Ultra-low Permeability Reservoirs Research Articles

Prediction Method of Well Pattern Infilling Effect in Ultra-low Permeability Reservoir of X Oilfield

In this paper, firstly, the introduction of well pattern infill in ultra-low permeability reservoir is analyzed in detail, and then combined with the change law of well pattern infill in ultra-low permeability reservoir and the prediction process of well pattern infill in ultra-low permeability reservoir, the prediction results of well pattern infill in ultra-low permeability reservoir are summarized.

Quantitative characterization of pore size and structural features in ultra-low permeability reservoirs based on X-ray computed tomography

The pore structure of ultra-low permeability sandstone (0.1 mD < K < 1 mD) is complex and has high heterogeneity, which leads to great challenges in reservoir characterization and effective evaluation. To study the effect of the heterogeneity of ultra-low permeability sandstone on permeability, a digital core model was established using X-ray computer tomography (CT) technology. Then a three-dimensional pore network model (PNM) in core samples was created using the “maximum ball method” algorithm. Finally, the geometric topology features of ultra-low permeability reservoirs were quantitatively characterized. According to the physical properties and test results of samples, the porosity distribution of targeted area ranged between 5.92% and 10.08%, and the permeability distribution range was 0.145 mD–0.75 mD, which was typical for an ultra-low permeability reservoir. The distribution of pore throat radii ranged from 0.27 μm to 1.29 μm, the shape factor was 0.04–0.06, the disconnected pores of the four samples made up between 16.89% and 58.71% of all pores, and the fractal dimension fluctuated between 1.05 and 1.5. Plane porosity also showed certain fractal characteristics. Correlation analysis showed that the disconnected isolated pores and the micron-scale pore throat radii of the reservoir sandstone were the main factors resulting in ultra-low permeability. The above-mentioned quantitative characterization parameters can be subsequently used to conduct microscopic seepage simulation studies of such reservoirs. • Build digital core based on CT scanning system. • Extract the core pore network model, and render the pore pressure, throat flowrate, and electricity conductivity. • A digital core pore structure evaluation method for Utral-low permeability sandstones was developed.

Research on the Technology of Profile Control and Flooding in JY Oilfield to Stabilize Production

JY oilfield is mainly an ultra-low permeability reservoir with low reservoir permeability. As the permeability decreases, the starting pressure gradient rises sharply, and the establishment of an effective displacement pressure system is slow. The main reservoir has entered the medium water-cut development stage. On the plane, water flooding intrudes along the dominant channels such as fractures and high-permeability strips, resulting in plane contradictions; on the profile, the production degree decreases, and the injection-production profile is unbalanced. In this paper, through the study of reservoir physical properties, water flooding and control and flooding mechanism and the implementation of fine profile control and flooding on a large scale, the well selection conditions of different reservoirs are obtained, and differentiated countermeasures are formulated. Four optimizations of injection mode to ensure continuous improvement of injection effect and economic benefits.

Evaluation and Potential Analysis of Fracture Network Fracturing in Oil Production X Plant

The oilfields developed by our factory are mainly ultra-low permeability reservoirs, and the problems of non-injection and non-production are prominent. When conventional oil well fracturing is used, there are problems such as insufficient water injection energy, low oil increase rate after fracturing, and short validity period, and it is difficult to achieve benefit management. To this end, since 2013, while controlling the under-injected wells, the application of fracture network fracturing has been gradually increased, and a total of 116 wells have been fractured. The contribution reached 4.13%, and the annual mitigation comprehensive decrease contribution was 3.62%.

Practice and cognition of effective water-flooding development mode in Gaotaizi block of ultra-low permeability reservoir

During nearly 25 years of water injection development in Gaotaizi reservoir of LHP oilfield, due to poor reservoir physical properties, poor adaptability of well pattern and difficulty in establishing effective displacement between oil and water Wells, linear water injection, infill adjustment and refracturing tests have been carried out successively. Although certain effects have been seen, the effects are short and unsatisfactory. In this paper, the microscopic pore structure, sensitivity and seepage characteristics of ultra-low permeability high platform reservoir are studied through core laboratory experiments. New technology of nonlinear test and low permeable physical simulation experiment, the research on the rules of the nonlinear characteristics of the reservoir fluid and the characteristics of movable oil through research has been clear about the dragon bubble oilfield high effective displacement distance platform layer, and the new fracturing technology and the development of the technology to adjust the organic combination, the displacement between well and well past into displacement between Wells and joint network, explore the ultra-low permeability reservoir to improve the single well production, new ways to improve the development effect, with the types of low permeability oilfield development effectively.

Numerical Simulation of Liquid-Solid Coupling in Multi-Angle Fractures in Pressure-Sensitive Reservoirs

This study clarifies the seepage characteristics of complex fractured pressure-sensitive reservoirs, and addresses a common technological problem, that is the alteration of the permeability degree of the reservoir bed (known to be responsible for changes in the direction and velocity of fluid flows between wells). On the basis of a new pressure-sensitive equation that considers the fracture directional pressure-sensitive effect, an oil-gas-water three-phase seepage mathematical model is introduced, which can be applied to pressure-sensitive, full-tensor permeability, ultralow-permeability reservoirs with fracture-induced anisotropy. Accordingly, numerical simulations are conducted to explore the seepage laws for ultralow-permeability reservoirs. The results show that element patterns have the highest recovery percentage under a fracture angle of 45°. Accounting for the pressure-sensitive effect produces a decrease in the recovery percentage. Several patterns are considered: inverted five- seven- and nine-spot patterns and a cross-row well pattern. Finally, two strategies are introduced to counteract the rotation of the direction of the principal permeability due to the fracture directional pressure-sensitive effect.

Research and application of large-scale fracturing imitating horizontal well technology in vertical well

Hailaer Basin is rich in geological reserves, but the proportion of undeveloped reserves is high, accounting for 30% of the proved reserves. In order to improve the production degree of reserves and single well production, and realize the purpose of high and stable production of the oilfield. Taking the ultra-low permeability reservoir of oilfield B in Hailaer Basin as an example, this paper puts forward the large-scale fracturing of vertical wells and water injection development technology of imitating horizontal wells. By forming directional ultra long fracturing fractures in the oil layer, this technology can effectively increase the reservoir conductivity, increase the oil well drainage area and water well control area, reduce the well pattern density and improve the production of single well. The research shows that the undeveloped reserves in Hailaer oilfield have the characteristics of low thickness, low permeability and low reservoir quality index. There are 55 large-scale mold fracturing wells in Hailaer oilfield, with an initial oil increase of 2.2 times. The sand amount of large-scale fracturing is 2.5 times that of ordinary fracturing, and the fluid amount and sand intensity are 4.5 times that of conventional fracturing. The vertical well large-scale fracturing imitating horizontal well technology is adopted in Oilfield B. The designed vertical well fracturing fracture is 600m long and 120m wide, and the production effect is good after fracturing. The research results are of great significance to the high and stable production of undeveloped reserves block in Hailaer oilfield and other similar oilfields.

Field test practice and understanding of effective utilization technology for dense and refractory reservoir in block A

In view of the ultra-low permeability reservoirs in Block A of Hailar Oilfield, it is difficult to establish an effective driving system between oil and water wells due to the influence of many oil-bearing strata, poor reservoir physical properties and large vertical span of oil layers. With the deepening of development, it is more difficult to use reservoirs. In order to realize the effective utilization of low permeability reservoirs in Beier Oilfield, the successful experiences of tight oil and Hailar large-scale fracturing in peripheral oilfields are summarized, and the effective utilization technology of large-scale fracturing supplementary energy development is explored. The large-scale fracturing evaluation of ultra-low permeability reservoirs and the optimization of potential well areas are carried out, so as to fully tap the

Injectivity and Plugging Characteristics of Co2-Responsive Gel Particles for Enhanced Oil Recovery in Fractured Ultra-Low Permeability Reservoirs

Injectivity and Plugging Characteristics of Co2-Responsive Gel Particles for Enhanced Oil Recovery in Fractured Ultra-Low Permeability Reservoirs

Eor Mechanism of Fracture Oil Displacement Agent for Ultra-Low Permeability Reservoir

Eor Mechanism of Fracture Oil Displacement Agent for Ultra-Low Permeability Reservoir

Nanoemulsions stabilized by anionic and non-ionic surfactants for enhanced oil recovery in ultra-low permeability reservoirs: Performance evaluation and mechanism study

Nanoemulsions stabilized by surfactant have a high application potential in enhancing oil recovery in ultra-low permeability reservoirs. In this work, a new nanoemulsion flooding system were prepared by microemulsion dilution method using D-limonene, non-ionic surfactant fatty alcohol polyoxyethylene ether (AEO), anionic surfactant Sodium dodecyl sulfate (SDS), n-amyl alcohol and NaCl solution. The displacement performances of nanoemulsions were evaluated by spontaneous imbibition and displacement experiments, and the enhanced oil recovery (EOR) mechanisms were studied by Zetasizer Nano Z instrument, interfacial tensiometer, and contact angle meter. The results showed that the nanoemulsion system with optimal mass fraction (0.30 wt%) could get an additional oil recovery of 20.32% and reduce the injection pressure by 10.62%. Besides, the spontaneous imbibition recovery could reach 51.39%, which was 10.04% higher than that of SDS+AEO. The greater EOR effects of the nanoemulsion system can attribute to three perspectives. Firstly, nanoemulsions with particle sizes ranging from 80 nm to 100 nm make it possible to enter small pore throats of ultra-low permeability reservoirs to start-up crude oil without increasing insert pressure. Secondly, the nanoemulsion system exhibits ultra-low IFT (less than 1 ×10−2mN/m) and can change the core surface from hydrophobic to hydrophilic, which could roll up the crude oil and separate them from the rock surface. Finally, the dissolving effect of the oil phase can disperse crude oil to enhance the solubilization effect of the micelles and extract more crude oil. The findings of this study can help for better understanding of the application of nanoemulsions to enhance oil recovery in ultra-low permeability reservoirs.

Preparation and performance evaluation of an active nanofluid for enhanced oil recovery in ultra-low permeability reservoirs

The presence of nano-pore throats results in oil recovery of less than 15% in ultra-low permeability reservoirs. In this work, a new type of nanofluid was developed using chemically modified ultra-small silicon dots (SiDots) dispersed in water for enhanced oil recovery (EOR) of ultra-low permeability reservoirs. First, the ultra-small SiDots were synthesized by the hydrothermal method. Then, active SiDots were obtained by grafting sodium p-aminobenzene sulfonate onto the surface of the SiDots at room temperature with glutaraldehyde as a crosslinking agent. The active SiDot nanoparticles spontaneously dispersed in water; thus, the active SiDot nanofluid could be prepared without an external force. The active SiDot nanofluid exhibited high interfacial activity, reducing the interfacial tension and increasing the expansion modulus of the oil–water interfacial film. In addition, the active SiDot nanofluid showed excellent temperature (110 °C) and salinity resistance (12 × 104 mg/L). The result of imbibition experiments showed that the maximum recovery rate of the active SiDot nanofluid was 38%. The recovery rate of the active SiDot nanofluid was>15% higher than that of brine water and 5% higher than that of surfactants. The active SiDot nanofluids exhibited excellent application potential for EOR in ultra-low permeability reservoirs.

Enhanced oil recovery mechanism by surfactant-silica nanoparticles imbibition in ultra-low permeability reservoirs

Due to the low permeability, small pore throat and poor pore connectivity of ultra-low permeability reservoirs, the development technology of ultra-low permeability reservoirs is different from the stimulation techniques of conventional oil reservoirs, making development more difficult. In recent years, nanoparticles have been widely used in the oil industry and have shown great potential in oil exploitation. However, the application of nanofluids in high temperature and high salinity formation is still facing great challenges. In this work, a new type of nanofluid was prepared by mixing silica nanoparticles with anionic surfactant. The nanofluids were stored at high salinity (30,000 mg/L) and high temperature (80 °C) for 3 weeks without any aggregates. The particle size and zeta potential of nanofluids with different concentrations and ratios were measured. The microscopic structure of nanofluids was characterized by transmission electron microscope (TEM). By measuring and comparing the oil–water interfacial tensions between different concentrations and ratios of nanofluids and crude oil, as well as the contact angles between high salinity simulated water (30,000 mg/L) and nanofluids, the application potential of nanofluids in oil exploitation is discussed. Compared with high salinity (30,000 mg/L) simulated water, the interfacial tension decreases by 99.98% after adding nanofluids. The contact angle increases by 20° with the addition of nanofluids comparing with single surfactant, and the rock surface changes from oil wet to water wet. The recovery of nanofluids with different concentrations and ratios was measured by spontaneous imbibition experiment. The imbibition recovery of high salinity (30,000 mg/L) simulated water was only 8.9%, and that of surfactant was 14.33%. With the addition of nanofluids, the imbibition recovery is significantly improved, up to 29%. The possible mechanism of nanofluids for enhanced oil recovery (EOR) is proposed and analyzed, which proves that nanofluids have great potential in EOR. The findings of this study can be helpful for better understanding of the flooding mechanism of nanoparticles and the mechanism of enhanced oil recovery by nanofluid imbibition.

Analysis of Controlling Factors at Separate Imbibition Stages for Ultra-Low-Permeability Reservoirs

Spontaneous imbibition is an important mechanism in naturally fractured reservoirs. In our previous studies on the effect of imbibition efficiency of ultra-low permeability reservoirs, we mostly focused on the relationship between macroscopic core recovery rate and influential factors. Additionally, we also mainly focused on the factors that control the final imbibition recovery for ultra-low permeability reservoirs. Through a large number of experiments, it was found that the factors affecting imbibition are different in separate stages. However, the relative importance of those factors in different imbibition stages was hardly studied. In this work, we tested six key factors, i.e., the core length, RQI, salinity, interfacial characteristics, initial oil saturation, and oil viscosity, in natural sandstone samples from Chang 6 in the Zichang area. Based on experimental results, we divided the imbibition process into three stages (i.e., the early stage, the middle stage, and the late stage) to quantify the effects of the controlling factors. The results show that the relative importance of the controlling factors is changing during the imbibition process. The weight of importance is obtained for those factors at each stage. In addition, a comparative model is established for the dual-porosity media from Chang 6 formation. The results show that the increase of the rock size can extend the imbibition period for the early and middle stages. Moreover, the weight of importance for the initial oil saturation, interfacial characteristics, and salinity are also analyzed in three imbibition stages. This study provides theoretical support to guide water injection in ultra-low-permeability reservoirs and to understand the formation of energy supplements and oil recovery during the imbibition process.

Research on Minimum Miscible Pressure Between Crude Oil and Supercritical Carbon Dioxide System in Ultra-Low Permeability Reservoir by the Long-Slim-Tube Experiment Method

Carbon dioxide (CO2) injection has become an important technology to enhance oil recovery in ultra-low permeability reservoirs. Compared with other CO2 flooding technologies, CO2 miscible flooding has a better development effect, and the minimum miscible pressure (MMP) is a key parameter to realize miscible flooding. Therefore, it is very important to accurately predict the MMP. The prediction methods of MMP generally include laboratory experiment method and theoretical calculation method. In this study, a long-slim-tube displacement experiment method was used to determine the MMP in the study area, and the experimental temperature and pressure were consistent with those under reservoir conditions. The research results show that the recovery ratio increased gradually with the increase of experimental pressure, but the increase amplitude gradually decreased. According to the relation curve between crude oil recovery ratio and experimental displacement pressure, when the experimental pressure was larger than 29.6 MPa, the recovery ratio did not increase significantly with the increase of displacement pressure, which indicates that the interfacial tension between crude oil and CO2 disappeared under this pressure and they reached a miscible state. It is speculated that the MMP between crude oil and CO2 system in the study area predicted by the long-slim-tube displacement experiment method was 29.6 MPa. The results of this study help to realize miscible flooding in ultra-low permeability reservoirs and thus enhance oil recovery.

Development theory and practice of water injection induced fractures in ultra-low permeability reservoirs

Development theory and practice of water injection induced fractures in ultra-low permeability reservoirs

Analysis of tight oil accumulation conditions and prediction of sweet spots in Ordos Basin: A case study

Tight sandstone reservoirs are widely developed in the Mesozoic Yanchang Formation of the Ordos Basin, China. There is a lack of understanding on the sedimentary setting, source-reservoir relationship and oil accumulation conditions in this area. In this study, through the comprehensive analysis of the distribution of tight oil, we evaluated the properties and petrological features of reservoir, geochemical characteristics of source rocks, the source-reservoir relationship, as well as the trapping, preservation and accumulation conditions of tight oil in the Chang 7 Member, and predicted the sweet spots of tight oil in the study area. The results show that the Chang 7 Member is a typical low-porosity and ultra-low permeability reservoir with great tightness, small pore throat and high capillary pressure, and must have been of near-source accumulation. The source rocks are mainly developed in the Chang 73 submember, and the reservoirs mainly occur in the Chang 71 and Chang 72 submembers, forming a combination mode of “lower source rock and upper reservoir”. Sandbodies with good connectivity and fractures being well developed in local areas are the main hydrocarbon transport systems. The abnormal high pressure caused by hydrocarbon generation and pressurization is the main driving force of tight oil accumulation. The mode of hydrocarbon transportation is dominated by the vertical or lateral migration from underlying source rocks or adjacent source rocks to reservoirs within a short distance. Following the integrated evaluation of lithology, physical properties and oil saturation of reservoirs and geochemical characteristics of source rocks, we grouped the sweet spots of Chang 7 Member into three types: Type I, Type II and Type III. Among others, the Type I sweet spots are the best in terms of porosity, permeability and source rock thickness and hydrocarbon enrichment which should be the focus of oilfield development. This study lays an important foundation for the economic and efficient development of tight oil in the Chang 7 Member of Heshui area, and has important implications on tight sandstone reservoirs in other regions of Ordos Basin in China.

Synergistic effects between anionic and amphoteric surfactants on promoting spontaneous imbibition in ultra-low permeability reservoirs: Study of mechanism and formula construction

Faster spontaneous imbibition in ultra-low permeability reservoirs ensures higher productivity. Surfactants can promote spontaneous imbibition by creating a strong water-wet condition while keeping the oil-water interfacial tension (IFT) at an intermediate level. In this paper, A surfactant mixture composed of Alpha Olefin Sulfonate (AOS, an anionic surfactant) and Cocoamidopropyl-Hydroxysulfobetaine (CHSB-35, an amphoteric surfactant)CHSB-35 was proposed to promote the spontaneous imbibition rate of Chang 9 reservoir, a sandstone reservoir with high salinity, and ultra-low permeability. The synergistic effects between AOS and CHSB-35 as well as the functional mechanisms were clarified by conducting spontaneous imbibition tests. Experimental results show that when the total surfactant concentration locates in the range of 0.20–0.35 wt%, the oil-water IFT can be lowered to an ultra-low level at a salinity of 11.2 wt%. However, the spontaneous imbibition rate was found to be higher at a total surfactant concentration around 0.10–0.15 wt% with intermediate IFTs and contact angles around 35°. Our results indicated that once surfactant changes the rock wettability from an oil-wet state to a water-wet state, ultra-low IFTs are unnecessary or should be avoided in ultra-low permeability reservoirs. Spontaneous imbibition tests show that the oil production rate of AOS-CHSB-35 mixture is four times faster than simulated water and two times faster than each single surfactant.

Carbon Dioxide Flooding Technology for Ultra-Low Permeability Reservoirs to Greatly Enhance oil Recovery

Low-permeability reservoir pressure is difficult to maintain, CO2 miscible flooding is difficult to achieve for low-permeability reservoirs, and near-miscible flooding is a promising technology for enhancing oil recovery for low-permeability reservoirs. Aiming at the complex geological and development characteristics of China’s continental low-permeability reservoirs, the system elaborated Sinopec’s CO2 flooding theory, reservoir engineering optimization design, injection and production engineering and anti-corrosion technology, production CO2 recovery and utilization, and other technical developments and field tests. Happening. Based on the research of CO2 flooding mechanism, this paper takes a well-known oil field H 28 reservoir as the target, and conducts an indoor evaluation of CO2 flooding methods through core physical simulation experiments. The pilot test of CO2 flooding field shows that CO2 flooding can significantly increase the productivity of ultra-low permeability oil wells, improve the development effect of oil wells, and meet the needs of ultra-low permeability reservoir development, and has broad application prospects.

Optimization of large-scale fracturing technology and improvement of development effect of hard-to-recover reservoirs

At present, the development of unconventional and low-permeability oil and gas reservoirs has become a hot spot of energy development at home and abroad. The typical feature of this kind of oil and gas reservoirs is that the reservoir permeability is very low, and certain transformation measures need to be taken before they can be put into operation. The reservoir volume transformation technology is one of the important technologies for the effective development of unconventional oil and gas reservoirs. In recent years, in order to improve the development effect of ultra-low permeability reservoir, Hailar complex fault block oilfield has carried out field application tests of volume transformation technology in different types of reservoirs year by year. By increasing the amount of fracturing fluid and fracturing sand, increasing the fracturing sweep volume and improving the reservoir seepage conditions, the effective production of the reservoir is realized. However, from the perspective of fracturing effects of different reservoirs, there will be great differences in fracturing effects under the same fracturing method. It shows that the effect of large-scale fracturing development of oil and gas reservoir is related not only to the fracturing mode, but also to the geological characteristics of the fracturing horizon. The in-depth study of the factors affecting the fracturing effect has important guiding significance for the development of low-permeability reservoirs.