In the VenezuelaExxonMobil Holdup Problem in Figure, suppose that the parties could initially agree to a binding

Question:

In the Venezuela–ExxonMobil Holdup Problem in Figure, suppose that the parties could initially agree to a binding contract that Venezuela would pay ExxonMobil x dollars if it nationalizes the oil fields. How large does x have to be for ExxonMobil to invest in Venezuela?