Multivariate optimization of tight core retrieval schedule based on numerical simulation. A novel approach

Salavat Y. Ishbulatov, Andrey V. Kazak

    Research output: Contribution to journalArticlepeer-review

    2 Citations (Scopus)

    Abstract

    The quality and safety of core recovery determine the success of the petrophysical and geomechanical analyses. It becomes crucial for low-permeable (tight) formations, including shales, where rock stress-strain and strength properties drive well completion and treatment design. There are few technologies providing sample condition monitoring while lifting and protecting the core from deformation/damaging and fluid release. A feasible option is to simulate core tripping and optimize core retrieval parameters such as lifting rate, number, and duration of stops to meet operational requirements (time, cost, rate). The article presents a new approach to solve the safe core tripping problem. Firstly, we discuss the implementation issues of state-of-the-art poroelastic Laplace-inversion-based analytical solutions and numerical approximation models. Then we introduce an approach based on the poroelastic model assuming vertically transversely isotropic permeability. The method features an updated equation for decompression and failure criteria, determined by the properties of the porous media of the rock. We used the obtained solution to simulate typical core tripping scenarios and optimize the core tripping schedule for total retrieval time. Finally, we discuss the account for micro fracturing, core damage mechanics, and improvements of decompression models. In summary, the article makes several practically essential conclusions. The strength properties — not only tensile strength but also fracture toughness of the rock are crucial for finding the optimal safe core tripping regime. The poroelastic simulation shows that tensile stresses cause fracturing of the core inner region; damage initiates from existing (natural or drilling-induced) defects (microfractures, cracks). The presented core tripping algorithm, unlike the existing ones, optimizes the tripping rate-depth profile intelligently depth-by-depth and does not require calculating the whole core lifting case. The application of the approach increases the prediction accuracy, avoids overestimation of the time required for a safe core tripping, and, in principle, allows estimating the degree of core damage.

    Original languageEnglish
    Article number107401
    JournalJournal of Petroleum Science and Engineering
    Volume195
    DOIs
    Publication statusPublished - Dec 2020

    Keywords

    • Core tripping schedule
    • Microfracturing
    • Poroelastic approach
    • Safe core retrieval
    • Simulation
    • Tight rocks

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