Downhole Testing Tools in Extreme Environments

Abstract

Hydrocarbon exploration and production has ventured into deeper, more corrosive environments, requiring continual technology changes to address the challenges presented by the new environments into which the oil field has moved. Testing technology has had to redefine the operating envelopes for its tools in order to meet the new requirements. Not only high-pressure and high-temperature tools have been needed, but more debris-tolerant tools 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: Ultra-deep waterExtreme high-pressureExtreme high-temperatureDebris presence. Ultra-deep-water wells are those that 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 were capable of functioning 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. In addition, a new generation of more debris-tolerant tools is available. The improved tools have 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. Subsea equipment also has required adaptation to harsh environments. A major engineering/service company has now developed new subsea safety-tree equipment to be placed inside the BOP stack; with this new equipment, the fracturing operation and the drill-stem testing can be performed in the same trip, since the safety valve system has the capability to maintain integrity when functioning in heavy proppant, high pressure, and high pump-rate conditions. This capability saves time and adds economic value as well as increased safety features to the jobs. This paper will discuss the innovations to testing technology as well as how formation evaluation jobs now can be performed satisfactorily in extremely hostile wells using the improved technologies. Best practice information that has now been gained concerning testing in extreme environments will also be presented.