Successful exploration and field development requires knowledge of fundamental reservoir and production properties. These properties can only be confidently measured by conducting a reservoir test, properly designed to measure pressure, temperature, and flow rate and sample for the zone of interest. Alongside the key task of gathering the necessary data and validating test objectives, this process involves the flowing of hydrocarbons through temporary equipment. It is therefore critical, to safely and efficiently manage the wellbore. A new wireless downhole reservoir testing system has been deployed in Saudi Arabia to meet reservoir testing challenges. This integrated system allows retrieval of downhole measurements throughout the test, control and verification of the tester and circulating valves, and selective activation of multizone perforating guns. This paper presents field cases demonstrating how the system has been used for these applications in an effort to reduce operational risks and improve certainty in reservoir testing results.

An operator successfully tested an offshore, exploration well in a high-pressure and a high-temperature (HPHT) reservoir, where the pressure exceeds 10, 000 psi and the temperature is approximately 400°F. The tested intervals are behind a 4.5-inch liner. Slimhole drillstem test (DST) tools have been considered but not selected due to the restricted internal diameter and limited intervention capability. Instead, a cased hole DST method has been selected in which DST tools are set in a 7-inch liner, and tubing-conveyed perforating (TCP) guns are run in the 4.5-inch liner on the bottom of a long tailpipe. The first DST has been successfully completed, with the pressure gauges located at the gauge carriers in the 7-inch liner, several thousand feet above the test interval. Pressure and temperature data from downhole gauges have been analyzed and found to exhibit significant wellbore-phase redistribution effects because of gauge location. This has resulted in significant uncertainty in reservoir characterization. Solutions considering the HPHT and slimhole design have been investigated. We present a unique method of placing the downhole gauges on top of the perforating gun during an HPHT well test operations where formation temperature exceeded 400°F. Five DSTs have been performed using this technique with successful recording of downhole pressure and temperature data, despite the perforating gun shock and hostile environment encountered. A comparison of pressure transient interpretations as well as a comparison of data gathered by the gauges located above the guns (immediately above the perforations) with the data from gauges in the 7-inch liner will be presented to show the potential for incorrect interpretation due to the gauge placement. We will also discuss the unseen behavior of flowing gas temperature at perforation depth based on actual temperature data recorded.

Exploration for heavy oil, in an offshore setting carries special challenges and risks, especially during the well testing phase. Bringing the heavy oil to surface and then disposing of this oil efficiently without polluting the offshore environment is a challenge. Flow testing oil with APIs as low as 8 degrees would be challenging in itself; when this oil is also sour, the challenges are magnified many-fold, especially when considering the limited space on offshore drilling rigs. Saudi Aramco has started a program aimed at exploration and evaluation of heavy oil reserves in the Arabian Gulf. The objective of testing this sour, heavy oil was to obtain reservoir fluid samples, get productivity data and characterize the reservoir. While attempting to dispose of the oil in an efficient manner, initial attempts to test this heavy oil were unsuccessful. Prematurely terminating these tests resulted in not obtaining all of the required test data. A heavy oil team was formed in early 2008 to determine solutions to the inability to properly characterize the reservoir on heavy oil well tests. This multidisciplinary team of professionals held two workshops, where heavy oil experts from major service companies provided their global expertise. This information was then blended with local operational requirements to create a unique well testing design. This design has successfully been implemented in two wells (onshore and offshore). The use of an Electric Submersible Pump (ESP) although common in production scenarios, was successfully implemented for the first time on a heavy oil drill stem test in Saudi Arabia. This paper summarizes the problems associated with testing heavy oil, the options studied, the reasons for selection of the chosen test method, the downsides of the selected plan, the trial testing on land and the successful implementation of the final plan in an offshore environment. It is a summary of the planning process necessary to get a good heavy oil test in a sensitive offshore environment.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractSaudi Aramco has recently embarked on an exploration program targeted at evaluating potential heavy oil reserves, offshore Saudi Arabia's eastern coast. The oil being tested is classified as heavy oil with an API gravity as low as 10 degrees (field measurement). Appraisal well testing in an offshore setting of such low API oil is difficult, especially when environmental considerations are of outmost importance. The tests objectives were to obtain accurate reservoir parameters, collect representative reservoir samples, and dispose of all produced hydrocarbons (heavy oil) without adversely impacting (spill/ polluting) the offshore environment. Being offshore, with limited space availability on jack-up rigs, it was also crucial that the design of the test equipment and procedures take into account the potential presence of Hydrogen Sulfide (H 2 S). This paper will present best practices, experience gained, and lessons learnt from appraisal well testing of heavy oil at offshore locations. Several offshore heavy oil well tests were successfully carried out, where all produced hydrocarbons were flared off without causing spills or polluting the sensitive marine environment.

No abstract