Fluid property sensors and associated methods of calibrating sensors in a subterranean well

A sensor system for use in a subterranean well, the sensor system comprising:

• a tubular string positioned in a wellbore, an annulus being thereby formed between the tubular string and the wellbore;
• a port formed through a sidewall of the tubular string and providing fluid communication between an internal flow passage of the tubular string and a zone intersected by the wellbore, a flowpath being thereby defined in the annulus between the zone and the port;
• a flow restriction in the flowpath between the zone and the port;
• and
• at least one sensor sensing pressure of fluid flowing through the flow restriction.

A sensor system for use in a subterranean well, the sensor system comprising:

• a housing assembly interconnected in a tubular string positioned in the well, the housing assembly having a flow passage formed longitudinally therethrough;
• at least one first gamma ray source;
• and
• a first gamma ray detector positioned opposite the flow passage from the first gamma ray source, such that fluid flowing through the flow passage passes between the first source and the first detector.

A method of sensing the density of a fluid flowing through a tubular string positioned in a well, the method comprising the steps of:

• positioning a first gamma ray source in a sidewall of a housing assembly, the housing assembly having a flow passage formed therethrough;
• positioning a first gamma ray detector in the housing assembly sidewall opposite the flow passage from the first gamma ray source, the first gamma ray detector being collimated by shielding such that a substantial fraction of gamma rays detected by the first detector originate in the first gamma ray source;
• positioning a second gamma ray detector in the housing assembly sidewall, the second gamma ray detector being shielded such that a substantial fraction of gamma rays detected by the second detector originate in background sources;
• connecting the first and second detectors to electronic circuitry that converts outputs of the first and second detectors into respective count rates;
• and
• computing an indication of fluid density from the count rates.

A method of sensing properties of fluid flowing in a subterranean well, the method comprising the steps of:

• positioning a tubing string in the well, thereby forming an annulus between the tubing string and a wellbore of the well, the tubing string including multiple ports providing fluid communication between the annulus and an interior flow passage of the tubing string;
• isolating portions of the annulus from each other, each annulus portion being in communication with a corresponding one of multiple zones intersected by the well, and each annulus portion being in communication with a corresponding one of the tubing string ports;
• and
• sensing multiple properties of fluid flowing into each of the ports utilizing multiple sensor systems interconnected in the tubing string, each sensor system being interconnected in the tubing string downstream of a corresponding one of the ports, and each sensor system including a fluid density sensor, a flowmeter, a temperature sensor, a pressure sensor and a selected one of a fluid dielectric sensor and a fluid conductivity sensor.

A method of calibrating multiple sensor systems interconnected in multiple branch tubing strings, each of the tubing strings including multiple flow control devices, each flow control device regulating fluid flow into one of the tubing strings and being positioned upstream of a corresponding one of the sensor systems relative to fluid flow in the corresponding one of the tubing strings, the method comprising the steps of:

• closing all flow control devices in all tubing strings other than a first one of the tubing strings;
• and
• with only a lowermost one of the flow control devices in the first tubing string being open, and then with successively next lowermost ones of the flow control devices in the first tubing string being opened, performing the following procedure for the open lowermost flow control device, and again performing the procedure after each successively next lowermost flow control device is opened:
• a) flowing fluid through the open one or more flow control devices into the first tubing string;
• b) measuring at the earth's surface at least one property of fluid flowing from the first tubing string;
• c) recording measurements received from sensors of the one or more sensor systems corresponding to the one or more open flow control devices;
• and
• d) determining calibration values for the measurements received from the sensors of the one or more sensor systems corresponding to the one or more open flow control devices.

A method of measuring fluid properties of fluid flowing in a subterranean well, the method comprising the steps of:

• positioning a tubing string in the well, thereby forming an annulus between the tubing string and a wellbore of the well, the tubing string including multiple ports providing fluid communication between the annulus and an interior flow passage of the tubing string;
• isolating portions of the annulus from each other, each annulus portion being in communication with a corresponding one of multiple zones intersected by the well, and each annulus portion being in communication with a corresponding one of the tubing string ports;
• sensing at least one property of fluid flowing between each corresponding zone and tubing string port;
• and
• calibrating the sensors by measuring properties of the fluid produced at the surface with at least one of the ports closed.

A method of measuring fluid velocity in a subterranean well, the method comprising the steps of:

• positioning a tubular string in a wellbore, thereby forming an annulus between the tubular string and the wellbore;
• forming a flow restriction in the annulus external to the tubular string;
• flowing fluid from a zone intersected by the wellbore, into the annulus, through the flow restriction and into the tubular string;
• and
• sensing pressure of the fluid flowing through the flow restriction.

A fluid density measurement system, comprising:

• at least one set of a gamma ray source and a gamma ray detector interconnected in a tubular string positioned in a subterranean well;
• electronic circuitry converting an output of the gamma ray detector into a gamma ray count rate;
• and
• software converting the gamma ray count rate into an indicator of fluid density.