Reducing Formation Testing Uncertainties Based from Data Integration Technique by Identifying Fluid Conductive Fractures in Basement Reservoirs

Ali Baradi¹ and Jan Steckhan^2
1Geoscience, Baker Hughes, Abu Dhabi, United Arab Emirates
²OMV, Vienna, Austria

Major hydrocarbon accumulations in Yemen are contained in fractured Basement. Along drilled basement sections, only restricted intervals account for flow. Porosity is mainly secondary, with fractures being the most important often only component.

The main challenge is as follows:
Which fractures are fluid conductive i.e. how to decide which fractures should be tested with a formation tester in order to reduce logging times/costs?

The challenge to accurately characterize the fractures is mainly related to the higher matrix densities, as a result of which “conductive” and “non-conductive” fractures have a similar response on both acoustic and micro-resistivity images (dark conductive on resistivity and low reflectance on the acoustic image). Hence the “classic” approach whereby a conductive fracture is interpreted as an open fracture is not valid for this specific case.

Baker Atlas Geoscience together with OMV has developed an integrated technique that increases the possibility of distinguishing fluid conductive fractures from non-conductive ones. An integration of acoustic transit time image, electrical/acoustic images, Stoneley wave, acoustic reflectance mapping and mud reports allowed the subsequence pressure testing program to be optimal.

The process resulted in a workflow for rush image processing in order to determine fractures with a good probability of flow and hence optimizing of the testing program for the dual packer formation tester.

OMV, an independent oil company exploring the Yemen basement, adopted the technique with success and quoted: "… it worked fine for almost 90% of the major fractures (40% success rate in the previous well)".

An integration of image data, core data and advanced acoustic application (near wellbore imaging) was conducted to evaluate the fractures properties with lithology along the well pathway.

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