Well testing operations in challenging environments are becoming more common, and as a result, testing technologies have had to continually improve or develop newer techniques that can meet the more corrosive needs in the new areas. These testing methods must not only achieve operational efficiency, increase personnel safety and protect the environment, they must address additional challenges in the new environments where current development is taking place. In spite of the ongoing improvements, however, there are still scenarios that remain problematic, and one the most challenging continues to be the production and well testing of heavy-oil reservoirs in sandstones or carbonates. This is particularly true when testing operations are performed offshore.
Heavy oils normally are defined as those with an API gravity below 20 degrees with very high viscosities, a variable that is a major factor in determining the flowing capacity of oil through the reservoir, the completion string, and surface facilities. Pressures and low temperatures can increase the viscosity of the oil to an even higher value, depending on the wellbore characteristics, geographical area, and the PVT properties of the crude. While most onshore reservoirs are produced using cold production or steam injection to reduce the viscosity, offshore environments present more difficult scenarios due to the low temperatures at the sea bed and in the ocean thermo-cline regions which further complicate the typical complexity of all operations in this type of environment.
Enhanced simplicity and reliability is critical in offshore development because of the increased intervention cost compared to the cost of onshore cases and the need to maintain environmental safety. Thus, careful initial planning of these operations remains paramount.
This paper reviews experiences that have occurred while testing heavy-oil reservoirs using a wide range of equipment configurations and procedures. The authors feel that this information will be extremely valuable for operators and service personnel who are planning well testing operations offshore.