Despite the vast differences in location and water depth, both the Montara and Macondo blowouts would have been prevented if negative pressure tests had been properly conducted and interpreted after the production casing had been set.
A negative pressure test simulates an underbalanced condition in which the formation pressure exceeds the pressure exerted by the fluid column. The purpose of the test is to determine if there are leaks in the casing shoe track, casing, or seal assembly. At Macondo, the test was conducted and the evidence of inflow is quite clear. Unfortunately, that evidence was misinterpreted. See slides 14-17 in the linked presentation.
At Montara, the testimony suggests that a negative pressure test was not properly conducted. PTTEP therefore had a false sense of security regarding the integrity of the casing shoe. See page 9 of this transcript.
Both wells subsequently flowed through the shoe track and inside production casing for a combined duration exceeding 5 months.
Bud's Offshore Energy (BOE) 