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Abstract: The Kurdamir-Topkhana Field of Kurdistan - Modelling Clinoforms, Diagenesis, and Porosity Distribution

Jean Hsieh, Normand Begin, Maz Qayyum, Talisman Energy Inc., part of the Repsol Group

The Kurdamir-Topkhana field of Kurdistan is a carbonate oil and gas reservoir that was deposited in a passive margin ramp setting during the Oligocene. It is dominated by alternations of grainstone/boundstone/rudstone and packstone/wackestone beds. Reflux dolomitization early in the Miocene has noticeably increased, in places, both the porosity and connectivity of at least the Upper reservoir interval, as interpreted from seismic inversion data. The Lower reservoir interval was less affected by dolomitization and exhibits good porosity development within individual clinoforms, but much poorer connectivity between clinoforms. The entire reservoir interval is located within two anticlinal four-way closures formed above the roof thrust of an anti-formal stack developed within deeper Mesozoic carbonates; much of the observed fracture network is a result of this deformation. Modelling this complex reservoir presents significant challenges, not least because of the interdependency of many of the reservoir’s key characteristics.

The depositional and diagenetic history of the reservoir was determined through the study of several cores cut from the wells drilled in the field along with an understanding of the regional setting. A 3D seismic survey was inverted for acoustic impedance and the presence of gas-filled porosity can be imaged through the AI volume. Combining the understanding gleaned from the core and seismic data with the fracture data from borehole image logs, a detailed reservoir model was built. The strategy and conceptual models used for building this geostatistical model will be presented, along with our interim products and the lessons we have learned thus far on combining data of different scales.

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Jean

Jean Hsieh

Repsol

Gulf Coast

Abstracts

  • 30515 From 2009-2011, drilling of several exploration wells in the Topkhana and Kurdamir blocks in southeast Kurdistan, Iraq has delineated a giant oil and gas field with over 4 billion barrels of liquids and over 6 TCF of gas in place. This Oligocene-aged, carbonate-hosted hydrocarbon accumulation is a combination structural and stratigraphic trap. The entire Oligocene succession is composed of interbedded limestone and dolomites with marlstones which were deposited in a carbonate ramp setting. The Oligocene Kirkuk Group is regionally composed of middle ramp foraminiferal and red algae grainstones as well as coral boundstones/rudstones that likely form small bioherms.  Much of the reservoir has good matrix porosity, but low permeability. However, reservoir quality is highly dependent on both the original depositional facies as well as the degree of dolomitization. Predicting the spatial distribution of the best reservoir quality is challenging. Early diagenesis includes micritization, cementation and compaction. These processes modify the depositional facies, but do not affect the porosity and permeability significantly. Dolomitization is the major diagenetic process that impacts reservoir quality. Oxygen and strontium isotopes suggest reflux dolomitization began near the end of the Oligocene and extended into the earliest Miocene. Full dolomitized facies have the best reservoir quality. Partially dolomitized facies generally have poorer permeability than non-dolomitized facies. Later diagenetic events, anhydrite and calcite cementation, have locally reduced permeability. The late stages of diagenesis are likely associated with the tectonic evolution of the Zagros fold-and-thrust belt. The spatial distribution of the best reservoir quality is dependent on where there is thorough dolomitization or preservation of original depositional porosity and permeability. Several cores were collected that span the range of depositional environments, diagenetic overprint and reservoir quality. We will present examples of each of these facies as well as supporting material that leads us to our current understanding of the reservoir. Using this base of knowledge, we can continue to interpret the recently collected and processed 3-D seismic data to better predict the spatial distribution of the best reservoir quality rock. Reservoir Quality Variations in the Oligocene Kirkuk Group at Topkhana-Kurdamir, Kurdistan, Iraq http://www.aapg.org/career/training/in-person/visiting-geoscientist/abstract/Articleid/30515/reservoir-quality-variations-in-the-oligocene-kirkuk-group-at-topkhana-kurdamir-kurdistan-iraq
    Reservoir Quality Variations in the Oligocene Kirkuk Group at Topkhana-Kurdamir, Kurdistan, Iraq

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