What is fracture closure pressure?

Fracture closure pressure is the minimum fluid pressure required to initiate the opening of a fracture.

What is closure stress?

The Fracture Closure Stress (FCS) concept describes the mechanism by which a fracture in a wellbore initiates and propagates. The FCS concept describes that a wellbore has stress holding the wellbore closed.

What is fracture pressure in oil and gas?

For drilling in the oil and gas industry and geothermal exploration and production, fracture pressure is the pressure required to fracture the formation and to cause mud losses from a wellbore into the induced fractures. Fracture gradient is obtained by dividing the true vertical depth into the fracture pressure.

What is fracture propagation pressure?

After a fracture is initiated, high-pressure fracturing fluid will flow into the fracture and propagate in it. The fracture propagation pressure is generally lower than the fracture initiation pressure, which usually appears as a peak at the beginning of the fracture pressure curve.

What is net fracture pressure?

Net pressure is essentially the difference between the fracturing fluid pressure and the closure pressure and is the driving mechanism behind fracture growth. The more pressure inside a fracture, the more potential there is for growth. The term net pressure is only used when the fracture is open.

What is fracture gradient?

Fracture gradient is defined by the Schlumberger Oilfield Glossary as the pressure gradient required to induce fractures in the rock at a given depth.

What is in situ stress?

In situ stress state is the original stress status in the rock before excavations or other perturbations. In situ stresses are also called far-field stresses. For example, the stress state before a borehole is drilled shown in Fig.

What is in situ method?

In situ refers to recovery techniques which apply heat or solvents to heavy crude oil or bitumen reservoirs beneath the earth’s crust. There are several varieties of in situ techniques, but the ones which work best in the oil sands use heat (steam).

What is minimum in situ stress?

Minimum in-situ stress is the threshold at which localized stress within a rock mass formation will cause a fracture to open. Trenchless construction planners assess measurements like this to gain an understanding of geological conditions that might affect operations.

What is minimum horizontal stress?

Minimum horizontal stress (sh) is one of the principle stresses that confined underground formations are subjected to. The other stresses are the vertical stress and the maximum horizontal stress. Hydraulic fracture propagates perpendicular to the minimum principle stress.

What is maximum and minimum stress?

The maximum stress refers to the maximum tensile stress while the minimum stress refers to the minimum compressive stress. The stress range was taken as the absolute difference between the maximum and minimum stress.

How do you calculate horizontal stress?

The horizontal stress is customarily expressed as a proportion of the vertical stress σH = K’o σv = K’o ρd gz (3.2) where K’o = coefficient of earth pressure at rest in terms of effective stresses (see equation (3.7)).

How do you measure maximum horizontal stress?

Maximum horizontal stress is usually determined from minifrac or leak-off tests, sonic logs, and borehole breakout analysis. Pressure at the wellbore is measured with gauges. where β is the inclination angle of the horizontal well from the vertical section.

How do you calculate minimum stress?

Quote from video:Next minimum stress that will be sigma d minus sigma b sigma d 2.27 minus sigma b 5.82 so from this the minimum stress value is minus 3.55 newton per mm square.

Which rock properties is used for minimum stress estimation?

Rock Mechanical Properties and In Situ Stresses



P_Tectonic=Tectonic pressure, psi. As can be seen in Eq. (13.14), Poisson’s ratio, vertical stress, Biot’s constant, and pore pressure primarily affect minimum horizontal stress.

How do you calculate vertical stress?

Total stress below a river or lake



The total stress is the sum of the weight of the soil up to the surface and the weight of water above this: Vertical total stress at depth z, s_v = g . z + g_w .

What is confinement pressure?

Confining Pressure is defined as the stress or pressure forced on a layer of soil or rock by the heaviness of the overlying substance.

What is coefficient of earth pressure at rest?

The coefficient of earth pressure at rest is defined as the ratio between the horizontal and vertical effective stresses. Thus, it is a parameter that expresses the natural state acting on the soil. Determining such value correctly should, therefore, be a common practice in engineering.

What is the excess pore pressure called?

excess hydrostatic pressure

Excess pore pressure is also known as excess hydrostatic pressure or hydrodynamic pressure.

What is difference between pore water pressure and excess pore water pressure?

Excess pore water pressure in the consolidation process is defined in two different ways: excess pore pressure is the excess over the hydrostatic pressure; excess pore water pressure is the pore pressure in excess of a steady-state flow condition.

What is consolidation stress?

The process of gradual transfer of stress from the pore pressure to effective stress with the associated volume change is referred to as consolidation.

Which type of soil has the maximum value of pore pressure parameter at failure?

Solution: The approximate value of pore pressure parameter at failure for very loose, fine saturated sand, saturated clays is 2 to 3. Solution: A negative pore pressure is developed when we apply load on a sample of clay or sand because both sand and clay tends to expand on loading.

What is pore pressure parameter?

Pore water pressures are important factors in determining soil strength. Dimensionless coefficients called ‘Pore pressure coefficients’ or ‘Skempton’s Pore Pressure Parameters A and B’ characterize the change in pore water pressure caused by a change in applied stress.

Can you have negative pore pressure?

Negative pore water pressure is a condition in soils when they are partially saturated. What happens is, surface tension is developed on the surfaces of water in the pores.

What affects pore water pressure?

The measurement of pore pressure during static soundings -the CPTU tests, depend on several factors: soil type, the degree of humidity, its stiffness, stress state, preconsolidation, water flow conditions and the degree of geological medium destruction as a result of mass movements [18] .

How do you increase your pore pressure?

The basic steps in performing a conventional 1D pore pressure analysis are:

1. Calculate total vertical stress (σv) from rock density.
2. Estimate vertical effective stress (σe)from log measurements (DT or RES) or seismic (velocity).
3. Pore pressure is then PP = σv – σe.

Why is pore pressure important?

So, pore pressure is very important to geophysicists, geologists, petrophysicists, and reservoir engineers. An accurate pore pressure prediction can help us to reduce drilling risk/hazard, to increase wellbore stability, to optimize casing seat selection, and for mud program design.