The Explorers 2009: Lower Cook Inlet risk, potential

The lower Cook Inlet basin contains as much as 36,000 feet of marine Mesozoic strata. In this area the Tertiary sequence that contains the oil and gas reservoirs in the upper Cook Inlet becomes very thin.

According to a 1995 MMS assessment, the Mesozoic of the lower Cook Inlet includes some potentially excellent oil source rocks. The middle Jurassic strata include the same source rocks as those that generated oil in the upper Cook Inlet.

The MMS assessment also says that there are some Mesozoic sandstones that have good reservoir potential.

But the chemical alteration and resulting reservoir degradation of some of the Mesozoic sandstones has cast something of a pall over prospects of finding viable hydrocarbon pools in these rocks, thus upping the ante on exploration risks, even although the regional distribution of the reservoir clogging alteration is not fully understood and some of the rocks may contain fracture systems that would allow fluids to flow.

To date, 11 exploration wells have been drilled in the offshore waters of the lower Cook Inlet. Two of the wells found significant oil shows but the oil finds proved uneconomic. Another well only found minor oil shows.