In this study, the comparison of the transient pressure responses of different wormhole patterns has been comprehensively studied. The modeling results show that transient pressure and production responses vary significantly due to different wormhole structures and reservoir area that embeds with the structure. A concept of effective wormhole coverage is proposed for the first time in this study and its corresponding wormhole model has been well established and validated to study the effective wormhole coverage for wells in the process of Cold Heavy Oil Production with Sand (CHOPS).

Type curves developed for CHOPS wells with wormholes in this study can be applied to analyze transient pressure and production data from wormholed heavy oil reservoirs. Effective wormhole coverage and branches can be reasonably estimated using type curve matching. This work helps offer important parameters in further optimization of post-CHOPS processes such as post-CHOPS EOR planning and infill well drilling.

Type curves for effective wormhole coverage with different numbers of effective wormhole branches were developed for CHOPS wells in this paper. Once either the transient pressure data or production data are matched with the developed type curves, the number of effective wormhole branches and match points are recorded. The effective wormhole coverage can be subsequently determined using the equations developed in this study. In addition, once the number of wormhole branches and effective wormhole coverage has been determined, sand production data can be utilized to help determine the diameter of effective wormholes. It should be noted that, prior to the use of the type curves, formation properties and foamy oil properties should be prior known information.

In CHOPS, the presence of wormholes is considered to be one of the most important factors which contribute to enhanced production rate. Due to the complexity of wormhole phenomena, few methods have been introduced to determine wormhole coverage quantitatively. The novel approach presented in this paper is aiming at providing quantitative information of wormholes by analyzing transient pressure, production rate, and sand production data simultaneously.

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