The Cusiana Field, Colombia, in Early Development: Results of a Sequence Stratigraphy Based Reservoir Description

Andrew J. Pulham

The Cusiana Field (BP, Ecopetrol, Total and Triton) is located in the Llanos Foothills of eastern Colombia. The Cusiana reservoirs range from late Cretaceous, passive margin deltaic to early Tertiary, early foreland basin estuarine-fluvial. The principal reservoir is the late Eocene-early Oligocene Mirador Formation which comprises over 50% of the original in place hydrocarbons.

During late 1993, as an aggressive appraisal program of the Cusiana field was nearing completion, a detailed reservoir description of the Mirador reservoir was constructed using sequence stratigraphic concepts. The data that supported this early description comprised analyses of 2,500 feet of conventional cores in 10 wells. There is no seismic data to support the reservoir description effort and the wells are typically several miles apart. During 1994 the early development of Cusiana moved ahead rapidly. New Mirador core has been acquired and at least 6 new wells have been drilled. The early sequence stratigraphic model is being tested.

The 1993 reservoir description focused on a recognition of important flooding surfaces and sequence boundaries that were used to subdivide the dominantly brackish-water Mirador Formation into predictive reservoir zones of contrasting net:gross and reservoir quality. This description has been robust in predicting the overall fabric of the Mirador reservoir during early development drilling. Individual reservoir elements, such as incised valleys, however, have been difficult to predict geographically. Blending the sequence stratigraphy with stochastic tools and techniques is currently seen as the way to improve the predictive success of future wells.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995