Economic Exploration Assessment of Hydrocarbon Leakage across a Fault. III. Hydrocarbon Leaks and Fault Locations

Abstract

This paper addresses the concerns of potential hydrocarbon leakage through a fault when there are changes in the location of the fault, its orientation, and its length in relation to a given sand body of known width. The probability that hydrocarbons interact with the fault is expressed in terms of the overlap length of the fault in the sand, and in terms of the sand width as well. When the probability that the fault is open or shut to hydrocarbon flow is added to the geometric probabilities as a basic variable, the uncertainties of the five parameters (fault length, sand body width, fault orientation, fault location in relation to the sand body, and probability the fault is open to hydrocarbon escape) are addressed in terms of Monte Carlo representations of the chances of retaining or losing hydrocarbons. The dominant contributions to the uncertainties of the fraction of hydrocarbons most likely lost or retained are also given so that one can determine which of the five basic parameters need to have their ranges of uncertainty narrowed first in order to improve on the probable estimates of hydrocarbon retention. Numerical illustrations are given to show how one goes about assessing these factors for a sand cut by a fault, and to illustrate the chances that the sand is hydrocarbon bearing or not due to possible loss through the fault.