Abstract
Even as new discoveries are developed and produced, substantial additional reserves can be secured by enhancing recovery from mature fields. It is known that one of the most cost-effective ways to revitalize mature fields is to institute an efficient workover program. These programs can be more effective because of the implementation of fracturing/refracturing techniques for unlocking new pay intervals or putting back on production existing, nonproducing stages. Fracture stimulation is commonly used to increase the production and improve the economics of oil and gas fields worldwide. In many cases, however, if the average production increase justifies the hydraulic fracture, very little effort is made to optimize the treatments. Further economic gains can be achieved through the optimization of the hydraulic fracturing process by improving the fracture model calibration and better understanding of reservoir parameters. This is particularly true in mature fields where the fracture geometry understanding is critical to avoid contacting a water zone or a gas cap in some cases. Also, sometimes there is an impact on the reserves determined by decline curve analysis (DCA) after the fracturing treatment.
The analysis of the fracturing model through pressure interpretation or fracture pressure analysis (FPA) provides powerful tools not only for understanding and improving the fracturing design parameters, but also for better understanding the reservoir parameters. On the other hand, reservoir transmissibility, a variable of significant importance in hydraulic fracturing design and production evaluation (PE), is frequently unknown because candidate wells either do not flow or pretreatment pressure transient tests are not available. The after-closure analysis (ACA), the component of the FPA in the after-closure region, allows for the identification of linear and radial flow and the determination of reservoir transmissibility and pressure from injection testing. The reservoir parameters determined with this method can be verified by comparison with results obtained from conventional well testing or pressure transient analysis (PTA) and rate transient analysis (RTA).
This paper presents a detailed analysis and comparison of the reservoir parameters obtained by FPA, PTA, and RTA in block 60 (Sacha field), a mature field located in the Oriente basin operated by Operaciones Rio Napo CEM. The three techniques have been integrated for reservoir modeling in a moderately permeable, underpressure, black oil sandstone reservoir allowing not only increasing the production but also the reserves in the hydraulically fractured wells.
