This paper presents the first application of a new wireline formation tester, the Modular Formation Dynamics Tester (MDT*), that successfully recovered bottomhole samples of a near-critical reservoir fluid. The tester device achieved this by controlling and minimising the pressure drop during sampling; in some cases just 0.5 bar was sustained. Full PVT laboratory study confirmed the purity and representativity of samples taken in this manner from two wells. Variations in the fluids’ properties with depth as determined from samples taken during DST's on older wells were subsequently revised to take into account this newer, more accurate fluid description.

The decision to sample a near-critical fluid using this wireline tester on the first well involved an element of uncertainty since such an operation had never been attempted before. However, in the case of the second well the decision was based on the knowledge and experience gained from the first, where overall performance of the tester and PVT quality of the samples were excellent. In fact, sampling in openhole with a wireline formation tester as explained above actually allowed dispensing with planned DST's in both wells, and hence proved to be a very cost-effective solution.

The same wireline tester that was used for sampling comes equipped with a new single-crystal quartz gauge, which displays quartz sensor accuracy and resolution but performs like a strain gauge in terms of dynamic response characteristics. Pressure profiles interpreted in all wells in the field, including data from the new quartz gauge, exhibit the typical characteristic of critical to near-critical reservoir fluids - no discernible gas-oil contact. The reservoir management implications of this result are discussed in the paper.

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