Well testing is a critical part of potential production assessment in deep and ultra-deep water well development. When target reservoirs produce heavy oil, gas, and condensate, or are high pressure/high temperature (HP/HT) environments, test designers in the operating company must not only focus on safety and risk mitigation for the operator, when planning these tests, but also must assure that the tests will gather enough data to justify the operational expense and potential risks inherent to these types of environments.
Deep-water production usually requires prolonged periods of low temperature and heat loss, which can affect production or result in hydrate formation. Intervention can be problematic and costly. Fluid volumes, well and water depths accessed can increase well-control time and expense for the operator. Also, since these well tests are conducted from mobile vessels, the alarm and subsea equipment philosophies are critical to the enhancement of safety and risk mitigation. Well-test design and string configuration must have flexibility but still must be capable of efficiently controlling the conditions listed above.
Obviously, these and many other issues must be fully understood by the operator if the program plan, equipment, and methodology have the capability to assess the challenges, ameliorate the risks, and provide contingencies for unexpected events that could occur.
This paper explores these issues as well as appropriate methodologies for mitigation. The merits and limitations of various solutions will be considered along with the basic philosophy of equipment consideration. Lessons learned from actual cases will be used to compare consequences of inadequate preparation to the benefits of proper design.
Also explained will be why particular methods and equipment should be used and why others are less desirable. Lessons learned and their application will be discussed, including:
Red, yellow, or degraded status decision making during dynamic-positioning (DP) vessel testing
Coiled-tubing usage criteria
Defining cushion-type criteria
Defining mud-type criteria
Hydrate prevention and mitigation
Importance of obtaining dynamic reservoir data efficiently and economically without risking the environment and personnel safety.