Usually, there is no need to frack an offshore reservoir, or even a conventional onshore reservior for that matter. A conventional reservoir is predominately a sandstone (90% of the time) or a carbonate (about 5%) of the time. The reason is simple, these rocks have high porosity and permeability (P&P) which allow the oil and gas to flow to the well-bore under natural reservoir pressure. Think of it as a sponge full of oil being squeezed from above by 3 miles of rock. If you poke a hole in that sponge and release the pressure, the fluids in the sponge will come to the surface. Simple physics. A shale reservoir however has very small P&P, fluids and gases normally cannot communicate with the well-bore because the pores in the rock are not in communication with each other, even with large differences in pressures. It is the fracking procedure that allows avenues for the oil and gas to flow to the wellbore, creating the permeability, but not the porosity.
However the main reason that is not done offshore is simple economics. Five Deepwater Offshore wells cost upwards of $500MM and can drain an area of 17,000 acres or more.. An onshore well, including the frack, costs about $10MM and can drain an area of about 40 acres. Therefore, the equivalent number of wells in an offshore shale would be 425*100MM. You get the point. If a company can drill a well into a deepwater sandstone with great P&P, drill 5 wells that drain a 250 million barrel field, why in the world would they bother with a shale zone that requires 425 wells AND very expensive fracking operations, to recover a fraction of those same reserves?
It's simply the economics of drilling and producing the reserves. |
