Fracturing Technology Research Articles

Mechanism and Control Technology of Rockburst Induced by Thick Hard Roof and Residual Coal Pillar: A Case Study

Rockburst caused by the fracture of thick hard roof and the instantaneous instability of residual coal pillar seriously jeopardize the deep coal mining safety. This study takes Boertai Coal Mine, Shendong, China, as the engineering background, in which dynamic instability mechanisms of the gob-side roadway surrounding rock are analyzed by integrating field research, theoretical analysis, and numerical simulation. The results show that the overlying residual coal pillar, side abutment pressures, and front abutment pressures together induce high static stresses in the surrounding rock of the gob side roadway, with peak values exceeding the in situ stress by one order of magnitude. High stresses accumulated in the goaf-side roadway surrounding rock can easily induce dynamic disaster. With the working face advanced, overburdens are caved in succession, resulting in a continuously decreasing of the overlying residual coal pillar width, once the working face entered the influence area of the residual coal pillar. As the morphology of abutment pressure in the residual coal pillar changes from “unimodal distribution” to “bimodal distribution,” the residual coal pillar gradually changes from elastic state to plastic state. When the width of the overlying residual coal pillar is less than the critical width, the thick hard roof and residual coal pillar structure (THRRCPS) lose stability suddenly, resulting in strong dynamic load on the surrounding rock of gob-side roadway. In order to prevent the rockburst of the gob-side roadway under the influence of THRRCPS, regional and local prevention measures are adopted to mitigate the accumulation of stress in the thick hard roof and gob-side roadway surrounding rock by hydraulic fracturing technology and large diameter pressure relief drilling hole.

Principal characteristics of marine shale gas, and the theory and technology of its exploration and development in China

The exploration and development theory and technology of marine shale gas with shallow burial depth of 3500 m in South China has become mature after more than 10 years of practice. In order to continuously promote the exploration and development of shale gas in China, based on the research results of many scholars, combined with production practice, the main characteristics of marine shale gas in China and the main theory and technology of exploration and development are further summarized. The results show that: (1) The basic characteristics of marine shale gas in southern China are marine deep-water shelf deposition, and organic-rich shale is distributed continuously in a large area; The organic matter is stored in situ after high thermal maturity gas generation, and the gas content of shale is affected by late tectonic activity; The reservoir space is dominated by nano-scale pores, and the reservoir is super-tight and ultra-low permeability, which has no natural productivity without well stimulation; Bedding and natural fracture affect the productivity of shale gas wells; The mechanical properties of shale rock determine the effect of horizontal wells. In the early stage of well production, the production rate is high and the decline is fast, while in the middle and late stage, the rate is low but the production cycle is long. (2) Based on the above characteristics, the theory of “sweet spot” and “sweet interval” of shale gas and the theory of effective development of artificial gas reservoir are established, that is, the sedimentary and tectonic interaction forms the “sweet area” or “sweet spot” of marine shale gas. Gas productivity is determined by geological and engineering factors, so the “sweet spot” must be found to develop. By constructing artificial gas reservoir through “making an artificial high permeability area, and reconstructing a seepage field”, the effective development of ultra-tight and low permeability shale gas reservoirs can be realized. It is the most effective technique for shale gas development to accurately create “transparent geological body” of reservoirs based on geology-engineering integrated evaluation technology and establish artificial gas reservoir through multi-stage fracturing technology. (3) The overpressure area in the southern Sichuan Basin is the “sweet area” for shale gas development. The “sweet interval” of the lower Silurian Longmaxi Formation with a thickness of 3–5 m and high brittle-rich organic matter is the optimal “golden target” for horizontal wells. (4) The development leapfrog from the first generation to the second generation has been realized by the key technology of multi-stage fracturing of horizontal wells. The EUR per well of Upper Ordovician Wufeng Formation and Longmaxi Formation in southern Sichuan has increased from 0.5 × 108 m3 in the initial stage to 1.0 × 108–1.2 × 108 m3 at present with a buried depth of shallower than 3500 m. (5) The effective area favorable for shale gas development in southern Sichuan is 2.0 × 104 km2, and it is estimated that the proven geological reserves of shale gas can reach 10 × 1012 m3. It is preliminarily predicted that the shale gas production in China will exceed 300 × 108 m3 in 2025 and reach 400 × 108 m3 in 2035.

Simulation Study for Hydraulic Fracture Monitoring Based on Electromagnetic Detection Technology

The stimulated reservoir volume (SRV) technology extends conventional fracturing technology. Understanding how to effectively and accurately determine modified fracture shape and volume is the key point to evaluating the stimulation effect. Using electromagnetic detection technology can provide a new option for measuring these parameters. By the finite method, the rationality of electromagnetic detection technology to obtain the relevant parameters of reconstruction fracture is testified through forward simulation. This study compared the signals of fractures with different conductivity, volume, and shape collected by electromagnetic detection tool, and the results show that the signals have a specific correspondence with fracture geometric parameters. According to the electromagnetic signal curve of the forward model, the description of propped fractures, including positions and sizes, can be realized.

Exploration, development, and construction in the Fuling national shale gas demonstration area in Chongqing: Progress and prospects

In September 2013, the National Energy Administration approved the establishment of Fuling national shale gas demonstration area (hereinafter referred to as the demonstration area), whose construction was completed in December 2015. After nearly one decade of development, it has grown into the main shale gas production base in China. In order to speed up the integration and breakthrough of China's shale gas theoretical understanding and exploration and development technology and effectively promote the great development of marine shale gas in China, this paper reviews and summarizes the development and construction history of the demonstration area, geological theory understanding, engineering technology and key equipment progress. And based on this, the future development direction of the demonstration area is predicted. And the following research results are obtained. First, shale gas exploration and development in the demonstration area is divided into three stages, i.e., exploration evaluation, phase I and II construction, and stacked development and adjustment. Second, the “binary enrichment” theory for marine shale gas and the engineering theory for efficiently developing gas reservoirs are innovatively established. Third, a series of supporting technologies are innovatively developed, such as optimized and fast drilling technology for shale gas cluster horizontal wells, differentiated network fracturing technology, high-efficiency gas production, gathering and transportation technology, and green development technology for karst mountains, and the localization of key equipment and tools is realized. Fourth, the efficient development of shallow overpressure shale gas reservoirs above 3500 m in depth and the effective development of shale gas reservoirs at the depth of 3500–4000 m are realized in the demonstration area. Fifth, the construction of the demonstration area in the future includes accelerating the development of normal-pressure deep shale gas, continuously tackling key shale gas EOR technologies, actively promoting the field application of new technologies and methods, and powerfully strengthening the construction of green demonstration areas. In conclusion, this demonstration area is the earliest one of four national shale gas demonstration areas, and its achievements will provide continuous guidance for the shale gas exploration and development in China and play a demonstrative and guiding role in promoting the development of shale gas geological theories and exploration and development technologies in China.

Hydrochemistry, Sources and Management of Fracturing Flowback Fluid in Tight Sandstone Gasfield in Sulige Gasfield (China)

Hydraulic fracturing technologies have been frequently utilized in the oil and gas industry as exploration and development efforts have progressed, resulting in a significant increase in the extraction of natural gas and petroleum from low-permeability reservoirs. However, hydraulic fracturing requires a large amount of freshwater, and the process results in the production of large volumes of flowback water along with natural gas. In this study, three tight sandstone gas wells were fractured in the Sulige gasfield (China), and a total of 103 flowback fluid samples were collected. The hydrochemical characteristics, water quality and sources of hydrochemical components in the flowback fluid were discussed. The results show that the flowback fluid is characterized by high salinity (Total dissolved solids (TDS) up to 38,268mg/L, Cl- up to 24,000mg/L), high concentrations of metal ions (e.g., Fe, Sr2+, Ba2+) and high chemical oxygen demand (COD). The flowback fluid is a complex mixture of fracturing fluid and formation water, and its composition is impacted by water-rock interactions that occur during hydraulic fracturing. The major contaminants include COD, Fe, Ba2+, Cl-, Mn and pH, which constitute a high risk of environmental pollution. Meanwhile, chemical elements such as K, Ba and Sr are unusually enriched in the flowback fluid, which has an excellent potential for recycle of chemical elements. The Sulige gasfield's flowback fluid recovery methods and treatment scenarios were discussed, taking into consideration the pollution and resource characteristics of the flowback fluid. Options for dealing with the flowback fluid include deep well reinjection, reuse for making up fracturing fluid, recycling of chemical elements and diverse reuse of flowback water. This research offers guidance for managing the fracturing flowback fluid in unconventional oil and gas fields.

Evaluation and Economics of Shale Gas Reserves in the Flysch-Eocene Formation of the Jaca Basin

The new international outlook for the gas sector suggests evaluating exploitable reserves in previously unconsidered areas including hydraulic fracturing technology. In order to estimate the amount of gas in the Jaca Flysch formation, the analysis of geological and geophysical logs and the volumetric method have been used. It has been taking into account the part of the formation likely to contain gas, the porosity (2.65%) calculated from sonic logs with Wyllie’s equation, the water saturation (35.3%) with Archie’s formula, and the initial gas formation volume factor (Bgi), estimated with MHA-P3 software with the reservoir pressure/temperature data 3600 psi/90 °C. The economic analysis of each well has been carried out based on three options, without stimulation, with 50% and 100% stimulation by fracking, and five possible construction costs (7.5–15 MM€). The impact of the use of the fracking technology on the production of the well is about 48%. The production rate and the economic impact that its exploitation would have on the domestic demand for natural gas has been analyzed, resulting in a significant contribution to the national energy mix of between 10–20% of consumption for several years.

Study on the Parameters of Strengthening Soft Surrounding Rock by Electric Pulse Grouting in the Mining Face

As an effective measure for the rapid fracturing of coal and rock, electric pulse fracture technology has been successfully applied in oil extraction and natural gas discharge. Using the electric pulse fracture mechanism, this technology can be applied to grouting reinforcement to improve the infiltration efficiency of grouting. In this study, we used a numerical simulation method to establish numerical models with different electric pulse peak pressures, different grouting times and different drilling spacing conditions Through numerical simulation studies, we found that the influence range of grouting reinforcement grows with the increased maximum pressure generated by the electrical pulse. The most economical and reasonable electric pulse parameter setting is 5 MPa for static grouting pressure and 100 MPa for peak electric pulse pressure. The best grouting time to keep pressure in the borehole is determined as 9 h, and the best borehole interval is 10 m. In addition, through the treatment of the soft roof of the Caojiashan coal mine, we also found that the reinforcement sample within the grouting reinforcement range had a compressive strength of more than 1.1 MPa; after each grouting reinforcement was completed, the hydraulic bracket could advance 12 m each time, which shows that the electric pulse grouting reinforcement technology has an obvious effect on the treatment of soft roof slab.

Study on the Shadow Effect of the Stress Field around a Deep-Hole Hydraulic-Fracturing Top-Cutting Borehole and Process Optimization

The clean utilization and green development of coal resources have become a research focus in recent years. Underground hydraulic fracturing technology in coal mines has been widely used in roof pressure relief, top coal pre-splitting, gas drainage, roadway pressure relief and goaf disaster prevention. Different in situ stress types cause great differences in the stress field around the boreholes, the critical pressure of the fracture initiation, and the direction of the fracture expansion trend; in addition, the stress shadow effect generated by the superposition of stress fields between boreholes relatively close together has a mutual coupling effect on the evolution of the stress field, the development of the plastic zone, and the crack propagation of the rock mass. Therefore, an effective method to solve the problem is to establish a mechanical model of hydraulic fracturing in boreholes for theoretical calculation, determine the influence mechanism of the crack shadow effect, and design a numerical simulation experiment of the equivalent stress fluid–solid coupling of hydraulic fracturing under different pore diameters and spacings. In addition, combining rock mechanics and fracture mechanics to analyze the influence of the shadow effect of the stress field between cracks on the evolution of the equivalent stress and the plastic zone is one of the important advances in this paper. Considering the engineering background of the site, the geological conditions and the requirements of general regulations, it is considered that the parameter selection of roof fracturing hydraulic fracturing technology in the Yushen mining area is more suitable when 0.12 m hole diameter and 3.5 m hole spacing are selected.

Multi-stage hydraulic fracturing technology in a well with horizontal working face

At present, hydraulic fracturing (HF) is still the most effective method of stimulating hydrocarbon flow and enhancing oil recovery in certain types of wells, particularly those with horizontal endings. In many regions, this is the only technology that enables development of fields with hard-to-recover reserves confined to low-permeability, poorly drained, heterogeneous and dissected reservoirs, which significantly increases hydrocarbon production and makes well construction economically viable. In this work, the authors have developed a new technology for interval hydraulic fracturing in a well with a horizontal target area, with the ability to inject fracturing fluid and hold excess pressure on either side of the fracturing unit by means of flap-type check valves. The fracturing is performed through a transport unit that runs directly through the casing and protects the plug from the abrasive effects of the gel-propellant mixture. After fracturing is complete, the transport unit is removed from the plug, and the rear cut-off valves are closed. No re-entry is possible after the adaptor has been removed from the well. For the next interval, the work cycle of plug, activation and fracturing is repeated using a new transport unit. For each repetition, the newly stimulated interval remains isolated until the fracturing operation is complete and all downstream plugs have been fractured. All installed plugs are drilled out before development. During all phases of the work, it is assumed that the well is prepared without the use of coiled tubing. The novelty and innovation lie in the technological solution of delivery to the target area and using easy-to-drill plugs to guarantee open interval separation and perform selective fracturing. Potential candidates are wells with 114 mm diameter casings with single- or multiple-acting fracturing sleeves to open-close after the horizontal part of the well has been prepared (the ‘equal-pass’ section requirement is for a 95 mm diameter bit). The proposed technical means and technology, in the opinion of the authors, will increase the efficiency of field development, reservoir conditions in which are characterized by low filtration parameters, high viscosity properties, etc. The authors do not think that the proposal will generally solve the problem of intensification of the inflow of reservoir fluid to the well and thereby increase oil recovery from the reservoir, but according to in their opinion, in some respects it will contribute to this. The final results will be obtained based on the results of extensive production tests.

Experimental study on fracture propagation and induced earthquake reduction by pulse hydraulic fracturing in shale reservoirs

Large-scale and complex cracks have always been the eternal goal of hydraulic fracturing (HF) technology in shale reservoirs, but there has been the public concern that the HF could trigger earthquake disasters. It is urgent to develop the new HF technology that can generate a large number of complex cracks and reduce the risk of induced earthquake. Herein, the fracture propagation, fluid pressure distribution and acoustic emission (AE) energy of four types of hydraulic fracturing are analyzed through laboratory experiment and numerical simulation in this study. The new rectangular pulse HF is proposed. It is concluded that the pulse HF with higher fluid pressure gradient takes a shorter time to fracture shale. It is easier to form complex cracks. Relying on reciprocating impact and strong “Water Hammer Effect”, the pulse HF can form a large number of micro-cracks and reduce the energy released at the moment of complete failure of shale. The research shows that the pulse HF with the larger pressure gradient performs better in fracturing shale and reducing the risk of induced earthquake. The rectangular pulse HF has more significant advantages than the sine and triangle pulse HF. It relies on low instantaneous rock rupture energy, long rupture time and widely distributed low energy rupture events to reduce induced earthquakes. These can help to develop the pulse HF technology and reduce the risk of induced earthquakes for shale gas exploitation.

Effects of Liquid CO2 Phase Transition Fracturing on Methane Adsorption of Coal

Liquid CO2 phase transition fracturing (LCPTF) is a kind of novel waterless fracturing technology for enhancing the coalbed methane (CBM) recovery. Relevant current studies are focused on exploring the transformed effect of LCPTF on the nanopore structure in coal. However, its influence on gas adsorption capacity has been rarely reported. This study addresses coal induced with LCPTF. The structure alterations of mesopores (2–50 nm) and macropores (>50 nm) and their effects on the gas adsorption capacity are evaluated with comprehensive measurements of a mercury intrusion porosimetry, low-temperature N2 adsorption, and isothermal adsorption. The results indicate that LCPTF has an enlarged effect on macropores, resulting in an increase in pore size and volume and a reduction of the pore specific surface area. The pore-enlarged-transformed effects of LCPTF cause an increase in pore size and a reduction of the pore volume and pore specific surface area of mesopores. The variations of the pore structure after LCPTF cause a reduction of the adsorption constant a and the increase in the adsorption constant b, indicating LCPTF’s reductive effect on adsorption capacity as well as its enhanced effect on desorption capacity. A novel effect evaluation method of LCPTF for improving CBM recoverability is proposed based on the variations of gas saturation and critical desorption pressure. This study examines, from the perspective of adsorption and desorption, the mechanism of LCPTF for enhancing CBM recovery, which provides theoretical guidance for LCPTF’s technical improvement and optimization of field application so as to secure a more reliable and efficient CBM recovery.

Feasibility and Mechanism of Deep Heavy Oil Recovery by CO2-Energized Fracturing Following N2 Stimulation

There are large, heavy oil reserves in Block X of the Xinjiang oilfields, China. Due to its large burial depth (1300 m) and low permeability (26.0 mD), the traditional steam-injection technology cannot be used to obtain effective development benefits. This paper conducts experimental and simulation research on the feasibility and mechanism of CO2-energized fracturing of horizontal wells and N2 foam huff-n-puff in deep heavy oil reservoirs with low permeability in order to further explore the appropriate production technology. The foaming volume of the foaming agent at different concentrations and the oil displacement effect of N2 foam at different gas/liquid ratios were compared by the experiments. The results show that a high concentration of foaming agent mixed with crude oil is more conducive to increasing the foaming volume and extending the half-life, and the best foaming agent concentration is 3.0∼4.0%. The 2D micro-scale visualization experiment results show that N2 foam has a good selective blocking effect, which increases the sweep area. The number of bubbles per unit area increases as the gas/liquid ratio increases, with 3.0∼5.0 being the optimal gas/liquid ratio. Numerical simulation results show that, when CO2-energized fracturing technology takes into account the advantages of fracturing and crude oil viscosity reduction by CO2 dissolution, the phased oil recovery factor in the primary production period can reach approximately 13.7%. A solvent pre-slug with N2 foam huff-n-puff technology is applied to improve oil recovery factor following primary production for 5∼6 years, and the final oil recovery factor can reach approximately 35.0%. The methodology formulated in this study is particularly significant for the effective development of this oil reservoir with deeply buried depth and low permeability, and would also guide the recovery of similar oil deposits.

Experimental study on fracture characteristics of coal due to liquid nitrogen fracturing

Liquid nitrogen (LN2) fracturing is expected to become an effective means of increasing coalbed methane production due to good reservoir adaptability. Advantages of the technology are the ultra-low temperature and huge gasification pressure during the fracturing, but how to give full play to the advantages of liquid nitrogen fracturing needs further exploration. In this paper, the fracture pressure, fracture degree, roughness of fracture surface and microstructure change of coal after LN2 fracturing are analyzed under different under experimental conditions, and the main factors affecting LN2 fracturing are discussed in combination with the numerical simulation results. The results show that the temperature rise and freeze–thaw treatment can effectively reduce the initiation fracture pressure of coal, with a decrease of more than 40%; The fracture degree and roughness of coal increase, especially the volume fracture of the freeze–thaw coal sample is the largest, and the cross-sectional area expansion rate (roughness index Sdr) increases as high as 325%. In addition, the SEM scanning results showed that the heating and freezing thawing treatment promoted the intergranular and transgranular destruction of the coal. Numerical analysis shows that temperature rise and freeze–thaw treatment can expand initial damage range around the borehole of LN2 fracturing instant, thereby promoting gas permeability efficiency, increasing pore pressure and improving the fracturing effect of coal. The temperature rise enhances the expansion effect of LN2 gasification, and the freeze–thaw treatment can give the full play to the low-temperature damage effect of LN2. Based on this, an improved technology of LN2 fracturing is put forward: Technology of fracturing and permeability enhancement with liquid nitrogen coupled high temperature.

Special Issue “Petroleum Engineering: Reservoir Fracturing Technology and Numerical Simulation”

Hydraulic fracturing is a technique that can provide space for oil and gas flow by pumping fracturing fluid into a reservoir to fracture rock and filling proppant to create fractures or fracture nets [...]

Numerical Simulation of Diverting Fracturing for Staged Fracturing Horizontal Well in Shale Gas Reservoir

Abstract Hydraulic fractures are difficult to initiate simultaneously during multi-cluster fracturing owing to the strong heterogeneity of shale reservoir and the stress interference effect between adjacent hydraulic fractures. Some hydraulic fractures can initiate early and propagate rapidly, whereas others exhibit late initiation (or even fail to initiate) and propagate slowly, resulting in non-uniform propagation behavior of multiple fractures. This non-uniform propagation behavior can significantly limit hydraulic fracturing performance in shale gas reservoirs. Therefore, the minimization of non-uniform propagation of multi-cluster fractures is important in improving the shale gas development. Currently, diverting fracturing technology is implemented to restrain overextended fractures while promoting restricted fractures to facilitate uniform propagation. Pumping diversion balls to block the perforations of overlong fractures has become an important method to improve non-uniform fracture propagation. This method is, however, limited by lagging behind of theoretical simulation, and significant blindness in the current implementation of diverting fracturing. A dynamic propagation model for multiple-cluster hydraulic fractures was established in the current study by considering the stress interference effect between adjacent fractures and the effect of flowrate dynamic adjustment by diversion balls. This model is effective for the dynamic simulation of fractures propagation after pumping diversion balls. A fractured well in the Changning block was used as an example for the simulation of the dynamic fracture’s extension and the distribution of SRV before and after diversion. The findings showed that the temporary plugging ball significantly promoted the uniform extension. The number of temporary plugging balls, the number of diversions, and the timing of diversion were then optimized. The simulation method developed in this study has important theoretical significance and field application value in guiding regulation of uniform expansion of fractures and improving optimization of diverting fracturing design.

Study on the influence of the tectonic evolution of Shuangyashan Basin on gas occurrence and extraction in mines

The formation and later evolution of coal-bearing basins in eastern Heilongjiang are controlled by multi-phase tectonic movements, and the Shuangyashan Basin is tectonically located at the southern end of the Sanjiang Basin in the northeast. The paper focuses on the regional geological and tectonic evolution of the Shuangyashan Basin and its influence on the gas occurrence law and extraction difficulty of the Jixian Coal Mine. The study determined that the gas occurrence of the mine in the Suibin-Jixian depression basin has regional aggregation and caprock sealing characteristics. The gas pressure and content of the 9# Coal Seam were measured in the underground test, and the results showed that the 9# coal seam is a hard-to-extract coal seam with low permeability. Aiming at the issue of hard-to-extract gas in 904 Working Face of 9# Coal Seam which is affected by depression basin and derived secondary tectonic conditions, numerical calculation and analysis of gas extraction effect of working face with different extraction parameters were carried out by COMSOL software, the results showed that: negative extraction pressure has less influence on gas extraction effect under basin conditions; when 113 mm diameter borehole is used for gas extraction, gas pressure decreases to 0.72 MPa; when the spacing of extraction borehole is 2 m, the gas pressure is reduced by 20%; when the coal seam permeability is increased by 10 times to more than 0.015 mD, the gas pressure is reduced by more than 50%. The optimized gas extraction scheme with 113 m diameter, 2 m borehole spacing, and 15 kPa negative pressure was proposed for the test working face, and combined with supercritical CO2 fracturing and permeability enhancement technology. Under underground measurement, the coal seam gas content was reduced by 39.7% compared to the original gas extraction scheme. It can be seen that the reasonable gas extraction scheme and coal seam pressure relief and permeability enhancement technology can significantly improve the gas extraction rate, and the extraction effect is remarkable.

Optimization of volume fracturing technology for shallow bow horizontal well in a tight sandstone oil reservoir

The physical property of Chang 6 reservoir in Yanchang oilfield is poor, and the heterogeneity is strong. Multistage fracturing of horizontal wells is easy to form only one large horizontal fracture, but it is difficult to control the fracture height and length. The new mining method of “bow horizontal well + multistage horizontal joint” can effectively increase the multistage horizontal joint’s spatial position, which improves the drainage area and stimulation efficiency of oil wells. Due to the reservoir’s low permeability and strong heterogeneity, the single well mode of “bow horizontal well + multistage horizontal fracture” cannot effectively produce Chang 6 reservoir. To improve the production degree of the g 6 reservoir, the fracture model is established using equivalent conductivity and the multigrid method. The pressure response functions of horizontal wells and volume fracturing horizontal wells are established by using the source function, and the relationship between reservoir permeability and starting pressure gradient in the block is calculated. On this basis, the reservoir productivity equation of the block is established, which provides a basis for optimizing the fracturing design parameters of horizontal wells. It is proposed that the flow unit should be considered in the design of fracturing parameters of horizontal fractures, the number of fractures should comprehensively consider whether the fractures can make each flow unit be used, and have large controlled reserves, and the scale of fracturing should comprehensively consider the output and cost. The fracture network model is established by using equivalent conductivity and multi-gridthod, and the volume fracturing design parameters of horizontal wells are optimized, considering the seepage characteristics of the flow unit. The fracturing design parameters of the horizontal section are further defined, which provides a theoretical basis for the efficient development of shallow tight reservoirs.

A COMPREHENSIVE REVIEW OF HYDRAULIC FRACTURING TECHNIQUES IN SHALE GAS PRODUCTION

Shale gas has emerged as a significant source of natural gas due to advancements in hydraulic fracturing and horizontal drilling technologies. This extraction method has facilitated drilling and production activities in regions previously untouched by oil and gas development. Hydraulic fracturing, a well-stimulation technique suitable for low and moderate-permeability reservoirs, relies on the successful drilling of horizontal wells and the creation of multiple hydraulic fractures to ensure economic viability. While shale gas presents significant energy production opportunities, concerns have been raised regarding its environmental impact. To mitigate these risks and determine the most effective approach for shale gas extraction, alternative fracturing technologies are being investigated. Notably, a considerable number of perforation clusters in shale gas horizontal wells do not contribute to production, highlighting the potential for refracturing. Therefore, a comprehensive analysis is required to evaluate the performance of hydraulic fracturing and alternative fracturing technologies in shale gas wells, considering factors such as cost-effectiveness, environmental impact, and gas extraction efficiency. This article aims to evaluate the hydraulic fracturing technology's capability to enhance gas recovery in shale gas formations as well as its environmental implications. The focus of this research is primarily on the hydraulic fracturing technique employed in shale gas development, its production capability, and associated environmental concerns. Through a systematic evaluation, this study provided valuable insights into the potential of hydraulic fracturing in maximizing gas recovery while addressing environmental challenges in shale gas formations.

Preliminary hydraulic fracturing campaign strategies for unconventional and tight reservoirs of UAE: Case studies and lessons learned

<abstract> <p>The challenges associated with applying hydraulic fracturing (HF) technology to tight carbonate reservoirs with very low clay content are substantial and demand a unique cost optimization strategy, especially in the context of low oil prices. This study discusses the challenges of applying HF technology to such reservoirs in the UAE. The work presents a comprehensive approach to assess and employ this technology, including a thorough study, a strategic roadmap, screening procedures, a fracturing workflow and strategy and an examination of the distinctive challenges and lessons learned from the process. The primary goal is to formulate a strategy that is applicable to tight and unconventional formations in the UAE, with a strong emphasis on cost optimization. Also, the evaluation methods of the fracturing technologies for these reservoirs were discussed, such as creating valid geomechanical properties to construct a Mechanical Earth Model (MEM) for successful execution and evaluating the reservoir quality. The results showed that conventional acidizing is not effective in stimulating the tight carbonate reservoirs, whereas acid-fracturing has successfully broken down the formation. It was also found that strategic planning, equipment availability, geomechanical studies and building an effective MEM are necessary for obtaining the optimum fracturing design and achieving successful development.</p> </abstract>

EVALUATION OF SUPERCRITICAL CO2 FRACTURING EFFECT IN DA'AN RESERVOIR OF SONGLIAO BASIN

Carbon dioxide (CO<sub>2</sub>) fracturing technology is introduced to improve the development effect of low permeability reservoirs. To understand the advantages of CO<sub>2</sub> fracturing and the mechanism of CO<sub>2</sub> assisting oil displacement efficiency, laboratory core displacement experiments and nuclear magnetic resonance (NMR) tests are conducted. For core displacement experiments, a water flooding, a water flooding-CO<sub>2</sub> huff and puff experiment are conducted. Water flooding simulates the oil displacement after hydraulic fracturing and the latter simulates the effect after CO<sub>2</sub> fracturing. Furthermore, an NMR test is conducted in each stage of the experiments to quantify the recovery degree of crude oil in different pore throats for a low-permeability reservoir. The results show that the water flooding recovery of the two cores is 31.26% and 30.14%, respectively. The CO<sub>2</sub> huff and puff enhanced oil recovery and subsequent water flooding are 11.48% and 5.19%, respectively. Compared with conventional hydraulic fracturing, CO<sub>2</sub> fracturing enhanced oil recovery by 15.55%. Furthermore, the crude oil recovery degree of water flooding in macro-pores is 75.71%, while that in mesopores is 62.17% and that in small pores is 7.49%. After CO<sub>2</sub> huff and puff, the recovery degrees in macropores, mesopores, and small pores are 99.10%, 67.51%, and 23.21%, respectively. It demonstrates CO<sub>2</sub> can penetrate deeply into the tiny pores that cannot be affected by water flooding for oil displacement, effectively increasing the swept volume and improving the oil recovery. Research shows the advantages of CO<sub>2</sub> fracturing and may help to enlarge its application in low-permeability reservoirs.