U.S. CRUDE SLATE GETS HEAVIER, HIGHER IN SULFUR

Edward J. Swain
Bechtel Corp.
Houston

Historical records of API gravities and sulfur contents of crude oil runs to U.S. refineries show that the quality of the U.S. crude oil pool is worsening.

This trend has, of course, been influenced by the increasing capability of U.S. refiners to process heavier and higher-sulfur crudes, the availability of such crudes, and, at times, attractive differentials between them and lighter crudes.

Ten years ago, the U.S. Department of Energy (DOE) started to report monthly and yearly composite values of API gravity and sulfur content for crude oils processed in refinery districts and Petroleum Administration for Defense (PAD) districts (Fig. 1).

The 10-year history of annual composite values for API gravity and sulfur content is shown in Table 1, for the U.S. in total, and by PAD district (PADD).

A simple regression analysis was conducted on each set of data and plotted to see how well actual data matched straight-line calculated data (Figs. 2-7). If the calculated trend line tracks the actual data, then it is reasonable to extrapolate the trend for the next 3-5 years.

The quality of crude oil processed by refineries is determined by:

• Crude-oil types available-domestic and foreign sources.

• Refinery configuration-downstream processing capabilities to handle crude oil quality variations.

• Crude-oil quality price structure.

• Marketable product slate that gives reasonably good refinery operating margins.

DATA ANALYSES

The following sections present the analyses of the collected and calculated data for the individual PADDs and for the U.S. as a whole. All conclusions are based on the available DOE data.

PADD 1

Refineries operating in PADD 1 have increased their usage of foreign crudes from a low of about 80% in the early 1980s to greater than 95% in 1990. Crude oil quality has declined slightly over the last 10 years.

The 10 and 5-year trends, in terms of API gravity and sulfur, are as follows:

• 1981-1990: -0.16 API/year, +0.015 wt % S/year.

• 1986-1990: -0.13 API/year, +0.044 wt % S/year.

Crude runs to PADD 1 refineries in 1990 were 1,284,200 b/cd.

PADD 2

Refineries operating in PADD 2 have increased the percentage of foreign crudes used from the lower 20s in the early 1980s, to 37% in 1990.

Crude oil quality has declined slightly over the last 10 years.

The 10 and 5-year trends are as follows:

• 1981-1990: -0.09 API/year, +0.022 wt % S/year.

• 1986-1990: -0.17 API/year, +0.017 wt % S/year.

Crude runs to PADD 2 refineries in 1990 were 3,012,000 b/cd.

PADD 3

Refineries operating in PADD 3 have increased the percentage of foreign crudes used from the upper 20s in the early 1980s, to almost 56% in 1990.

Crude oil quality has declined rather quickly over the last 10 years.

The 10 and 5-year trends are as follows:

• 1981-1990: -0.25 API/year, +0.030 wt % S/year.

• 1986-1990: -0.18 API/year, +0.049 wt % S/year.

Figs. 2 and 3 show historical-vs.-calculated data for gravity and sulfur, respectively, over the 10-year period.

It appears that the decrease in gravity has slowed over the last 5 years, while sulfur content has increased at a fairly rapid pace.

Some data to consider about PADD 3 refineries in 1990 are:

• Crude runs were 6,059,900 b/cd.

• Refineries operated at 89.6% of operable capacity.

• Crude oils input to refineries had a composite API gravity of 33.10 and sulfur content of 1.14 wt %.

• Foreign crude oil receipts were 3,254,900 b/cd.

• The top five countries from which foreign crudes were imported were Saudi Arabia (857,500 b/cd), Mexico (513,600 b/cd), Venezuela (414,300 b/cd), Iraq (399,800 b/cd), and Nigeria (261,100 b/cd)

• Alaskan crude oil receipts were 157,000 b/cd.

PADD 4

Refineries operating in PADD 4 are fairly well isolated from foreign crude oils other than Canadian crudes. These refineries process local crudes from Colorado, Montana, Utah, and Wyoming.

Use of Canadian crude oils has averaged about 15% of crude runs during the last 5 years, up from 10% in the early 1980s.

Crude oil quality has changed little over the last 10 years, with sulfur actually decreasing, though sulfur data are rather poor. The 10 and 5-year trends are as follows:

• 1981-1990: -0.03 API/year, -0-002 wt % S/year.

• 1986-1990: -0.22 API/year, +0.028 wt % S/year.

Crude runs to PADD 4 refineries in 1990 were 459,800 b/cd.

Crude quality trends for the 5-year period indicate that the rate of gravity decrease has accelerated significantly, and that there has been a slight increase in sulfur content.

It should be noted, however, that crude oils processed in PADD 4 are typically of good quality-35.9-36.2 API, 0.85-0.90 wt % S.

PADD 5

Refineries operating in PADD 5 have reduced their usage of foreign crude oils from a high of about 14% in 1980, to a low of about 9% in 1990.

Crude oil quality has declined slightly over the past 10 years, though sulfur data for the region are rather poor.

The 10 and 5-year trends are as follows:

• 1981-1990: -0.07 API/year, +0.017 wt % S/year.

• 1986-1990: +0.22 API/year, +0.016 wt % S/year.

Figs. 4 and 5 show historical-vs.-calculated data for gravity and sulfur, respectively, over the 10-year period.

It appears that the 10-year trend toward decreasing gravity has reversed in the last 5 years, and that sulfur is increasing at about the same rate for both periods.

The reversal of the gravity trend was caused by decreased usage of Alaska North Slope (ANS) crude, which has been replaced primarily by lighter crudes from the Pacific Rim countries. The use of foreign crudes may increase in the next few years as the production of ANS declines.

It should be noted, however, that crude oils processed by PADD 5 refiners (most of whom are in California) are of rather poor quality, typically 25.0-26.0 API and 1.05-1.10 wt % S.

Some data to consider about PADD 5 refineries in 1990 are:

• Crude runs were 2,593,300 b/cd.

• Refineries operated at 86.8% of operable capacity.

• Crude oils input to refineries had a composite API gravity of 25.65 and a sulfur content of 1.11 wt %.

• Foreign crude oil receipts were 231,800 b/cd.

• The top five countries from which foreign crudes were imported were Indonesia (83,400 b/cd), Australia (41,600 b/cd), Malaysia (20,400 b/cd), China (16,300 b/cd), and Mexico (14,900 b/cd).

• Alaskan crude oil receipts were 1,433,700 b/cd.

TOTAL U.S.

The API gravity of crude oils processed in U.S. refineries appears to be declining rather quickly-about 0.20 API/year-over the past 10 years. There has been a slight increase in sulfur content-about 0.023 wt %/year-over the 10-year period.

The 10 and 5-year trends are as follows:

• 1981-1990: -0.20 API/year, +0.023 wt % S/year.

• 1986-1990: -0.22 API/year, +0.016 wt % S/year.

Figs. 6 and 7 show historical-vs.-calculated data for gravity and sulfur, respectively, over the 10-year period.

There has been a slight acceleration in the rate of gravity decrease for the 5-year period, but the rate of sulfur content increase has slowed down.

U.S. refineries east of the Rocky Mountains are processing crudes with a composite gravity of greater than 31 API, and sulfur content slightly greater than 1 wt %. These crude oils are considered in the medium-to-high gravity, low-to-medium sulfur group.

As crude oils produced worldwide increasingly fall into the medium gravity group (20.0-30.0 API), U.S. refiners will need to modify their heavy ends processing units to meet the demands of manufacturing transportation fuels.

BIBLIOGRAPHY

"Petroleum Supply Annuals," U.S. Department of Energy.

Copyright 1991 Oil & Gas Journal. All Rights Reserved.