Horizontal Borehole Stability in Naturally Fractured Reservoirs

Horizontal Borehole Stability in Naturally Fractured Reservoirs Jincai Zhang; Jincai Zhang University of Oklahoma Search for other works by this author on: This Site Google Scholar J.-C. Roegiers J.-C. Roegiers University of Oklahoma Search for other works by this author on: This Site Google Scholar Paper presented at the SPE/CIM International Conference on Horizontal Well Technology, Calgary, Alberta, Canada, November 2000. Paper Number: SPE-65513-MS https://doi.org/10.2118/65513-MS Published: November 06 2000 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Zhang, Jincai, and J.-C. Roegiers. "Horizontal Borehole Stability in Naturally Fractured Reservoirs." Paper presented at the SPE/CIM International Conference on Horizontal Well Technology, Calgary, Alberta, Canada, November 2000. doi: https://doi.org/10.2118/65513-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll ProceedingsSociety of Petroleum Engineers (SPE)SPE/CIM International Conference on Horizontal Well Technology Search Advanced Search AbstractFor modeling naturally fractured reservoirs, the dual-porosity poroelastic model is effective and accurate to characterize stresses as well as flow fields. A generalized plane strain and dual-porosity finite element solution has been developed for analyzing horizontal borehole stability. Two kinds of failure criteria (spalling and collapse) were included. Results show that horizontal borehole stability depends strongly on the in situ stress state, the borehole orientation, time, mud pressure and fracture characteristics.IntroductionBorehole stability is a very important issue in the gas and oil industry as it can result in substantial expenditures having thus a significant impact on reservoir production. Stability of circular openings has been considered and studied in different contexts by many disciplines. New challenges have also emerged since it became necessary to study borehole stability for horizontal and inclined boreholes, boreholes drilled in poorly consolidated formations, boreholes in naturally fractured media and in very deep formations. The borehole stability problem can be considered by separating the potential rock failure mechanisms into the following four categories (Roegiers, 1990)1:Failures related to pre-existing or drilling-induced formation damage;Failures caused by induced stress concentrations;Failures attributed to deliberate or unintentional additional stresses; and,Failures related to shock-wave loading.More than 90 percent of horizontal wells have open-hole completions2. In order to control borehole instability, prepacked gravelpacks, wire-wrapped screens, and slotted liners have been used, while pre-perforated liners are usually run to prevent hole collapse3. Because of high perforation and stimulation costs, horizontal wells are cased and cemented only when wellbore and formation problems are not remediable under open-hole completion scenarios.Traditionally, borehole stability analyses were based either on elasticity or on the poroelasticity theory, in which the host rocks around the borehole are assumed to be homogeneous. However, such solutions may result in erroneous conclusions for naturally fractured porous media because the fractures introduce important heterogeneities.In this paper, a dual-porosity fluid flow and deformation system, including fractures and intervening porous blocks, is considered. For modeling three-dimensional engineering structures featuring elongated shapes, such as boreholes, etc., the pseudo-three-dimensional generalized plane strain method is more effective and accurate to characterize the rock deformations and fluid flow than the classical plane strain approach. A generalized plane strain finite element solution was, therefore, developed for analyzing borehole stability problems.For a specific case, the calculated results demonstrate that the borehole failure becomes time-dependent. The stability not only depends on the magnitudes of original stresses, but also on the orientation of the borehole. The results also show that the mud weight of the drilling fluid is an important factor to control any instability.Generalized Plane Strain ConceptMost problems, such as, wellbores, tunnels and dikes are characterized by a cross-sectional geometry that is usually invariant along their longitudinal direction. These problems are defined as pseudo-two-dimensional, or belonging to the generalized plane strain category. In such problems, material anisotropy and three-dimensional stress and strain state can be considered, but they have a functional dependence on only two spatial variables4. Therefore, only a two-dimensional domain discretization is needed for numerical solutions. Keywords: petroleum society, borehole stability, mpa, borehole orientation, borehole, instability, complex reservoir, fractured reservoir, fracture, horizontal borehole stability Subjects: Reservoir Characterization, Unconventional and Complex Reservoirs, Reservoir geomechanics, Naturally-fractured reservoirs This content is only available via PDF. 2000. SPE/PS-CIM International Conference on Horizontal Well Technology You can access this article if you purchase or spend a download.

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