Optimization of Sea Water Pumping System
AFT Fathom™ Technical Paper
Authors: Joseph M. Thorp, Aramco Services Company and Jeffrey A. Olsen, Applied Flow Technology
Presented at the 24th International Pump Users Symposium (now the Turbomachinery and Pump Symposia)
ABSTRACT
This paper describes the optimization of a high-pressure seawater pipeline being constructed to increase oil production from an oil field in Khurais, Saudi Arabia. Consisting of approximately 145 km of pipeline and several pumping stations, the optimization addressed both initial operational requirements and planned expansions over ten years and included both first and life-cycle costs.
Key to this optimization were the capabilities provided in AFT Mercury* (now the Automated Network Sizing Module), Applied Flow Technology’s system optimization software. Starting from a well-engineered design, life cycle cost savings of $104 million was realized demonstrating the significant savings possible from using optimization technology.
*The IntelliFlow® technology featured in this paper has since migrated from AFT Mercury and AFT Titan to become the Automated Network Sizing (ANS) Module for AFT Fathom™ and AFT Arrow™. This module utilizes similar methods to provide the cost minimization as presented in this paper.
Conclusion
It is important to note that this study started from a well-engineered design and that through optimization additional cost savings and increased system capacity were realized.
Tradeoffs in first and life-cycle costs were able to be easily
examined. Changes to the system were quickly made to the model and the analysis rerun in the optimization software tool. This demonstrated the benefits of using such techniques to lower costs and increase performance during system design.
Case B was recommended and constructed. This used a 60 inch diameter pipeline made from X-70 steel with a wall thickness of 0.679 inches until the 44.8 miles (72.1 km) point and then a 0.551 inch wall for the remainder of the line. The maximum pipeline pressure for the 2.14 Mbbl/day design flow was 967 psig at the supply pump discharge, which was 85 percent of the maximum allowable operating pressure.
Figure 7 in the paper shows the static pressure along the length of the pipeline for the initial design point flow rate of 2.14 Mbbl/day. The increase in pressure between 15 and 30 miles was due to the
pipeline elevation decreasing over this section. The pressure for the
Original Case is also shown for comparison.
Below is an excerpt from the paper. Use the link above to view the full paper.
INTRODUCTION
The design and operating variables that most impact pipeline
pump life-cycle costs have been presented in the literature (Thorp,
2001). Users continue to rely on new and innovative approaches to
satisfy consumer needs for reliable, low-cost, and environmentally
friendly oil supply. Opportunities for achieving these requirements
have been necessitated through larger economies of scale
stemming from burgeoning world oil demand. To that end, Saudi
Aramco is implementing a historically-significant project to
increase future production by increasing the total amount that can
be extracted from existing fields. One method to increase the
amount of oil that can be extracted from an oil field is through
enhanced recovery using water injection. This is accomplished by
injecting high-pressure water into the reservoir thereby forcing
more oil out of the field. Many of the Saudi Arabian oil fields are located in the hot, dry, sandy desert on the eastern portion of the
country. In the desert, water is a scarce commodity; however, there
are vast amounts of water in the seas that border the country. A
large technical hurdle that must be overcome is transporting the
seawater to the oil fields over a variety of terrains using a network
of pipelines and pumping stations.
As new oil fields are developed and old ones brought back into
production, an ever growing network of seawater pipelines is pushed
farther and farther inland. This can be a costly operation, but is also a
good candidate to use optimization to find cost-cutting opportunities.
The design study described in the paper was focused on
determining the best configuration of pipeline material and sizes,
pumps, and pumping stations to meet both the current seawater
requirements and to have the flexibility to scale to accommodate
the increased demands in the future.
Optimization techniques have been used for many years on
structural applications (Schmit, 1960; Vanderplaats, 1999a) but their
use on pumping systems design is relatively new. Combining both
systemwide flow analysis and optimization techniques provides a
powerful new approach to lower costs and increase performance
during system design (Hodgson and Walters, 2002; Walters, 2002).
The existing Qurayyah seawater treatment plant, located on the
Persian Gulf, south of Ad Dammam and Dhahran, will send treated
water westward to Ain Dar located on the north portion of the
Ghawar oil field (Figure 1). The Ghawar oil field is the world’s
largest, producing about 4.5 million barrels per day, roughly 5.5
percent of the world’s daily production, and has the highest
sustained oil production rate achieved by any single oil field in
world history (Croft, 2005). It stretches 174 miles from north to
south and 16 miles across to encompass 1.3 million acres (Durham,
2005). There have been 3400 wells drilled into this reservoir since
the field was brought online in 1951.
Located west of Ghawar are the Khurais, Abu Jifan and Mazalij
oil fields (Figure 2). Khurais is the closest and by far the largest
being 78.9 miles (127 km) long and covering 1116 sq miles (2890
sq km) (Saudi Aramco, 2007). It is about 155 miles (250 km)
southwest of Dhahran and 186 miles (300 km) northeast of Riyadh,
the Saudi capital. Khurais is of similar structure and lies parallel to
Ghawar, but is smaller in size. Saudi Aramco has initiated a major
project aimed at increasing the production at Khurais from 300,000
to 1.2 million barrels per day by 2009 (Croft, 2005; Oil and Gas,
2006), which would make it the largest incremental increase in
world oil supply in the 75 year history of Aramco.
Meeting increasing oil demand from China, India, and other
developing countries is the fundamental purpose of this project. To
accomplish this at the lowest possible life-cycle, cost numerical
optimization methods were used.
SCOPE OF STUDY
General Overview
Existing operations currently use treated seawater pumped from
the Persian Gulf to Ain Dar on the northern side of the Ghawar oil
field. The idea is to use this source and pump it an additional
90.4 miles (145.5 km) westward to Khurais. The general system
guidelines called for two supply pumps at Ain Dar that would send
the seawater though a single, terrain-following pipeline. Pipe was
delivered to the site in 80 foot sections where welding of the
pipe sections and bending were performed in-situ as required by
the terrain.
When the seawater arrived at Khurais, booster pumps would
increase the pressure to meet the suction requirements of the
high-pressure injections pump. The tradeoff of incorporating
booster pumps and operating at a lower pipeline pressure versus
operating the pipeline at a higher pressure and eliminating the
booster pumps was a major design consideration.
Original Design
The study started from a well-engineered design, which will be
referred to as the Original Case. This called for two supply pumps,
three booster pumps and five water-injection pumps. The pipeline
was specified using X-60 steel with a 64 inch inner diameter and a
constant wall thickness of 0.562 inches throughout. Figure 3 shows
an overview of the original system.