Field-Scale and Wellbore Modeling of Compaction-Induced Casing Failures
- L.B. Hilbert Jr. (Exponent Failure Analysis Assocs. Inc.) | R.L. Gwinn (Aera Energy LLC) | T.A. Moroney (Aera Energy LLC) | G.L. Deitrick (Shell E&P Technology Co.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- June 1999
- Document Type
- Journal Paper
- 92 - 101
- 1999. Society of Petroleum Engineers
- 3 Production and Well Operations, 4.6 Natural Gas, 1.2.2 Geomechanics, 5.5 Reservoir Simulation, 5.1.2 Faults and Fracture Characterisation, 3.3 Well & Reservoir Surveillance and Monitoring, 5.6.1 Open hole/cased hole log analysis, 5.5.8 History Matching, 4.3.4 Scale, 1.10 Drilling Equipment, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 4.1.2 Separation and Treating, 1.9.4 Survey Tools, 1.6 Drilling Operations, 1.2 Wellbore Design, 2.4.3 Sand/Solids Control, 5.3.4 Integration of geomechanics in models, 4.1.5 Processing Equipment, 6.5.2 Water use, produced water discharge and disposal, 1.14 Casing and Cementing
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Presented in this paper are the results and verification of field- and wellbore-scale large deformation, elasto-plastic, geomechanical finite element models of reservoir compaction and associated casing damage. The models were developed as part of a multidisciplinary team project to reduce the number of costly well failures in the diatomite reservoir of the South Belridge Field near Bakersfield, California. Reservoir compaction of high porosity diatomite rock induces localized shearing deformations on horizontal weak-rock layers and geologic unconformities. The localized shearing deformations result in casing damage or failure. Two-dimensional, field-scale finite element models were used to develop relationships between field operations, surface subsidence, and shear-induced casing damage. Pore pressures were computed for eighteen years of simulated production and water injection, using a three-dimensional reservoir simulator. The pore pressures were input to the two-dimensional geomechanical field-scale model. Frictional contact surfaces were used to model localized shear deformations. To capture the complex casing-cement-rock interaction that governs casing damage and failure, three-dimensional models of a wellbore were constructed, including a frictional sliding surface to model localized shear deformation. Calculations were compared to field data for verification of the models.
Compaction of oil and gas reservoir rock is the source mechanism for costly problems in petroleum fields all over the world. Major problems have been documented for fields in Norway, Russia, Italy, Venezuela, Japan, and in the United States in California, Texas, and the Gulf of Mexico.1 For example, reservoir compaction in the Ekofisk field in the North Sea has reportedly caused subsidence greater than 16 ft, resulting in $400 million to jack up offshore platforms and repair related damage.2-4 Reservoir compaction in the Wilmington Field near Long Beach, California, caused earthquakes, resulted in surface subsidence of as much as 33 ft, and resulted in hundreds of well failures and damage to surface facilities and structures.5 By 1962, the problems in the Wilmington Field and surrounding areas required expenditures exceeding $100 million for repairs and damage mitigation.
Reservoir compaction is often viewed as a large-scale problem in rock mechanics, with the scale of deformation measured on the order of hundreds to thousands of feet. Understanding the reservoir compaction mechanisms that cause surface subsidence can be done with analytical models or large-scale, two- and three-dimensional computer simulations.1,6-11 Reservoir compaction, however, causes significant operational problems on a much smaller scale, the wellbore scale. It has been well documented that reservoir compaction can cause casing failures by tension, buckling, collapse, and shearing. In particular, compaction-induced shearing causes severe localized deformation of casing over small lengths, often less than 10 ft.5-13 The interaction of soft rock with casing governs the geometry of the deformed casing. If effective and lasting damage mitigation and failure prevention measures are to be designed and implemented, then understanding the mechanisms of shear-induced casing damage is required.
Field-scale computer models have proved beneficial to understanding the relation between compaction and localized shear deformations.6-11 Compaction induces bending and shear deformations around the edges of the area of surface subsidence, or the "subsidence bowl." Under such shear deformations, thin weak-rock layers and geologic unconformities fail. Shear-induced, relative motions on these layers, called "slip," cause localized shear deformation. It is not feasible to include the details of wellbores in field-scale models. The field-scale models are large, requiring substantial costs and computer resources. Instead, it is necessary to relate shear-induced slip, computed from large-scale models, to either observations of casing shear damage or the results of wellbore-scale modeling.
This paper presents the results of a multiscale study to determine the causes and mitigation of casing damage and failures in Section 33 of the South Belridge Field near Bakersfield, California, USA. First, the documented history of subsidence and compaction-induced wellbore damage and failures in the Belridge Field is reviewed. A brief introduction to computational geomechanics is included next. The results are presented of a field-scale, two-dimensional, plane-strain, elasto-plastic finite element model of a cross section of Section 33. Results are then presented from an elasto-plastic, three-dimensional finite element model of a single wellbore. It is shown how deformations on these different scales were related using field data and model results. Damage and failure mitigation measures were investigated using this wellbore-scale model, and the results are discussed. Finally, conclusions are summarized.
The Belridge Field and Historical Problems
The Belridge Field is located about 45 miles west of Bakersfield, California (Fig. 1). It has been produced since 1911 and is now recognized as one of the largest oil producing reservoirs in the United States14 and has well-documented problems associated with reservoir compaction.6-10,12
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