OVERVIEW

Economic analysis and reserves have been discussed widely in the petroleum engineering literature and more recently in the Petroleum Society of CIM Monograph No. 1, Determination of Oil and Gas Reserves, published in 1994. It has been shown in previous chapters, that other things being equal, a smaller number of wells is required to drain efficiently a naturally fractured reservoir as compared with a conventional homogeneous reservoir. Furthermore, the importance of drilling directional and horizontal wells for the purpose of intercepting the larger possible number of high inclination and vertical fractures has been stressed.

Following a basic introduction of key economic yardsticks for decision making, this chapter presents methods for handling economic aspects of acceleration projects such as those that occur in many naturally fractured reservoirs.

In general, fractured reservoirs should have larger spacing than homogeneous reservoirs. For example, Baker and Lucas (1972) have noted that practical experience and detailed economic evaluations have led to the conclusion that 640 acre is the optimum spacing for the Altamont trend. Closed spacing proved uneconomic.

Daniel (1954) indicated that the fractures are so closed at Kirkuk field (Iraq), that only a few wells located at the base of the highest dome (Baba) would be enough to drain the entire reservoir. A 2-mile spacing was expected to give adequate drainage (spacing of approximately 1280 acres).

In discussing the Ain Zalah field (Iraq), Daniel (1954) indicated that the degree of fracturing was so intense that drainage from the first and second pay could probably...