Page 21 - Well Control for Completions and Interventions

Introduction and Well Control Fundamentals 15

Figure 1.8 Overpressure at reservoir crest.

formation is 2325 2 (2000 3 0.1) 5 2125 psi. At 5000 ft, the formation
is normally pressured and has an equivalent mud weight of 8.94 ppg. A
well drilled into the crest at 3000 ft would need 13.62 ppg (0.708 psi/ft)
mud to balance reservoir pressure.

1.1.4.1 Under-compaction in massive shale beds
Immediately following deposition, shale has high porosity. More than
50% of the total volume of un-compacted muds and clays can be the
water in which the solids were deposited. Normally, during compac-
tion, water is squeezed out of the formation, and porosity reduces as
the weight of overlying new sediment increases. If the removal of the
water is impeded, fluid pressure in the shale increases, since the
trapped water has a very low compressibility coefficient. A porous
fluid-filled shale supporting heavy overburden weight abnormally is
likely to be over-pressured.