Reservoar Engineering Flashcards
Draw an anticline containing oil, water and gas. Explain why the distribution of fluid phases is as indicated. If you have a homogeneous reservoir rock where is the water saturation highest and lowest?
The fluids are distributed in different layers due to difference in density. In a homogeneous reservoir rock is the water saturation highest in the bottom of the reservoir.
Explain how grain size and grain size distribution affect the porosity of a rock.
The porosity of samples is inversely related to the grain size and decreases linearly as grain size increases.
(By theory grain size should not affect porosity, it however shows that coarser sand have lower porosity than fine sand. Because coarse sand in many cases are spherically shaped, it can be packed denser, and therefore finer sand often have higher porosity. )
Sorting. Well sorted formation have higher porosity because poorly sorted formation have more small particles that is filling space between the main grains.
What is the common definition of effective and total porosity in core samples? Why is this distinction important? Please name measurements giving total and effective porosity.
Effective porosity. The fraction of interconnected pore space in the rock and the rock itself. For granular rocks like sandstone, the effective porosity can approach the total porosity. In limestone and shale there could be huge differences between effective and total porosity. This porosity is measured with Helium porosity, gravitational methods and Mercury injection.
Total porosity. Relation between space in the rock and the rock itself. This type of porosity is measured by imaging methods.
What is the definition of Laplace pressure, Δp?
Laplace pressure is the pressure difference between the inside and the outside of a curved surface that forms the boundary between the fluid regions
What is the definition of capillary pressure, pc?
Capillary pressure is defined as the difference in pressure across the interface between two immiscible fluids, say oil and water, in the reservoir
Define the term wettability. Define contact angle and draw a drop of water in an oil.water-solid system where water is wetting phase….
Wettability is the ability of a liquid to spread over a surface. It can be measured by the contact angle between the liquid and the surface.
Wettability is measured by measuring the contact angle. Lower contact angle signifies greater wettability, whereas higher contact angle infers lower wettability.
There is a direct relationship between contact angle and surface energy—that is, the contact angle decreases with surface energy.
Name at least three rock parameters that affect rock porosity
Grain size, sorting, shape, moisture, material composition, cementation
Define all parameters and specify units in the Darcy system
Darcy’s law is an equation that describes the flow of a fluid through a porous medium.
Darcy velocity 𝑢 is the ratio of volumetric rate to cross-sectional area perpendicular to flow, 𝑄/𝐴, Darcy’s law for linear flow of an incompressible fluid can be expressed as:
Q/A = u = (k/Mu) * ((p1-p2)/L)
Q is volumetric flow rate(m^3/s)
A is cross sectional area (m^2)
U is the flow velocity (Darcy velocity)
L is length of a sandpack (m)
P1-p2 is the pressure difference between inlet and outlet (atm)
K is absolute permeability (D)
Mu is viscosity (Pa * s)
CO2 will be stored in a 100% water saturated subsurface rock formation. Water is the wetting phase. Mention the parameters / data you need for evaluation of how much CO2 that
can be injected (stored). Is this a drainage process or an imbibition process?
Injection volume(storage) - depth (p,T), rock volume, porosity, residual Sw where CO2 has flooded and how much of the reservoir is flooded by CO2. This is a drainage process since the wetting phase decreases in saturation when CO2 is injected.
What is free water level?
Free water level is the depth where the capillary pressure is zero. Below FWL the water saturation is 100%.
When we produce an oil reservoir, there is a lot of oil left at abandonment. Which parameters are important regarding the degree of oil recovery? Explain briefly two laboratory methods for determining the degree of wettability of an oil-water-solid system.
Important parameters are viscosity and mobility.
Wettability can be determined by the contact angle method and the Amott method. In contact angle we place a drop of fluid surrounded by the other fluid on a solid surface and read the angle. Amott is a core test based on spontanteou and forced production stages.
