LUKOIL's geologists in Iraq have confirmed prospectivity of the Mishrif and Yamama horizons upon drilling the first exploratory well, Eridu-1, at the Block 10 project.

Olga Mikhaylova, PR Manager , Region 1

According to ancient Sumerian mythology, Eridu was the first city that appeared on Earth after light was separated from darkness and human civilization came into being. It was here that the Garden of Eden and Tree of Life were located. Today any visitor will find an immense desert with a giant mound, which covers an ancient Sumerian ziggurat.

Walk but a few dozen kilometers from this ancient site, and you'll find a modern oil derrick, the very one that was recently used to drill the first exploratory well, Eridu-1, at the Block 10 project in southern Iraq's Muthanna and Thi Qar provinces. And while local archaeologists prowl the desert to this day in search of ancient ruins, modern oilmen look for riches in the form of giant hydrocarbon reserves.

In 2016 those hopes were finally justified. A 3168-meter well showed the perspective horizons of the Mishrif and Yamama formations.

But the story doesn't end there. Block 10 has become LUKOIL's first project in Iraq that was started from scratch without any prior geological knowledge. The company first had to de-mine 5,665 sq km territory, located 120 kilometers outside of Basra, and then conduct extensive 2D seismic survey.

When LUKOIL launched the Block 10 project, no prior exploratory wells had been drilled in the area. The best data available came from seismic surveys carried out in the 1980s. Eventually around 3500 linear kilometers of old data combined with 2022 linear kilometers of new seismic data would reveal the information necessary to build a structural-geological model of the Block 10 area.

Then came the interesting part. Geologists previously working in Iraq had searched for and found large hydrocarbon reservoirs connected to structural anticline traps. They had surmised that during the Earth's Cretaceous period the area had contained a shallow sea with possible barrier reefs. The reefs and the nearby fragmented limestone may have contained large oil deposits.The geologists suddenly had a model that was based on a non-anticline trap composed of a reef and its fragmented limestone components, which they used to decide where to drill the exploration well.

Thanks to Block 10 team and its manager Victor Nosenkov efforts, we turned a new page in southern Iraq's geological exploration history. Future projects are likely to search for non-structural underground objects not common to the area, which nonetheless may contain significant hydrocarbon reserves. Meanwhile LUKOIL has big plans for Block 10. The trap in question has an area of approximately 300 square km. The company will have to drill more exploration wells here to confirm geological model. The team will also have to conduct 3D seismic survey in the future.

The results of drilling on the Block 10 are a point of pride for LUKOIL and its Japanese partner INPEX, as well as their Chinese BGP and BOHAI subcontractors. Most importantly, this a big success for Iraq. Its oil industry just got a new boost.

"Our success was based on the highquality work and professionalism of our geologists, who were able to bypass analytical traditions and interpret the area's seismic data in a new, informal way. When we saw reef anomalies on the seismic sections, we understood that we should look for reef bodies and everything connected to them instead of the usual structured objects. We analyzed the geological maps of the region, looked at existing reservoirs like Nassiria and Garaf and found a certain pattern to how these anomalies were spread out. Later, when we drilled to the main horizon of the Mishrif formation, we saw the actual body of the reef. It actually existed and is now a major collector holding oil deposits. Our colleagues at Iraq's Ministry of Oil were happy to say that they, too, will now start to use this new approach toward searching for nonstandard oil reservoirs thanks to LUKOIL's efforts. They want to continue their work with LUKOIL, including searching for unstructural stratigraphic traps."

GEORGIY ODOLEEV Exploration Manager

Reefs and Structural Traps

Ancient reefs buried within stratigraphic sections are of considerable interest to geologists because they provide paleo-environmental information about the location in Earth's history. In addition, reef structures within a sequence of sedimentary rocks provide a discontinuity which may serve as a trap or conduit for fossil fuels or mineralizing fluids to form petroleum or ore deposits.

A structural trap is a type of geological trap that forms as a result of changes in the structure of the subsurface, due to tectonic, diapiric, gravitational and compactional processes. These changes block the upward migration of hydrocarbons and can lead to the formation of a petroleum reservoir.

Structural traps are the most important type of trap as they represent the majority of the world's discovered petroleum resources. The three basic forms of structural traps are the anticline trap, the fault trap and the salt dome trap.

Source: Wikipedia