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Structural Modeling and Its Impact on Development of the Piedemonte Area, Eastern Cordillera Fold and Thrust Belt, Colombia

Abstract

The Piedemonte area was initially tested, in the late 1990's, by a few wells to the north of the large discoveries of Cusiana and Cupiagua fields. These wells in this fold and thrust belt were based on 2D seismic with poor imaging, and more importantly, on structural models based on the discoveries to the south. Risk was high, but based on the large discoveries to the south, several wells were drilled and some successfully found productive thrust sheets in this area. Owing to economics at the time, they were not produced immediately. Later completions and the beginning of production (2001-2007) started to show the production potential and possible reserves of these gas-condensate reservoirs. Based on this potential, 3D seismic was acquired, but again, the imaging of the productive thrust sheets and surrounding area was poor, even with iterations of processing. The poor seismic image has made development of these resources difficult and with high uncertainty on position, extent and size of the traps. With the recognized potential in the area, a tested structural model was key to guiding drilling while minimizing risks, as well as providing a model to better estimate potential reserves. Due to the poor imaging, a structural model was initially developed based in large part on the initial wells. First, a network of 2D sections was developed, and the fault network was tested through iterations of 2D restoration and balancing. The tested network of sections was expanded as new well data filled in some of the larger gaps, with adjustments to the model as indicated by the new data. The sections provided a template for a 3D model, where further restoration and balancing tests have been applied. Based on the structural modeling, successful drilling (14 productive wells) has continued in the area and the reserves have been effectively developed, in spite of high drilling costs. The drilling has confirmed the extensive lateral extent of the thrust sheets, as predicted in the initial models. With carefully placed wells additional rock volumes have been tested, new thrust sheets have been discovered, greater gas columns were proven and the extensive connectivity within these naturally fractured thrust sheets has been demonstrated. Uncertainty in this area of poor seismic image remains high, but structural modeling aided greatly in developing these resources effectively.