Abstract
The presence of conductive and extended heterogeneous features not connected to the wellbore and located beyond the investigation depths of standard characterization tools can be the reason for unexpected loss of net pressure during stimulation treatments due to the hydraulic fracture breakthrough into these heterogeneous areas. In current field practice, if such breakthrough occurs, it is considered as bad luck without the possibility of the quantitative analysis. This mindset can be changed in favor of the stimulation and reservoir management success using an approach that ties the thorough fracture pressure analysis with the output of the specific acoustic reflectivity survey capable of identifying position, shape, and orientation of far-field heterogeneous features.
The approach consists of four steps and is applicable to cases when the hydraulic fracture experiences breakthrough into the heterogeneity. First, before the stimulation treatments, at the reservoir characterization stage, a borehole acoustic reflectivity survey is run. Gathered data are interpreted and visualized according to a specific workflow that yields the image of the heterogeneous areas located around the wellbore in the radius of several tens of meters. Second, the hydraulic fracturing treatment is performed, and fracture pressure analysis is performed, which identifies the pressure drops typical for the breakthrough. Third, after the breakthrough into the heterogeneity is confirmed, the distance to this heterogeneity is used as a marker for calibration of the fracture properties and geometry. Finally, the post-stimulation pressure and production data are used to define the properties of the heterogeneous features, such as conductivity and approximate dimensions.
The comprehensive field application example of the suggested approach confirmed its effectiveness. For the tight carbonate formations, the heterogeneity in a form of fracture corridor was revealed by the acoustic reflectivity survey at least 20 m away from the wellbore. The breakthrough into this heterogeneity was observed during the acid fracturing treatment. The distance to the heterogeneity and observed pumping time to breakthrough were used as markers characterizing fracture propagation; reservoir and rock properties were adjusted using a fracturing simulator to obtain this fracture propagation. Finally, the post-stimulation production data were analyzed to determine infinite conductivity of the fracture corridor and quantify its extent downward. Data gathered during reservoir and hydraulic fracture properties calibration allowed for optimization of stimulation strategy of the target layer throughout the field; the information about the heterogeneity’s properties allowed for optimization of the completion and reservoir development strategy.
Unconventional Well Test Analysis for Assessing Individual Fracture Stages through Post-Treatment Pressure Falloffs: Case Study