Natural Fracture Network Analysis on Unconventional Reservoirs in the Middle Magdalena Valley, Colombia

Rodriguez Carreño, Claudia E.¹; Higuera-Díaz, I. Camilo; Forero , Silvia P.; Ceron Abril, John; and Barrera Montiel, Paola A.
¹[email protected]

Understanding of natural fractures is critical in developing unconventional hydrocarbons reservoirs. In reservoirs where permeability and porosity are low, the presence of natural fractures may enhance or detriment the quality of a stimulated reservoir. Then characterizing natural fractures in terms of types, intensity, and distribution helps predicting the best combination of favorably oriented fracture networks, open fracture systems and intensely fractured intervals to model and stimulate a reservoir.

To understand the geometry and kinematics of natural fractures in the fine-grained Cretaceous rocks of the central part of the Middle Magdalena Basin in Colombia, we characterize the fracture network in several wells. We characterize fractures in each well from three sources: Mapping the fractures in a 2D slab, interpreting resistivity images of well logs, and extracting fractures from a 3D CT-scan volume. There is a certain level of redundancy in the sampling obtained from these datasets but each dataset provides data unique to them in terms of scaling, continuity of record, 3D geometry, identification of fracture fills, and kinematic indicators.

Using the resulting composite natural fracture map, we estimate statistical parameters to characterize the fracture network. One, we measure the total fracture intensity coefficient using a moving window average. Two, we estimate the ratio between strata confined and unconfined fractures. Finally, we determine a relationship between open and close fractures. In addition, we derive a geometric and kinematic model that show six fracture networks: a bedding-parallel, a hinge-parallel, a cross-fold, two hinge-oblique, and a strike-oblique families. All families are present through the sequence, but the higher density corresponds to the cross-fold, and the bedding-and hinge-parallel fracture networks.

Cross-correlation between fracture coefficients and families with the mineralogy, free-gas content and geomechanical measurements for each well show that intervals with high-fracture densities developed in rocks that are silica-rich and that those intervals present high contents of free gas. Our model for natural fractures shows a well-developed and well-connected network with fracture intensity dependent on bedding thickness, and the mineralogy and type of cement. A second prediction from our model is that two fracture families are optimally oriented for stimulation with respect to the current stress field.

AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013