Critical Crash Pressure of Deep Well Pipes
It is useful to know the critical subsidence pressures of deep well pipes by pipe manufacturers and users.
The geological units and structures show different characters as you go deep into the soil and the problems that may be encountered in the wells are different. Under normal conditions, vertical stresses increase with depth and are greater than horizontal stresses. But; Tectonic stresses, Geological structural changes, Structure of faults and folds, Temperature of the environment, Discontinuity of the layers events such as increase the horizontal stresses and in some cases the horizontal stresses can be greater than the vertical stresses. When choosing a well pipe, especially horizontal stresses should be known and pipe selection should be made accordingly.
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While vertical stresses (Sv) increase linearly with depth in normal soils, horizontal stresses (Sh) also increase parallel to these.
Sh / Sv = k; expressed as k = V / (1-V).
V = Poisson ratio is 0.25 in rocks with elastic behavior and 0.50 in rocks with plastic behavior.
In normal grounds;
Sv = g.h and Sh = k.Sv = (V / (1-V)). G.h.
Here;
h = height, g = density of the rock.
As a result of the studies carried out in different regions and rocks; 0,3 + 100 / h <k <0,5 + 1500 / h
The correlation has been obtained.
When the deep well pipes are lowered into the well, in vertical forces due to their own weight; It is also subjected to lateral forces during graveling, cleaning of drilling mud and well development (pumping). It is essential that pipes withstand these lateral forces and they can withstand these forces up to critical collapse pressures. For this reason, the lateral forces that will occur in the wells should be found and should be taken into account in pipe selection.
Critical collapse pressure,
It is given by the equation Pk = (2E / 1-V2) .1 / (SBO-1) 2).
Here;
Pk = Critical slump pressure, E = Modulus of elasticity, V = Poisson ratio, SBO = Standard size ratio (D / t). Critical settling pressure in horizontal slot filtered pipes is about 0.5 - 0.7 of closed pipes.
