| الملخص | Abstract
This research was carried out on a laboratory scale to evaluate the characteristics of Arduma and Kilo 180 sand deposit as proppant (frac sand). Each sand deposit was studied for its: particle size distribution, roundness and sphericity, mineralogy, turbidity and crush resistance. The sand characteristics should meet the specifications set by American Petroleum Institute API (RP- 56)1995 for proppant.
In general Arduma sand is well agreed with the proppant specification and can present a good reserve for its production. The results obtained (except the crush resistance of kilo 180 sand), are in accordance with the API standard requirements.
Key: frac, sand
Introduction
Silica sand or Industrial sand is a high purity quartz (SiO2) sand deposited by natural processes. Depending on its chemical and physical characteristics, silica sand is used in many fields as glass sand, foundry sand, fillers, abrasives and hydraulic fracturing sand (also named as frac sand or proppant by the petroleum industry). Frac sand is the sand that is pumped into the well during fracture operation .Since the sand is carried along with the fluid into the fracture, it will remain in the fracture when the pressure is removed, keeping the fracture propped open and allowing a good means by which the hydrocarbons can flow to the well bore. The frac fluids are designed to flow well and carry the sand during pumping, but then change to more of a gel when pumping stops, holding the sand in place until the fracture closes, trapping the sand between the rock layers. After that, the frac fluid decomposes and will flow again so that it does not obstruct the flow of hydrocarbons, but the sand has been trapped by the rock and kept the fracture propped open (Robinson et al., 2010). In Iraq silica sand deposit, practically that of Arduma region (western desert) was allocated mainly to the glass and ceramic industry and no record had been established for used as proppant.
Experimental work
Raw silica sand samples from Arduma and Kilo 180 sand deposits were subjected to quartering and dividing using rotary sample divider to get a representative sample. The chemical analyses of both sands are presented in table (1). The recommended methods for frac sand as given in API (RP-56) specifications are:
Sieve analysis
According to the American petroleum institute’s specification API (RP-56) six recently calibrated U.S.A. sieves sizes (6\12, 8\16, 12\20, 16\30, 20\40, 30\50, 40\70, 70\140), mesh are selected to obtain the required sand size. Sixteen tests have been done using six recently calibrated U.S.A. sieve sizes, the sample weight of each Arduma and Kilo 180 sands used in the test were shacked by a sieves shaker type (RETSCH). The weight of sand retuned is determent on each sieve. The percentages of passing and total of percentages retained are calculated both Arduma and Kilo 180 were in the size range of 70/140 mesh.
Sphericity and roundness
This simply estimates how closely the quartz grain conforms to a spherical shape and its relative roundness. Roundness of each grain was determined; recorded and an average roundness was obtained for the sample .The results were then compared with the Krumbein Roundness and Sphericity chart to determine the degree of Roundness and Sphericity. The Roundness and Sphericity of Frac sand should be 0.6 or greater, (Krumbein, w.c.).
Evaluation of sand solubility in acid
This test is to determine the amount of non-quartz minerals that is soluble in acid present in sand (e.g. carbonates, iron oxide, clay …. etc). The acid solubility content should be less than 3%, API (RP-56).
Turbidity
Turbidity refers to the amount of silt/ clay sized particles in the sand sample. The results of Arduma and Kilo 180 meet the requirement that is set by the industry for turbidity. According to the API (RP-56) standards, the sand should have a maximum turbidity value of (250FTU) or less.
Crush resistance
Crush resistance is the resistance of a quartz grain under compressive loading. This is a function of grain brittleness, which correlates with grain shape, and the internal structure of the grain itself, as well as overgrowth on the grain. The suggested maximum fines for frac sand 70/140 mesh crush resistance should be 6%, API (RP-56).
3. RESULTS AND DISCUSSION:
Frac sand must be >99% (SiO2 ), therefore two sand deposits (Arduma and Kilo 180 sands) have been selected for this work due to their high silica content as shown in table (1) other required properties were tested and the results are presented and discussed here below.
1. Sieve Analysis Tests
Table (2) and (3) show that the sand of desired particle size of (-212+106) µ or (70/140) mesh for both Arduma and Kilo 180 sands are corresponding to the API specification. A minimum of 90 % of the tested sand sample should fall between the designation sieve sizes 70\ 140 mesh.
2. Roundness and Sphericity Test
Numerous methods have been published to measure and report sand grain shapes and geometric identities. Some involve tedious measurements; others required visual comparisons. All required some skill and judgment on the part of the technician. Table (4) and (5) show the results of average roundness of 20 grains compared with the Krumbein chart. The two sand samples (Arduma and Kilo 180) show ideal values of roundness and sphericity, the result was (0.9) for both.
3. Evaluation of Sand Solubility in Acid Test
According to the API (RP-56) standard, the acid – soluble material in frac sand with the particle size rang (70\140) mesh should not exceed the value of 3 %.This results indicate that both sands (Arduma and kilo 180) are of a high purity and clear from other minerals and impurities. Table (6) shows the results of both (Arduma and kilo 180) sands.
4. Turbidity Test
The turbidity results are given in table (7), they indicated that the two sands tested meet the requirement API standards as the turbidity is less than 250 FTU. These results indicate that both sands (Arduma and kilo 180) are clear of clay.
5. Crush Resistance Test
According to the API standard (RP-56) (6%), by weight of fine generation after pressure was exerted on this sand is allowed only. Arduma sand shows (7%) of fine by weight and it display a high crush resistance comparing to kilo 180 sand which resulted in (10%) by weight of fine. Particle shape could influences the crush resistance of the sand, angular grains for example tends to crush easier in comparison to round ones. Furthermore, tectonic movements, depositional history, cementation and pitted grains could weaken the quartz grains. As a result, product from those deposits fails the crush resistance test (Mark.Z. 2007). Using microscope type (Leica DM 2500 p) showed that most Kilo 180 grains are pitted, for this reason the crush resistance test had been failed.
References
American Petroleum Institute, 1995. Recommended practices for testing sand use in hydraulic fracturing operation.API recommended practice 56, 2nd edit.
Krumbein, W.C., and Sloss, L.L., 1963. Startigraphy and sedimentation, 2nd edit. W.H.Freemen and company, San Frencisco, p,1and2.
Mark.Z. 2007.The API specification set down for silica sand used in hydraulic fracturing, drilling minerals.
Robinson, K., Brid, P., 2010. Heemskirk Consolidated Limited / Australia.
Table.1: Chemical analysis of Arduma and kilo 180 sands
Sample Chemical composition %
SiO2 Fe2O3 Al2O3 CaO MgO SO3 L.O.I. Na2O K2O P2O5 Total
Arduma sand 98.45 0.09 0.62 0.17 0.03 0.06 0.44 0.02 0.03 0.01 100
Kilo 180 sand 98.36 0.11 0.29 0.37 0.03 0.40 0.32 0.02 0.03 0.01 100
Table 2: Shows the results of sieve analyses of Arduma sand sample
cumulative passing % cumulative retained % ًWt % Sieve size ( micron ) Sieve size (Mesh)
51.63 48.4 48.4 300 50
14.93 85.1
36.7 212 70
9.42 90.61 5.51 150 100
0.8 99.23 8.62 125 120
0.4 99.63 0.40 106 140
0.1 99.83 0.3 75 200
0 100 0.1 pan
100 total
Table 3: Shows the results of sieve analyses of Kilo 180 sand sample
umulative passing % cumulative retained % ًWt % Sieve size ( micron ) Sieve size (Mesh)
42.59 57.41 57.41 300 50
12.63 87.37
29.96 212 70
1.81 98.19 10.82 150 100
0.41 99.59 1.4 125 120
0.11 99.89 0.3 106 140
0.01 99.99 0.1 75 200
0 100 0.01 pan
100 total
Table 4: Roundness and Sphericity of Arduma sand Table 5: Roundness and Sphericity of Kilo180sand
Grains Sphericity Roundness
1 0.88 0.9
2 0.9 0.93
3 0.89 0.9
4 0.88 0.9
5 0.88 0.85
6 0.83 0.80
7 0.88 0.85
8 0.83 0.80
9 0.78 0.76
10 0.86 0.84
11 0.85 0.82
12 0.92 0.90
13 0.83 0.80
14 1.0 1.1
15 0.84 0.80
16 0.85 0.83
17 0.60 0.64
18 0.93 0.91
19 0.93 0.90
20 0.91 0.90
Average 0.9 0.9
s Sphericity Roundness
1 0.85 0.83
2 0.92 0.90
3 0.84 0.81
4 0.90 0.91
5 0.84 0.82
6 0.95 0.92
7 0.87 0.85
8 0.86 0.82
9 0.92 0.90
10 0.95 0.92
11 0.90 0.91
12 0.86 0.84
13 0.93 0.90
14 0.87 0.84
15 0.90 0.92
16 0.83 0.80
17 0.76 0.72
18 0.95 0.92
19 0.90 0.91
20 0.85 0.82
Average 0.9 0.9
Table 6: shows the solubility in acid of Arduma and Kilo180 sands
Sample Material solubility
(weight percent)
Arduma 2.73
Kilo180 2.2
Sample Turbidity(FTU)
Arduma 16.65
Kilo 180 0.23
Table 7: The turbidity of Arduma and Kilo 180 sands | en_US |
