Scaling Challenges in Geothermal Wells

Applying SAGD design to Geothermal applications

The Industry Challenge:

A major geothermal operator was experiencing issues with calcium carbonate scaling in their production wells.  The cause was mainly attributed to the well-known pH effects related to CO2 solubility during production, resulting precipitation of calcium carbonate.

The operator was generally satisfied with the performance of their chosen chemical scale inhibitor; however, the injection system had two main drawbacks:

  1. if the capillary injection lines became plugged, corroded or otherwise damaged, detection was difficult, which then led to incidences of wellbore scaling, loss of production and high-cost fishing operations; and
  2. removal of the capillary injection system for servicing or inspection required pulling the production equipment- a time, labour and cost intensive operation.

How We Help:

The solution was developed through a 5 step, multi-phased project:

Problem investigation and ranking of potential solutions – The first step was to work with the operator to fully define the problem and investigate potential solutions. Solutions were then ranked using a semi-quantitative evaluation matrix approach, based on how well the solutions met various functional requirements. The chosen solution was a Coiled Tubing (CT) serviceable chemical injection system, which borrowed from experience and equipment commonly used to deploy downhole instrumentation in Canadian high-temperature Steam Assisted Gravity Drainage (SAGD) wells.

Design and manufacturing – The next step was to bring in local thermal wellhead and CT instrumentation vendors in Edmonton, Alberta to contribute to the new completion design. While employing SAGD wellhead design features and making use of various “off-the-shelf” components, the design also allowed the operator to continue to use their existing downhole and surface equipment (primarily the pump and drive components).

Wellbore “stack-up” test – An assembly test was performed in the Deep Well Simulator (DWS), a 0.8m x 45m vertical pressure vessel in C-FER’s Edmonton laboratory facility. The main objective was to ensure that all components were compatible, while also familiarizing field personnel with the equipment in a controlled environment without potential well control hazards. The wellbore was constructed which included all downhole components.  A CT unit was then used to test the installation and removal of the chemical injection system.

Coiled Tubing weak-point testing – The new CT injection system incorporates a weak-point in the tubing and capillaries that can be “pulled off” in the event of downhole sticking. To ensure that the system worked as designed, an instrumented pull test to failure was performed in C-FER’s UTS load frame.

Field installation – Currently, three systems are installed in the field with up to 8-1/2 months of run-time and no issues experienced. A fourth installation is planned on a high-value producer towards the middle of 2018.

 




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