Hydrocarbon production and exploration has ventured into deeper, more hostile environments, and this change has required continual operational change to enable operators to address the challenges presented by the more hostile environments into which exploration has now moved. Testing technology has had to redefine the operating envelopes for its scenario to meet the requirements presented by the more extreme conditions in the newer environments. Not only high-pressure and high-temperature tools have been needed, but tools that are more debris-tolerant have been needed as well.
This paper discusses the application of downhole testing tools in formation evaluation jobs in extremely hostile environments; these include testing in such conditions as:
Case history information will also be presented where a downhole testing operation was performed in a high pressure and high temperature offshore well northeast of Brazil.
The definition of ultra-deep water is when wells have at least 10,000 feet of water depth, and HP/HT well environments include those with bottomhole pressures above 10,000 psi and bottomhole temperatures above 300° F. When environments have bottomhole pressures above 15,000 psi and temperatures above 350° F, the wells are considered as extreme HP/HT.
Many testing operations have been severely challenged by these scenarios as downhole tools available for standard projects only could function efficiently to approximately 350° F and up to 10,000 psi of pressure. Now, special tools are available for conditions with temperatures of up to 450° F and 30,000 psi of hydrostatic pressure with maximum 15,000 psi of differential pressure. To function in higher pressures and temperatures, the drill-stem test (DST) string design should meet its capabilities and scenarios variation should be considered.
The addition of these tools has enabled high-quality well testing to be performed safely, and when the tools are used in wells where solids problems are not anticipated and unexpected debris does occur, they can avoid the unexpected rig time previously required to clean the well, further enhancing economic efficiency. Debris-tolerant tools also have allowed fracturing and acid operations to be performed with a test string, and with the same string, the well can be opened to a well-testing operation without compromising the functioning of the downhole tools. This capability saves time and adds economic value to the job.
This paper also discusses how formation evaluation jobs now can be performed satisfactorily in extremely hostile wells using the improved technology and the best practice information that has now been gained concerning testing in in this type of scenario.