Impact of Capillary Pressure and Critical Properties Shift Due to Confinement on Hydrocarbon Production from Shale Reservoirs
Abstract/Contents
- Abstract
- Interest in understanding the underlying physical mysteries that result in production through liquid rich shale reservoirs, is growing globally. A swiftly expanding branch of science termed as ‘nano-fluidics’ deals with studying fluid flow in nano-spaces and often accompanies computationally expensive molecular simulations. Compositional modeling of hydraulically stimulated naturally fractured liquid-rich shale (LRS) reservoirs is a complex process that is yet to be fully understood. This work aims to explore and integrate some of the key fundamentals of confined fluid flow in nano-pores with a fully compositional reservoir simulator. Two phenomena, capillary pressure and critical property shifts, that become significant due to multiphase flow in nano-pores have been singled-out from various potential forces that arise at such small scales. LRS modelling capability of Automated Differentiation based General Purpose Research Simulator (AD-GPRS) was extended by making capillary pressure a function of pore radius. This was done by modifying vapor liquid equilibrium calculations to incorporate phase pressure differences that arise in tight pores. Using this formulation, fluid phase behavior properties were studied first using simple binary mixtures and later extended to a Bakken fluid sample. Our findings indicated that capillarity is a function of several phenomena which include pore size, fluid composition and reservoir pressure. Additionally capillary pressure was found to lead to bubble point suppression, reduction in oil density and viscosity, and increase in gas density and viscosity. Bakken fluid phase properties were found to deviate from bulk behavior up till pore radii of approximately 100 nm. The study was then extended to a realistic hydraulically fractured shale reservoir model with a horizontal producer, and cases were run using Bakken fluid model. Reinforcing the findings of fluid phase behavior observed for simpler systems, oil production showed an increase, while gas production decreased as the pores got tighter. As expected, this change in production was found to be zero when the reservoir pressure is above the fluid bubble point pressure. However, a significant difference in hydrocarbon production and recovery due to capillarity was seen when the reservoir pressure fell below the bubble point pressure. Additionally, the importance of properly characterizing fractures was found to be important as their presence reduces the influence of capillarity. Further on, since shale reservoirs can contain pores of sizes ranging from 100 nm (micro-pores), two realistic pore size distributions (PSD) that are typically found in shale reservoirs were explored. The differences in production showed that capillary pressure is uniquely tied to the specific PSD of the reservoir. Moving further from the impact of pore size, the impact of varying fluid composition on the impact of capillary pressure was tested next. Since, many shale reservoirs such as Eagle Ford, contain a wide spectrum of hydrocarbon fluids ranging from low GOR black oil to volatile, rich and lean gas condensates, wet gas and even dry gas, and since these fluid compositions have been shown to vary spatially within the play, the findings of this work are important. Bakken fluid composition was varied by increasing the compositions of light, mid-heavy and heavy components turn by turn. It was found that the impact of capillarity varies with the initial shape of the fluid mixture phase envelope. The lower the initial critical pressure, the greater will be the impact of capillarity. In Bakken’s case, the magnitude of capillarity increased from relatively lighter compositions to mid-heavy compositions and then decreased again as the amount of heavier components was increased. Finally, the impact of confinement on critical properties was studied. Using the correlations developed using molecular simulations that have been published previously, shift in critical properties of Bakken fluid sample were computed. Both critical temperature and pressure reduced as the pore size was decreased. It was shown that this reduction is greater for heavier components. We next ran simulations using the shifted critical properties. Both oil and gas production showed an increase.
Description
| Type of resource | text |
|---|---|
| Date created | August 2015 |
Creators/Contributors
| Author | Haider, Batool Arhamna |
|---|---|
| Primary advisor | Aziz, Khalid |
| Degree granting institution | Stanford University, Department of Energy Resources Engineering |
Subjects
| Subject | School of Earth Energy & Environmental Sciences |
|---|---|
| Genre | Thesis |
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Preferred citation
- Preferred Citation
- Haider, Batool Arhamna. (2015). Impact of Capillary Pressure and Critical Properties Shift Due to Confinement on Hydrocarbon Production from Shale Reservoirs. Stanford Digital Repository. Available at: https://purl.stanford.edu/ww908xv4517
Collection
Master's Theses, Doerr School of Sustainability
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