Shale shakers Suction line

LOST CIRCULATION

CORROSION

INTRODUCTION
Corrosion is the destruction of metal by chemical or electrochemical interaction with the environment. In drilling the main effect of corrosion is weakening of the drill pipe resulting in washouts or pin failure.
The major corrodants encountered are carbon dioxide (CO2), hydrogen sulphide (H2S) and dissolved oxygen (O2). In salt based drilling fluids the corrosion potential can be enhanced by the presence of dissociated ions. Influencing factors are the chemical composition of the fluid, temperature, velocity, pressure and metallurgy. The specific reactions are complex with more than one type of corrosion possible. Specific details on the reactions and interplay should be sought from the corrosion engineers.

MONITORING

The corrosion coupon is a ring placed into a tool joint. It gives an accurate measure of the corrosion rate taking place inside the drill string. The coupon must be accurately weighed and visually checked.
The galvanic probe gives a continuous, and instantaneous reading, of the corrosion taking place on two sacrificial pieces of metal (brass and iron). It gives an qualitative indication of changes to the corrosion rate
7 Formation Pressures

SEDIMENTARY ROCK FORMATION

Generally, in oilfield drilling the formations penetrated have been built up by the deposition of sediments. As this process continues the underlying material is subjected to increasing force. Interstitial water is gradually squeezed out and the minerals are compacted into sedimentary rocks.

STRESSES

The stresses acting on the rock in the subsurface can be resolved into three orthogonal components. These are called the principal stresses (σ_n).
Normally both the vertical and horizontal principal stresses will increase with depth. The two are related by the fact that the rock is laterally constrained by the neighbouring rock. However regional tectonics may cause other effects. If the stresses are of different magnitude then the convention is: σ₁ > σ₂ > σ₃.

The vertical, or overburden, stress is generally expressed as a gradient; S/z. This can be derived by integrating the formation density log.
As a rule of thumb: Overburden Gradient ≈ 22·6 kPa/m (1 psi/ft)
Each principal stress is composed of two elements: the stress exerted on the rock (σ_f) and that exerted on the pore fluids (p_f).