four affected wells in both TX and TY by 64.15% and 17.74%, respectively.

The variations in daily oil production from the four wells are detailed in Figure 8. The trend in overall oil production can be divided into four phases. During the first phase, oil production increased significantly in well 748 and decreased slightly in well 719, resulting in a fluctuating increase in overall oil production. Seven days after the injection of fuzzy-ball fluid, the second phase was entered, and the oil production of the four wells stabilized. Among them, well 748 had the highest oil production of 4.73 t/d, which accounted for 62% of the total oil production. After stable production up to the 13th day, the oil production of well 748 suddenly decayed, while the oil production of wells 734 and 719 displayed intermittent changes, resulting in fluctuating changes in the overall oil production, and this is the third phase. After the 23rd day, they entered the fourth phase, in which the overall oil production stabilized at 12.62 t/d. During this phase, well 734 had the highest production contribution of 44%, followed by well 948 with 28%, while wells 719 and 732 had the lowest production contribution of 14%.

Experiments indicated that fuzzy-ball fluids significantly enhanced oil recovery post-water flooding compared to surfactants and polymers. Field tests in the Karamay oilfield revealed that the injection of fuzzy-ball fluids sealed high-permeability layers and diverted fluid flow towards low-permeability layers, increasing the average daily oil production of the tested wells. A detailed analysis of the daily oil production from four wells showed a pattern of initial increase, stabilization, fluctuation, and final stabilization in oil production after the injection of fuzzy-ball fluids. Lastly, laboratory studies confirmed that fuzzy-ball fluids improved low-permeability core recovery rates by over 35% and overall core recovery rates by over 11% compared to surfactants and polymers [30].

3. Limitations in Application and Progress in Solutions

3.1. Limited Studies on Pressure Capacity Impacting Fracturing and Acid-Squeezing Operations

The mechanism of fuzzy-ball fracturing involves a process of enhancing and toughening the fracturing mechanism. However, systematic customization has not been explicitly established. Jiang (2019) conducted experiments to evaluate rock mechanics before and after injecting fuzzy-ball plugging agents to determine their adaptability in deep carbonate reservoirs during diverted fracturing [24]. This was the first assessment of fuzzy-ball plugging agents used for temporary plugging acidification in carbonate rock deep wells. Yang (2021) carried out experiments and applications of a novel fuzzy-ball fracture-height-control technology [29]. By optimizing the composition of the fuzzy-balls, they were able to control the fracture height, which helped avoid communication with the water layer and reduce ineffective proppant support longitudinally. The studies mentioned above contribute valuable insights into the efficiency and effectiveness of fuzzy-ball fluids in fracturing operations. Jiang highlighted their adaptability in diverted fracturing, which previously lacked systematic evaluation. These advancements indicate a promising direction for enhancing the efficiency of fracturing and acid-squeezing operations using fuzzy-ball fluids. However, it is important to note that the existing research is limited, and there is a significant need for comprehensive studies to establish systematic customization and optimization of fuzzy-ball fluids for varying reservoir conditions and operational requirements.

3.2. Limited Studies on Key Factors Influencing Fluid Resistance and the Design of Water Techniques for Gas Control

A summary of the advantages and limitations observed in field extraction is essential. Meng (2021) evaluated the water-control effects of fuzzy-ball fluids in the Linxing area by investigating deep coalbed methane wells during a trial mining process [31]. The study showed that fuzzy-ball fluids increased the flow resistance of both water and gas, but the increase in water resistance was more significant, enabling water control. The unsatisfactory production of gas wells after water plugging could be due to insufficient gas production capacity of the formation or the irrational use of fuzzy-ball fluids. Therefore, it is necessary to adjust the properties of the fuzzy-ball fluid system and the amount of plugging agent to increase the breakthrough pressure of formation water for steady gas control.

Wei (2022) experimented on fuzzy-ball-fluid water control in a gas reservoir [32]. The one-dimensional core displacement experiment was performed with fuzzy-ball fluids, and the water-control effect was evaluated. Furthermore, nuclear magnetic resonance experimental methods were used to analyze the water-control mechanism of fuzzy-ball fluids from a micro-pore-structure perspective, providing a theoretical basis for water control in fuzzy-ball-fluid gas reservoirs.

3.3. Study on Flow Efficiency in Oil and Gas Water Channels and Its Effect on Enhanced Oil-Recovery-Process Design

Investigating the mechanism to improve application accuracy is essential. Research on the flow characteristics of fuzzy-ball fluids in porous media, the effect of fuzzy-ball fluids in enhancing recovery rates, and the optimization of field techniques is required.

The main mechanisms of fuzzy-ball-fluid oil displacement include emulsification, squeezing, wedging, and entanglement. In fuzzy-ball base fluids, emulsification is the primary mechanism, as they contain surfactants such as dodecyl dimethyl amine oxide and dodecyl sulfonic acid sodium, which can emulsify crude oil into droplets of varying sizes, thereby enhancing oil displacement efficiency. Fuzzy-ball structure, being highly deformable, can effectively squeeze residual oil columns, films, and blind ends and carry away the small oil droplets from their original regions. The fuzzy structure of the fuzzy-balls exerts a force between the fuzzy-ball and the core pore walls, gradually wedging into the oil film and reducing the interaction force between the oil film and the core pore walls. This enhances the oil displacement efficiency.

Fuzzy-ball fracture-height-control technology can regulate the fracture height in fracturing operations and is useful in avoiding issues like fuzzy-ball temporary plugging for diverted fracturing. The mechanical mechanism of fuzzy-ball-fluid-diverted fracturing was studied based on tight sandstone formations, which helps enhance the applicability of fuzzy-ball temporary plugging for diverted fracturing technology in tight sandstone formations [33]. Whether this mechanical mechanism applies to other formations and the relationship between the new fracture extension morphology and the fuzzy-ball fluid properties and construction parameters needs further research.

Hydraulic fracturing often requires fracture-height control. Through the optimization of fuzzy-ball components, it is possible to control the fracture height with fuzzy-ball fracture-height-control products, avoiding communication with water layers and reducing ineffective proppant support longitudinally. Fuzzy-ball fracture-height-control technology holds significant research value and application prospects.

In summary, fuzzy-ball fluids, due to their unique structure and mechanisms, can be applied to various enhanced extraction techniques with relatively good results, offering new alternatives for extraction fluids. However, research and field applications concerning fuzzy-ball fluids are still not sufficient and need further investigation for process optimization and efficiency improvement.

4. Conclusions and Recommendations

(1) This review sequentially retraces the advancements in the application of fuzzy-ball fluid in drilling and well-repair processes. Particularly, this fluid has been found to enhance a formation’s pressure-bearing capacity and incrementally increase the resistance to oil, gas, and water flow. Among these advancements, fuzzy-ball fluid increased production by 22.16–660%, water production decreased by 7.5–88.2%, and rock strength increased by 10–38.4% in different areas. Consequently, its incorporation into procedures aimed at augmenting production in oil and gas wells has evolved progressively. This methodical exposure addresses the industry-wide challenge where peers lack a comprehensive understanding of drilling fluid applications, often leading to incomplete knowledge and sub-optimal designs. The insights presented here are poised to facilitate the expansion of fuzzy-ball fluid applications and foster research into their underlying mechanisms.

(2) Despite extensive data collection encompassing articles, patents, project research reports, and on-site application reports, there is a possibility of information loss. Therefore, some assertions within this paper might appear to be arbitrary or one-sided, which could potentially mislead the readers.

(3) As a future direction, there will be a concerted effort to holistically supplement and refine the information within this paper. This is aimed at providing the readers with a more comprehensive overview of the performance and applications of fuzzy-ball fluid, ultimately supporting more informed decision-making.