摘要：

Outcrop studies integrated with subsurface data of core, cuttings and different well logs were used to investigate reservoir characteristics of the Middle-Late Eocene Pila Spi Formation at Taq Taq oil field of Kurdistan Region of northeastern Iraq. Reservoir studies include petrographic investigations, microfacies analyses and petrophysical evaluation in an attempt to provide an insight regarding the reservoir potential. The Pila Spi Formation is subdivided into four distinctive lithofacies (P1-P4), characterized by dolostones, dolomitic limestones and limestones. Several types of dolomite were recognized ranging from early diagenetic fenestral fine crystalline to late diagenetic coarse crystalline dolomite, which had positively influenced the reservoir characteristics by enhancing inter-crystalline, intra-skeletal and micro-vug porosity, especially for lithofacies units P2 and P3. Reservoir porosity is heterogeneous in distribution and ranges from 5 to 20%. Using porosity cut-off values of 8.2%, and water saturation cut-off values of 24%, six porosity units were identified from top to bottom (PU1-PU6). The best unit is PU2 (15 m thick), which is characterized by medium crystalline dolomite mosaic with average effective porosity of 21.5%. Permeability ranges between 0.1 and 1 md. Flow unit differentiation is discussed in term of porosity-permeability cross-plot and reservoir pore-throat classification (R35). Results indicate that most of the Pila Spi reservoir is of micro-port (matrix) flow type. However, reservoir quality enhancement is attributed to fracturing.

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