Fuzzy-ball Fluid Research Articles

Plugging Efficiency in Fractured Carbonate Gas Reservoirs Using Fuzzy-Ball Fluids Combined with Solid Plugging Agents

Loss encountered during workover operation is a common challenge in the development of fractured carbonate gas reservoirs. Fuzzy-ball fluid, a non-solid phase plugging material developed based on Fuzzy Sealaplugging Theory, has been widely used in killing the well. However, in the plugging of fractured carbonate gas reservoirs, a substantial volume of Fuzzy-ball fluid is required and the pressurization process is time-consuming, which greatly impairs its application. In this study, solid plugging agents including calcium carbonate and fibers are introduced into Fuzzy-ball fluids to improve the plugging efficiency of large-scale macro-fractures. In particular, the plugging performance was evaluated by the indoor plugging of a synthetic core containing a 5 mm wide wedge-shaped fracture, as well as by field trials in two wells. The results show that the plugging ability of the new fluid increases as the concentration of calcium carbonate or fiber increases. Moreover, a more significant enhancement of plugging efficiency was achieved by fibers. In field applications, the use of Fuzzy-ball fluids with calcium carbonate or fibers reduced the volume of fluid consumed by 33~74% and decreased the pressurization time by 33~69%. Therefore, by combining solid plugging agents with Fuzzy-ball fluids, the dual demand for plugging efficiency and cost-effectiveness for fractured carbonate gas reservoirs is achieved simultaneously, which provides an alternative technique for addressing fluid loss in fractured carbonate gas reservoirs.

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

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.

Experimental study on the degree and damage-control mechanisms of fuzzy-ball-induced damage in single and multi-layer commingled tight reservoirs

Fuzzy-ball working fluids (FBWFs) have been successfully applied in different development phases of tight reservoirs. Field reports revealed that FBWFs satisfactorily met all the operational and reservoir damage control requirements during their application. However, the damage-control mechanisms and degree of formation damage caused by fuzzy-ball fluids have not been investigated in lab-scale studies so far. In this study, the degree of fuzzy-ball-induced damage in single-and double-layer reservoirs was evaluated through core flooding experiments that were based on permeability and flow rate indexes. Additionally, its damage mechanisms were observed via scanning electron microscope and energy-dispersive spectroscopy tests. The results show that: (1) For single-layer reservoirs, the FBWF induced weak damage on coals and medium-to-weak damage on sandstones, and the difference of the damage in permeability or flow rate index on coals and sandstones is below 1%. Moreover, the minimum permeability recovery rate was above 66%. (2) For double-layer commingled reservoirs, the flow rate index revealed weak damage and the overall damage in double-layer was lower than the single-layer reservoirs. (3) There is no significant alteration in the microscopic structure of fuzzy-ball saturated cores with no evidence of fines migration. The dissolution of lead and sulfur occurred in coal samples, while tellurium in sandstone, aluminum, and magnesium in carbonate. However, the precipitation of aluminum, magnesium, and sodium occurred in sandstone but no precipitates found in coal and carbonate. The temporal plugging and dispersion characteristics of the FBWFs enable the generation of reservoir protection layers that will minimize formation damage due to solid and fluid invasion.

Mechanism of enhanced oil recovery by fuzzy-ball fluid as a novel oil-displacement agent

Fuzzy-ball fluid is a two-phase fluid composed of fuzzy-ball and base fluid. It can enhance oil recovery by approximately 30% after water flooding and polymer flooding, which has been demonstrated in laboratory experiments and field applications. However, the EOR mechanism of fuzzy-ball fluid still needs further research. In this study, the microstructure of fuzzy-ball was observed using optical and cryo-scanning electron microscopy. The EOR mechanism of fuzzy-ball fluid was investigated by the microscopic glass etching model experiment and inter-molecular force calculation. EOR contribution ratio of three parts of fuzzy-ball was evaluated by the single core flooding experiment. Results showed that fuzzy-ball was further subdivided into fuzzy-ball structure and floss structure. Correspondingly, the EOR effects of fuzzy-ball fluid were mainly divided into three parts: (a) base fluid. Emulsification was the main way for base fluid to enhance oil recovery; (b) fuzzy-ball structure. According to the distribution characteristics of residual oil, the EOR mechanisms of fuzzy-ball structure were mainly as follows: wedging displacement for membranous oil, squeezing-carrying mechanism for columnar oil, and extruding-squeezing mechanism for blind-end oil; (c) floss structure. Floss structure enhanced oil recovery mainly through entanglement and carrying mechanism. Moreover, the EOR contribution ratio of base fluid, fuzzy-ball structure, and floss structure are 18.35%, 50.94%, and 30.71%, respectively. This study elucidates the EOR mechanism of fuzzy-ball fluid and provides guidance for its subsequent field application and performance improvement.

Enhancing the production of tight sandstone gas well through fuzzy-ball fluid temporary plugging with diverting fractures and water cutting after refracturing in one operation

Refracturing is one of the most effective techniques to enhance the production of tight sandstone gas (TSG) well. Many TSG gas wells are facing the problem of water invasion after refracturing, the formation water may gradually occupy the gas-producing channels, preventing high gas productivity. In this paper, we newly developed a fuzzy-ball temporary plugging fluid (FTPF) with diverting fractures and water cutting after refracturing in one operation. The temporary plugging and water breakthrough control capabilities of the FTPF system were evaluated through the true triaxial large-scale core diversion fracturing experiment and matrix core and artificial fracture waterproof experiments. Meanwhile, the permeability damage evaluation experiments were performed to analyze the reservoir recovery ability. Results showed that the pressure-bearing capacity could reach up to 62.6 MPa, the rock fracture pressure was increased by 5–10 MPa compared with the initial hydraulic fracturing and an apparent fracture network structure was formed after refracturing. The breakthrough pressure gradients of simulated formation water were 2–10 times higher than that of nitrogen after the cores (including matrix and cores with 4 mm fractures) were plugged with FTPF, indicating its good water cutting ability. Before and after gel breaking, the permeability recovery value of the matrix core and the artificial fracture core was about 85–98%. The on-site application of FTPF to the refracturing of two TSG wells in the Sulige Gas Field in Northwest of China displayed that the average gas production has been enhanced by 64.8%. It is proposed that fuzzy balls can easily enter and gather at the tip of the initial fractures and form a stable pressure-bearing structure due to its viscoelastic properties and deformability. In addition, the hydrophilic fuzzy-ball core agents can adsorb on the rock's surface and form a polymer membrane, increasing the resistance of water flow.

Enhancing the Production of Tight Sandstone Gas Well Through Fuzzy-Ball Fluid Temporary Plugging with Diverting Fractures and Water Cutting after Refracturing in One Operation

Enhancing the Production of Tight Sandstone Gas Well Through Fuzzy-Ball Fluid Temporary Plugging with Diverting Fractures and Water Cutting after Refracturing in One Operation

High Blocking Capacity of Fuzzy-Ball Fluid to Further Enhance Oil Recovery after Polymer Flooding in Heterogeneous Sandstone Reservoirs.

Even after a long time of polymer flooding, over half of the crude oil is still trapped in the reservoir due to the poor plugging capacity. It has been demonstrated that fuzzy-ball fluid can be utilized as an effective plugging fluid. The idea of further increasing oil recovery by fuzzy-ball fluid following polymer flooding drew us to investigate it due to its high performance and effect. In this paper, seepage behavior experiments and parallel core displacement experiments were carried out to evaluate the plugging ability and oil displacement effect of fuzzy-ball fluid. Also, the microscopic blocking mechanism of fuzzy-ball fluid was observed. The results showed that fuzzy-ball fluid has a good plugging capability thanks to the pressure consumption and accumulation plugging mechanisms. The resistance coefficient and residual resistance coefficient of fuzzy-ball fluid are also substantially greater than those of the polymer, at 76.25–239.96 and 13.95–49.91, respectively. Due to its outstanding plugging capability, fuzzy-ball fluid can achieve complete fluid diversion, with the flow fraction of the high-permeability core reduced to nearly 0% and that of the low-permeability core increased to nearly 100%. As a result, low-permeability core oil recovery and total oil recovery both can be enhanced by 46.12–49.24 and 22.81–24.40%, respectively. A field test of fuzzy-ball fluid flooding was carried out in wells TX1 and TX2 which have been flooding with polymers. After the fuzzy-ball fluid was introduced, total daily oil production increased by 64.15%. Fuzzy-ball fluid can significantly boost oil recovery after polymer flooding, according to laboratory and field trials, providing a technical solution for heterogeneous sandstone reservoirs to further enhance oil recovery.

Formation damage mitigation mechanism for coalbed methane wells via refracturing with fuzzy-ball fluid as temporary blocking agents

During drainage and production from coalbed methane (CBM) wells, the reservoir is prone to formation damage in the form of blockage of the seepage channels by coal fines or invasion of external water, which inevitably causes a significant decline in the productivity of the wells. To restore their productivity, temporary blocking materials (TBMs) are typically used to seal the original fractures for refracturing treatments. In this study, a special fuzzy-ball temporary blocking fluid (FTBF) was designed to effectively mitigate the formation damage through the refracturing operation. The performance of the FTBF was analysed via experiments, application to two case studies, and its formation damage mitigation mechanisms. The following results were obtained: (1) From the experimental analysis, it was observed that the FTBF increased the water resistance in the fracture and it was less than the gas resistance. (2) In Case one, there was no gas production before the refracturing; however after the refracturing, the daily gas production rose to 494 m3. In Case two, the daily gas production of the well before the refracturing was intermittent and less than 80 m3; however, after the refracturing, the gas production remained stable at 220 m3. (3) The analysis of damage mitigation mechanisms revealed that firstly, sodium dodecyl sulfate improved the viscoelasticity of FTBF and its chemical affinity to water, which enhanced the mitigation of the formation damage by water invasion; secondly, the viscoelastic characteristics of the vesicles enabled it to modify the mechanical properties of the rock and consequently improving the refracturing process; thirdly, sodium dodecyl benzene sulfonate provided excellent dispersion stability by adsorption of coal fines in the proppant pack to enhance the fracture conductivity. This study provided a reliable basis for understanding the mechanisms and application of FTBFs in mitigating the formation damage through refracturing CBM wells.

Fuzzy-ball fluid self-selective profile control for enhanced oil recovery in heterogeneous reservoirs: The techniques and the mechanisms

Conventional water flooding and polymer flooding are common approaches to improve oil recovery. However, flooding agents injected into heterogeneous reservoirs preferentially enter the seepage channels in high-permeability zones. As a result, it is difficult to displace the hydrocarbons in low-permeability areas. Therefore, using the agents with selective plugging capability to block the high-permeability channels and promote the subsequent displacement in the low-permeability area has become a potentially preferable solution for enhanced oil recovery (EOR) in heterogeneous reservoirs. In this study, the techniques and mechanisms of the novel fuzzy-ball fluid for enhancing oil recovery in heterogeneous reservoirs are discussed. Laboratory tests were conducted using 45 mm × 45 mm × 300 mm artificial cores with permeability ranging from 200 to 1200 mD to simulate the formation channels. Two cores with different permeabilities were connected in parallel to simulate the heterogeneous formations. The oil displacement performance of fuzzy-ball fluid was compared with that of polymer and surfactant fluids. Flooding the cores with fuzzy-ball fluid could significantly increase the oil recovery rate of the low-permeability cores. Field tests were conducted in two polymer injection wells located in a heterogeneous conglomerate reservoir in Karamay Oilfield, China. After fuzzy-ball fluid flooding, the average daily liquid production rate decreased, the average daily oil production rate increased and the overall water content decreased. There was a significant improvement in oil displacement effect in low-permeability areas.

The environmental friendliness of fuzzy-ball drilling fluids during their entire life-cycles for fragile ecosystems in coalbed methane well plants.

To protect the vulnerable ecosystems in coalbed methane(CBM) well plants from the pollution of drilling fluids, the environmental friendliness of fuzzy-ball drilling fluids was evaluated. Further, the combination of solidification and in-situ landfill were proposed to optimize their waste disposal. Firstly, the samples for tests were collected from the well plants. Then, their environment-related properties were evaluated with the indicator vector from wastewater perspective to monitor their environmental friendliness. Lastly, comparative analysis of two wells in Linfen, China was conducted concerning engineering and economic parameters. Results showed that these indicators of the new fuzzy-ball drilling fluids and their raw materials were within the ceiling limits of related national standard, whereas those of waste fuzzy-ball drilling fluids exceeded the limits. The mechanical strengths of the waste drilling fluids solidified directly could meet the practical transport demand, and their leachates met the standardized requirements due to the strong biodegradability of fuzzy-ball fluids. Field studies demonstrated the economic effectiveness of fuzzy-ball drilling fluids, reconciling the conflict between environment-protecting and cost-reducing. In conclusion, fuzzy-ball drilling fluids are feasible for fragile ecosystem protection in CBM well plants. The environmental friendliness relies on their material, structural and functional basis.

Piston-like plugging of fuzzy-ball workover fluids for controlling and killing lost circulation of gas wells

During well-killing operations for the workover of low-pressure gas wells, formation pressure should be balanced so as to guarantee well control safety by preventing natural gas overflow. In this paper, a laboratory evaluation was conducted with fuzzy-ball fluids as killing fluids. The results show that, the fuzzy-ball fluid, with a density of 0.5–1.5 g/cm3 and a viscosity up to 78,50,000 mPa·s at a low shear rate, realizes controllable performance and forms piston-like plugging slugs of solid-free high structural strength on natural gas wellbore after bonding. During well workover, multiple fluid column pressures were set up by injecting fuzzy-ball fluids with different densities at various rates. Owing to high structural strength of the fluids at a low shear rate, natural gas breaks through only inside the piston-like slug and cannot flow upwards to the ground, so the pathways of natural gas in the wellbore are isolated from the ground surface. Moreover, the fluid can wholly move up and down like a piston-like plug, with the change of formation pressures or the tripping of pipe strings. Like the conventional operations, the production can be restored after the workover, so long as the fluid in wellbore is cleaned by means of gas lift. In a natural gas field in NW China, where the formation pressure coefficient dropped to 0.60–0.82, three wells were fully filled with fuzzy-ball workover fluids for 7 days and another three wells were treated with the piston-like plugs of fuzzy-ball workover fluids for only 3 days. They all presented better technical results. The technology provides a new way for low-pressure gas well workover.

Pressure and Temperature Bearing Capacities of Fuzzy-Ball Fluid

Pressure and Temperature Bearing Capacities of Fuzzy-Ball Fluid

A Multifunctional Drilling Fluid for Coalbed Methane Drilling

With extremely complicated geological conditions, there is abundant coalbed methane in the China's Ordos Basin Area. As a result of coexistence of different pressure systems in the same one naked well section, there are so many problems taking place occasionally during the drilling process, such as the formation lost circulation and collapse, which require the drilling fluid with a perfect rheology behavior and inhibitive to improve the well-bore containment. The coalbed methane well completions are diverse, usually including vertical well, horizontal well, multi-branch well, and other different well types. So the drilling fluid must have cuttings carried effectively and protect formation damaged to ensure that the process of drilling is security and smooth. Lots of drilling methods are used in the coalbed methane drilling, besides normal nearly balanced drilling, the under balance drilling fluids such as the air, fog, foam, etc particularly improved. All this drilling fluids require itself working compatibility with other fluids in the hole. Therefore, the special state-funded science and technology project has developed a novel bionic Fuzzy-Ball drilling fluid to meet the coalbed methane. Without additional equipments, this novel drilling fluids can be made, with non-solid phase and low density, 0.8~1.0 g/cm3. The inert solids can also be used to adjust the property to more than 1.0g/cm3, matching the near/under-balanced drilling. The formation well-bore containment can effectively improve to meet to the more than 1000 meters coalbed methane drilling in the open or low pressure formation, To portable cuttings effectively under low rate, the ratio of yield point and plastic viscosity can be adjusted to 1.0Pa/mPa•s or more. Combined with the air drilling, this novel Fuzzy-Ball material could not be converted to fluid to solve the formation water production, cavings, completion and other operations. 10 wells application of using the Fuzzy-Ball drilling fluid to complete the coal bed methane wells overcoming water production, collapse, lost circulation and air drilling etc, taking five branches well FL-H2-L, "U" horizontal well DFS-02-H2, water production and collapse well J35, air drilling CLY22 for examples, are introduced to indicate the bionic Fuzzy-Ball fluid application on the coalbed methane drilling spot.

A Multifunctional Drilling Fluid for Coalbed Methane Drilling

With extremely complicated geological conditions, there is abundant coalbed methane in the China's Ordos Basin Area. As a result of coexistence of different pressure systems in the same one naked well section, there are so many problems taking place occasionally during the drilling process, such as the formation lost circulation and collapse, which require the drilling fluid with a perfect rheology behavior and inhibitive to improve the well-bore containment. The coalbed methane well completions are diverse, usually including vertical well, horizontal well, multi-branch well, and other different well types. So the drilling fluid must have cuttings carried effectively and protect formation damaged to ensure that the process of drilling is security and smooth. Lots of drilling methods are used in the coalbed methane drilling, besides normal nearly balanced drilling, the under balance drilling fluids such as the air, fog, foam, etc particularly improved. All this drilling fluids require itself working compatibility with other fluids in the hole. Therefore, the special state-funded science and technology project has developed a novel bionic Fuzzy-Ball drilling fluid to meet the coalbed methane. Without additional equipments, this novel drilling fluids can be made, with non-solid phase and low density, 0.8~1.0 g/cm3. The inert solids can also be used to adjust the property to more than 1.0g/cm3, matching the near/under-balanced drilling. The formation well-bore containment can effectively improve to meet to the more than 1000 meters coalbed methane drilling in the open or low pressure formation, To portable cuttings effectively under low rate, the ratio of yield point and plastic viscosity can be adjusted to 1.0Pa/mPa•s or more. Combined with the air drilling, this novel Fuzzy-Ball material could not be converted to fluid to solve the formation water production, cavings, completion and other operations. 10 wells application of using the Fuzzy-Ball drilling fluid to complete the coal bed methane wells overcoming water production, collapse, lost circulation and air drilling etc, taking five branches well FL-H2-L, "U" horizontal well DFS-02-H2, water production and collapse well J35, air drilling CLY22 for examples, are introduced to indicate the bionic Fuzzy-Ball fluid application on the coalbed methane drilling spot.