Assessment of unconventional oil and gas resources in the Jurassic Sargelu Formation of Iraq, 2014

The U.S. Geological Survey (USGS) quantitatively assessed the potential for unconventional (continuous) oil and gas resources within the Jurassic Sargelu Formation of Iraq. Organic-rich shales of the Jurassic Sargelu Formation are one of the main petroleum source rocks for conventional fields in the Arabian Peninsula. The Sargelu Formation consists of marine shales, with as much as 10 weight percent sulfur-rich Type IIS organic matter, deposited in a relatively deep, anoxic Jurassic depocenter. The potential for volumes of oil retained in the Sargelu Formation source-reservoir rock system following oil migration, cracking, or degradation is the focus of this assessment. Conventional oil and gas resources of Iraq were assessed by the USGS in 2012.

The USGS assessment methodology consists of a well-performance approach that recognizes the geologic variability within assessed reservoirs. For non-U.S. assessments, the USGS assesses shale-gas or shale-oil reservoirs that (1) contain greater than 2 weight percent total organic carbon (TOC), (2) are within the proper thermal maturity window for oil or gas generation, (3) have greater than 15-m thickness of organic-rich shale, and (4) contain Type I or II organic matter. These specific USGS criteria when applied to any given shale-oil or shale-gas reservoir might significantly reduce the potential resource assessment area compared to maps made with greater than 1 weight percent TOC.