American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.


Previous studies have indicated a substantial difference in fluid leak-off behavior of fracturing fluids under dynamic and static conditions. The present study is an attempt to determine the factors that contribute to this difference and to improve the ability to predict fluid leak-off behavior of well predict fluid leak-off behavior of well completion fluids. This paper describes two equipment designs developed and results obtained by using this equipment to test several types of fracturing fluids.

For a given fluid there appears to be an optimum fluid velocity along the core surface for minimum leak-off. Contrary to previous studies, fluid leakoff under dynamic conditions is usually less than or approximately equal to that obtained under static conditions. This may be attributed to the quick, effective sealing or plugging of pores on the core surface by the correct size of particles. Particles that may cause bridging (thus, Particles that may cause bridging (thus, inefficient sealing) are removed from the core surface by gravity action or fluid motion in the equipment described.

Leak-off behavior of fluids in the two equipment designs described depends upon whether the test fluid falls under the category of gel, suspension, or colloid.


The phenomenon of fluid leak-off through porous media occurs in the process of drilling, cementing and process of drilling, cementing and stimulating a well. The standard procedures recommended by API for evaluating fluid leak-off characteristics of fracturing fluids, drilling fluids and cement slurries are basically static in nature, although the actual phenomenon takes place under dynamic conditions. Here place under dynamic conditions. Here the term dynamic refers to fluid motion along the core surface and static refers to the lack of motion along the core surface. The validity of the static leak-off test is often questioned. But the reasons for continuing a static test are its simple operational features and procedures. Also, lack of a simple and procedures. Also, lack of a simple and better standardized dynamic fluid leakoff device that can be used on a routine basis is another reason for continued usage of the static test.

Several studies have been published related to static and dynamic behavior of fracturing fluids and drilling fluids. Significant differences in the results have been reported, depending upon the nature of fluid tested and the particular dynamic equipment used. particular dynamic equipment used. This paper describes two separate equipment layouts, each of which can be used to study static and dynamic fluid leak-off characteristics of different fluids.

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