Volume 40: Energy Transitions toward Carbon Neutrality: Part III

An Effective Model for Well-testing Interpretation on Carbonate Reservoirs with Complex Cave Connections Quanyu Pan, Linsong Cheng, Yuanzheng Wang, Pin Jia, Zhikai Wang

Abstract

The fracture-caved gas carbonate reservoirs raise serious concerns in China. However, there are numerous large-scale caves in the fractured-caved gas reservoirs due to the structural fracture and dissolution. To solve the problems of fracture-caved gas reservoirs, like strong heterogeneity, obvious differences in fracture-caved connection characteristics, and great difficulty in well testing. In this paper, a novel pressure transient analysis model under a complex fracture-caved connection mode is established to estimate fracture region and cave parameters. First, governing equations considering the coupling of fracture linear flow and cave storage flow are derived. Furthermore, the dimensionless fracture pressure solution in Laplace space is solved after dimensionless treatment, and the dimensionless bottom-hole pressure solution in real space is produced using the Stehfest numerical inversion method. Finally, the flow phases are divided, and a multi-parameter sensitivity analysis is performed after identifying the type curves of the complex fracture-caved connection mode. The results indicate that the conductivity and length of the fracture region have the greatest influence on the start time and duration of linear flow, whereas the volume of the cave has the greatest influence on the storage flow. Matching with the recorded pressure and flowrate data, the established pressure transient analysis model can effectively invert the fracture length, conductivity, and cave volume of fracture-caved reservoirs, which provides a basis for evaluating the geological characteristics and underground reserves of fracture-caved gas reservoirs and has significant guiding significance for the development of carbonate reservoirs.

Keywords Carbonate reservoirs, Large caves, Pressure transient analysis, Fracture-caved gas reservoirs