Plate tectonic structural geology to detailed field and prospect stress prediction

Abstract

Arguably the first successful application of the theory of continental drift to petroleum exploration was in 1959 by the pioneers S. W. Carey and L. G. Weeks whose collaboration led to the discovery of the world class Gippsland Basin. Plate tectonics, as the theory is now known, was still nascent and not prominent during peak global oil exploration success in the 1960s. As discovery rates continue to decline, large scale description of separating and colliding continents has become increasingly impotent in the ever more complex hunt for the next barrel. Emphasis is turning from new basins and plays to smaller intra-basin discoveries related to a more detailed understanding of basin forming faults and their local stress effects on traps and trap geometries. Improved oil recovery is not only about finding new fields, but also demands detailed stress information for horizontal wellbore stability to economically and effectively increase reserves and recovery rates by extracting new oil from old fields. As a result, expensive wellbore based measurements have been deployed in the past 15 years. These precision measurements have then been averaged between wells for stress prediction but stress directions are known to vary abruptly by up to 90° over distances of less than 3 km. A solution lies in the seismic recognition of globally synchronous compressional pulses which, like a heartbeat, have added predictability of stress fields hence to stress analysis. This repetition of stress provides a workflow for stress consistent seismic interpretation that can predict horizontal and vertical changes in the direction of the maximum horizontal compressional component of a stress SH (SHD) and also in the magnitude of the stress, SHM. It is now possible to derive pre-drill at any desired point, important exploration and production variables such as stress related fault seal and open fracture orientation. Similarly, important reservoir development parameters such as fracture gradients and wellbore stability prediction will maximise recovery efficiencies and reduce development costs. This technique will also aid in effective carbon dioxide sequestration, a challenging new field of endeavour.