Development Of Low Permeability Reservoirs Research Articles

Development Adjustment Scheme of a Low-Permeability Reservoir in the SN Oilfield

Due to the complexity of low-permeability reservoirs, there is no set of established plans to adjust the development of specific low-permeability reservoirs, and the final development adjustment plan should be determined through comprehensive consideration of many aspects. At present, the development of low-permeability reservoirs in the SN oilfield faces problems. It is urgent to formulate corresponding development adjustment plans to improve the current development situation. In view of the problems of the current development surface of low-permeability reservoirs in the SN oilfield, this paper used the previous research results of a low-permeability reservoir development adjustment for reference, evaluated the reservoir development effect, analyzed the remaining oil distribution via numerical reservoir simulation, and finally designed and optimized a development adjustment plan. The research results show that the injection–production ratio and pressure of low-permeability reservoirs in the SN oilfield were generally maintained, the oil production decreased, the water cut increased, and the remaining recoverable reserves were considerable; the historical matching quality of a reservoir numerical simulation was good. There was more remaining oil in the northeast of the J007 well block and the north of the J008 well block, and the potential of the L2 and L3 layers was great. The remaining oil was mainly concentrated in the areas with high positions, poor physical properties, and imperfect well patterns; the predicted cumulative oil production of Scheme IV in 15 years and recovery were the highest, with the best development effect and the highest economic benefit. This was determined as the development adjustment plan for low-permeability reservoirs in the SN oilfield. The research results of this paper aim to improve oil production, the ultimate recovery factor, and economic benefits of low-permeability reservoirs in the SN oilfield, and to provide a reference for the development of similar oilfields.

Study on Production Characteristics during N2 Flooding in Low Permeability Reservoirs: Effect of Matrix Permeability and Fracture

The N2 flooding enhanced oil recovery process is an important technical means for the development of low permeability reservoirs due to its good energy enhancement effect and good injectivity. Low permeability reservoirs have a large permeability span and strong heterogeneity, which will have a significant impact on gas injection development. In order to explore the influence of matrix permeability and fractures on the production characteristics of N2 flooding, this study conducted a series of displacement experiments with full-scale matrix permeability (0.1–50 mD) and different fracture conditions. The research results indicate that, in non-fracture low permeability cores, the pressure difference decreased with the matrix permeability increase, and the volume of N2 injection required to achieve the highest injection pressure decreased. In addition, the increase in matrix permeability accelerates the gas breakthrough and gas channeling, but is beneficial for improving no-gas oil recovery and ultimate oil recovery due to the decrease in crude oil flow resistance. The impact of different matrix permeability ranges on production characteristics varies. When the matrix permeability is less than 2 mD, the characteristics of oil and gas production are significantly affected by changes in matrix permeability. When the matrix permeability is greater than 2 mD, the impact of changes in matrix permeability on development effectiveness is weakened. The existence of fracture causes a high permeability channel to appear in the low permeability matrix, exacerbating the gas breakthrough and channeling, and significantly reducing the utilization of matrix crude oil (about a 50% decrease in oil recovery). The increase in matrix permeability is beneficial for weakening the heterogeneity between fractures and the matrix, alleviating the gas channeling, thereby increasing the swept volume in the low permeability matrix and improving oil recovery.

Effect of water saturation on CO2 minimum miscibility pressure and oil displacement performance

The CO2 miscible flooding is an effective technology for development of low permeability reservoirs due to high oil displacement efficiency. However, CO2 miscible flooding for tertiary recovery technology typically occur after water flooding. Water hindered the contact and mass transfer of CO2 and oil, produce water resistance effect. Water can block CO2 and contact and mass transfer of crude oil (ie water blocking effect). The impact of this effect on the miscibility pressure and oil displacement effect is still unclear. In this study, homogeneous artificial cores with the same permeability as the reservoir were designed according to the miscible mechanism. Subsequently, the minimum miscibility pressure(MMP) between CO2 and crude oil at different water saturation was measured by the coreflood test. Based on the MMP, CO2 miscible flooding experiments were conducted by natural cores at different water saturation. The results showed that when the water saturation was 30%, 45%, and 60%, respectively, the corresponding MMP between CO2 and crude oil was 18.56, 19.48, and 21.76 MPa. The higher the water saturation, the longer the gas breakthrough time. But the oil recovery factor did not rise with the increase of water saturation. When the water saturation was 45%, the oil recovery factor in the miscible flooding experiment was the highest. In addition, the higher the water saturation, the weaker the CO2 extraction of various components in the crude oil. And the light components below C5 were most affected by water saturation. The mechanisms underlying these results are discussed. This study contributes to the development of CO2 miscible flooding reservoir plan.

ANALYSIS OF EFFICIENCY OF HORIZONTAL WELLS WITH MULTI-STAGE HYDRAULIC FRACTURING ON THE EXAMPLE OF KONDINSKOYE FIELD

In the structure of potential oil reserves in Western Siberia, the share of hard-to-recover reserves (HRR) is growing. At the same time, a significant share of these reserves is concentrated in low-permeability reservoirs. Horizontal wells using multi-stage hydraulic fracturing are the basis of technological solutions used for cost-effective development of low-permeability reservoirs by Russian oil and gas producers [1-4]. Due to the high efficiency of the subsea development systems with MSHF, oil production from such facilities exceeds oil production from traditional reservoirs and accounts for more than 60 % of the total oil production of the Company's fields [5]. The following characteristics are identified as the key parameters of the horizontal section, the number of hydraulic fractures, as well as the specific weight of the injected proppant at the frac stage. The decisions approved as part of the design documents for the development of facilities with TPP indicate a tendency to increase the length of the horizontal hole and the number of frac operations with a decrease in the specific mass of proppant on the port. The article examines the impact of these characteristics on the technological efficiency of wells. The purpose of the work is to assess the feasibility of increasing the technological complexity of HW with multi-stage hydraulic fracturing of the MSHF formation in the form of increasing the number of stages and length of the horizontal hole, as well as the specific mass of proppantane in the example of the AS10/1 Kondinskoye field development target. Within the framework of the study, three types of HW with MSHF were identified, the technological effectiveness of which was assessed in two ways. The first method consisted in comparing the magnitudes of the dimensionless productivity coefficient Jd (d. units) of three different types of wells with a horizontal end in relation to directional wells (FWS with frac) of the environment. Taking into account the similarity of the geological conditions of the neighboring wells, this method made it possible to assess how effectively the completion of the horizontal wells under study was completed. The multiplicity assessment methodology was developed by RN-BashNIPIneft LLC [6]. The second method was to compare the ratio of dimensionless productivity factor to the specific weight of proppant Jd/Mpr _ specific of the identified types of HW with multi-stage hydraulic fracturing (MSHR). This approach made it possible to take into account the effective thickness and permeability of the formation in the well drilling zone, as well as the weight distribution of the injected proppant. The results showed that if the length of the horizontal hole is constant, an increase in the number of frac stages while reducing the proppant weight on the port is impractical. Confirmation was also obtained based on statistical data that there is a relationship between the cumulative fluid withdrawal and the weight of the injected proppant. It has been established that drilling HW with multi-stage hydraulic fracturing of the (MSHF) formation of the most common type (1000 m, 10 stages) is not optimal for the study target: for a length of 1000 m, the maximum number of stages should be limited to 7–8 units per well. Further monitoring and analysis of production wells with horizontal termination is recommended to collect more statistical data and compare them over time.

An overview of efficient development practices at low permeability sandstone reservoirs in China

Low permeability sandstone reservoirs in China typically have more complicated geological conditions, pore structures, and flow characteristics as compared to medium-to-high-permeability sandstone reservoirs. Traditional geological and seepage theories, and engineering methods are not applicable to the development of these low permeability reservoirs, and wells drilled into them often produce oil and gas at very low rates. Recent breakthroughs in reservoir exploitation technology have greatly improved the productivity of low permeability reservoirs, making them the primary target for oil exploration and extraction in China. The development theories and practices applied to low permeability reservoirs in China are reviewed in this study— based on relevant geological and engineering practices, including drilling, fracturing, recovery, and surface engineering. A unique series of technological advances that aid the development of low permeability reservoirs in China are summarized here. This study may serve as a meaningful guide in achieving scale efficiency for the development of low permeability reservoirs.

Study on the influencing factors of productivity under pressure drive development in low permeability reservoir

The productivity of low-permeability reservoirs is affected by multiple factors. After the development of water injection by pressure drive, it will also be affected by factors such as construction, resulting in large differences in the productivity of different oil wells. According to reservoir engineering knowledge, the factors affecting the productivity of pressure drive water injection development are preliminarily determined. The conceptual model of pressure drive water injection development of low permeability reservoir is established by numerical simulation method. Combined with orthogonal design, the main control factors of pressure drive water injection development productivity are determined. The main control factors include injection production well spacing, water injection volume of pressure drive measures, water content before pressure drive, porosity, and quantitative analysis of the main control factors. Through correct analysis and evaluation of these factors, it provides guiding significance for the productivity prediction of pressure drive water injection development in low permeability reservoirs and the optimization of pressure drive water injection scheme.

A COMPARATIVE STUDY ON THE OIL RECOVERY PERFORMANCE OF THE CO2 AND N2 HUFF-N-PUFF PROCESSES IN LOW PERMEABILITY CORES

The gas huff-n-puff process has been widely employed in low permeability reservoir development practices. At present, the understanding of synergistic effects of different injection fluids and rock permeability is still limited and is worthy of in-depth investigation. Therefore, laboratory studies on oil recovery performance of supercritical CO<sub>2</sub> (scCO<sub>2</sub>) and N<sub>2</sub> huff-n-puff processes in ultra-low (< 0.5 mD), extra-low (0.5-1 mD), and average-low permeability (1-10 mD) core samples were systematically investigated. More effective cycles could be achieved in the CO<sub>2</sub> huff-n-puff process than in the N<sub>2</sub> process. The CO<sub>2</sub> huff-n-puff operation could produce 29.9% oil in the ultralow permeability core, which is obviously higher than 20.2% for N<sub>2</sub>. With increasing core permeability, the oil recovery ratio for both the scCO<sub>2</sub> and N<sub>2</sub> huff-n-puff processes increases as well. Laboratory results show oil recovery ratios of 33.1% and 47.3% for the scCO<sub>2</sub> process in 0.5 mD and 10 mD cores and 36.3% and 49.1% for the N<sub>2</sub> process in 0.5 mD and 9.5 mD cores, respectively. Although the oil recovery rates for the N<sub>2</sub> and CO<sub>2</sub> huff-n-puff processes are close in the 0.5 mD and 10 mD cores, the effective oil extraction pressure for the scCO<sub>2</sub> puff process is found to be 5~10 MPa, which is much higher than 0~2 MPa for the N<sub>2</sub> puff process. The study's findings can help provide a better understanding of the oil extraction behaviors in the huff-n-puff process with different injection fluids as well as in different low permeability cores.

Experimental Investigation on the Imbibition Behavior of Nanofluids in the Tight Oil and Gas Reservoir through the Application of Nuclear Magnetic Resonance Method

Tight oil and gas resources are widely distributed and play an important role in the petroleum industry. Due to its nanoscale pore-throat characteristics, the capillary effect is remarkable, and spontaneous imbibition is very beneficial to the development of low-permeability reservoirs. In this study, the imbibition experiments of 2D nano blackcard, nanoemulsion, and water were carried out, respectively. The pore-throat fluid distribution characteristics before and after core imbibition were analyzed with nuclear magnetic resonance technology, and the enhanced oil recovery effects of 2D nano blackcard nanoemulsion, and water were comprehensively evaluated. The results show that the final recovery factors of cores soaked in 2D nano blackcard (0.005 ωt%) and nanoemulsion (0.02 ωt%) or imbibed in water are 32.29%, 26.05%, and 7.19%, respectively. It can be found that 2D nano blackcard is the fluid with the best imbibition effect. In this work, a new type of 2D nano blackcard was proposed and identified as a functional imbibition fluid for enhanced oil recovery in tight reservoirs, providing a practical reference for the effective development of tight, low-permeability oil and gas reservoirs.

Analysis on the mechanism and characteristics of nanofluid imbibition in low permeability sandstone core pore surface: Application in reservoir development engineering

In this work, the mechanism of nanofluid imbibition in the development of low permeability reservoirs is studied. Firstly, by analyzing nuclear magnetic resonance (NMR) curves and imaging maps, the imbibition displacement effects of low-permeability reservoirs in water and different nanofluids are compared. Subsequently, the influence characteristics of rock modification mechanism of nanofluid on imbibition displacement are analyzed by three-phase contact angle experiments. Finally, the attraction forces between oil and rock surfaces with different properties are measured by atomic force microscopy (AFM) experiments, and the influence of wetting inversion of nanofluids on the adsorption between oil and reservoir rocks is evaluated. The results show that the relaxation time map area of the core treated with nanofluid is smaller than that of the core treated with water, and the NMR images show that the nanofluid has a higher sweep efficiency, indicating that nanofluid can improve the oil displacement efficiency of low-permeability reservoirs. The higher the nanoparticle concentration of fluid, the more significant the effect. In addition, the effect of nanofluids on oil displacement efficiency in small pores and large pores of the reservoir is obvious, and the increase amplitude is 30 % and 50 %, respectively. Scanning electron microscope (SEM) images show that nanoparticles adsorbed on the reservoir inner wall exert a wetting inversion effect, leading to changes in reservoir wettability and promoting imbibition oil displacement, which is also reflected in the NMR maps. Contact angle experiments show that nanofluids convert the lipophilicity of rock surface into hydrophilicity, and the contact area between oil and rock shrinks due to the change of wettability and the decrease of interface energy, which weakens the adsorption between the two, promotes capillary imbibition of fluid and oil displacement. The AFM experiment confirms that nanoparticles reduce the microscopic adsorption force between oil and rock through wetting inversion and interface energy reduction. It is less difficult for the fluid to peel oil from the reservoir rock, which promotes the oil displacement. The studies show that nanofluid imbibition has advantages in the field of low permeability reservoir development.

CO2 responsive expansion hydrogels with programmable swelling for in-depth CO2 conformance control in porous media

Considerable research efforts have been devoted to finding and developing the oil locked within low-permeability reservoirs. The oil-rock interaction exacerbated in tiny pores and heterogeneities in formation epitomize the challenges accompanying the development of low-permeability reservoirs. CO2 flooding has become a promising treatment to increase displacement efficiency and formation energy for enhanced oil recovery. Nevertheless, due to the mismatch in the viscosity of CO2 with that of the crude oil and the intrinsic heterogeneity of the reservoir, gas channeling is inevitable, resulting in low oil recovery and low CO2 storage efficiency. This paper is motivated to fabricate CO2 intelligent responsive hydrogel that exhibits a delayed swelling: the hydrogel will uptake water and swell when encountering CO2 or H+, to strengthen the plugging capacity for the gas channeling. A two-step method was used to prepare CO2 responsive (CR) hydrogel which has good injection performance and can form gel in-situ to control the gas channeling in low-permeability reservoirs. To achieve the above functions, CR polymer with acrylamide (AM) and N-[3-(Dimethylamino) propyl] methacrylamide (DMAPMA) was synthesized by aqueous free-radical copolymerization. CR hydrogel was prepared by crosslinking CR polymer with polyethyleneimine (PEI). Then 1.2 wt% CR polymer and 0.2 ∼ 0.4 wt% PEI were determined as the optimal synthetic formulation of CR hydrogel which is capable of maintaining stability at 80 ℃ for more than 30 days without dehydration. The gelation time was more than 24 h indicating that the CR hydrogel has good injection and in-depth migration ability. Also, the swelling behaviors of CR hydrogel were studied, and the hydrogel can expand more than 10 times in acidic conditions (pH ∼ 4.5) with respect to about 2 times in neutral conditions (pH ∼ 7). The expansion mechanism is further revealed and proved to be feasible for CO2 channeling control.

Experimental investigation of zwitterionic surfactant-based silica nanofluid spontaneous imbibition at high salinity and elevated temperature conditions

High-efficiency development of low permeability reservoirs is significant to maintaining a balance between energy supply and social needs. Surfactant-based nanofluids with an excellent interfacial activity that can penetrate the small throats and narrow pores are considered promising EOR agents. However, the applications of nanofluids in harsh reservoir conditions remain to be challenging due to high stability requirements. In this work, a highly stable active nanofluid that could withstand high salinity (API brine) and elevated temperatures was prepared by mixing zwitterionic hydroxypropyl sulfobetaine surfactant with low-molecular-weight ligand modified silica nanoparticles. At a surfactant/nanoparticle concentration ratio of 0.5, the spontaneous imbibition recovery factor of dodecyl hydroxypropyl sulfobetaine-based nanofluid was 2.61 times higher than API brine, 1.29 times higher than API brine-based nanofluid and 0.37 times higher than surfactant alone. Meanwhile, the impacts of surfactant carbon chain length, permeability as well as hydrochloric acid were included. Experimental results indicated that surfactants with longer carbon chain length would destabilize the nanofluids due to increasing hydrophobic interactions, and nanoparticle aggregation/precipitation would impose adverse impacts on spontaneous imbibition because of pore/throat plugging. Though increasing permeability could partially ease the negative plugging effects, the potential risks should never be overlooked. Properly using hydrochloric acid could greatly enhance the stability of nanoparticles by forming an “H+” protection layer and extend their applications to over 80 °C, but the presence of acid also disturbed the adsorption behaviors of surfactants, therefore, different phenomena were noticed when the nanofluid formula changed. A good spontaneous imbibition system should possess both IFT reduction and wettability alteration capabilities, and nanoparticles’ ability to adsorb and disperse polar compounds such as asphaltene should be fully fulfilled. This study provides new guidance for nanofluid formulation to support the effective development of low-permeability oil reservoirs.

Research on Percolation Characteristics of a JANUS Nanoflooding Crude Oil System in Porous Media.

According to the research status of low-permeability reservoir development, in order to find an intelligent and efficient displacement method, a Janus smart nanocapsule (embedding nanomaterials with surfactant function into the polymer) is developed in this paper. There are two kinds of phase fluids in the migration of porous media, the initial Janus intelligent microcapsule slow-release liquid (dissolved and undissolved AP-g-PNIPAAM and Janus functional particle ternary dispersion) and the later AP-g-PNIPAAM and Janus functional particle binary dispersion. Comprehensively, using the indoor oil displacement experiment, the seepage characteristics of the Janus smart nanocapsule (JSNC) in porous media are studied, and their macro and micro oil displacement mechanisms are revealed. Research shows that Janus intelligent microcapsules have good mobility control ability in low-permeability heterogeneous reservoirs. The displacement performance of stepped differential pressure shows that the displacement medium can expand the swept volume. The research results presented can show that the JSNC oil displacement system has great application potential for the development of low-permeability reservoirs.

Production Behavior Analysis of Multibranched Horizontal Oil Well considering Reservoir and Well-Type Factors

Multibranched horizontal well is an important means to develop low permeability reservoirs. Fishbone multibranched horizontal well has the advantages of increasing drainage area, reducing drilling number, utilizing existing wells, and saving oilfield development cost, especially for marginal oilfield exploitation. The morphological structure of fishbone multibranched horizontal well is very complex, so the numerical simulation study is of great significance to guide the production of fishbone multibranched horizontal well. In this paper, the numerical model is established for fishbone multibranched horizontal well in the oil reservoir. The finite element method is used to numerically solve the mathematic model. The oil well production can be achieved by using the material balance method. Sensitivity analysis is made on the important reservoir and well-type factors that affect the production behavior and transient pressure distribution of fishbone multibranched horizontal well. It is concluded that the effective reservoir thickness and flowing bottomhole pressure have great influence on the productivity, but the influence of heterogeneity is not obvious. The length of main wellbore has great effect on the productivity in the early stage. Fishbone multibranched horizontal wells should be placed in the middle of the reservoir to increase productivity. Branch length, branch angle, branch number, and branch spacing are important parameters affecting the productivity of fishbone multibranched horizontal well. The variation of these parameters has obvious influence on the stimulation effect in the early stage of production, but the influence degree is different. Under the premise of drilling technology and drilling safety, the comprehensive impact of these four factors on productivity should be considered simultaneously. The presented model and obtained results not only enrich production behavior analysis of fishbone multibranched horizontal well but also have significance on formulation of stimulation measures and efficient low permeability reservoir development.

Laboratory Study on the Oil Displacement Process in Low-Permeability Cores with Different Injection Fluids

Although flooding technology has found wide application in low-permeability reservoir development practices, the oil recovery enhancement mechanisms for different injection fluids still lack specific focus based on comprehensive investigations. Therefore, in this paper, supercritical CO2 (ScCO2), N2, and water injection processes in oil-saturated low-permeability tight cores were comparatively studied. To reveal the effect of physicochemical properties of the injection fluid on the oil recovery efficiency, the Berea sandstones with three permeability levels and kerosene were employed in this study to exclude other parameter influences. The flooding processes employing various injection media were investigated based on quantitative comparisons of the oil recovery factor and the displacement pressure difference at two system pressures. The experimental results show recovery efficiencies of 59–91 and 84–92% with the increasing permeability for the ScCO2 injection process at system pressures of 15 and 25 MPa, respectively, which are much higher than 26–40 and 21–52% in the N2 case and 43–46 and 45–49% in the water cases. Interfacial tension (IFT) measurement results indicate that miscibility conditions have been achieved for the ScCO2/oil system, thus leading to much higher oil recovery. On the other hand, the pressure difference results show a similar magnitude of 10 MPa/m for both ScCO2 and N2 processes, which is much lower than the 100 MPa/m for the water flooding cases. Comprehensive comparison shows that ScCO2 shows great advantages in the application of unconventional reservoirs. It is expected that our research work could enrich the investigations of CO2 flooding and the in-depth understanding of the mechanisms and better guide the utilization of CO2.

Analysis of reducing pressure and increasing injection in high pressure water injection block of low permeability reservoir

The plugging phenomenon near the well zone of oil injection well will seriously affect the water injection development of oil field, and then affect the exploitation of oil resources. The water injection development of low permeability reservoir is affected by various factors. Due to the large difference between layers and the serious interference between layers, the physical property of oil layer is relatively poor, and the water injection pressure shows a trend of increasing year by year, which has a great impact on the development of oil resources. As the oilfield development benefit is not ideal, it is necessary to take reasonable measures to reduce the pressure of water injection to ensure the effect of water injection to improve the recovery of the reservoir. At present, the technology has been mature, which can reduce the pressure of water injection and ensure the oil recovery rate. The application in several oil Wells has verified the correctness of this conclusion.

Analysis of low permeability reservoir development technology

As an important energy source for social production and development, oil is non-renewable. In the process of development and utilization, attention should be paid to continuously improve the exploitation technology, enhance the ability of oil exploration, and strengthen the development of low permeability reservoir resources, so as to provide sufficient oil resources for social production and development. However, low permeability reservoir resources have their own characteristics and are limited by multiple factors in the process of exploitation. It is difficult to improve the exploitation efficiency of low permeability reservoir resources without adopting corresponding exploitation technology. This it is scientific and reasonable exploitation of low permeability oil reservoir resources technology are analyzed and discussed, in the comprehensive analysis based on the characteristics of low permeability oil reservoirs, mining characteristics, puts forward the well pattern optimization, waterflood recovery, fracturing technology and mining method, working for the effective implementation of the low permeability reservoir development provides the technical support, also need to continue well technology application in the construction process in the future.

Preparation and application of targeted response nanocapsules for oil displacement

Based on the purpose of forming a new method to improve the oil recovery of low-permeability reservoir, this paper proposes the concept of “intelligent nanocapsules flooding” and develops an intelligent targeted oil displacement agent. The intelligent nanocapsule is a new way to embed surfactant into polymer, which has the advantage of avoiding invalid loss of surfactant in the capsule. In this paper, nanoscale silicon dioxide was prepared by sol–gel method, Janus silica nanoparticles were synthesized by Pickering emulsion preparation, and a Janus functional particle with targeted migration was obtained by coupling agent modification. The amphiphilic temperature responsive polymer AP-g-PNIPAAM was synthesized by atom transfer radical polymerization. The capsule wall prepared in this paper has temperature sensitivity, and Janus functional particles in the core play a targeted role. The oil displacement experiments were carried out on five parallel core models with different grade differences. The results show that when the permeability grade of the parallel combined model rises from 2.05 to 21.57, the oil recovery of Janus intelligent microcapsule dispersion system also increases from 11.16% to 20.75%, with an increase rate of 9.59%. The research results of this paper are helpful to promote the further development of low permeability reservoir.

46. A MASSIVELY PARALLEL ASSAY OF TRANSLATION FOR DETERMINING THE IMPACT OF DE NOVO AUTISM SPECTRUM DISORDER-ASSOCIATED VARIANTS IN 5′ UNTRANSLATED REGIONS

Based on the purpose of forming a new method to improve the oil recovery of low-permeability reservoir, this paper proposes the concept of “intelligent nanocapsules flooding” and develops an intelligent targeted oil displacement agent. The intelligent nanocapsule is a new way to embed surfactant into polymer, which has the advantage of avoiding invalid loss of surfactant in the capsule. In this paper, nanoscale silicon dioxide was prepared by sol–gel method, Janus silica nanoparticles were synthesized by Pickering emulsion preparation, and a Janus functional particle with targeted migration was obtained by coupling agent modification. The amphiphilic temperature responsive polymer AP-g-PNIPAAM was synthesized by atom transfer radical polymerization. The capsule wall prepared in this paper has temperature sensitivity, and Janus functional particles in the core play a targeted role. The oil displacement experiments were carried out on five parallel core models with different grade differences. The results show that when the permeability grade of the parallel combined model rises from 2.05 to 21.57, the oil recovery of Janus intelligent microcapsule dispersion system also increases from 11.16% to 20.75%, with an increase rate of 9.59%. The research results of this paper are helpful to promote the further development of low permeability reservoir.

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.

Simulation of imbibition in porous media with a tree-shaped fracture following the level-set method

Imbibition is an important mechanism for enhancing oil recovery in low-permeability reservoirs, such as shale and tight sandstone, and a tree-shaped network has been successfully used to characterize fracturing fracture. Therefore, understanding the imbibition mechanism in porous media with a tree-shaped fracture (TFPM) is important for developing low-permeability reservoirs. In this study, a simulation model for imbibition in TFPM was established based on the level-set method, and the model was verified by comparing it with an analytical solution. The influences of the fracture width, bifurcation angle, tortuosity, and water flow rate on imbibition in TFPM were then discussed. Based on the results, the following points have been established: (1) During the early stage, the imbibition in TFPM included countercurrent and a combined imbibition, and only countercurrent imbibition occurred during the later stage. (2) At a constant fracture width ratio, increasing the primary fracture width could reduce the residual oil in the TFPM, thereby improving the oil recovery factor. (3) At a fracture bifurcation angle ranging from 0° to 45°, the oil recovery factor increased as the bifurcation angle increased. (4) At a fracture tortuosity of 1.0 to 1.24, changes in tortuosity had little effect on the oil recovery factor during the early stage of imbibition, while it significantly affected the distribution of the residual oil. (5) At a water flow rate of 5 mm/s, the simulated oil recovery factor in the TFPM was highest. This investigation can provide a reference for the development of low-permeability reservoirs.