The Effect of Formation Flow on the Integrity of Perforated Casing
- Phillip D. Pattillo (Amoco Production Co.) | Michael B. Smith (Amoco Production Co.)
- Document ID
- Society of Petroleum Engineers
- Society of Petroleum Engineers Journal
- Publication Date
- October 1985
- Document Type
- Journal Paper
- 637 - 646
- 1985. Society of Petroleum Engineers
- 1.2.1 Wellbore integrity, 4.3.4 Scale, 5.8.5 Oil Sand, Oil Shale, Bitumen, 4.1.2 Separation and Treating, 5.8.7 Carbonate Reservoir, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 1.6.9 Coring, Fishing, 2.2.2 Perforating, 1.2.2 Geomechanics, 1.6 Drilling Operations, 2.4.3 Sand/Solids Control, 5.3.4 Integration of geomechanics in models, 1.14 Casing and Cementing, 1.14.1 Casing Design
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This paper summarizes an analysis of formation/casing deformations in a chalk reservoir. The study is linked to the development of a poroelastic-plastic model of ductile rocks. Applications of the model include an analysis of chalk production into perforated casing and a discussion of the effects of such production on collapse integrity of the casing.
The deleterious effects of near-wellbore formation movement on the cross-sectional integrity of casing is well documented in the literature. The most common occurrences of this phenomenon are associated with the creep of salt sections. However, similar problems have been discovered in the attempts to recover Athabasca oil sands. In dealing with the flow of formations (such as salt), one is confronted typically with the exposure of the casing cross section to a nonuniform stress field induced either by massive flow of the formation in a preferential direction or by local collapse of the wellbore. while usually in the absence of adequate protection from a competent cement sheath. It has been demonstrated both analytically and experimentally that such nonuniform, cross-sectional loads can reduce drastically the collapse resistance of coincident casing strings. The purpose of this paper is to discuss an additional source of nonuniform. cross-sectional loading. Whereas the loads associated with salt flow represent an ever-present danger whose origin can be traced to the introduction of the wellbore into a nonproductive subsurface layer of viscous potential, the nonuniform loads discussed here are limited to productive formations. Furthermore, the origin of nonuniform loading discussed here can be traced directly to production operations - namely, the presence of perforations and the reduction in near-wellbore pore pressure accompanying exploitation of a hydrocarbon reservoir. Finally, although this discussion focuses on experiences encountered with respect to a particular field and formation rock type, the indication is that similar problems can be expected from a variety of reservoirs. During, the early stages of field-development drilling, three wells suffered collapse opposite the producing formation during initial testing. The producing formation is an overpressured, fractured, highly porous ( phi 45%) chalk that has exhibited a tendency to flow with production. production. This paper presents the results of a study aimed at providing an accurate model of the continuum behavior of providing an accurate model of the continuum behavior of the formation. Applications of the model include an analysis of chalk production into perforated casing and a discussion of the effects of such production on collapse integrity of the production casing. Conclusions from this study have been segregated to reflect the various stages of the analysis.
Outline of Study
Of paramount importance to this study was the investigation of the integrity of the 7-in. [17.8-cm] production liners during reservoir depletion. This objective was created as a direct result of the casing failures experienced in the exploratory wells. To organize the presentation of the analysis, the study is reviewed in four stages. presentation of the analysis, the study is reviewed in four stages. 1. Formulate Model. The purpose of this portion of the study was to review all available experimental tests on the producing formation or acceptable substitutes and to determine a satisfactory model to describe initial yield and subsequent inelastic behavior of the formation. 2. Duplicate Experimental Observation. With an acceptable model for chalk response to simple loading patterns chosen, it was then appropriate to attempt to patterns chosen, it was then appropriate to attempt to duplicate the results of experiments that have been performed on the Dania chalk, a formation similar in performed on the Dania chalk, a formation similar in constitution to the objective reservoir. In particular, the tests reported by King and Holman* were judged an acceptable starting place for determining the applicability of the model to loading patterns more nearly approaching actual near-wellbore behavior. 3. Determine Near-Wellbore Stress Fields. Assuming that the experimental work of King and Holman could be adequately modeled, the next step involved an investigation of the stress field existing in the chalk in the vicinity of perforated casing to determine the nonuniform tractions to which the casing would be exposed. 4. Investigate Casing Integrity. The last portion of the investigation was devoted to an analysis of the integrity of the 7-in. [17.8-cm] production liners subjected to surface tractions determined in Step 3.
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