Improving Petroleum System Identification in Offshore Salt Environments: Gulf of Mexico and Red Sea Case Studies

Abstract

Abstract Offshore exploration is a costly endeavor that entails multi-million dollar expenditures to acquire synthetic aperture radar data, electromagnetic data, 2-D seismic data, as well as 3-D seismic data to evaluate subsurface structures and systems. However, while these technologies lend an understanding to the geologic structure of subsea systems, these do not address the critical question of the presence of a petroleum system (i.e. charge). This case study was conducted by Anadarko Petroleum Corporation in their Marco Polo field in the Gulf of Mexico. The project focused on improving the mapping of hydrocarbons from petroleum systems by augmenting seismic with additional technologies such as detailed multibeam bathymetry, side scan sonar, and acoustic backscatter to acquire high-resolution sea floor characterization and ultra-sensitive hydrocarbon detection to provide hydrocarbon detection with a thousand times greater sensitivity than traditional methods. The high resolution geophysical data significantly improved the ability to locate macroseep sites. Additionally, the ultra-sensitive hydrocarbon system was able to identify hydrocarbons from both macroseepage and microseepage. Thus, hydrocarbons were detected in one hundred percent of the core samples, instead of 10% as found with traditional methods. While the Marco Polo site focused on macroseepage acquisition the Red Sea case study focused on microseepage acquisition. The Red Sea area that was overlain by 8,000 ft of evaporitic salt and anhydrite sequences that also contained inter-bedded shale sequences. The field was a fractured sub-salt rift basin producing from the Miocene Kareem and Rudeis formations. The client had drilled two producing wells, but had also drilled three dry wells. The thick salt sequence made seismic data difficult to interpret and the extensive faulting added additional risk to the exploration efforts. Given the complex geologic system and the difficulties associated with the seismic imaging, ultra-sensitive hydrocarbon mapping was employed to add understanding to the geologic structure and add clarity to the boundaries of the hydrocarbon accumulations. Liquid hydrocarbons were detected through the 8,000 ft salt sequence and then mapped across the field indicating areas of high probability of oil locations and areas of low probability. The probability map correctly predicted the previously drilled producing and dry wells. The hydrocarbon survey results also identified two three-way closures in the field as well as a potential fault not identified by seismic data. Subsequent to the study a well was drilled based on the survey results and produced 800 bopd, lending credence to the hydrocarbon probability maps generated by the survey. The result was the use of new technologies to derisk offshore exploration efforts by more effectively determining the presence of an offshore petroleum system through salt sequences. Additionally, it mapped reservoir boundaries and defined reservoir sweet spots with better pressure and porosity thus enhancing improved production.