This paper was prepared for presentation at the 1999 SPE Annual Technical Conference and Exhibition held in Houston, Texas, 3–6 October 1999.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractOil production wells on gas lift are sometimes unstable at low gas lift rates, even though steady-state flow analysis gives most efficient production at these gas lift rates. Unstable production, often called heading, may lead to periods of reduced or even no liquid production followed by large peaks of liquid and gas. This results in average oil production less than expected, and oil and gas production less than the systems design capacity to allow for the production peaks without causing shutdowns.To solve the problem the amount of lift gas is normally increased beyond the most optimum rate. When the lift gas supply is limited, other gas lifted wells must then be shut in.This paper describes one field proven sequence based automation for oil production, plus a new model-based automatic controller. Both technologies solve the problem of unstable production from gas lifted wells through manipulation of the production and/or the gas-injection chokes. The sequence-based automation and the model-based controller stabilize the production at operating points that would be unstable under standard operation. Field measurements such as wellhead pressure, annulus pressure etc. are inputs to the controllers (or are used by the controller).Examples are given of the model-based controller working together with realistic transient flow models of gas lift wells. Testing of the model-based controller on real unstable wells is planned. Production Gas Injection Region of optimum lift gas utilisation STABLE UNSTABLE Fig. 1-Typical lift performance relationship curve for a gas lifted well.

A control system for macro-mini manipulators is presented. A position transformation from the end-effector reference to joint coordinates is found using kinematic optimization. Decoupling and optimal control is used to coordinate the motion of the macro and micro part. The redundant manipulator will then have the speed of the micro manipulator and the large workspace of the macro manipulator. When optimal control is used, the redundant manipulator may be even faster than the micro manipulator provided that a suitable performance index is used. The performance of the manipulator is optimized over the whole reference, and this will give better results than the purely kinematic instantaneous optimization which is the dominating technique in research literature

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