The Southern Alberta Institute Of Technology (SAIT) has been contracted by the Petroleum Technology Alliance Of Canada (PTAC) to evaluate different aspects of the current well abandonment practices in Alberta. This report looks at both the minimum length of an in casing cement plug required to withstand 7000 kPa in a pressure balanced test design, and an evaluation of cement strength using neat Class G hydrated in different wellbore fluid environments.
- PRESSURE TEST CEMENT PLUG OBJECTIVE:
Determine minimum cement plug length (+/- 0.5 meters) to hold 7 MPa in 114mm, 139mm and 177.8 mm casing for 60 minutes minimum. Samples to have radial, external pressure balanced support. A failure is determined by any leakage past the cement plug, or cement plug movement. Leakage past cement plugs of 0.5, 1.0, and 1.5 m occurred in all the 114, 139 and 178 mm casing samples tested. A 2.0 m long plug was tested in the 178 mm casing size and this proved to be the quickest sample to leak. The leaks seemed to travel in a linear path along one side of the cement plug. Only one plug moved and it moved 2 mm. This was a 1.5m long plug in 178 mm casing. Reasons for this movement are not known. Based on these results, it is unclear whether longer plug lengths could contain 7000 kPa without leakage. It is believed however, that longer plug lengths would eliminate the possibility of cement plug movement.
- TEST PLUGS IN WELLBORE FLUID ENVIRONMENTS OBJECTIVE:
Observe and measure the 10 day and 30 day compressive strength of Oilwell Class “G” neat cement, with a density of 1900 kg/m3. These cement samples are to be hydrated in typical wellbore fluid environments that could have a detrimental impact by contaminating the cement or altering its chemistry. These environments are fresh water, fresh water with corrosion inhibitor, produced water, 3% KCL water, and crude oil. Cement to be placed in these different fluid environments using through tubing and dump bailing methods. Compressive strength of samples increased with hydration time regardless of the fluid environment. The crude oil environment caused a small reduction in compressive strength, while the other fluids tested were about equal. The crude oil samples showed oil staining within the broken test samples broken during compression testing. The tubing placement and dump bailing methods employed showed good displacement of the wellbore fluid environment at the bottom of the samples. Some small wellbore fluid voids were evident along the sides of some of the samples placed.