Authors: Antonio Velásquez (presenter), Ricardo Zavala, Enrique Casaña, Mauricio Afanador, Juan Carlos Llinás, Mauricio Pulido, Oscar Moreno, Sandra Montoya, Fabio Malagón, Helga Nino, Andrea Ortíz-Karpf, John Londoño, Pranab Sen, Ecopetrol, S.A.
The AVO technology has become a key tool for the exploration efforts in the offshore Caribbean frontier. In recent years, it emerged as an interesting gas-prone basin with a multitude of reservoirs with characteristic elastic properties and seismic responses. This work reveals and describes the type of AVO reservoirs encountered in three geologic provinces of the offshore Caribbean: Guajira Offshore, Magdalena Fan and Sinú Offshore. In general, DHI analysis based on AVO has been a powerful tool to predict hydrocarbon accumulations. However, key geologic processes control the seismic response differently at each structural province.
Using elastic data from recent wells, the seismic signatures were modeled, classified and analyzed, and their meaning as possible DHI’s widely discussed. The AVO response of hydrocarbon-filled sands varies in the whole spectrum of the Rutherford and Williams (1989) classification. In general, DHI analysis based on AVO has been a powerful tool to predict gas accumulations. However, the composition of the sediments (e.g., sand and shale proportions), the changes in pressure or stress regime, as well as the burial history and the sedimentation rate, strongly affect the rock properties and the seismic response, making the fluid prediction quite challenging. Furthermore, low gas-saturated reservoirs, tuned amplitudes and poor quality of pre-stack data are the most common sources for pitfalls.
In the Sinú Province, Pleistocene gas-saturated turbidities exhibit class III AVO and create classical bright spots relatively easy to identify. However, thinly bedded sands are tricky to characterize if the gross thickness approaches tuning. The Magdalena Fan Province mostly has confined channel-like Pliocene reservoirs, also with class III AVO gas sands, but fizz reservoirs and tuned amplitudes commonly generate high risk of pitfalls. Finally, the Guajira Province that is geologically more diverse, exhibit high impedance reservoirs, aged Miocene and Oligocene. Typically, class I or IIp AVO signatures affected by tuning are not properly imaged and represent the most challenging reservoirs to accurately predict fluids from seismic data.
Antonio Velásquez, Ecopetrol S.A.
Antonio graduated from Universidad Nacional de Colombia with a BSc degree in Geology. He also holds a MSc in Geology from the same university and a MSc in Geophysics and Seismology form the Colorado School of Mines.
With 15 years of experience in the industry, he currently works at Ecopetrol Brasil as Exploration Assets Manager, where he leads the exploration team responsible for prospect generation and maturation, and is also on charge of project management, economical evaluations, TCR / Alt.TCR roles in partnerships and operations follow-up in offshore assets located in both PreSalt and Ecuatorial Magin basins.
Antonio is a member of AAPG, SEG, EAGE and ACGGP.