SELECTION OF GRAVEL FOR OIL WELLS

Selecting the type and size of gravel
The success of a gravel packing depends on the correct selection of gravel size, type and proper placement of the gravel surrounding the slotted pipe or screen. If the size of the gravel used is not properly selected, the arena of training will be controlled and migrated to the packing of gravel, thus reducing the effective permeability and restrict production. The gravel pack should be placed completely around the grid as possible cavities present in the package allow the migration and production of formation sand.

The size selection of Gravel Pack:
Various techniques have been published for selecting the size of sand, gravel packing to control formation sand production. The most widely used today was developed by Saucier:

Saucier’s work from the basic premise that the optimal control of the sand is achieved when the average size of sand in the package is not more than six (6) times the average size of the formation sand grains (D50 ), he relied on a series of experiments with flow through cores, where half of the core was composed of gravel packing and the other half training was sand. Then modify the relationship of the average size of grains of sand, gravel packing / average size of sand grains training in a range between two (2) and ten (10), to determine exactly what the control Optimal sand.

Selection of Gravel Pack Type:
The selection of the type of gravel for the package, is determined by two main features, the well depth and method of production (with or without steam injection)

  • * Packaging shallow wells steam injectors: For wells packed steam injector deposits, we recommend the use of synthetic gravel. Due to the negative effect that has the steam injection process in some minerals such as quartz and silica is commonly present in both the field and in the natural gravel used for packaging. Laboratory and field studies have shown that natural gravel and sand training can be dissolved rapidly in the vapor stream, quartz and other siliceous minerals have low solubility at room temperature but at elevated temperatures normally reached during steam injection these minerals are broken down faster especially siliceous are they who are mainly the rock matrix. The effects of steam dissolution occurs not only at the site but also in the packaging, which is composed entirely of quartz grains which remain unchanged at pH below 9.5. Synthetic gravels have a higher resistance to high temperatures generated during steam injection (600 ° F). Das8 Underdown and evaluated the behavior of different types of materials when subjected to high temperatures and changes in pH, noting that the synthetic gravels have a weight loss of 3.5% at a pH of 11 to 600 ° F, much lower compared to Ottawa natural gravel obtained from 46.1% weight loss at a pH of 11 and a temperature of 540 ° F.
  • * Packaging shallow wells without steam injection: For wells in fields not packed steam injectors, we recommend the use of imported natural gravel.
  • * Packaging into deep wells, deep well packaged, recommended the use of synthetic gravel. Because they have a lower production of fines during the packing process the natural gravel.

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