Effects of pore structure on the moveable oil saturation in water-driven tight oil sandstone reservoirs

Liu, Hongping; Yong, Luo; Meng, Yujing; Xiao, Gaojian; Zhao, Yang; Zhou, Sibin; Shao, Longkan

doi:10.1016/j.petrol.2021.109142

Cited by 14 publications

(6 citation statements)

References 28 publications

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“…In the early stage, many scholars have done much more research on water flooding development [27,28]. Liu et al [29], used the Chang8 reservoirs and Chang9 reservoirs dense sandstones of the Honghe Oilfield as a study object, investigated the effect of pore structure on oil saturation. It was concluded that the affected area of most low permeability samples is larger than hyperpermeable samples after water flooding.…”

Section: Introductionmentioning

confidence: 99%

The Microscopic Production Characteristics of CO2 Flooding AF-Ter Water Flooding for Tight Oil Sandstones Reservoirs Utilized NMR and Microscopic Visualization Apparatus

Xue,

Gao,

et al. 2024

Preprint

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The microscopic pore structure of tight sandstone reservoir significantly influences the characteris-tics of CO2 flooding after water flooding. The research was conducted using various techniques such as casting thin sections, high pressure mercury injection, scanning electron microscopy, Nu-clear magnetic resonance (NMR) testing, and a self-designed high-temperatures and high-pressures microscopic visualization displacement system. Three type cores with different pore structures were selected for the flooding experiments and the microscopic visualization displace-ment experiments, including CO2 immiscible flooding, near-miscible flooding, and miscible flood-ing after the conventional water flooding. The characteristics of CO2 flooding and the residual oil distribution after water flooding were quantitatively analyzed and evaluated. The results show that: (1) During the water flooding process, the oil produced from type I and type III samples mainly comes from large and some medium pores. Oil utilization of all pores is significant for type II samples. The physical properties and pore types have a greater impact on water flooding. Type I and II samples are more suitable for near-miscible flooding after water flooding. Type III samples are more suitable for miscible flooding after water flooding. (2) In the CO2 flooding, oil recovery increases gradually with increasing pressure for all three types of samples. Type II core samples have the highest recovery. Before miscibility, the oil recovered from type I and type II samples was primarily from large pores, however, the oil recovery mainly comes from medium pores when reaching miscibility. As for the type III samples, the oil produced in the immiscible state mainly comes from large and medium pores, and the enhanced oil recovery mainly comes from medium and small pores after reaching the near-miscible phase. (3) It can be seen from the microscopic re-sidual oil distribution that oil recovery will increase as the petrophysical properties of the rock model improve. The oil recovery of near-miscible flooding after water flooding regarding the type II model is up to 68.11%. The oil recovery of miscible flooding after water flooding about type III model is the highest at 74.57%. With increasing pressure, the proportion of flake residual oil grad-ually decreases, while the proportion of droplet-like and film-like residual oil gradually increases. Type II samples have a relatively large percentage of reticulated residual oil in the near-miscible stage.

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Section: Introductionmentioning

confidence: 99%

The Microscopic Production Characteristics of CO2 Flooding AF-Ter Water Flooding for Tight Oil Sandstones Reservoirs Utilized NMR and Microscopic Visualization Apparatus

Xue,

Gao,

et al. 2024

Preprint

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“…At present, China is vigorously developing the exploration and development theory and technology of tight oil, and tight oil production is expected to further increase . The biggest feature of tight oil reservoirs is that their pore size is very small, and fluid seepage is very difficult. , Traditional water flooding is difficult to establish an effective displacement pressure gradient between water injection wells and oil production wells due to the ultrahigh seepage resistance. , For some tight oil reservoirs with developed natural fractures, due to the great difference in seepage capacity between fractures and the matrix, water flooding will quickly form burst flooding in the fracture channel, thereby resulting in extremely low sweep efficiency. − Due to the special performance of tight oil reservoirs during water flooding, water huff and puff oil production technology is regarded as one of the key means to exploit tight oil reservoirs. − Its construction process is divided into three stages. First, a certain volume of water is injected into the reservoir through a production well, then the well is soaked for a period of time, and finally, oil is produced through the production well.…”

Section: Introductionmentioning

confidence: 99%

“…7 The biggest feature of tight oil reservoirs is that their pore size is very small, and fluid seepage is very difficult. 8,9 Traditional water flooding is difficult to establish an effective displacement pressure gradient between water injection wells and oil production wells due to the ultrahigh seepage resistance. 10,11 For some tight oil reservoirs with developed natural fractures, due to the great difference in seepage capacity between fractures and the matrix, water flooding will quickly form burst flooding in the fracture channel, thereby resulting in extremely low sweep efficiency.…”

Section: Introductionmentioning

confidence: 99%

The Law and Mechanism of the Sample Size Effect of Imbibition Oil Recovery of Tight Sedimentary Tuff

Yang

Dong

et al. 2022

ACS Omega

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Imbibition is an important mechanism to improve the recovery factor (RF) of a tight oil reservoir. Accurately evaluating the oil production capacity of tight oil reservoirs by imbibition is of great significance for the formulation of oilfield production plans and productivity prediction. However, there is currently no unified regulation on the selection of rock sample size in tight oil reservoir imbibition evaluation experiments, resulting in great differences in reservoir imbibition oil production capacity obtained from rock samples of different sizes, which brings great challenges to the efficient development of tight oil reservoirs. To clarify the law and mechanism of the rock sample size effect of tight core imbibition oil recovery, this paper takes the newly discovered tight sedimentary tuff (TST) oil reservoir as an example. First, several representative real cores were collected. Then, their wettability and pore structure characteristics were analyzed. Finally, physical simulation experiments of imbibition under different rock sample sizes were conducted. The results show that the TST has very favorable imbibition conditions, which are manifested in the following: (i) the wettability is weakly hydrophilic to hydrophilic; (ii) the mineral composition is tuffaceous minerals, calcite, and quartz, without clay minerals; (iii) micro-nanoscale pores are developed; and (iv) the pore throats are evenly distributed. In the imbibition experiments of rock samples of different sizes, the oil production characteristics of the core surface, the variation form of imbibition rate, pore production characteristics, and the influence mode of imbibition pressure on imbibition do not have the sample size effect. However, the RF of the spontaneous imbibition has an obvious sample size effect, and there is a good exponential function relationship between the imbibition RF and the specific surface area (SSA) of cores. The fundamental reason why the rock sample size effect of the TST imbibition oil recovery is relatively stable and has strong regularity is that its pore structure and wettability are relatively homogeneous and stable. The change of rock sample size does not have a great impact on the distribution of the core pore structure and wettability, resulting in no significant change in its imbibition power, resistance, and distance. Therefore, the main factor determining the imbibition RF of rock samples with different sizes is their SSA. The research results of this work can provide an important theoretical basis for understanding the law and mechanism of TST imbibition oil recovery and unifying the imbibition experimental results of small-sized rock samples.

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“…The microscopic pore structure of tight oil reservoir is extremely complicated because of the low porosity and permeability, often associated with extensive compaction and cementation. The 3-D network of pores of different shapes and sizes in tight reservoirs is the critical factor in controlling fluid flow and determining oil and gas productivity [19,20]. Microscopic pore structure can significantly impact fluid flow in tight oil reservoir since they may contain immobile, capillary-bound waters that are only in diffusional contact with mobile pores waters.…”

Section: Introductionmentioning

confidence: 99%

Study on Micro-Nano Pore Characteristics and Classification of Tight Sandstone Reservoir Based on Q-Cluster

Zhao

Wang

et al. 2022

Geofluids

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To realize the quantitative classification and comprehensive evaluation of the tight oil reservoir in the 4th of Quantou Formation in Songliao Basin, the pore structure of tight oil reservoir was quantitatively analyzed. In this study, experiments based on the constant-speed mercury injection, nuclear magnetic resonance, and micron CT are based on the observation of cast thin sections, and scanning electron microscope is conducted. The result shows that a tight oil reservoir space is mainly composed of the intergranular dissolved pore, residual intergranular pore, and intragranular dissolve pore. There are few intercrystalline pore and fracture at the same time. The average pore radius is 1.28~4.58 μm, and the average throat radius is 0.52~1.27 μm. Hence, there is a typical micro-nano throat combination with micropores. The pore throat composition and pore structure of reservoirs differ in reservoir with different physical properties. The reservoir quality depends on pore structure especially the throat radius. And the microthroat is a critical factor for permeability. Based on Q-cluster analysis, tight oil reservoirs are classified into three types. The analysis was based on the data such as max throat radius, average throat radius, displacement pressure, median pressure, and permeability. Finally, the reservoirs in the study area are mainly II and I types.

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Effects of pore structure on the moveable oil saturation in water-driven tight oil sandstone reservoirs

Cited by 14 publications

References 28 publications

The Microscopic Production Characteristics of CO2 Flooding AF-Ter Water Flooding for Tight Oil Sandstones Reservoirs Utilized NMR and Microscopic Visualization Apparatus

The Microscopic Production Characteristics of CO2 Flooding AF-Ter Water Flooding for Tight Oil Sandstones Reservoirs Utilized NMR and Microscopic Visualization Apparatus

The Law and Mechanism of the Sample Size Effect of Imbibition Oil Recovery of Tight Sedimentary Tuff

Study on Micro-Nano Pore Characteristics and Classification of Tight Sandstone Reservoir Based on Q-Cluster

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