Developing a hydrate-monitoring system

A major challenge in offshore development is to ensure unimpeded flow of hydrocarbons. Managing solids such as hydrates is the key to the viability of developing a deepwater prospect. Common methods to prevent and reduce hydrate risks are generally based on injection of thermodynamic inhibitors to prevent hydrate formation, or use of kinetic hydrate inhibitors to sufficiently delay hydrate nucleation/growth. Currently, the amount of inhibitor required is either calculated and/or determined based on lab experiments. The amount of inhibitor depends on various parameters, including, water cut, inhibitor loss to hydrocarbon phases, aqueous and non-aqueous fluid compositions, operating conditions. Generally, a safety factor is considered and the resulting inhibitor is injected upstream without much downstream measurements. Despite the usual safety margins, gas hydrates are formed, which could result in serious operational and safety concerns. This is mainly caused by changes in the system conditions (e.g., rates and water cut) and/or malfunction of the equipment. In most cases, the amount of inhibitor is more than necessary and is not adjusted with seasonal changes, affecting CAPEX/OPEX. As a result of a joint industry project, several novel techniques, based on downstream and online measurements, have been developed. These techniques could be divided into the following categories: 1. Monitoring hydrate safety margin to optimize inhibitor injection rates. The system determines the amount of inhibitor in the aqueous phase and the degree of inhibition they can offer. 2. Detecting initial hydrate formation, as an early warning system against hydrate blockage. The system detects the changes in the system caused by hydrate formation with the aim of giving the operator enough time to prevent a blockage. The main advantages of these techniques include minimizing the amount of inhibitor required and preventing pipeline blockages caused by hydrates, hence the cost of inhibitor; impact on the environment; cost of remedial actions; and deferred production. A number of techniques have been investigated during this project, with some techniques selected for prototype development. The developed prototypes have been tested in the project sponsors' laboratories and some in commercial production. In this paper, an update on the latest results of this new approach in flow assurance control is presented. Copyright © 2009 Society of Petroleum Engineers.