Page 243 - A Practical Companion to Reservoir Stimulation

PRACTICAL COMPANION TO RESERVOIR STIMULATION

0 4000 8000 12,000
Pressure (psi)

Figure P-87-Solubility of nitrogen in crude oil and water.

P-8.2: Proppants gives the API-recommended sieves for testing various
The quality of the proppant used has a direct impact on the proppant sizes.
conductivity of the fracture. One of the most difficult prob- The proppant should have a roundness and a sphericity
lems in checking the quality of a proppant is obtaining a good value of 0.6 or greater, an arbitrary measurement where
representative sample. The sample should be provided on proppant grains are examined at low magnification and com-
location, compiled from a flowing stream of proppant rather pared to the roundness and sphericity chart developed by
than a sample from the storage vessels. Therefore, the sand is Krumbein and Sloss, 1963 (Fig. 5-29, Reservoir Stimula-
sampled as it is loaded into storage. The top of the proppant tion).
siting storage will almost surely contain a much higher vol- To ensure the proppant is low in contaminants, a solubility
ume of fines than the rest of the proppant. The sampling test in 12-3 hydrochloric-hydrofluoric acid should be per-
procedure outlined in the API Recommended Practices for formed. Sand often contains contaminants such as feldspars
Testing Sand Used in Hydraulic Fracturing Operations should or clay, which will be soluble in this acid. Pure quartz sand is
be followed. not affected by this acid. In this test, as described by the API,
The proppant should be sieved to ensure that the correct 5 g of sand are placed in 100 ml of acid, heated to 150°F for
size proppant is used. Some artificial proppants may have a 30 min, and then filtered and dried. The amount of mass lost
much narrower range of proppant sizes because of the controls to the test is then measured. The maximum solubility for 6/12
used during manufacturing. The API lists a given set of sieve through 30/50 mesh sands is 2% and 3% for 40/70 through
sizes that are to be used for each proppant mesh size. Ninety 70/140 mesh. This test should be conducted before moving
percent of the sample should fall between the largest and the the proppant to location.
smallest sieve size of the proppant (between the 20 and 40 A simple turbidity test providing similar information can
mesh screens for a 20/40 proppant). In addition, less than be performed on location. Proppant is poured to the 20-ml
0.1 % of the total sample should remain on the largest sieve, mark on a standard 4-oz. prescription bottle, and then dis-
and less than 1% should fall through to the pan. Table P-18 tilled water is added to the 100-ml mark on the bottle. A black

P-82