Formation Evaluation Lessons Learned in Thrust & Belt Frontier Exploration Wells - Kurdistan Region (IRAQ)

Lessons Learned presented herewith could be summarized as Knowledge gained through the solution to a problem that has been implemented and proven to be effective.

In this case predrilling Formation Evaluation challenges in this frontier exploration region (Iraqi Kurdistan) differed from execution phase requirements. Solutions provided and execution issues to cope with the real Formation Evaluation challenges are presented herewith, as a start up for discussion.

It is worth noting that Pre/drilling scouting concerning available technology in country helped to define required Formation Evaluation program and provide flexibility, even with an active contract, to mobilize required tools.

Low Porosity Fractured Carbonate presents several challenges from data acquisition and Formation Evaluation point of view. Experience gained during the drilling campaign demonstrated that:

1. Error tolerance in porosity evaluation is very low.
   • Diversified porosity data acquisition, epithermal neutron and Nuclear Magnetic Resonance, was paramount for enhanced porosity evaluation. The former was less affected by borehole environment and the latter is independent from lithology and pore space hydrogen.
   • Accurate knowledge of reservoir mineralogy to minimize impact of any kind of anhydrite content. Induce Gamma Spectroscopy, even without chemical radioactive source, was a useful technology.
2. Sub hydrostatic reservoir conditions. Even though just minor losses occurred, wireline logging pressure data demonstrated that the reservoir was sub-hydrostatic. Lessons learned in this region demonstrates that even under this circumstances (sub hydrostatic carbonate reservoirs) wireline logging pressure data is able to provide accurate fluid gradient even in low motilities scenario. Accurate stations selection, variable fluid chamber tool and exploration boldness proved to be paramount.
3. Formation Evaluation workflow (technology in country) helped to define final logging acquisition program and cope with operating program modifications. Fracture analysis from Electrical Borehole Images and Full Waveform Acoustic tools was also integrated for reservoir summation inputs.