Production and Prospectivity in a Structurally Complex, High-Taper Triangle Zone, Gibraltar Area, Eastern Cordillera, Colombia

Abstract

Gibraltar field, in the northern part of the Eastern Cordillera fold and thrust belt, produces gas-condensate at high rates from Eocene Mirador Formation sandstones. It is located in a triangle zone that displays complex structures. There are numerous other similar structures as well as a significant potential extension of the field, but developing and exploring in the area depends on the structural interpretation from sparse data. The data in the area is limited to: 1) three wells from a single pad with associated logs, tops, dips and production data, 2) widely spaced 2d seismic data that typically has poor imaging in the triangle zone, and 3) surface data. The surface geologic mapping, while of variable reliability, is a key component to interpreting the structures in this high-taper triangle zone. The area is a typical triangle zone, with unfaulted, basinward-dipping syntectonic strata at the topographic front, and stacked thrust sheets wedged under and uplifting the basinward-dipping strata beneath a passive roof detachment. The stacked thrust sheets contain the proven and potential reservoir units. In the southern segment of the triangle zone, the dip of the basinward-dipping strata is high, up to 50-55 degrees, thus it is a high-taper triangle zone, in contrast to well-known low-taper triangle zones such as the Southern Canadian Rockies triangle zone. This high-taper style of triangle zone requires a tight stacking of several thrust anticlines, and this conforms to the scale and style seen at the surface where the sub-detachment thrust sheets are exposed. The mechanical stratigraphy controls in large part the scaling of the structures and it is expected that this scaling will be consistent throughout the area where the stratigraphy of the thrust sheets is similar. In the northern segment there is initial development of the triangle zone as to the south, but ongoing later faulting steps forward into another triangle zone where the main compression direction changed from east to southeast, aligned with the Venezuelan Andes trend in the latest part of development. Section balancing and structural modeling, utilizing the surface and well data, have provided a new view of the potential in this area. The detailed structural modeling has defined a probable extension to the field as well as highlighting several other prospective structures, in spite of limited data and poor quality seismic data.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016