3-D Seismic As An Exploration & Production Tool: The Campos Basin Experience

Abstract

At present, over 50 hydrocarbon accumulations have been discovered in the Campos Basin, six of them corresponding to giant oil fields, located in deep waters. In most of these accumulations, a very important factor is the complex reservoir distribution, requiring fine tunned exploration, appraisal and development tools. In this scenario, 3-D seismic method has been playing a majorrole. As a typical risk minimizing tool, 3-D seismic surplus the conventional wisdom which directed the 3-D efforts towards the optimization of appraisal well location. Today, in the Campos Basin, the same technique is already considered a standard tool for earlier and later stages in the Exploration & Production processes. The main benefit of using 3-D seismic data is positioning the wells in predictable areas of better reservoir conditions and eventually, allowing the identification of fluid types, enhancing discoveries and production. A historical comparison of extort and results in the Campos Basin indicates an improvement in performanceand a progressive reduction in the number of wells, at the expense of an increase in 3-D seismic application. At the same time, the overall expenditure in explorationdecreased, while production and reserves increased. INTRODUCTION The Campos Basin is located offshore Rio de Janeiro state, southeastern Brazil. It extends roughly from thecoast line to the 3,400m isobaths and covers an area of about 100,000km2 (Fig. 1). Exploration activities began in 1968 with seismic investigation and exploratory drilling started in 1971. The ontinuous exploratory activity led to the discovery of thefirst commercial oil accumulation in 1974, Garoupa field, in Albian carbonate reservoirs. Alter the first discovery, an aggressive exploratory program was carried on in the Campos Basin with intensive seismic acquisition and drilling activities, holding the basin today the largest oil reserve in Brazil. So far, over 50 oil accumulations have beendiscovered, including six giant oil fields in deep waters. Around 600 exploratory wells have been drilled and365.000km of seismic data lines have been acquired including 248.000km of 3-D seismic, most of them in deep waters. After nearly two decades of the first commercial discovery, the Campos Basin total reserves (proven, probable and possible) reached, by the end of 1994, 7.9 billion the barrels of equivalent oil, which represents 77% of the Brazilian reserves. The present production is 525 housand barrels of equivalent oil per day corresponding to 61% of the total Brazilian production. TECTONIC AND SEDIMENTARY EVOLUTION The origin of the Campos Basin is related to the breakup of the Gondwana super continent and the drifting apart of the South American and African plates. Two structural styles can be observed in the basin. The oldest one is related to Early Cretaceous block faulting affecting mainly pre-Aptian rift sediments and basement voicanics. The youngest one is mainly relatedto post-Aptian salt tectonics 12 including extensional structures such as listric faults. The rift phase in the Early Cretaceous is represented by a series of horsts and grabens, oriented according to structural patterns from the Precambrian shield.