Well-Test Planning in Deepwater Wells in High-Pressure, High-Temperature Environments-The Brazil Experience

Abstract

Abstract High pressure/high temperature (HP/HT) deepwater areas continue to present the most challenging conditions for performing well-testing evaluation. Wells are defined as deepwater when they are at least 15,000 feet deep and are considered HP/HT when they have bottomhole pressures of approximately 10,000 psi and bottomhole temperatures in excess of 300ºF. Several wells under these extreme environmental conditions have been tested in Brazil operations, and these attempts have verified the importance of the proper preliminary analysis of test parameters according to the specifications of the prospect, the requirements at surface, and the possible impact of testing on bottomhole conditions. Typical variables such as high hydrostatics and high temperatures are usually considered, but it is also important to assess the types of operations involved during the test that could increase the value of the different physical variables in such a way that the tool string could be damaged. Often, combined variables can surpass the design characteristics of the test tools and could result in loss of the test or even the well. Thus, it is critical that design specifications of the necessary equipment and operational limitations be considered with a detailed analysis of operations and alternatives in a HAZID/HAZOP. Complete tables including equipment specifications and mechanical characteristics of the equipment to be used must be compiled in order to identify the limits for the entire operation. The electronic restrictions, where applicable, must be evaluated as well. Once, all the information is collected, a computer model can be built using several specialized software programs in order to properly analyze the different parameters that can not be visualized at first sight but can seriously affect equipment performance during performance of the job. That model then must be reviewed. Parameters such as flowing and static temperatures at surface, at sea bead, and bottomhole as well as flowing and static pressures must be analyzed since tri-axial forces acting on the string as a result of the operational sequence could change input specification parameters. Drag and torque models resulting from any rotation of the string (ex., setting mechanical packers) must also be analyzed. Simulation of any wireline or slickline operations also should be reviewed to ensure that these operations will be successful during gun correlation, realtime data acquisition, or setting of plugs needed to isolate any zone. This paper focuses on the steps that should be followed to enable successful well-testing evaluations in HP/HT environmental conditions. With the planning described, it is possible to minimize the risks that can negatively impact testing operations. The planning, design criteria and tools required to perform successful well-testing evaluation in severe well conditions will be discussed in detail. The steps implemented for designing deepwater well-tests can provide a safety envelope for equipment and help assure that the operations will be successfully performed. Introduction Well tests have been conducted using different downhole tools and designs to work in extreme environmental applications. Proper planning is the key to performing more accurate, representative, and more successful well testing evaluations in deepwater well environments.