The present invention generally relates to core holders used in testing core samples, and more particularly to a core holder utilizing a modular sleeve.
In geological exploration, the physical characteristics of an underground formation are of paramount importance. Permeability, a measure of resistance to fluid flow, is a particularly important factor that affects the method of oil recovery to be used for a particular well.
To determine permeability, a core sample is removed from the underground formation. The core sample is placed in a core holder, where it is subjected to heat and pressure conditions comparable to those underground. Fluid is then forced through the core sample at high pressure. The permeability of the core is indicated by the change in pressure at various points along the length of the core.
During testing, the core is encased in a rubber sleeve. Because pressure measurements must be taken at various points along the core's length, pressure taps must be provided. In at least one type of sleeve, the taps are molded directly into the rubber sleeve. Such a sleeve with integral pressure taps is relatively expensive.
The conditions involved in core testing cause the rubber sleeve to deteriorate rapidly. A core, and its encasing sleeve, may be subjected to pressures greater than 10,000 pounds per square inch, and temperatures near 400.degree. F., for example. When testing under these conditions, the rubber sleeve may have to be replaced after every test.
Conventional core holders accommodate sleeves of a certain length. If a core to be tested is too long for the sleeve, a core holder with a longer sleeve must be used. As a result, core holders of various sizes are frequently maintained in the same laboratory. Because each core holder demands its own supply of sleeves, a great variety of sleeves of different lengths must be manufactured and kept in stock.
Therefore, there is a need for a core holder using a sleeve that does not require pressure taps molded into the material so that each sleeve is relatively less expensive, and that can be used with different lengths of cores so that an inventory of different length sleeves is not required.