Confinement Affects Phase Behavior of Petroleum Fluids in Shale Reservoirs

2018 ◽  
Author(s):  
Sheng Luo
Keyword(s):  
Phase Behavior ◽  
Shale Reservoirs

Nanopore Compositional Modeling in Unconventional Shale Reservoirs

2016 ◽  
Vol 19 (03) ◽  
pp. 415-428 ◽  
Author(s):  
Najeeb S. Alharthy ◽  
Tadesse W. Teklu ◽  
Thanh N. Nguyen ◽  
Hossein Kazemi ◽  
Ramona M. Graves
Keyword(s):  
Phase Behavior ◽  
Oil Recovery ◽  
Flow Behavior ◽  
Flow Characteristics ◽  
Gas Production ◽  
Eagle Ford ◽  
Compositional Modeling ◽  
Shale Reservoirs ◽  
Behavior Shift

Summary Understanding the mechanism of multicomponent mass transport in the nanopores of unconventional reservoirs, such as Eagle Ford, Niobrara, Woodford, and Bakken, is of great interest because it influences long-term economic development of such reservoirs. Thus, we began to examine the phase behavior and flow characteristics of multicomponent flow in primary production in nanoporous reservoirs. Besides primary recovery, our long-term objectives included enhanced oil production from such reservoirs. The first step was to evaluate the phase behavior in nanopores on the basis of pore-size distribution. This was motivated because the physical properties of hydrocarbon components are affected by wall proximity in nanopores as a result of van der Waals molecular interactions with the pore walls. For instance, critical pressure and temperature of hydrocarbon components shift to lower values as the nanopore walls become closer. In our research, we applied this kind of critical property shift to the hydrocarbon components of two Eagle Ford fluid samples. Then, we used the shifted phase characteristics in dual-porosity compositional modeling to determine the pore-to-pore flow characteristics, and, eventually, the flow behavior of hydrocarbons to the wells. In the simulation, we assigned three levels of phase behavior in the matrix and fracture pore spaces. In addition, the flow hierarchy included flow from matrix (nano-, meso-, and macropores) to macrofractures, from macrofractures to a hydraulic fracture (HF), and through the HF to the production well. From the simulation study, we determined why hydrocarbon fluids flow so effectively in ultralow-permeability shale reservoirs. The simulation also gave credence to the intuitive notion that favorable phase behavior (phase split) in the nanopores is one of the major reasons for production of commercial quantities of light oil and gas from shale reservoirs. It was determined that the implementation of confined-pore and midconfined-pore phase behavior lowers the bubblepoint pressure, and this, in turn, leads to a slightly higher oil recovery and lesser gas recovery. Also it was determined that the implementation of midconfined-pore and confined-pore phase-behavior shift reduces the retrograde liquid-condensation region, which in turn, leads to lower liquid yield while maintaining the same gas-production quantity. Finally, the important reason that we are able to produce shale reservoirs economically is “rubblizing” the reservoir matrix near HFs, which creates favorable permeability pathways to improve reservoir drainage. This is why multistage hydraulic fracturing is so critical for successful development of shale reservoirs.

Confinement Effects on Phase Behavior of Hydrocarbon in Nanochannels

2015 ◽  
Author(s):  
M. Alfi ◽  
H. Nasrabadi ◽  
D. Banerjee
Keyword(s):  
Phase Behavior ◽  
Bubble Nucleation ◽  
Well Performance ◽  
Pvt Properties ◽  
Bubble Point Pressure ◽  
Numerical Predictions ◽  
Fluid Properties ◽  
Different Temperatures ◽  
Point Pressure ◽  
Shale Reservoirs

Several researchers have recently studied the phase behavior of petroleum fluids in shale systems. There is a general agreement that the confined PVT properties in shale are substantially different from the corresponding bulk properties. These differences have significant impact on the prediction of well performance and ultimate recovery in shale reservoirs. Experimental measurements of fluid properties in shale rocks are currently not available. This has led to significant amount of uncertainty in phase behavior calculations for shale reservoirs. In this study, experimental validation of numerical predictions for phase behavior of various hydrocarbons confined in nanochannels was performed using a nanofluidics platform. The nanofluidics platform was designed, fabricated and tested at different temperatures. Design of the nanochannel is described in this paper. In this study, a nanochannel device (similar to Duan and Majumdar 2010) was designed, fabricated, packaged and tested. The reservoirs in the nanofluidic chip were filled with various hydrocarbon liquids (e.g. n-decane). The temperature was varied at a constant pressure, during which epifluorescence imaging was performed to measure the bubble nucleation temperature, i.e., the temperature corresponding to the formation of the first bubble of gas (i.e., to determine bubble-point pressure and temperature relationship).

Effect of Confinement on Pressure/Volume/Temperature Properties of Hydrocarbons in Shale Reservoirs

SPE Journal ◽  
2016 ◽  
Vol 21 (02) ◽  
pp. 621-634 ◽  
Author(s):  
T.. Pitakbunkate ◽  
P. B. Balbuena ◽  
G. J. Moridis ◽  
T. A. Blasingame
Keyword(s):  
Phase Behavior ◽  
Phase Diagrams ◽  
Energy Resource ◽  
The United States ◽  
Confined Space ◽  
Bulk Fluid ◽  
Mixture Phase ◽  
Fluid Properties ◽  
Shale Reservoirs ◽  
Gcmc Simulations

Summary Shale reservoirs play an important role as a future energy resource of the United States. Numerous studies were performed to describe the storage and transport of hydrocarbons through ultrasmall pores in the shale reservoirs. Most of these studies were developed by modifying techniques used for conventional reservoirs. The common pore-size distribution of the shale reservoirs is approximately 1 to 20  nm and in such confined spaces that the interactions between the wall of the container (i.e., the shale and kerogen) and the contained fluids (i.e., the hydrocarbon fluids and water) may exert significant influence on the localized phase behavior. We believe this is because the orientation and distribution of fluid molecules in the confined space are different from those of the bulk fluid, causing changes in the localized thermodynamic properties. This study provides a detailed account of the changes of pressure/volume/temperature properties and phase behavior (specifically, the phase diagrams) in a synthetic shale reservoir for pure hydrocarbons (methane and ethane) and a simple methane/ethane (binary) mixture. Grand canonical Monte Carlo (GCMC) simulations are performed to study the effect of confinement on the fluid properties. A graphite slab made of two layers is used to represent kerogen in the shale reservoirs. The separation between the two layers, representing a kerogen pore, is varied from 1 to 10  nm to observe the changes of the hydrocarbon-fluid properties. In this paper, the critical properties of methane and ethane as well as the methane/ethane mixture phase diagrams in different pore sizes are derived from the GCMC simulations. In addition, the GCMC simulations are used to investigate the deviations of the fluid densities in the confined space from those of the bulk fluids at reservoir conditions. Although not investigated in this work, such deviations may indicate that significant errors for production forecasting and reserves estimation in shale reservoirs may occur if the (typical) bulk densities are used in reservoir-engineering calculations.

Effect of Nanoscale Pore-Size Distribution on Fluid Phase Behavior of Gas-Improved Oil Recovery in Shale Reservoirs

SPE Journal ◽  
2020 ◽  
Vol 25 (03) ◽  
pp. 1406-1415
Author(s):  
Sheng Luo ◽  
Jodie L. Lutkenhaus ◽  
Hadi Nasrabadi
Keyword(s):  
Pore Size Distribution ◽  
Phase Behavior ◽  
Pore Size ◽  
Size Distribution ◽  
Oil Recovery ◽  
Gas Injection ◽  
Fluid Phase ◽  
Improved Oil Recovery ◽  
Nanoscale Pore ◽  
Shale Reservoirs

Summary The improved oil recovery (IOR) of unconventional shale reservoirs has attracted much interest in recent years. Gas injection, such as carbon dioxide (CO2) and natural gas, is one of the most considered techniques for its sweep efficiency and effectiveness in low-permeability reservoirs. However, the uncertainties of fluid phase behavior in shale reservoirs pose a great challenge in evaluating the performance of a gas-injection operation. Shale reservoirs typically have macroscale to nanoscale pore-size distribution in the porous space. In fractures and macropores, the fluid shows bulk behavior, but in nanopores, the phase behavior is significantly altered by the confinement effect. The integrated behavior of reservoir fluids in this complex environment remains uncertain. In this study, we investigate the nanoscale pore-size-distribution effect on the phase behavior of reservoir fluids in gas injection for shale reservoirs. A case of Anadarko Basin shale oil is used. The pore-size distribution is discretized as a multiscale system with pores of specific diameters. The phase equilibria of methane injection into the multiscale system are calculated. The constant-composition expansions are simulated for oil mixed with various fractions of injected gas. It is found that fluid in nanopores becomes supercritical with injected gas, but lowering the pressure to less than the bubblepoint turns it into the subcritical state. The bubblepoint is generally lower than the bulk and the degree of deviation depends on the amount of injected gas. The modeling of confined-fluid swelling shows that fluid swelled from nanopores is predicted to contain more oil than the swelled fluid at bulk state.

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