Using a Physical Wellbore Model To Study Formation Damage Problems in Well Completions
- D.B. Burnett (Westport Technology - ITT Research Inst.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- March 1995
- Document Type
- Journal Paper
- 61 - 65
- 1995. Society of Petroleum Engineers
- 2.7.1 Completion Fluids, 1.6.9 Coring, Fishing, 1.10 Drilling Equipment, 2.2.3 Fluid Loss Control, 4.3.4 Scale, 2 Well Completion, 1.8 Formation Damage, 4.1.2 Separation and Treating, 4.1.5 Processing Equipment, 2.4.3 Sand/Solids Control, 2.4.5 Gravel pack design & evaluation, 2.2.2 Perforating, 1.6 Drilling Operations, 5.4.2 Gas Injection Methods, 5.5.2 Core Analysis
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This paper describes the design and operation of a high pressure, high temperature wellbore model using either consolidated or unconsolidated core material. It can be configured with up to eight perforated cores representing varied zonal permeability. The model is set up for flow in either the injection or the production direction. It is acid rated and fluids can be pumped at rates to 130 BPD. Gravelpacking is accomplished in the model with either water or polymer carrier fluids.
The model is used to perform laboratory evaluations of completion practices and stimulation techniques. We have evaluated the formation damaging potential of commonly used loss circulation materials and the inability to clean up some of these materials in unconsolidated formations. We have used the model to demonstrate the benefits of gravel pre-packing to avoid loss in perforation flow capacity. We have also evaluated diverting agents designed to improve coverage and stimulation of damaged zones.
The development of a scaled wellbore model began in 1988 in the SOHIO laboratories in Irving, Texas. Field operations in one of the shallow sand reservoirs on the North Slope of Alaska had resulted in severe well damage problems associated with the completion fluid. Others also recognized completions problems with damaged perforations.1 Our initial laboratory studies showed the need for tests in experimental apparatus that provided a realistic wellbore geometry. When tests were run in perforated cores at simulated flow rates, we observed the formation damaging characteristics of traditional loss circulation pills and the failure of cleanup fluids to perform their function adequately.
With the backing of BP Exploration (who assumed responsibility for SOHIO operations in 1989) our group designed and constructed an operating model of a wellbore section. The model has been in operation since 1990 utilized in a joint industry R&D project (CEA-21). In May, 1993 IIT Research Institute (IITRI) acquired Westport and its staff and currently supervises a second jointly funded research program (CEA-66), evaluating new completion practices.
Gravelpacking operations in the laboratory have been studied for some time.2-4 Researchers have even used wellbore models to evaluate techniques and materials.5 Most focused however, on gravel packing and not the effect of loss circulation materials in perforated core material. It was felt that a new model with a true wellbore geometry would offer a more realistic way to test certain completion practices.
Design of a Wellbore Model Apparatus
When the design team planned for the construction of the model, we realized that the apparatus would have to operate at elevated temperature and pressure. Because we were interested in evaluating acid cleanup practices, all wetted materials would have to be acid rated. Next, the model would utilize core material of different permeability so that a zoned reservoir could be modelled.
The use of perforated cores was a departure from other studies. Halleck6 had defined flow in perforations. The team therefore had a model for radial flow from the perforations in the core holder design. The design also specified core holders that would accommodate high confining pressures. For safety and for data precision, the model operations were to be automated. All systems would have to fit within a fume hood and be explosion proof rated.
Our goal was to construct a model that was adaptable enough to use for a wide range of experiments. Some of the specific tests initially planned for the model were:
Study of formation damage caused by loss circulation materials (LCMs) in perforations
Study of cleanup efficiency of acids and solvents in removing LCMs from perforations
Effect of different permeability on cleanup efficiency
Comparison of performance of commonly used LCMs.
Effectiveness of diverting agents.
The model was constructed and began operations after the laboratory had been relocated to Houston Texas. The facility is now Westport Technology Center International, -IIT Research Inst.
Description of the Model
Fig. 1 is a photograph of the model. Fig. 2 is a schematic of the extended model set up in a gravel pack mode. The wellbore itself is constructed of 316L SS. It is 7.0 in. in diameter, 24 in. long (standard) and 60 in. long (extended). The standard configuration has 4 perforation openings phased at 90°. Each is 0.75 in. in diameter. The wellbore can be equipped with a gravel pack screen. Fluids can be pumped into and out of the inner screen volume or outside of the screen, from either the top or the bottom of the model. The extended model can be configured to allow diverting agents tests and other investigations.
Two 30 gal. Teflon coated tanks contain brine and a refined oil. Each is equipped with an immersion heater with a temperature controller. Two smaller tanks (Hastalloy) contain LCM slurries and acids. Flexible high pressure lines run to and from the model and cores. Each core has a flowmeter upstream of the common manifold connecting effluents (from injection mode).
Fluids are pumped with either a variable rate duplex pump (capable of rates to 5 gpm at 2000 psi) or a Moyno pump (not shown) capable of rates to 8 gpm at 500 psi. LCM slurries and gravel pack sand are pumped with the Moyno pump.
Fig. 3 is a schematic of a consolidated core. The core has a drilled perforation 0.75 in. in diameter and 5 in. in length. All fluids enter or exit from the perforation. Fluids can flow radially from the perforation to the outer edge of the core. A metal sheath encircles the outside of the core, with rods providing a standoff area allowing fluid flow. A collector plate fits at the rear of the core.
Four types of consolidated core material have been used. Berea, a ubiquitous selection, serves for low permeability material. A ceramic core serves for high permeability material. Either core from the Hickory Creek sand (Brady, TX) or from the Gypsy sand (Cherokee County, OK) serve as moderate permeability material.
Operating the Model
The model and its associated equipment fit inside a fume hood. All valves are operated remotely from the computer controller. Data acquisition and control are provided by Labview© (National Instruments, Austin TX).
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