Abstract

A case study is presented in this paper on converting producer wells to injector wells in the recently developed Buzzard Field located in the Northern Sea, approximately 60 km northeast of Aberdeen. The field was discovered in 2001, development drilling commenced in 2005, and the first production from the field started in early 2007. To meet the monitoring objectives, operator selected a permanent downhole monitoring system (PDMS) for measurements of pressure, temperature, flow rate, and distributed temperature. Each well was equipped with three permanent optical sensors: pressure/temperature sensor, two-phase flowmeter, and DTS. The PDMS system was designed to accommodate the expansion of the field: as new wells are added to the field, optical sensors for the new wells are also added into the sensor pool and the same surface instrumentation drives the data acquisition process for all sensors via a multiplex device. There are currently more than 30 wells in the field and new wells are being added on a regular basis.

In 2011, operator decided to convert two producer wells to injectors. The first well was designated for water injection and the second one for gas injection. The conversion for the water injector was completed in late October 2011. One of the critical issues in this conversion process was to determine the flow rates of the injected fluid precisely to better manage the injection process as this could have a large impact on oil production economics. The optical flowmeters have originally been installed as two-phase flowmeters in the production mode for the Buzzard Field, but it was also well-established that single-phase versions of optical flowmeters have served successfully in a number of water-alternating-gas (WAG) injector applications as reported by other operators.

In this particular case, operator and the equipment manufacturer worked together to make sure that the conversion process was successful from the flow measurement standpoint. True to the "intelligent completion concept", in the process of changing the service from producer to injector, no hardware or software changes were made in the flowmeter and the surface instrumentation. The only change was associated with the fluid parameter file in the flow computer which is a part of the surface instrumentation. The process also highlighted the true bidirectional capability of the in-well optical flowmeter, something that most other flow measurement technologies are not capable of doing even at the surface. Furthermore, the process is also independent of the type of the fluid whether the injected fluid is water or gas. Recently, operator completed the gas injector and the injection process started with low flow rates. Currently, the flowmeter reports sound velocities only but it is expected to report flow rates as the gas injection rate is increased above the sensing threshold of the flowmeter.

This work describes the producer-to-injector conversion process as well as the experiences associated with it. It also demonstrates how the collaboration between the operator and the equipment manufacturer can lead to a success story in implementing a service change without compromising intelligent completion.

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