Increased Heavy Oil Extraction Due to Steam-injection Boiler Control

Higher crude prices are leading producers to reevaluate costs of extraction from heavy oil fields. In steamflooding, control of saturated steam is vital for maximizing yield. A Chinese manufacturer of steam-injection boiler automation equipment, Xinjiang Shuangcheng Electrical Automation Engineering Co., Ltd., has found inductive conductivity sensors combine resilience and accuracy, helping their customers to extract greater quantities of crude.

It is not surprising that the demand for oil in China has grown exponentially in recent decades. China's domestic oil industry has developed considerably since the first major reserves were discovered in the northeast of the country in the 1950. Over the following six decades, annual output has increased from 90,000 tons to 250 million tons (two thirds of the country's current needs). As estimates place a requirement of 600 million tons by 2020, China's oil companies are desperate to extract as much crude from their fields as possible. With light crude reserves dwindling, attention has moved to the country's substantial heavy oil fields. The Liaohe and Karamay fields in the Xinjiang region are major onshore heavy oil sources with a combined annual output of approximately 11 million tons. Steamflooding (driving high-temperature, high-pressure steam into the crude to reduce its viscosity and make extraction easier) is the primary delivery method. The proportion of saturated steam is an important index in steam management as a 1 % increase in dryness yields an additional 0.2 % of crude. However, if steam dryness is too high (becomes superheated) it endangers the safety of the boiler, while too low a content means the steam will lack sufficient energy to extract the crude. It is therefore essential to conduct real-time monitoring and control of steam dryness.

Automated control of steam boilers
Xinjiang Shuangcheng Electrical Automation Engineering Co., Ltd. is a high-tech company engaged in the development and production of industrial automation equipment as well as system integration. With its strong R & D capability and comprehensive management system, the company is dedicated to the R & D of oilfield automation projects and system integration of GIS / computer / security monitoring. The company prides itself in delivering systematic, precise and practical solutions for various oilfields in the Xinjiang region. Automated control systems for the dryness control of oilfield steam-injection boilers is typical of the solutions developed by Xinjiang Shuangcheng. With the combined adjustment of steam and water in accordance with the dryness quality index for production, the system automatically detects and controls the steam quality during boiler operation.

Continuous dryness monitoring for steam control
In-line dryness monitoring is a pre-requisite for achieving automatic control over the saturated steam, as only in-situ measurements can offer accurate, real-time data for control systems. As a significant quantity of salt is normally present in the water used for the steam injection boilers, conductivity measurement is commonly adopted for in-line dryness monitoring. The saturated steam dryness content can be calculated by measuring the ratio between the conductivity of inflow water (post treatment) and that of the water from the boiler. All conductivity sensors used by Xinjiang Shuangcheng in previous dryness control systems were electrode based. Technicians at the company noted that such sensors would adversely affect the accuracy of the dryness measurement due to electrode polarization, pollution and scaling, particularly when using brackish water in the boiler. Within one month of a new sensor being installed, there would be a minor deviation of the measured dryness value. The aberration would gradually increase, eventually becoming significant. Although regular cleaning would minimize the problem, after half a year the electrode would fail and require replacement. This would cause great inconvenience to the site operator, severely impacting the realization of automatic control and leading to huge material waste. In an effort to alleviate the situation, Xinjiang Shuangcheng technicians began looking for an alternative measuring system. After learning of METTLER TOLEDO's InPro 7250 inductive conductivity sensors and Cond Ind 7100 transmitter, they contacted us and obtained a test system.

High reliability of inductive sensor design
The InPro 7250 conductivity sensor is an electrodeless design. It features an inductive coil which is protected from the measuring media by a highly resilient coating. Inductive conductivity sensors require no polarization and are largely immune to scaling and pollution. The InPro 7250 is often used for general conductivity determination over a wide measurement range, while the measuring range encountered by Xinjiang Shuang-cheng's dryness control systems mainly cover narrow ranges at opposite extremes. When polluted water is the source, conductivity of inflow water is approximately 5.6 ms/cm2 and the conductivity of boiler water is approximately 20 ms/cm2. If clean water is the feed, the conductivity of inflow water is approximately 0.35 ms/cm2, and for boiler water is approximately 1.2 ms/cm2. Xinjiang Shuangcheng technicians were interested to find out if the InPro 7250 would have the precision they required to measure accurately within such diverse ranges. After many tests, the technicians were pleased to discover that the InPro 7250 determined conductivity with high accuracy in both situations, and the METTLER TOLEDO solution was selected for their dryness control system. The system sub-sequently won a major Chinese science prize for its dryness monitoring and control method."Perfect solution"Lv Qi, Chief Engineer at Xinjiang Shuangcheng is highly satisfied with the InPro 7250's performance: "We believe that this conductivity sensor is the perfect solution to the incorrect dryness measurement caused by electrode polarization and pollution when using electrode-based conductivity sensors. It is an ideal choice for long-term in-line conductivity testing in automatic dryness control sys-tems of oilfield stream-injection boilers."

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