Abstract:

Extended leak-off tests are important in petroleum engineering for obtaining underground stress information, which is critical for issues such as wellbore stability, lost circulation, casing design, hydraulic fracturing, sand production, and reservoir compaction and subsidence. The signatures of extended leak-off tests are very different between permeable formations (e.g. sandstones) and impermeable formations (e.g. shales). A proper understanding of this difference is important for test interpretation, particularly for the determination of minimum horizontal stress. Based on numerical simulation analyses, this paper contains a detailed comparison of extended leak-off tests in permeable and impermeable formations. The comparison results show that permeability and its related phenomenon such as fluid leak-off can significantly influence pressure versus time response of an extended leak-off test and lead to interpretation difficulties. Traditional interpretation methods using time development of bottom hole pressure cannot provide accurate estimate of minimum horizontal stress in impermeable formations due to the negligibly small leak-off through fracture faces to the surrounding formation. The numerical model developed in this paper provides a method for aiding interpretation and design of extended leak-off tests

Introduction

Knowledge of minimum horizontal stress (Shmin) is important in many aspects during the life of oilfield development. It impacts all the development phases from well design to well abandonment. Shmin is a key factor for design of well trajectory and casing programs, and prediction of wellbore stability and lost circulation in the drilling and completion phases (Feng et al., 2015; Feng and Gray, 2016a, 2016b; Raaen and Brudy, 2001). It is also one of the most critical elements for hydraulic fracturing design to maximize the recovery of unconventional reservoirs. In the production phase, Shmin is a required parameter for evaluation of sand production, reservoir compaction, and surface subsidence. For the well abandonment phase, knowledge of Shmin is needed to determine the abandonment plug setting depths to ensure the long-term integrity of the abandoned well. In addition, fluid injection operations, such as produced water injection, waterflooding, steam injection, cuttings reinjection and carbon dioxide injection, have become essential elements of field development worldwide. The long-term integrity of reservoir caprock has become a major safety concern surrounding these operations. Shmin is a key input for developing reliable, full-scale mechanical earth models and other analytical or empirical models for addressing this safety concern (Chan et al., 2015).

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