To date, the Lower Jurassic Butmah Formation (also known as the Sarki Formation) has not widely been regarded as a productive target for hydrocarbon exploration in Kurdistan. However, detailed sedimentological and structural evaluation of core acquired from four wells in the Shaikan and Sheikh Adi Fields, together with test data has yielded promising results. These studies have determined that fracture style, intensity and fill vary according to lithology. Lithology types penetrated in core include a range of dolomitic facies intercalated with anhydrite and limestones.
The mid-upper section of the Butmah Formation is characterised by lithologies and textures indicative of shallow tidal / algal flat deposits whereas deposition in a shallow, locally agitated, shelfal or lagoonal setting is inferred for the uppermost section. The succession demonstrates an overall upwards deepening or transgression. This study presents the results generated from core logging and petrographic analysis and attempts to characterise the formation in terms of depositional facies and broad sedimentary trends.