Exploration • Drilling • Field Services
Economical decisions are acceptable as long as the engineering constraints are met
Doug Kolak explains how crucial the role of water injection systems are to effective flow supply extraction.
W
orld demand for oil is set to increase 37 per cent by 2030, according to Energy Information Administration’s (EIA) annual report. Taking
this into account and considering that the number of known wells is shrinking it comes as no surprise that it is becoming increasingly expensive to locate and extract supply. Tis highlights the critical roles efficiency and complex extractions have to play in each operation, especially when dealing with subsea wells which can cost upwards of $100 million to initiate production. Increasing supply from an existing well or drilling into a new pocket can be an option for many, but without taking the proper considerations into systems and production efficiency it may not profitable.
Te need for a constant and longer flowing supply is crucial to effective extraction. Achieving optimum extraction relies on a number of systems working together effectively and none more so important than an efficient water injection system. Correctly designed, it can prolong the oil extraction and provide a constant flow of supply. Any water injection system should be optimised
to deliver the correct amount of water to the current set up and take into consideration any unforeseen eventualities that may occur due to the increase in production. A major factor to consider in the design of water injection systems is surge pressure, also known as ‘Water Hammer’. Te consequences of which can be catastrophic and irreparable. A pressure surge can happen, but engineering your system to minimise the instances and impact should be a must.
Identifying surge cases Surge analysis is not only pertinent to conceptual designs but also to expansion of existing systems. Surge analysis on water injection systems is performed to determine the maximum pressure surges that can occur as a result of transient events such as rapid valve closure during pipeline operation, or pump trip and restart operations.
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Te first step in any surge analysis is to identify credible cases where surge can arise. For example, closure of a single valve in a complex water injection network is unlikely to be an issue; however, closure of all wells while water injection pumps continue to operate (eg, due to malfunction of a facility’s shutdown system) is potentially a serious concern. As is the loss of LP (Low-Pressure) hydraulic fluid as a result of umbilical failure which occurs if all wells are closed at the drill centres. Of course there is also operator error to factor in that can result in mistaken valve closures.
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