Normal Compaction

Abnormally High Pressure Due to Hydrocarbon Column o o o

CL LU Q

1GGG

  1. Pressure on the Gas-Water Contact
  2. Less Gas Column

Pressure = G.1G x 1GGG' = 1GG psi

  1. Pressure at top of Sand = 269G psi
  2. Abnormal Gradient at top Sand

269G psi

Figure 1.12

1. Pressure on the Gas-Water Contact

279G psi

2. Less Gas Column

Pressure = G.1G x 1GGG' = 1GG psi

  1. Pressure at top of Sand = 269G psi
  2. Abnormal Gradient at top Sand

269G psi

Figure 1.12

SECTION 1 : FUNDAMENTAL PRINCIPLES OF WELL CONTROL

Onshore, since the sediments tend to be more compacted, the overburden gradient can be taken as being close to 1.0 psi/ft. Offshore, however the overburden gradients at shallow depths will be much less than 1.0 psi/ft due to the effect of the depth of seawater and large thicknesses of unconsolidated sediment. This makes surface casing seats in offshore wells much more vulnerable to break down and is the reason why shallow gas kicks should never be shut in. See Fig 1.13

Fracture Gradient Comparisons

(for illustration purposes only)

Hydrostatic due to sea water 1500 x 0.445 = 667.5 psi V

Pressure due to overburden 1500 x 1.0 = 1500 psi

Pressure due to overburden 1500 x 1.0 = 1500 psi

G ft

15GG ft

Total Overburden 2167.5 psi (0.723 psi/ft)

SGGG ft

Pressure due to overburden 3000 x 1.0 = 3000 psi

Total Overburden 3000 psi (1.0 psi/ft)

Pressure due to overburden 3000 x 1.0 = 3000 psi

Total Overburden 3000 psi (1.0 psi/ft)

Hydrostatic due to sea water 1500 x 0.445 = 667.5 psi

Pressure due to overburden 10500 x 1.0 = 10500 psi

Pressure due to overburden 10500 x 1.0 = 10500 psi

G ft

15GG ft

12GGG ft

Total Overburden 11167.5 psi (0.93 psi/ft)

Pressure due to overburden 12000 x 1.0 = 12000 psi

Total Overburden 12000 psi (1.0 psi/ft)

Pressure due to overburden 12000 x 1.0 = 12000 psi

Total Overburden 12000 psi (1.0 psi/ft)

Figure 1.13

SECTION 1 : FUNDAMENTAL PRINCIPLES OF WELL CONTROL

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