Typically the reservoir evaluation in deep water wells (DWW) drilled by Petroleos Mexicanos (PEMEX) in southern Gulf of Mexico has been made conventionally using Drill Stem Testing (DST) operations that can take up to 23 days. This represents a significant investment in cost and time to the operator in their effort to evaluate reservoirs. The challenge was to evaluate more accurately and efficiently to reduce costs and improve reservoir characterization in these deepwater plays.

In this paper, wireline formation testers (FT) are used in openhole DWW for a variety of applications including characterization of the fluids and determination of key reservoir parameters by interval pressure transient testing (IPTT), also referred to as a mini-DST. Real-time monitoring, analysis and job optimization by senior technologists are essential steps in performing a successful logging program. Historically, the wireline programs to evaluate the zones of interest in the Tertiary approximated 8 days that included several gas zones. The new protocol brought an operational advantage to PEMEX by reducing the time required to identify and characterize zones of interest compared with conventional methods. The results included optimization of the production test programs and reduced time/costs for the well production testing stage.

The project has four major steps:

The first stage includes the identification of gas bearing sandstones and will determine the preliminary program. The highly laminated structures are evaluated with special wireline logs that include nuclear magnetic resonance (NMR), high resolution imaging and elemental capture spectrometry. After the zones are identified, the pressure profile will be analyzed with a PressureExpress (XPT) tool that is wireline combinable and allows for efficient pressure formation testing.

In the second stage, the pressure gradients are evaluated resulting in fluid types in the reservoir and mobilities for each flow unit. These results will be used to define the Mini DST stations.

The third phase involves the use of the Modular Formation Dynamics Tester (MDT) with the Live Fluid Analyzers (LFA) to characterize the fluid type in each layer. Formation fluid samples are taken according to the program’s acquisition priorities. The dual packer MDT module allows for isolating each individual layer to perform mini-DST’s that can be used to evaluate and determine the formation’s permeability and skin factor.

Finally a nodal analysis was performed using the permeability values from mini-DST. The results showed very good agreement between the rate predictions from the MDT fluid and pressure data versus the conventional DST results. This helped Pemex in strategic forecasting of production rates and reserves classification while saving rig time.

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