Pressure transient analysis of unsteady-state inter-porosity flows for slanted wells in fractured-vuggy carbonate reservoirs

Articles in Press

Document Type : Research Article

Authors

1 National Key Laboratory of Oil & Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, China.

2 Tarim Oilfield Company, PetroChina, Korla, Xinjiang 841000, China.

3 Liquor Making Microbial Application & Detection Technology of Luzhou Key Laboratory, Luzhou Vocational & Technical College, Luzhou, 646000, China.

4 Institute of Petroleum & Gas Engineering, Chongqing University of Science and Technology, Chongqing, 401331, China.

5 Xi'an Sanwei Technology Development Co., LTD, Xi’an, 710021, China.

Abstract

To address the significant challenges posed by multiscale heterogeneity in fractured-vuggy carbonate reservoirs, we have developed a comprehensive triple-porosity pressure transient model specifically tailored for slanted wells. A central innovation of this work is the rigorous incorporation of a unified unsteady-state interporosity flow mechanism. This approach accurately describes the dynamic fluid transfer from both spherical matrix blocks and a distinct vug system into the interconnected natural fracture network, thereby avoiding the limitations of simplified pseudo-steady state assumptions. The model also integrates essential near-wellbore effects such as wellbore storage and skin factor. Leveraging source function theory and the principle of superposition, a new semi-analytical solution was derived in the Laplace domain, with the real-time pressure response obtained via the Stehfest numerical inversion algorithm. Based on this solution, characteristic type curves were generated, revealing a key diagnostic feature: two successive troughs on the pressure derivative plot. These troughs represent the sequential fluid supply, first from the more permeable vugs and subsequently from the low-permeability matrix. Extensive sensitivity analyses systematically quantified the influence of well geometry and critical reservoir parameters on pressure behavior. Finally, a field example from a carbonate reservoir validated the model's practical applicability, demonstrating excellent agreement with actual test data. Consequently, this work offers a more robust tool for well test interpretation in these highly complex formations.

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Scientia Iranica

Articles in Press, Accepted Manuscript
Available Online from 23 June 2026

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History

  • Receive Date: 28 September 2025
  • Revise Date: 31 January 2026
  • Accept Date: 20 May 2026

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