Applications of Material Balance for Determining the Dynamic Performance of Fractures in a Dual-Porosity System in HP-HT Reservoirs

Abstract

Fractured systems are paramount to the productivity of carbonated formations; this is the main reason why the on-time appraisal of fractures behavior in High Pressure-High Temperature (HP-HT) Naturally Fractured Reservoirs (NFR) is decisive for the optimum selection of the exploitation strategy of the field. Considering the classifications for NFR proposed by R. Nelson and R. Aguilera, it is prone to apply the dual-porosity material balance to know the fractured network performance in different types of NFR during its exploitation, and to match the production history based on the discretization of the acting drive indices and its impact on the fractured system, resulting in one recovery factor for the matrix, and another for fractures. Several HP-HT Naturally Fractured Reservoirs (NFR) were analyzed and the material balance models were adjusted to the values of compressibility obtained from real saturation data observed in cores and petrophysical evaluations based on rock quality, rock typing and computed through correlations in order to obtain the performance of the fractured system, indicating the corresponding contribution of both to the total reservoir production; therefore it is possible to calculate a single recovery factor for fractures and other for the matrix only, and consequently, determine the type of NFR whose behavior is representative of the pressure-production history matching, agreeing with the numerical simulation model. Moreover, Pressure Transient Analysis (PTA) was considered as a good source of information to determine some critical data that are useful for the calibration of dual-porosity material balance models and the resultant description of fracture behavior for the optimum characterization of NFR, despite of the fact that well tests are not always available for every single well and the adverse wellbore effects involved that could cause interpretation problems. Additionally, it was possible to determine the matrix block size with applied material balance and well testing, achieving a better understanding of NFR. In this paper we present some cases of study of NFR hydrocarbon producers from Mesozoic age in the Southeast of Mexico with the applied methodology in order to reevaluate them, achieving important conclusions with the results obtained.