Gas lift well surveillance

A method for evaluating the performance of a gas lift well, the method comprising:

• injecting a tracer into an annulus formed between a well casing and a production tubing of the gas lift well, the annulus including a lift gas, the gas lift well further including one or more points of communication between the annulus and the production tubing, wherein each of the one or more points of communication corresponds to a valve position;
• measuring, over a period of time, a concentration of the tracer present in a substance retrieved from the gas lift well;
• determining one or more actual travel times of the tracer based on a deviation of the concentration of the tracer measured over the period of time from a pattern present in a baseline tracer concentration, wherein each of the one or more actual travel times of the tracer corresponds to a point of entry of one or more points of entry of the lift gas into the production tubing;
• segmenting the gas lift well into a plurality of ranges of well depth;
• determining one or more lift gas loss parameters, each of the one or more lift gas parameters corresponding to a point of entry, each of the one or more lift gas loss parameters accounting for an effect of entry of a portion of the tracer into the production tubing at the corresponding point of entry on the actual travel time of the tracer that enters the production tubing at each point of entry located at a depth greater than the corresponding point of entry;
• calculating a velocity of the lift gas in the annulus and a velocity of the lift gas in the production tubing for each of the plurality of ranges of well depth based on:
• (i) the one or more lift gas loss parameters, and
• (ii) a plurality of pressures, each of the plurality of pressures corresponding to one of the plurality of ranges of well depth;
• and
• determining the one or more points of entry of the lift gas into the production tubing based on:
• (i) the one or more actual travel times of the tracer, and
• (ii) the velocity of the lift gas in the annulus and the velocity of the lift gas in the production tubing calculated for each of the plurality of ranges of well depth,
• wherein one or more of the steps of the method are controlled by at least one computer processor executing one or more computer program instructions stored on at least one memory device operatively coupled to the at least one processor.

A method for evaluating the performance of a multiple installation gas lift well, the method comprising:

• injecting a tracer into an annulus formed between a well casing and two or more production tubings of the gas lift well, the annulus including a lift gas, the two or more production tubings being capable of fluid communication with the annulus and being substantially incapable of fluid communication with each other, the gas lift well further including one or more points of communication between the annulus and each of the two or more production tubings, wherein each of the one or more points of communication corresponds to a valve position;
• and
• for each of the two or more production tubings:
• measuring, over a period of time, a concentration of the tracer present in a substance retrieved from the each of the two or more production tubings;
• determining one or more actual travel times of the tracer based on a deviation of the concentration of the tracer measured over the period of time from a pattern present in a baseline tracer concentration, wherein each of the one or more actual travel times of the tracer corresponds to a point of entry of one or more points of entry of the lift gas into the each of the two or more production tubings;
• segmenting the gas lift well into a plurality of ranges of well depth;
• determining one or more lift gas loss parameters, each of the one or more lift gas parameters corresponding to a point of entry, each of the one or more lift gas loss parameters accounting for an effect of entry of a portion of the tracer into the each of the two or more production tubings at the corresponding point of entry on the actual travel time of the tracer that enters the each of the two or more production tubings at each point of entry located at a depth greater than the corresponding point of entry;
• calculating a velocity of the lift gas in the annulus and a velocity of the lift gas in the each of the two or more production tubings for each of the plurality of ranges of well depth based on the one or more lift gas loss parameters;
• and
• determining the one or more points of entry of the lift gas into the each of the two or more production tubings based on:
• (i) the one or more actual travel times of the tracer, and
• (ii) the velocity of the lift gas in the annulus and the velocity of the lift gas in the each of the two or more production tubings calculated for each of the plurality of ranges of well depth,
• wherein one or more of the steps of the method are controlled by at least one computer processor executing one or more computer program instructions stored on at least one memory device operatively coupled to the at least one processor.

A non-transitory computer-readable medium storing a computer program for evaluating the performance of a gas lift well that includes a well casing, a production tubing, an annulus formed between the well casing and the production tubing, the annulus including a lift gas, and one or more points of communication between the annulus and the production tubing, wherein each of the one or more points of communication corresponds to a valve position, the computer program comprising computer program instructions for:

• measuring, over a period of time, a concentration of the tracer present in a substance retrieved from the gas lift well;
• determining one or more actual travel times of the tracer based on a deviation of the concentration of the tracer measured over the period of time from a pattern present in a baseline tracer concentration, wherein each of the one or more actual travel times of the tracer corresponds to a point of entry of one or more points of entry of the lift gas into the production tubing;
• segmenting the gas lift well into a plurality of ranges of well depth;
• determining the one or more lift gas loss parameters, each of the one or more lift gas parameters corresponding to a point of entry, each of the one or more lift gas loss parameters accounting for an effect of entry of a portion of the tracer into the production tubing at the corresponding point of entry on the actual travel time of the tracer that enters the production tubing at each point of entry located at a depth greater than the corresponding point of entry;
• calculating a velocity of the lift gas in the annulus and a velocity of the lift gas in the production tubing for each of the plurality of ranges of well depth based on the one or more lift gas loss parameters;
• and
• determining the one or more points of entry of the lift gas into the production tubing based on:
• (ii) the one or more actual travel times of the tracer, and
• (ii) the velocity of the lift gas in the annulus and the velocity of the lift gas in the production tubing, that are calculated for each of the plurality of ranges of well depth.