Imbibition Recovery Research Articles

Effect of Dynamic Imbibition on the Development of Ultralow Permeability Reservoir

To explore the methodology for improving ultralow permeability reservoir recovery, cores of ultralow permeability reservoirs in China’s Ordos Basin were selected to study the dynamic imbibition micromechanism of crude oil in nanopore throat through core-flooding laboratory experiment and nuclear magnetic resonance (NMR) observation. In the meantime, the microimbibition characteristics and dynamic discharge of oil between matrix and fracture in partially closed boundary reservoirs were simulated to utmostly reflect the actual reservoir conditions. Our findings suggest that dynamic imbibition between fracture and matrix serves the core technology for improving the recovery of ultralow permeability reservoirs, while the main factors affecting dynamic imbibition efficiency include wettability, permeability, injection rate, fracture, water huff and puff cycles, and soaking time. Wettability, in particular, weighs the most, and imbibition can take place either on water-wet rocks or transformed oil-wet rocks with an imbibition agent added in during the waterflooding process. Meanwhile, the higher the permeability is in place, the greater the dynamic imbibition recovery might achieve. The experiments indicate that the dynamic imbibition recovery of a fractured core is 16.26% higher than that of a nonfractured core. Additionally, fractures can not only enhance imbibition recovery but also accelerate the occurrence of dynamic imbibition. The optimal water injection rate of dynamic imbibition is 0.1 mL/min; the reasonable huff and puff cycle of the ultralow permeability reservoirs tends to be two to three cycles; the optimal soaking time of ultralow permeability reservoir is speculated to be 30 days. Finally, the field practice shows that after Stimulated Reservoir Volume (SRV) and dynamic imbibition in 5 horizontal wells in An83 oilfield, there is a remarkable drop in water cut and a noticeable rise in oil production. This research underpins the significance of a dynamic imbibition effect in the development of ultralow permeability oilfield.

Laboratory optimization of surfactant imbibition in high temperature and high salinity fractured reservoir

This paper focused on surfactant evaluation targeting the harsh reservoir conditions (high temperature and high salinity fractured reservoir). Six kinds of surfactants were selected and evaluated in terms of interfacial tension (IFT) and contact angle. . S-6 and S-7 presented the best potential ability in IFT reduction among all kinds of surfactant solutions, which were in the 10−2mN/m magnitude. The experiment results showed that the contact angle on oil-wet glass slide at the concentration of 0.2% S-6 was 58°, which is in water-wet region; while other surfactants cannot change the surface wettability. . Finally, the micromodel flooding tests were conducted using S-6, S-7 and S-8 to study both effects of wettability alteration and IFT reduction ability on EOR. The micromodel work was based on an oil-wet etched glass. Compared with S-7, the recovery increase of S-6 was about 12%, indicating that with the similar abilities of IFT reduction for surfactant solutions, the one with stronger wettability alteration ability could lead to a higher oil recovery. As a result, S-6 had better potential in providing higher oil recovery as an imbibition agent. Numerical simulation using UTCHEM suggested that with the increase of injection rate and the decrease of IFT, the imbibition recovery is increased.

Study of a low-damage efficient-imbibition fracturing fluid without flowback used for low-pressure tight reservoirs

The oil production from the low-pressure tight reservoirs in China decreases sharply after fracturing under natural depletion. To supply the formation energy and displace oil through imbibition instead of flowback, a novel nanoparticle-enhanced supramolecular fracturing fluid (NESF) was developed. It consisted of 0.10 wt% hydrophobically modified hydroxypropyl guar (HMHPG), 1.00 wt% synthesized hydrophilic gemini surfactant (HGS), and 0.05 wt% hydrophobically fumed nanosilica (HNS). A series of experiments were conducted to characterize the molecular structure of HGS and evaluate the heat/shear resistance, rheological property, proppant suspension and transportation, formation damage, and imbibition efficiency of NESF. Finally, the oilfield practical application of NESF fracturing without flowback was carried out. The results showed that the heat resistance and the interfacial property of NESF were improved by HNS and HGS respectively. Besides the favorable common properties, a low oil permeability loss rate of 9.40%, a high fracture conductivity retainment rate of 95.11%, and a high imbibition recovery factor of 19.43% were realized by NESF. The accumulative oil production of the well stimulated by NESF without flowback was increased by 13.55% and the decline rate of oil production was reduced from 14.70% to 5.22% in the first 6 months.

Effect of viscosity on oil recovery by spontaneous imbibition from partially water-covered matrix blocks

Spontaneous imbibition is an important mechanism of oil recovery from fractured reservoirs and unconventional reservoirs. Oil is produced by combining co- and counter-current imbibition when the matrix blocks was partially covered by water. In this paper, we focused on the effect of viscosity ratios on oil production by spontaneous imbibition and established the numerical model for one-dimensional linear imbibition with TEO-OW boundary conditions, which was validated by the experimental data. The effect of viscosity ratio on co- and counter-current imbibition is investigated and scaling result of the imbibition recovery curve for wide range of viscosity ratio using the conventional scaling equation was tested, which indicates that the close correlation was achieved only when oil-water viscosity ratios are higher. Then, a modified scaling equation was developed based on the piston-like assumption for one-dimensional co-current imbibition and close correlation of imbibition recovery curves was achieved when viscosity ratios are lower. Finally, correlation of imbibition recovery curves was improved for wide range of viscosity ratios by combining conventional and modified scaling equation. Results show that since the shape of imbibition recovery curves is not similar for different viscosity ratios, it is difficult to obtain the perfect correlation using the constant viscosity term.

Imbibition and Oil Recovery Mechanism of Fracturing Fluids in Tight Sandstone Reservoirs

The fracturing fluid residing in a reservoir undergoes spontaneous imbibition. Here, to explore the mechanism of fracturing fluid imbibition and oil displacement, experiments on the spontaneous imbibition of fracturing fluid under different influencing factors were conducted on a core sample from the Ordos Basin of the Chang 8 formation. Combined with nuclear magnetic resonance technology, we quantitatively evaluated the degree of oil production of different pores during the fracturing fluid displacement process. Experimental results show that fracturing fluid salinity, fracturing fluid interfacial tension, and crude oil viscosity are negatively correlated with oil recovery. The phenomenon of microscale imbibition oil displacement occurs in pores of various scales in the core. The imbibition scale was between 0.10 and 1608.23 ms. The degree of crude oil production in the pores at each scale increased with increasing imbibition time. Moreover, the crude oil viscosity, fracturing fluid salinity, and fracturing fluid interfacial tension are negatively correlated with the degree of oil production at various pore scales. Decreasing crude oil viscosity significantly improves the degree of small-pore (0.1–16.68 ms) crude oil production; the low interfacial tension possesses a higher degree of oil production in the large pores (>16.68 ms), and the increment in the degree of oil production under different salinities of the small pores (0.1–16.68 ms) is greater than that of the large pores (>16.68 ms).

A new slick water system for hydraulic fracturing in tight reservoir to enhance imbibition oil recovery

In order to give full play to the role of imbibition of capillary force and enhance oil recovery of ultralow permeability sandstone reservoir after hydraulic fracturing, the mixed water fracture technology based on functional slick water is described and successfully applied to several wells in oilfield. The core of the technology is determination of influence factors of imbibition oil recovery, the development of new functional slick water system and optimization of volume fracturing parameters. The imbibition results show that it is significant effect of interfacial tension, wetting on imbibition oil recovery. The interfacial tension decreases by an order of magnitude, the imbibition oil recovery reduces by more than 10%. The imbibition oil recovery increases with the contact angle decreasing. The emulsifying ability has no obvious effect on imbibition oil recovery. The functional slick water system considering imbibition is developed based on the solution rheology and polymer chemistry. The system has introduced the active group and temperature resistant group into the polymer molecules. The molecular weight is controlled in 1.5 million. The viscosity is greater than 2mPa·s after shearing 2h under 170s-1 and 100℃. The interfacial tension could decrease to 10-2mN/m. The contact angle decreased from 58° to 22° and the core damage rate is less than 12%. The imbibition oil recovery could reach to 43%. The fracturing process includes slick water stage and linear gel stage. 10% 100 mesh ceramists and 8% temporary plugging agents are carried into the formation by functional slick water. 40-70 mesh ceramists are carried by linear gel. The liquid volume ratio is about 4:1 and the displacement is controlled at 10-12m3/min. The sand content and fracturing fluid volumes of single stage are 80m3 and 2500 m3 respectively. Compared with conventional fracturing, due to imbibition oil recovery, there is only 25% of the fracturing fluid flowback rate when the crude oil flew out. When the oil well is in normal production, about 50% of the fracturing fluid is not returned. It is useful to maintain the formation energy and slow down the production decline. The average cumulative production of vertical wells is greater than 2800t, and the effective period is more than 2 years. This technology overcoming the problem of high horizontal stress difference and lack of natural fracture has been successfully applied in Jidong Oilfield ultralow permeability reservoir. The successful application of this technology not only helps to promote the effective use of ultralow permeability reservoirs, but also helps to further clarify the role of imbibition recovery, energy storage and oil-water replacement mechanism.

Pore-scale visual investigation on the spontaneous imbibition of surfactant solution in oil-wet capillary tubes

ABSTRACT Surfactant assisted spontaneous imbibition is a feasible method for enhanced oil recovery in the reservoirs. A series of pore-scale visual spontaneous imbibition experiments of surfactant solution in oil-wet capillary tubes with six different diameters (10 μm~60 μm) are thoroughly investigated. The results showed that the final imbibition recovery exhibited a rise and fall tendency in sequence with the increase of capillary tube diameter. The combination of the Marangoni effect and diffusion effect was the dominant power to render the oil be expelled, and the wettability alteration was principally conducive to the migration of expulsion oil. Additionally, emulsification entrainment was beneficial to imbibition recovery.

Mechanism of using liquid nanofluid to enhance oil recovery in tight oil reservoirs

Liquid nanofluid (LNF) has been widely used for enhanced oil recovery (EOR) in tight oil reservoirs in recent years. However, the mechanism of oil recovery by LNF flooding is still unclear. In this study, a series of experiments were conducted to explore this problem. The properties of LNF were first evaluated by testing contact angles and particle size distributions. Then, the blocking and adsorption in the matrix were investigated. After that, the imbibition with nuclear magnetic resonance (NMR) was conducted to evaluate the imbibition recovery and process. Finally, the retained permeability was studied through pressure transmission tests. Our results showed that the LNF can be transported in the nano-scale pores and pore throats without bridging in the formation. This increased sweep volume and efficiency while maintaining low adsorption. During the imbibition process, with the wettability alteration and proper interfacial tension, the LNF entered small pores first to displace oil. Moreover, when injected into the reservoir, LNF in pores could avoid the exhaustion of formation pressure to prolong the effective production period. Finally, the higher retained permeability could reduce the flow resistance and energy consumption while increasing the production indirectly. Our study has not only provided a method to evaluate a chemical fracturing fluid additive but also revealed a new mechanism of LNF flooding in tight oil reservoirs.

Analysis of the Static and Dynamic Imbibition Effect of Surfactants and the Relative Mechanism in Low-Permeability Reservoirs.

Establishing an effective displacement system for conventional water flooding development in low-permeability reservoirs is difficult, with generally low liquid and oil production and a worse water flooding effect. Imbibition oil recovery technology has received increasing attention from oil development workers because of its simple operation, low cost, and good oil increase effect. To explore the method and mechanism to further improve the effect of imbibition oil recovery, we study the imbibition and oil recovery effect and its influencing factors in a low-permeability reservoir in the Dagang Oilfield based on evaluation indexes of the adhesion work reduction factor, ratio of capillary force to gravity NB–1, regression analysis of the recovery rate of imbibition, proportional relationship with spontaneous imbibition, and dynamic imbibition effect in crack rocks. Results show that reducing the interfacial tension of the surfactant on the imbibition process has a dual effect. The selection of the surfactant for fractured tight reservoirs should not excessively pursue ultralow interfacial tension, and it should consider the surface wettability environment favorable for imbibition to ensure that a sufficient driving force can be provided. In the initial imbibition stage, the capillary force is large, the velocity of water imbibition in pores is fast, and the oil recovery rate is high; the holding time of the imbibition process is important to imbibition recovery. With the increase in imbibition time, the capillary force weakens, and the imbibition speed decreases to zero. With the increase in injection volume, reservoir pressure, pressure holding time, and imbibition cycles, the oil recovery increases, but the amplification of oil recovery decreases. From the technical and economic viewpoints, the optimal slug size, throughput cycle, and pressure holding time of the target reservoir are recommended as follows: 0.5 PV,three3 rounds, and greater than 96 h, respectively.

Enhanced fossil hydrogen energy recovery through liquid nanofluid huff-n-puff in low permeability reservoirs

Surfactant huff-n-puff can enhance fossil hydrogen energy recovery from low permeability reservoirs. However, due to the high cost and adsorption of surfactant, its commercial application is limited. Liquid nanofluid (LNF) has been widely used in hydraulic fracturing since it can significantly reduce the adsorption. In this study, a series of experiments were conducted to investigate the potential of LNF huff-n-puff. First, the spontaneous and dynamic imbibition with NMR was conducted to study the imbibition oil recovery for the LNF. The results showed that the spontaneous imbibition recovery of LNF is 1.43 folder than brine. Besides, the LNF enters the small pores first in spontaneous imbibition. In the process of dynamic imbibition, the LNF enters the larger pore with smaller resistance first, then enters the small pore around the flow path. After dynamic imbibition, the imbibition recovery in small pores increased 54%. Moreover, pressure transmission tests (PTT) were conducted to evaluate the increasing rate of reservoir pressure. This work provides a new view of how surfactant or LNF functions in the process of huff-n-puff.

Analyzing Single- and Two-parameter Models for Describing Oil Recovery in Imbibition from Fractured Reservoirs

The imbibition process is known as one of the main production mechanisms in fractured reservoirs where oil/gas-filled matrix blocks are surrounded by water-filled fractures. Different forces such as gravity and capillary play a role in production from a fractured reservoir during imbibition and complicate the imbibition process. In previous works, single-parameter models such as the Aronofsky model and Lambert W function were presented to model imbibition recovery from matrix blocks. The Aronofsky model underestimates early time recovery and overestimates late time recovery, and Lambert W function is suitable for water wet cases. In this work, a data bank of different experimental and numerical imbibition recovery curves at various rock and fluid properties were collected. Then, a rigorous analysis was performed on the models utilized to describe oil/gas recovery during the imbibition process. In addition to investigating the single-parameter models, two-parameter models used for dose-response modeling, including Weibull, beta-Poisson, and Logit models were examined. The results of this work demonstrate that using two-parameter models can improve the prediction of imbibition behavior. Moreover, among the two-parameter models, the Weibull has the capability to describe the imbibition process better. The Aronofsky model underestimates early time recovery and overestimates late time recovery, and Lambert W function is suitable for water wet cases. In this work, a data bank of different experimental and numerical imbibition recovery curves at various rock and fluid properties were collected. Then, a rigorous analysis was performed on the models utilized to describe oil/gas recovery during the imbibition process. In addition to investigating the single-parameter models, two-parameter models used for dose-response modeling, including Weibull, beta-Poisson, and Logit models were examined. The results of this work demonstrate that using two-parameter models can improve the prediction of imbibition behavior. Moreover, among the two-parameter models, the Weibull has the capability to describe the imbibition process better.

Precise Identification of Water Flooded Degree and Oil-water properties of Reservoir Based on Logging Interpretation

The crude oil reserves are very rich in the peripheral tight oil-water layer. However, due to the lack of effective production technical means, reserves utilization is relatively low. Imbibition flooding is one of the critical technical measures for the efficient development of (weak) hydrophilic tight oil-water layer. To obtain high efficiency production technology for weak hydrophilic tight oil-water layer, we investigated the imbibition flooding effect of negative/non-ionic surfactant “HLX”, “SYH (petroleum sulfonate) +Na2CO3”, cationic surfactant “YANG” and non-ionic surfactant “DCY” on weak hydrophilic core with permeability of about 2.0 × 10−3 μm2. The study results suggest that the imbibition recovery rate and imbibition rate are affected not only by the interfacial tension of the oil-water layer but also by the rock pore wettability. The physical simulation experimental results indicate that the “YANG” and “DCY” imbibition can change the wettability of rock pore surface and reduce the interfacial tension. Hence, the imbibition flooding effect is relatively good, and the recovery rate is significantly increased.

Characteristics of pore structure of tight gas reservoir and its influence on fluid distribution during fracturing

Micro-pore structural characteristics are complex in tight gas reservoirs, and it affects the fluid flow. Hydraulic fracturing is the key technique for economic gas production from tight reservoirs. In the fracturing process, fracturing fluid imbibes into reservoir matrix driven by capillary force and affects the dynamic distribution of reservoir fluid. It is thus of great interests to investigate the micro-pore structural characteristics, and its relationship with the dynamic distribution of fluid. In this study, cores from the Yanchang tight sandstone reservoirs in the Ordos basin were selected to evaluate the micro-pore structural characteristics and dynamic distribution of fluid. High-pressure mercury injection (HPMI), constant-rate mercury injection (CRMI), and low-pressure nitrogen gas adsorption (LP-N2GA) are used to evaluate the structural characteristics of micro-pores. The results show that average pore radius of samples ranges from 131.25 μm to 191.10 μm, with an average value of 170.42 μm, and the average throat radius ranges from 1.15 μm to 4.07 μm, with an average value of 2.489 μm. The pores are mainly closed small pores, and some H3-type crack-type pores are present. Imbibition, centrifugation experiment and nuclear magnetic resonance (NMR) techniques were used to study the dynamic distribution of fluid. The results show that imbibition recovery ranges from 40.04% to 87.29%, with an average of 62.14%, and movable fluid saturation ranges from 48.20% to 94.74%, with an average of 76.61%. The fluid during imbibition and the movable fluid during saturation were primarily distributed in mesopores and macropores. Results of statistical analysis suggests that the pore-throat structure is among the key factors impacting the imbibition recovery and movable fluid saturation.

Experimental Study of Imbibition with Normal Fracturing Fluid in Low-permeability Reservoirs

As the volume of fracturing fluid injected in the formation is getting larger and larger, there is more attention paid to the imbibition efficiency of the broken fracturing fluids. The fracturing fluids, including water-base gel fracturing fluid, thickened water fracturing fluid, slippery water fracturing fluid, emulsified fracturing fluid and clean fracturing fluid were chosen to do the spontaneous imbibition experiment with natural core samples from the Ordos Basin. Furthermore, the correlation between the parameters including viscosity, interfacial tension and contact angle and the recovery ratio was studied respectively. The result showed that the broken fracturing fluids of water-base gel and thicken water performed the highest recovery ratio of spontaneous imbibition, which were 23.1% and 20.6% respectively. Meanwhile, the correlations between those parameters and recovery ratio were contact angle, viscosity of broken fluids and interfacial from in turn in the experimental situation. What’s more, both the contact angle and the viscosity showed negative correlation to imbibition recovery ratio while the interfacial tension showed positive correlation. This study provides help to the researchers to understand the mechanism of fracturing fluids imbibition in low permeability reservoirs.

Enhancement of capillary imbibition by Gamma-Alumina nanoparticles in carbonate rocks: Underlying mechanisms and scaling analysis

Due to the oil-wet nature of carbonate reservoirs, performance of capillary imbibition is relatively weak in these reservoirs. One of the possible solutions to promote capillary imbibition is using nanoparticles (NPs) for wettability alteration purposes. In this study, imbibition efficiency of Gamma-Alumina (Ɣ-Al) NPs with different concentrations was investigated in low permeable, oil-wet carbonate rocks at 80 °C. The underlying mechanisms of Ɣ-Al NPs to enhance imbibition oil recovery were explored by analyzing dynamic contact angle profile, interfacial tension (IFT) of crude oil/Ɣ-Al nanofluid, size distribution of Ɣ-Al NPs and the inverse bond number. Results showed that Ɣ-Al NPs increased oil recovery to as much as 11.5% of the original oil in place (OOIP), while no oil was obtained by water imbibition in the native rock. The increase of Ɣ-Al concentration from 0.01 to 0.3 wt% showed a positive impact on the oil recovery, while further increase to 0.5 wt% provided lower incremental oil. The oil recovery results were consistent with dynamic contact angle profiles in which Ɣ-Al NPs successfully altered rock wettability from oil-wet to more water-wet conditions, but a less water-wetness was obtained for 0.5 wt% Ɣ-Al nanofluid. Also, scanning electron microscopy and energy dispersive X-ray analyses verified that the rock wettability alteration occurs mainly due to the adsorption of Ɣ-Al NPs on the carbonate surface. It was found that Ɣ-Al NPs exhibited a slight reduction in IFT from 15 to 11 mN/m, which provided a weak contribution in the oil recovery. Also, a new scaling equation was proposed to describe capillary imbibition process influenced by rock wettability alteration. The scaling equation successfully captured the oil imbibition recovery with different wettability conditions. This study supports the EOR potential of Ɣ-Al NPs in oil-wet carbonates and also emphasizes the important role of wettability function to upscale capillary imbibition processes from core to field scale.

Modeling of Co-current Spontaneous Imbibition Oil Recovery from Partially Covered Homogeneous Hydrocarbon Reservoir

In this paper, an approximate integral equation solution for a horizontal, unsteady flow of two viscous incompressible fluids is derived. Wettability variation of the porous medium is also considered in the present study. The non-wetting phase recovery fraction is obtained in terms of dimensionless time for 1D model from the derived solution. The derived approximate recovery fraction has been compared with the existing experimental data and empirical correlations for spontaneous imbibition from water-wet medium. It is observed that the normalized water saturation profiles show sharp gradients indicating some instability of the water front. Hence, a linear stability analysis is developed to study viscous instability of the co-current spontaneous imbibition. Viscous instability phenomenon for a two-phase oil–water system is also discussed. The corresponding instability number related to co-current imbibition recovery is estimated. The present study clearly spells out the effect of the instability number on the recovery process and estimates a critical instability number for co-current spontaneous imbibition.

Analysis on the influencing factors of imbibition and the effect evaluation of imbibition in tight reservoirs

Abstract To exert the imbibition between cracks and matrix effectively and enhance the development effect of tight oil reservoirs, a physical simulation method for imbibition in different scales of cores is developed by combining a high-pressure large-model physical simulation system and nuclear magnetic resonance technology (NMR) to investigate the influencing factors of imbibition process in tight reservoirs, and construct a quantitative evaluation method for the imbibition in water flooding. The results show that in the process of counter-current imbibition, the lower the permeability, the later the oil droplet precipitation, the longer the imbibition equilibrium time, and the lower the recovery degree. Fractures can effectively expand the area of imbibition and the front edge of imbibition in the contact between the dense matrix and water, reduce the resistance of oil discharge, and improve the imbibition speed and the degree of recovery. The more hydrophilic the rock, the higher the imbibition rate and imbibition recovery of tight rocks. In the process of co-current imbibition, the lower the permeability, the more obvious the imbibition, and the displacement recovery is positively correlated with permeability, while the imbibition recovery is negatively correlated with the permeability. It also shows that the imbibition distance of the cyclic water injection is greater than that of the counter-current imbibition, and the higher the permeability and the injection multiple, the longer the imbibition distance. The combination of large-scale volume fracturing with changing reservoir wettability and cyclic water injection is conducive to improving the imbibition ability of tight reservoirs.

New insights into spontaneous imbibition in tight oil sandstones with NMR

Previous research has confirmed that substantial yield has been recovered in the soaking period after hydraulic fracturing. Spontaneous imbibition (SI) is the primary mechanism responsible for the enhanced oil production and has become an effective oil recovery method with regards to unconventional reservoirs. Despite the importance of SI, an in-depth understanding of the features of SI in tight reservoirs is still inadequate. In this article, nuclear magnetic resonance (NMR) T2 was employed to study the dynamic behavior of imbibition in tight sandstone samples from Yanchang formation, Ordos Basin. Additionally, high-pressure mercury intrusion (HPMI) and the initial T2 of a core sample were combined to characterize pore structures of tight rocks and oil distributions in various pores at different imbibition stages. Then, the effects of gravity, anisotropic pore structure, and non-wetting phase (NWP) viscosity on imbibition recovery were determined via the variations in T2 spectra for each sample. The results show that the tight cores feature a multiscale pore structure. Sub-micropores is the dominant type providing the major contribution to oil recovery, while nanopores have largest imbibition efficiency due to the larger capillary force. Gravity of fluids has a non-trivial effect on SI and cannot be neglected in tight samples under two-ends-open (TEO) or one-end-open (OEO) conditions; this seemingly counterintuitive finding is because the capillary force is weakened by the resistance force caused by the intricate flow paths and other possible surface forces at the nanoscale. Imbibition performance in a tight medium is strongly related to its pore structure. The variations in directional permeabilities, relative permeabilities and capillary pressure functions resulting from highly anisotropic samples greatly affect both the ultimate oil recovery and imbibition rate for tight samples under TEO condition, but only impact imbibition rate under all-faces-open (AFO) condition. Furthermore, because tight oil has a narrow range of viscosity, the imbibition behavior in tight samples may not be sensitive to the oil viscosity. It would be hoped that the insights gained from this study can help to improve our understanding of imbibition characteristics in tight reservoirs and develop new scaling models for the predication of oil recovery.

Experimental Simulation on Imbibition of the Residual Fracturing Fluid in Tight Sandstone Reservoirs

Fracturing is a fundamental technique for enhancing oil recovery of tight sandstone reservoir. The pores in tight reservoirs generally have small radii and generate tremendous capillary force; accordingly, the imbibition effect can significantly affect retention and absorption of the fracturing fluid. In this study, the imbibition behaviors of the fracturing fluid were experimentally investigated, and the effects of interfacial tension, (IFT) permeability, oil viscosity, and the salinity of the imbibition fluid were determined. In addition, combining with nuclear magnetic resonance (NMR)-based core analysis, fluid distribution, and the related variations in imbibition and displacement processes were analyzed. Finally, some key influencing factors of imbibition of the residual fracturing fluid, the difference and correlation between imbibition and displacement, as well as the contribution of imbibition to displacement were explored so as to provide optimization suggestions for guiding the application of oil-displacing fracturing fluid in exploration. Results show that imbibition recovery increased with time, but the imbibition rate gradually dropped. There exists an optimal interfacial tension that corresponds to maximum imbibition recovery. In addition, imbibition recovery increased as permeability and salinity increases and oil viscosity decreases. Furthermore, it was found that extracted oil from the movable pore throat space was almost equal to that from the irreducible pore throat space during imbibition and their contribution in the irreducible pore throat space was greater than in the movable pore throat space in the displacement process. Hence, imbibition plays a more important role during the displacement process in the reservoirs with finer porous structure than previously thought.

Mathematical modeling of co-current spontaneous imbibition in heterogeneous porous medium

Abstract Fractured carbonate reservoirs are principal crude oil and natural gas resources. These reservoirs are composed of matrix block with interconnected network of fractures. Oil or gas recovery from such low porous and low permeable reservoirs is important because a large amount of such hydrocarbon fluids are trapped inside those reservoir formulations. Water-flooding or more specifically spontaneous imbibition is one of the most effective recovery mechanisms to increase the production from fractured reservoirs. However, the performance of water-flooding mainly depends on the wettability of the reservoirs. In co-current imbibition, wetting phase displaces the non-wetting phase in such a way that the non-wetting phase moves in the same direction of the wetting phase. Hence the corresponding mathematical model requires a total flux condition. This study deals with the mathematical modeling of co-current spontaneous imbibition from heterogeneous porous reservoirs. The resulting governing equations are highly non-linear in nature. We solve these equations numerically and show that the co-current imbibition recovery is very much sensitive to the viscosity ratio, porosity variation models and the wettability of the reservoir. The impact of the viscosity ratio on the water saturation gradient and the end point mobility ratio is also analyzed. In addition, the variations in the heterogeneity and wettability of the medium and the corresponding influence on the sweeping efficiency of the co-current imbibition is investigated.