Reservoir sampling and pressure (RS&P) testing acquisitions are fundamental in Exploration settings to evaluate reserves and/or well productivity. Wireline Formation Testing (WFT) is well known in our industry for conventional reservoirs. However, there has not been any available WFT technology to perform these acquisitions in Naturally Fractured Carbonate (NFR) formations under HPHT conditions. A new platform developed for all terrains of formations and environments was used for the first-time in in Mexico, allowing to conduct a full RS&P program to delineate reserves in a large gas condensate reservoir.

The new platform consists of a new focussed radial probe inlet, featuring a dual flowline with dual downhole pumps to allow focused sampling mode. Given the larger flow area of the new probe system, flow tests can be conducted in sub mD permeability zones, typical in NFR carbonates, and fluid identification can be performed in-situ while flowing thanks to a group of new sensors. Sampling for PVT analysis is achievable, and sample quality is ensured via the focused sampling system. Post sampling buildups provide pressure transient test data which allow characterizing the layer productivity.

The new technology was employed in two appraisal wells belonging to the Veracruz basin in Mexico. The reservoir facies are constituted by packestone and wackestone carbonates belonging to the mid Cretaceous, over very large thickness. Reservoir quality lies in vugular porosity and micro-fractures; however, the matrix porosity is low. The petroleum system originates from the Upper Jurassic source rocks which led to gas condensate hydrocarbons at the reservoir level today.

Preliminary simulations indicated that despite the low matrix quality, with the new platform, it would be possible to test and recover quality samples within 4-8 hours depending on the invasion depth scenario and with a drawdown below 300 psi. Four conclusive tests were made in the first well which helped the operator delineate reserves and two conclusive tests were made in the other well fulfilling objectives and following the designed test durations and outcomes, in temperature conditions up to 182 °C and pressure of 20kpsi. The lowest mobility flow test and fluid identification was conducted in 0.06 mD/cP.

The new platform test results compared very well with actual test results that were conducted.

These two cases highlight the possibility to test and sample fluids in HPHT conditions, NFR reservoirs with tight matrix properties with the new formation testing platform, in environments where previously formation testing was not possible. A significant amount of Mexican carbonate reservoirs faces this extreme environment.

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