(6fe) Evaluation of Wax Precipitation Behavior of Wax Deposit: The Effect of Oil Flow Condition

Authors: 
Gao, X., China University of Petroleum-Beijing
Huang, Q., China University of Petroleum-Beijing
Li, W., China University of Petroleum-Beijing
Dong, X., China University of Petroleum-Beijing
Ren, Y., Shanghai Jiao Tong University
Research Interests: Petroleum Storage and Transportation Engineering

Teaching Interests: Petroleum Storage and Transportation Engineering

EVALUATION OF WAX PRECIPITATION BEHAVIOR OF WAX DEPOSIT: THE EFFECT OF OIL FLOW CONDITION

Xuedong Gao1, Qiyu Huang1,*, Yijie Ren2, Weidong Li1, Xue Dong1

1 Beijing Key Laboratory of Urban Oil and Gas Distribution Technology, China University of Petroleum-Beijing, Beijing, China

2 Shanghai Jiao Tong University, Shanghai, China

ABSTRACT

Wax deposition is a major flow assurance challenge in waxy crude oil production and transportation. Wax precipitation behavior, playing some important role in wax strength, is considered to be a decisive factor that affects wax deposit property and further determines pipeline pigging. It is intrinsically correlated to the oil flow condition. This paper aims to provide some qualitative and quantitative insights into the relationship between oil flow condition and wax precipitation behavior of wax deposit. A laboratory-scale flow loop apparatus was employed. Four sets of crude oils collected from field were used. Variations of wax content and wax appearance temperature (WAT) of wax deposit against shear stress, radial temperature gradient and radial wax molecule concentration gradient near the pipe wall were well studied.

Differential scanning calorimetry (DSC) tests on wax deposits indicate that higher shear stress and radial temperature gradient ratchet up the wax content and WAT and down the wax molecule concentration gradient. Based on this, empirical formulas for predicting the wax content and WAT were developed. Verification experiments show that for wax content, the maximum and average relative deviations are 21.5% and 13.2%, respectively. As for WAT, the maximum and average absolute deviations are 5.4°C and 3.6 °C, respectively.

By investigating the variations of wax content and WAT of wax deposit against shear stress, radial temperature gradient and radial wax molecule concentration gradient, this paper promotes the understanding of how oil flow condition affects the wax precipitation behavior of wax deposit. Pipeline pigging can also enjoy some benefits from this work.

Keywords: wax deposition; wax precipitation behavior; oil flow condition

(A) (B)

Figure 1. Effect of wall shear stress on wax content and WAT of wax deposits: (A) wax content and (B) WAT.

(A) (B)

Figure 2. Effect of radial temperature gradient on wax content and WAT of wax deposits: (A) wax content and (B) WAT.

(A) (B)

Figure 3. Effect of radial wax molecule concentration gradient on wax content and WAT of wax deposits: (A) wax content and (B) WAT.

Table 1. Verification results for the empirical formulas

Number

Wax content (%)

WAT (°C)

Measured value

Calculated value

Relative deviation

Measured value

Calculated value

Absolute deviation

1

39.6

34.7

-12.4

55.2

51.8

-3.4

2

41.9

46.3

10.5

56.0

58.8

2.8

3

20.9

25.4

21.5

48.4

53.8

5.4

4

21.6

20.9

-3.2

45.7

49.5

3.8

5

38.9

42.5

9.3

53.3

58.6

5.3

6

66.2

58.0

-12.4

63.1

66.7

3.6

7

26.6

30.1

13.2

53.4

55.5

2.1

8

41.2

35.5

-13.8

65.

61.3

-3.7

9

40.9

48.4

18.3

64.9

68.3

3.4

10

46.8

38.6

-17.5

58.7

56.4

-2.3

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