An Evaluation of Concentric Casing for Nonuniform Load Applications
- P.D. Pattillo (Amoco E&P Technology Group) | Z.A. Moschovidis (Amoco E&P Technology Group) | Manohar Lal (Amoco E&P Technology Group)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- September 1995
- Document Type
- Journal Paper
- 186 - 192
- 1995. Society of Petroleum Engineers
- 1.6 Drilling Operations, 1.6.3 Drilling Optimisation, 1.14.3 Cement Formulation (Chemistry, Properties), 4.3.1 Hydrates, 1.14.1 Casing Design, 4.1.2 Separation and Treating, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 4.1.5 Processing Equipment, 5.8.5 Oil Sand, Oil Shale, Bitumen, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 1.14 Casing and Cementing, 1.8 Formation Damage
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This study offers both theoretical and experimental evidence of the benefits of running a concentric casing configuration in a nonuniform load environment. The study is further enhanced by numerical modeling, particularly with regard to determining the sensitivity of the configuration to key variables. The alternative of running a single string of heavy-wall casing also is discussed.
In the past, the industry has realized enhanced casing integrity opposite deforming formations by applying concentric casing - i.e., the positioning of dual casing strings connected by a cement sheath opposite the offending rock. For example, in both the massive South Gharib salt of the Gulf of Suez and the operations-induced flow of the oil sands in Athabasca, implementation of concentric casing has proved a viable means of providing completion integrity in the presence of weak rock.
In spite of these successes, concentric completions are not a panacea. Although the concentric configuration prevented cross-sectional collapse in Athabasca, the completion string continued to bend with the induced formation flow. It is important, therefore, to ascertain the type of deformation mechanism active in a given locale and then decide whether concentric casing can mitigate that mechanism.
This study is divided into the following sections:
1. Theoretical rationale. We do not assume a priori that concentric configurations are superior to single-casing cross sections. Rather, for completeness, we begin with the failure mechanics that suggest concentric configurations as the solution to a particular class of problems.
2. Experimental evidence. Laboratory investigations have reinforced the theoretical propositions. Furthermore, the experimental evidence suggests variable sensitivities that confirm the conclusions of numerical analysis.
3. Quantitative comparisons. We use a series of finite-element executions to demonstrate the advantage to be gained from concentric strings and the sensitivity of that advantage to such parameters as centralization and the competency of the cement sheath.
These steps are intended to provide sufficient background from which to offer recommendations regarding the installation of concentric completions in a particular operating environment.
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