HPHT DST UK
Introduction
Axis first got involved in this HPHT project back in 2011 when we undertook a feasibility/concept study to better understand how a well test could be planned, delivered and executed safely on this HPHT prospect. The primary objective from the outset was to provide our client with an optimal technical, commercial and practical solution to define the reservoir contribution from the HPHT prospect.
The original well was side-tracked off the mother bore in 2014 due to casing wear damage seen below the casing hanger. The sidetrack resulted in a delay to the test due to encroaching winter weather and there were further delays due to the uncertainty of the 2014 oil price decline. The well was plugged and suspended for a number of months pending a decision to test.
The test was eventually approved in the summer of 2015 and the Axis team began planning this complex HPHT well test. After more than four years of on/off planning and preparation, the re-entry into the well commenced onboard a semi-submersible drilling rig.
Workscope
Various stages of the project were completed over a period of more than 4 years and included the following key tasks:
- Feasibility / concept study on HPHT prospect
- Development of conceptual design
- Detailed well test planning including:
- Basis of design documentation
- Equipment procurement requirements
- Well test programme
- Operational risk assessments
- Detailed time and cost estimate (for AFE purposes)
- Specialist production technology support including:
- Inflow Performance, Tubing Stress Analysis [TSA] including temperature results and hydrate study
- Updating existing appraisal TSA WellCAT model with higher production rates and GOR values
- Verifying the DST string meets the client design criteria
- Determine the string (gauge) movement for all production and build up periods
- Determine expected flowing temperatures are within the BOP operating temperature limits
- TCP specialist attended the construction of the TCP guns and QC of this activity
- Facilitation and delivery of a detailed HAZOP study on the proposed well testing operations planned for the well
- Facilitation and delivery of a detailed TWOP, to further analyse and capture risks associated with the testing programme and operations
- Offshore execution and supervision of the DST
- Post-test close out of the project
Outcome
Reservoir pressures encountered were well in excess of 14,000 psia and good representative fluid samples were collected safely as part of the well test programme.
The many challenges encountered during this project included the planning and execution of a PLT, an uncommon operation on HPHT wells. This proved to be a particularly challenging part of the operation with toolstrings getting “stuck” downhole and changes being made to the configuration of the tool string in an attempt to alleviate these problems. Further “sticking” issues lead to concerns of overheating and the instruments losing valuable data, however after much perseverance the tool string was retrieved to surface and all data was successfully recovered. A great result for all concerned.
This project was a great success with all objectives being met safely and recovery of the DST tools at surface, with minimal loss of days. Axis have had some fantastic feedback from our client, and this project is a great example of where the Axis multi-disciplined team working together to deliver excellent service to our clients. Our operational and PT teams performed exemplary work in all aspects of the planning and execution of a complex DST.
The “switch on” and “switch off” nature of this project over a long period of time also demonstrates how we can add significant value to our clients and their operations. A number of “lesson learned” were documented and discussed with our client and the key service providers, this is important in the process of continual improvement and should ensure that future HPHT well test operations benefit from this learning.
