Analysis of bottom hole pressure instability in ultra deep fracture-vuggy type condensed gas reservoirs

Abstract

Accurate bottomhole pressure is crucial for tracking gas well performance. However, ultra-deep fracture-vuggy reservoirs are characterized by a complex mix of matrix, fractures, and vugs, plus condensate gas phase changes, which makes interpretation difficult. To solve this, unsteady pressure buildup data and production data were combined to build a well test interpretation model. A new pseudo-pressure function based on mass flow was used, and the wellbore storage model was updated based on pressure gauge depth. The well-vug part was solved directly and the fracture-vug-fracture part was solved step by step. The final theoretical chart was verified against existing literature. It is shown by our analysis that early flow is mainly affected by wellbore storage and skin factor; the linear flow stage is controlled by fracture zone length and flow conductivity; the storage stage is influenced by vug volume; and the timing of linear flow is shifted by two-phase, adsorption, and dry gas zones that are created by condensate degree. Real production data are closely matched by the model, and our understanding of these complex reservoirs is deepened, and better gas field development is supported.