Acquiring Formation Pressure Data in Low Permeability Reservoirs as an Aid to Evaluating Reservoir Connectivity

Peter Weinheber¹, Edward Boratko¹, EB Dussan V¹, Marco Rueda¹, Adriaan Gisolf¹, Kilamba Diogo Contreiras², Francisco Van-Dúnem², and Robert Spaeth^3
1Schlumberger, Luanda, Angola
²Sonangol P&P, Luanda, Angola
³Marathon, Houston, TX

The data provided by wireline formation testers (WFT) is critical to the evaluation and understanding of petroleum reservoirs. Pretest pressures, gradients and mobilities are generally regarded as essential inputs to the reservoir evaluation model. However, acquiring this data in low permeability reservoirs can prove challenging. There is no stable flowing pressure during the pretest, build-up times can be long and the confidence level of the final pressure is often uncertain

New generation formation testing tools that extend the range of pretest rates and volumes have greatly improved the quality of WFT data acquired in low permeability reservoirs. Job design and planning has always been important for the proper acquisition of formation test data. Several new options, made available through the enhanced capabilities of the new generation of tools, makes packer/probe and parameter selection even more critical. Additionally, the challenges of the low permeability environment require specific attention to real time quality control and evaluation of the test data as it is acquired.

In this paper we use examples to discuss best practices for formation testing in low permeability reservoirs. We show the pitfalls that can arise with incorrect test design as well as the improvements brought by the latest tools when correctly configured. While there is usually confidence in the mobility data from high permeability reservoirs the numbers generated from low permeability reservoirs is often suspect: pretest volumes are typically very low and there is no stable flowing pressure.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery