Approach to Casing Design for Service in Compacting Reservoirs (1995)

Approach to Casing Design for Service in Compacting Reservoirs E.P. Cernocky; E.P. Cernocky Shell Exploration and Production Company Search for other works by this author on: This Site Google Scholar F.C. Scholibo F.C. Scholibo Shell Exploration and Production Company Search for other works by this author on: This Site Google Scholar Paper presented at the SPE Annual Technical Conference and Exhibition, Dallas, Texas, October 1995. Paper Number: SPE-30522-MS https://doi.org/10.2118/30522-MS Published: October 22 1995 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Cernocky, E.P., and F.C. Scholibo. "Approach to Casing Design for Service in Compacting Reservoirs." Paper presented at the SPE Annual Technical Conference and Exhibition, Dallas, Texas, October 1995. doi: https://doi.org/10.2118/30522-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 Annual Technical Conference and Exhibition Search Advanced Search AbstractDepletion of unconsolidated sand reservoirs can cause compaction of the reservoir sand. This strain transfers load to the casing. and this can kink and crush the casing, preventing workovers and requiring redrilling wells (Figure 1). Early redrilling can have significant negative impact on project earning power, so it is necessary to design casing to withstand compaction loading. This paper explains Shell Oil's new compaction design philosophy for casing to be run in some highly compactive Gulf of Mexico reservoirs. The paper explains the technical tools used to quantify compaction loading; the relative importance of different casing damage mechanisms; and Shell's approach to designing casing to mitigate the influence of compaction.Shell's approach to compaction emphasizes minimizing column buckling under axial compaction loads and collapse under transverse compaction loads. The approach to buckling is based on a model that quantifies the ability to work through buckled casing. The approach to collapse is based on a model linking depletion to the load transferred between the sand, cement, and casing. The compaction solution is specialized to Gulf of Mexico sand and reservoir characteristics.Casing design is only one aspect of the multidisciplinary solution to the compaction problem. Compaction-tolerant sand control must be included in the completion design, and advanced core testing must be used to link the casing design to the stress-strain behavior of unconsolidated sands. Where historical damage exists, downhole casing logging has been used to guide and validate the solution. These other facets of compaction technology go beyond the scope of this paper but have been addressed by Shell Oil's integrated approach to the compaction problem.Introduction to the Compaction ProblemDepletion of the reservoir pressure increases the effective stress acting on the reservoir sand. For an unconsolidated sand, the increase in stress causes large compaction strain (several percent). This strain in the sand can cause corresponding severe deformation in the casing (Figure 1). The deformation does not breach the casing, but it prevents workovers and recompletions through the casing and requires costly redrilling of the well. For deep offshore wells, early casing damage at relatively low compaction strain can significantly decrease project earning power, so there is incentive to take early design steps to mitigate compaction-driven casing damage.The solution to this problem is to design casing, cement support, and sand control that are compaction resistant to a reasonable and practical degree. Doing this requires quantitative understanding of the damage mechanisms and the way that a specific amount of depletion strains the sand and deforms the casing. The solution also requires quantitative understanding of the parameters that affect the ability of the casing to resist compaction loading. Blind overdesign of the casing is not a viable solution. Overdesign is ineffective if a critical damage mechanism is overlooked. Overdesign also can have unacceptable economic cost (how much collapse strength is enough?) and unacceptable increased risk to the completion design, the well inflow, or the clearances between tight strings run inside one another. In order to develop a guideline for design of casing in compacting reservoirs, Shell used a combination of finite element analysis and analytical modeling to quantify and rank damage mechanisms as functions of depletion, sand compaction tendency. cement placement, well angle, and casing D/T ratio and grade.Compaction is not new, and much work has been done on this topic. Much work has dealt with shallow reservoirs where compaction leads to surface subsidence. This is an ancient problem (e.g., aquifer depletion). and References 2–11 are only a few examples of work in this area.P. 731 Keywords: reservoir characterization, casing design, pressure depletion, reservoir, pay zone, society of petroleum engineers, upstream oil & gas, depletion, subsidence, damage mechanism Subjects: Drillstring Design, Casing and Cementing, Reservoir Characterization, Reservoir Fluid Dynamics, Torque and drag analysis, Casing design, Integration of geomechanics in models This content is only available via PDF. 1995. Society of Petroleum Engineers You can access this article if you purchase or spend a download.