Economic Exploration Assessment of Hydrocarbon Leakage across a Fault. II. Charged Sand before Faulting

Abstract

That faults cross-cut sands and cause leakage of hydrocarbons, either out of the upthrown and downthrown sand system or from the downthrown sand to the upthrown sand, is well known The decision to drill either or both of such sands depends on what it is one assesses as the likely hydrocarbon potential of the total system and also for each sand independently. This paper provides a quantitative procedure to determine a strategy for deciding what to drill. The economic worth for such a sand system depends on the chances the sands were originally hydrocarbon charged, and on the leakage possibilities for each sand, together with the recharge of the upthrown sand from the downthrown sand, and seems not to have received a quantitative investigation to date. In addition, at the exploration stage the amount of detailed information about such a fault cut system is limited, so that any and all assessments of parameters influencing the economic worth are also uncertain. This paper shows how one can include uncertainties caused by such “fuzzy” parameters in attempting to decide on a drilling strategy geared to satisfying corporate mandated economic returns criteria. Numerical illustrations are given to show how the strategies to decide to drill either only the downthrown sand, or only the upthrown sand, or to drill both sands can be brought to a rational form so that corporate decision-makers can compare and contrast the three strategies under the same quantitative framework.