Unstructured PEBI Grid-Based Pulse Well Testing for Fractured Caved Reservoirs

The distribution and volume of karst caves are the core parameters for the development of fractured cave reservoirs. In this paper, the single-phase seepage equation is adopted to describe the pressure variation in the fracture system, the wave equation is introduced to characterize the pressure dynamics in the cave, and based on the discrete technology of unstructured grid and finite volume method, the numerical simulation algorithm of fractured caved reservoirs is realized. This framework uniquely enables the inversion of physically meaningful karst cave parameters—specifically volume and location—directly from interference/pulse test data, bridging a significant gap between conventional statistical multi-porosity models and practical reservoir characterization needs. Using this algorithm program, a simulation study was conducted on the impulse well test responses of active wells and observation wells in fractured caved reservoirs. Studies show that the volume of karst caves with connectivity and the distance between the active well and the karst cave are the key factors affecting the pressure response of the observation well: the larger the volume of the karst cave, the smaller the variation range of the pressure of the observation well; The greater the distance between the active well and the cave, the smaller the variation range of the observation well pressure. Based on the above rules, this paper proposes for the first time to use the pressure response and derivative historical fitting method of the observation well in pulse well testing to inversely explain key parameters such as the volume and location of the karst cave. This research provides a theoretical basis for the application of pulse well testing technology in the evaluation of fractured caved reservoirs.