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A Passive Safety Cap for an Aging Cell

IP.com Disclosure Number: IPCOM000222427D
Publication Date: 2012-Oct-04
Document File: 6 page(s) / 344K

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The IP.com Prior Art Database

Abstract

Drilling and other oilfield fluids are commonly aged at elevated temperatures to evaluate long-term fluid performance with thermal aging and degradation. Performance measures, such as fluid loss and rheology, of thermally aged and un-aged fluids provide data to determine optimal drilling and completion fluid formulations and treatments. These data help fluids engineers to design a fluid’s composition and suitability for specific well temperature conditions. Specialized aging cells, such as those available from Fann Instrument Company, provide a means to hold and age fluids. Aging begins by only partially filling the cell with a test fluid and installing the cell cap. Afterwards, the cell is pressurized with a gas such as nitrogen to several hundred psig before aging in an oven (or a roller oven) at temperatures sometimes exceeding 400 F. An inherent safety problem exists in the current aging cell design; there are no mechanisms or safeguards to prevent the user from over filling the cell with a fluid. If the cell is overfilled, the test fluid has insufficient room to expand as it heats up. Thus, the cell pressure can easily exceed the cell’s peak operating and burst pressure. The method presented herein provides a passive safety feature to remediate this problem and help ensure operator safety.

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Page 01 of 6

A Passive Safety Cap for an Aging Cell

Abstract

Drilling and other oilfield fluids are commonly aged at elevated temperatures to evaluate long-term fluid performance with thermal aging and degradation. Performance measures, such as fluid loss and rheology, of thermally aged and un-aged fluids provide data to determine optimal drilling and completion fluid formulations and treatments. These data help fluids engineers to design a fluid's composition and suitability for specific well temperature conditions.

Specialized aging cells, such as those available from Fann Instrument Company, provide a means to hold and age fluids. Aging begins by only partially filling the cell with a test fluid and installing the cell cap. Afterwards, the cell is pressurized with a gas such as nitrogen to several hundred psig before aging in an oven (or a roller oven) at temperatures sometimes exceeding 400 F.

An inherent safety problem exists in the current aging cell design; there are no mechanisms or safeguards to prevent the user from over filling the cell with a fluid. If the cell is overfilled, the test fluid has insufficient room to expand as it heats up. Thus, the cell pressure can easily exceed the cell's peak operating and burst pressure. The method presented herein provides a passive safety feature to remediate this problem and help ensure operator safety.

Aging Cell Design Criteria

Design engineers must consider the contents of a pressure vessel (cell) and the cyclic thermal conditions a test cell will experience during mechanical design process. Most fluids have a higher thermal expansion coefficient than most cell materials. This is the case for most drilling and completion fluids.

In most cases, the fluid components will be oils; such as diesel, esters, mineral oils and olefins; water and brines or emulsified combinations of these. Usually a compressible gas space above the test fluid is required for thermal aging. The compressible gas space helps to keep the cell pressure within the cell's design pressure range. Functionally, the gas volume must be large enough to offset the thermal expansion of the fluid.

Many companies have off-the- shelf aging cells that have this potential safety problem of an inadequate gas space. For example, Fann Instrument Company offers aging cells with designs that do not restrict their use if over-filled. An example of these cells is shown in Figure 1.


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Figure 1 ‐ Aging cell

These cells are similar to other manufacturers in design and construction. They typically provide operation to 2500 psig. In the following example, the cell pressure excursion with increasing temperature can easily exceed the cell pressure rating. Thus, these cell designs can expose operators to potential hazards.

The pressure increase of a closed cell completely filled with typical base oil is shown in the following example. Here, the cell has no gaseous cap and is sealed without any initial pressure. As the cell is hea...