FORMATION DAMAGE

The formation damage is defined as the change of porosity and permeability in nearby areas around the well. It can vary from a few millimeters to a few inches thick within the formation.
CONVENTIONAL TYPES OF DRILLING LATERAL

1. Balanced or balance (Overbalance)

Ph (hydrostatic pressure)> = Pr

Baleo training

2. Unbalanced (Underbalance)

The shots must cross the area of damage and the invasion of fluid into the well.

Today:

* Penetration: up to 152 cm (6 in.)
* Diameter: 1.22cm (0.48 inches)

The productivity of a well may be fully or partially reduced due to damage in the vicinity of the well by:

* Loss of fluids within the formation and plaster produced by the mud during the drilling of
* For calcareous incrustations
* Formation of emulsions
* Paraffin deposits during the working life of the well

An assessment of the extent of damage will be of great help, especially to determine the treatment required for removal.

The possible existence of damage is determined by testing of wells, production tests, etc..

Tests of wells can be draw down or build up.

The production tests consist of comparing the production of the well with other neighbors

The pressure tests are affected by the flow. You can recognize the following types of flow:

* Radial flow converges to the well
* Linear: if the fracture has high conductivity, the dominant factor will flow from the formation into the fracture
* Bilinear: If the fracture is not high conductivity of its effect on the flow should be considered

DEVIATION OF THE LINE FOR EFFECT OF STORAGE AND / OR DAMAGE

If at the end of a well it was damaged the advantages of making the same fracture immediately has the following advantages:

* This is the time to do it cheaper
* The reservoir pressure is the maximum possible, so that treatment fluid will be easily retrievable and cleaning will be complete
* Relates well productivity and symptomatic
* A well with good productivity and energy and with damage only need a small fracture to break the damage volume
* If low productivity has been determined, with or without injury, a fracture should be of great penetration to increase well productivity
* But fracturing a well that produces at its first stage with good efficiency and without damage is not profitable
* When you start the decline of the well is economically viable stimulation
* When the permeability is low there should be a deep fracture

FLOW EFFICIENCY

Is the relationship between the actual flow rate and flow rate would have an ideal pit with the same pressure drop:

J EF = real / ideal J = (P – PWF – Change of Pooh) / (P – PWF)

The inverse of the EF is the ratio of damage:

RD = 1 / EF = J ideal / real J

The skin factor is equal to:

FD = 1 – EF = Change Pse / (P – PWF)

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