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<p>The present study evaluates the heterogeneity of the reservoir and the generation potential of the X field in the northwestern Zagros Basin, Kirkuk Governorate, Iraq. Four wells (X-89, X-91, X-92, X-122) penetrating the Tarjil, Baba, and Bajawan formations were used to estimate the volume of shale (Vsh), porosity (PHIT and PHIE), water saturation (Sw), and net-to-gross ratio (N/G). These parameters were then incorporated into 3D reservoir models of the Petrel software using the Sequential Gaussian Simulation (SGS) method to map the spatial distribution of reservoir quality. Cross-plots of N-D and M-N illustrate the dominance of dolomite as the main reservoir lithology with variable dolomitic limestone contents. Integration of lithological findings with wth petrophysical parameters and 3D modeling to enhance reliability since cross-plotting is inadequate to characterize reservoir quality. Vsh values in the Tarjil Formation are 3–31%, with PHIE of 5–22% in two wells. Well X-92 has PHIE values ranging between 5 and 20%, X-122 has higher quality with PHIE of 12–22% and low Sw (2–5%), with net pay up to 20.0&#xa0;m and N/G up to 97.6%. Similarly, the promising Baba Formation (100–120&#xa0;m) exhibits improved reservoir properties, characterized by low Vsh (1–37%), high PHIE (4–27%), and Sw between 2 and 38%, with net pay up to 40.5&#xa0;m, and N/G reaching up to 94.6%. These findings are also confirmed by the low bulk volume of water (BVW) of less than 5% confirming movable hydrocarbon contents in these intervals. Conversely, the Bajawan Formation, which is the thickest Oligocene layer (120–140&#xa0;m), is more heterogeneous as indicated by variable Vsh values that vary between 1 and 91%, PHIE of 1–29%, Sw of 4% to 100%, net pay up to 14.5&#xa0;m, and N/G commonly &lt; 20%. 3D and 2D models indicate lateral and vertical heterogeneity where high reservoir quality zones are clustered mainly around X-91, X-92, and X-122 wells, especially in the central and northwestern part of the field, with hydrocarbon-bearing zones occurring between 1410 and 1710&#xa0;m. Overall, the cross-plotting interpretation, CPI evaluation, and 3D petrophysical modeling findings illustrated that the Tarjil and Baba formations as the major hydrocarbon-bearing zones in the Zagros Basin.</p>

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Petrophysical evaluation and 3D reservoir modeling of oligocene intervals in the Zagros Basin, Iraq

  • 期刊论文

  • 发表日期：

    2026年2月16日

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  • Ali S. Abbas,
  • Ali H. Dohan,
  • Doaa T. Fadhil,
  • Abbas F. Gharib,
  • Mohammed Y. Najmuldeen,
  • Ayshagul S. Najmuldeen

摘要

The present study evaluates the heterogeneity of the reservoir and the generation potential of the X field in the northwestern Zagros Basin, Kirkuk Governorate, Iraq. Four wells (X-89, X-91, X-92, X-122) penetrating the Tarjil, Baba, and Bajawan formations were used to estimate the volume of shale (Vsh), porosity (PHIT and PHIE), water saturation (Sw), and net-to-gross ratio (N/G). These parameters were then incorporated into 3D reservoir models of the Petrel software using the Sequential Gaussian Simulation (SGS) method to map the spatial distribution of reservoir quality. Cross-plots of N-D and M-N illustrate the dominance of dolomite as the main reservoir lithology with variable dolomitic limestone contents. Integration of lithological findings with wth petrophysical parameters and 3D modeling to enhance reliability since cross-plotting is inadequate to characterize reservoir quality. Vsh values in the Tarjil Formation are 3–31%, with PHIE of 5–22% in two wells. Well X-92 has PHIE values ranging between 5 and 20%, X-122 has higher quality with PHIE of 12–22% and low Sw (2–5%), with net pay up to 20.0 m and N/G up to 97.6%. Similarly, the promising Baba Formation (100–120 m) exhibits improved reservoir properties, characterized by low Vsh (1–37%), high PHIE (4–27%), and Sw between 2 and 38%, with net pay up to 40.5 m, and N/G reaching up to 94.6%. These findings are also confirmed by the low bulk volume of water (BVW) of less than 5% confirming movable hydrocarbon contents in these intervals. Conversely, the Bajawan Formation, which is the thickest Oligocene layer (120–140 m), is more heterogeneous as indicated by variable Vsh values that vary between 1 and 91%, PHIE of 1–29%, Sw of 4% to 100%, net pay up to 14.5 m, and N/G commonly < 20%. 3D and 2D models indicate lateral and vertical heterogeneity where high reservoir quality zones are clustered mainly around X-91, X-92, and X-122 wells, especially in the central and northwestern part of the field, with hydrocarbon-bearing zones occurring between 1410 and 1710 m. Overall, the cross-plotting interpretation, CPI evaluation, and 3D petrophysical modeling findings illustrated that the Tarjil and Baba formations as the major hydrocarbon-bearing zones in the Zagros Basin.