Effect of Pore Size Distribution on Phase Behavior of Sour Gas and Hydrocarbon Mixtures in Tight Oil Reservoirs

2020 ◽  
Author(s):  
Lei Wang ◽  
Jamilyam Ismailova ◽  
Yeldana Uteubayeva ◽  
Jiaheng Chen ◽  
Klara Kunzharikova
Keyword(s):  
Pore Size Distribution ◽  
Phase Behavior ◽  
Pore Size ◽  
Size Distribution ◽  
Oil Reservoirs ◽  
Tight Oil ◽  
Hydrocarbon Mixtures ◽  
Tight Oil Reservoirs ◽  
Sour Gas

Effect of Pore Size Distribution on Phase Behavior of Sour Gas and Hydrocarbon Mixtures in Tight Oil Reservoirs (Russian)

2020 ◽  
Author(s):  
Lei Wang ◽  
Jamilyam Ismailova ◽  
Yeldana Uteubayeva ◽  
Jiaheng Chen ◽  
Klara Kunzharikova
Keyword(s):  
Pore Size Distribution ◽  
Phase Behavior ◽  
Pore Size ◽  
Size Distribution ◽  
Oil Reservoirs ◽  
Tight Oil ◽  
Hydrocarbon Mixtures ◽  
Tight Oil Reservoirs ◽  
Sour Gas

scholarly journals Nanopore Confinement Effect on the Phase Behavior of CO2/Hydrocarbons in Tight Oil Reservoirs considering Capillary Pressure, Fluid-Wall Interaction, and Molecule Adsorption

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-18
Author(s):  
Zhixue Zheng ◽  
Yuan Di ◽  
Yu-Shu Wu
Keyword(s):  
Phase Behavior ◽  
Pore Size ◽  
Capillary Pressure ◽  
Confinement Effect ◽  
Oil Reservoirs ◽  
Co2 Injection ◽  
Tight Oil ◽  
Tight Reservoirs ◽  
Tight Oil Reservoirs ◽  
Nanopore Confinement

The pore sizes in tight reservoirs are nanopores, where the phase behavior deviates significantly from that of bulk fluids in conventional reservoirs. The phase behavior for fluids in tight reservoirs is essential for a better understanding of the mechanics of fluid flow. A novel methodology is proposed to investigate the phase behavior of carbon dioxide (CO2)/hydrocarbons systems considering nanopore confinement. The phase equilibrium calculation is modified by coupling the Peng-Robinson equation of state (PR-EOS) with capillary pressure, fluid-wall interaction, and molecule adsorption. The proposed model has been validated with CMG-Winprop and experimental results with bulk and confined fluids. Subsequently, one case study for the Bakken tight oil reservoir was performed, and the results show that the reduction in the nanopore size causes noticeable difference in the phase envelope and the bubble point pressure is depressed due to nanopore confinement, which is conductive to enhance oil recovery with a higher possibility of achieving miscibility in miscible gas injection. As the pore size decreases, the interfacial tension (IFT) decreases whereas the capillary pressure increases obviously. Finally, the recovery mechanisms for CO2 injection are investigated in terms of minimum miscibility pressure (MMP), solution gas-oil ratio, oil volume expansion, viscosity reduction, extraction of lighter hydrocarbons, and molecular diffusion. Results indicate that nanopore confinement effect contributes to decrease MMP, which suppresses to 650 psi (65.9% smaller) as the pore size decreases to 2 nm, resulting in the suppression of the resistance of fluid transport. With the nanopore confinement effect, the CO2 solution gas-oil ratio and the oil formation volume factor of the oil increase with the decrease of pore size. In turn, the oil viscosity reduces as the pore size decreases. It indicates that considering the nanopore confinement effect, the amount of gas dissolved into crude oil increases, which will lead to the increase of the oil volume expansion and the decrease of the viscosity of crude oil. Besides, considering nanopore confinement effect seems to have a slightly reduced effect on extraction of lighter hydrocarbons. On the contrary, it causes an increase in the CO2 diffusion coefficient for liquid phase. Generally, the nanopore confinement appears to have a positive effect on the recovery mechanisms for CO2 injection in tight oil reservoirs. The developed novel model could provide a better understanding of confinement effect on the phase behavior of nanoscale porous media in tight reservoirs. The findings of this study can also help for better understanding of a flow mechanism of tight oil reservoirs especially in the case of CO2 injection for enhancing oil recovery.

Effect of Pore-Size Distribution on Phase Transition of Hydrocarbon Mixtures in Nanoporous Media

SPE Journal ◽  
2016 ◽  
Vol 21 (06) ◽  
pp. 1981-1995 ◽  
Author(s):  
Lei Wang ◽  
Xiaolong Yin ◽  
Keith B. Neeves ◽  
Erdal Ozkan
Keyword(s):  
Phase Transition ◽  
Phase Change ◽  
Pore Size Distribution ◽  
Phase Behavior ◽  
Pore Size ◽  
Capillary Pressure ◽  
Size Distribution ◽  
Hydrocarbon Mixtures ◽  
Nanoporous Media ◽  
Light Oil

Summary Pore sizes of many shale-oil and tight gas reservoirs are in the range of nanometers. In these pores, capillary pressure and surface forces can make the phase behavior of hydrocarbon mixtures different from that characterized in pressure/volume/temperature (PVT) cells. Many existing phase-behavior models use a single pore size to describe the effect of confinement on phase behavior. To follow up with our earlier theoretical studies and experimental observations, this research investigates the effect of pore-size distribution. By use of a vapor/liquid equilibrium model that considers the effect of capillary pressure, we present a procedure to simulate the sequence of phase changes in a porous medium caused by a pore-size distribution. This procedure is used to simulate depressurizations of a light oil and a retrograde gas confined inside nanoporous media, the pore-size distributions of which are characteristic of tight reservoirs. The fluid compositions are representative of typical reservoir fluids. Predictions of the model show that phase transition in nanoporous medium with pore-size distribution is not described by a single phase boundary. The initial phase change in the large pores alters the composition of the remaining fluid, and, in turn, suppresses the next phase change. For the two cases studied, models with and without capillary pressure gave similar predictions. For light oil, capillary pressure still noticeably increased the level of supersaturation, and the critical gas saturation had a strong influence on the properties of produced fluids. For retrograde gas, the effect of capillary pressure was insignificant because of the low interfacial tension (IFT). Despite the choice of fluids, calculations indicate that the smallest pores are probably always occupied by hydrocarbon liquid during depressurization.

scholarly journals Pore-Scale Simulation of Confined Phase Behavior with Pore Size Distribution and Its Effects on Shale Oil Production

Energies ◽  
2021 ◽  
Vol 14 (5) ◽  
pp. 1315
Author(s):  
Jingwei Huang ◽  
Hongsheng Wang
Keyword(s):  
Phase Equilibrium ◽  
Equation Of State ◽  
Pore Size Distribution ◽  
Phase Behavior ◽  
Pore Size ◽  
Size Distribution ◽  
Critical Role ◽  
Shale Oil ◽  
Pore Scale ◽  
Modified Equation

Confined phase behavior plays a critical role in predicting production from shale reservoirs. In this work, a pseudo-potential lattice Boltzmann method is applied to directly model the phase equilibrium of fluids in nanopores. First, vapor-liquid equilibrium is simulated by capturing the sudden jump on simulated adsorption isotherms in a capillary tube. In addition, effect of pore size distribution on phase equilibrium is evaluated by using a bundle of capillary tubes of various sizes. Simulated coexistence curves indicate that an effective pore size can be used to account for the effects of pore size distribution on confined phase behavior. With simulated coexistence curves from pore-scale simulation, a modified equation of state is built and applied to model the thermodynamic phase diagram of shale oil. Shifted critical properties and suppressed bubble points are observed when effects of confinement is considered. The compositional simulation shows that both predicted oil and gas production will be higher if the modified equation of state is implemented. Results are compared with those using methods of capillary pressure and critical shift.

Micro/Nanopore Systems in Lacustrine Tight Oil Reservoirs, China

2021 ◽  
Vol 21 (1) ◽  
pp. 599-607
Author(s):  
Qiyan Li ◽  
Songtao Wu ◽  
Xiufen Zhai ◽  
Songqi Pan ◽  
Senhu Lin
Keyword(s):  
Pore Size ◽  
Carbonate Rocks ◽  
Sedimentary Rocks ◽  
Oil Reservoirs ◽  
Reservoir Rock ◽  
Tight Oil ◽  
Storage Space ◽  
Tight Oil Reservoirs ◽  
Mixed Layers ◽  
Tight Rocks

A nanoscale pore throat system develops extensively in rocks of unconventional reservoirs serving as both source and reservoir rock. The nanoscale pores provide the main storage spaces, accounting for 70% to 80% of the total unconventional tight reservoirs in China. As one of most important unconventional petroleum accumulations, tight oil has accumulated in more than 20 lacustrine strata since the Permian in China. Three types of tight oil reservoirs were identified based on the lithology and provenance in the lacustrine basins, including terrigenous sandstone, endogenous carbonate rocks and mixed sedimentary rocks. The micro/nanopore structures of these tight rocks were investigated with the application of optical microscopy, scanning electron microscopy (SEM), mercury injection capillary pressure (MICP), gas adsorption (GA) and nuclear magnetic resonance (NMR). The results indicated that the pore systems were connected by nanoscale throats dominated the storage spaces of the lacustrine tight oil reservoirs, while there were obvious differences among these three tight rocks, including pore types, pore size and movable fluid distribution. (i) The terrigenous sandstones, which were represented by the Triassic Chang 7 tight sandstones in the Ordos Basin and Cretaceous Quantou tight sandstones in the Songliao Basin, were mainly arkoses, and their storage space was mainly composed of dissolution pores and intraclay mineral pores. Feldspar, rock fragments and carbonate cements were the majority of the dissolved components, and the diameter of dissolution pores ranged from 1 micron to 50 microns. Abundant intrakaolinite and illite/smectite mixed layers pores were developed, and the pore size was 10 nm to 500 nm. The MICP and GA data suggested that storage spaces were connected by throats with diameters of 10 nm˜300 nm. (ii) The endogenous carbonate rocks, which were represented by the Jurassic Da’anzhai limestones in the Sichuan Basin, were the tightest rocks with porosities of less than 5% and permeabilities of less than 0.01×10−3 μm2. The calcite dissolution pores and fractures with diameters of 10 nm˜500 nm were the most important storage spaces. The majority of pore systems were connected by throats with diameters of 6 nm˜100 nm based on the MICP and GA data. (iii) The tight mixed sedimentary rocks, which were represented by the Permian Lucaogou Formation in the Junggar Basin, were complex in lithologic composition, and dolostones and dolomite sandstones were the most important exploration targets. The interdolomite pores were the dominant storage spaces, in which abundant illite/smectite mixed layers were filled, and the pore size ranged from 50 nm to 50 microns. The MICP and GA data showed that the storage space was dominated by throats with diameters of 10 nm˜200 nm, and their volumetric contributions could reach over 70%. These results could provide a reference for future tight oil research and exploration in China.

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