Study of high permeability fracture zones through structural mapping and numerical modeling in jandaíra formation, potiguar basin
Fractures; Karst; Numerical Model; Jandaíra.Formation
The effect of the presence of fractures on the fluid flow in reservoirs is now the subject of critical interest for the oil industry. In the case of carbonate rocks, the study of the contribution of fractures on reservoir efficiency becomes more complex due to the reactive nature of these rocks concerning the circulating fluids and the high tendency of karstfication. Fractures act as agents that concentrate fluid and exert structural control on the formation of karst, concentrating dissolution along the structural grid. For the oil industry, this scenario may be favorable because of increased porosity and permeability of secondary fractures, but it also presents risks to the operation, hence the growing interest in karst occurrence prediction associated with fractures on carbonate reservoirs. This study investigates, under the geomechanical point of view, how the presence of faults and joints influences the development of karst observed in carbonate rocks. The Jandaíra Formation was selected as a geomaterial, analogue to fractured carbonate reservoirs in marginal basins of Brazil. The methodology adopted for this study included: (i) the use UAV images for mapping structural lineaments and the occurrence of karst features on the outcrop; (ii) numerical modeling of the effect of the current tensions on the structures identified. Comparing the results of numerical modeling to the mapping performed on the images and field observations, it was found that the regions of numerical models where the largest dilatancy values occurred coincided with regions on the ground (fault terminations and cross fractures) where there is concentration of dissolution and formation of karst. Therefore, this study established that there is a possible relation between stress concentration and dissolution location along the structural frame observed in fractured and karstfied flagstones of Jandaíra Formation and showed that the dilatancy process is probably responsible for the occurrence of preferential dissolution controlled by fractures in carbonate rocks.