Depositional environment and petrophysical properties study of mishrif formation in Tuba oilfield, Southern Iraq

Abstract EN

Mishrif Formation is considered as one of the main productive reservoirs in southern of Iraq that comprises an important place into the stratigraphic column of the middle Cretaceous.

It reflects the continuous deposition on a shallow carbonate platform developed during theUpper Cenomanian – Early Turonian period.

Core samples were collected from selected wells in Tuba oilfield, southern Iraq (Tuba-4, 5, 6, 7, 8, and 12).Petrographic and microfiches studies have been made by means of microscopic examination of (150) thin sections.

Microfiches analysis showed the occurrence of rudist, red and green algae, large and small benthic Foraminifera, Echinoid and Pelloidal zone and they form the major part of micrite or spary calcite groundmass.

Five main Paleoenvironment were identified within Mishrif succession represented by deep marine, shallow open marine, restricted open marine, rudist biostrom and shoal.

In which there were distinctive distribution of main and sub micro facies of diverse in both effect and intensity by dissolution, dolomitization, neomorphism, cementation and micritization.

The most effective diagenesis processes were both dolomitization and dissolution.

On the other hand, well log analysis revealed the domination of primary porosity (Interparticle and Intraparticle) and minor content of secondary porosity (Vug, moldic and channel).

Five reservoir units were identified in the studied sections of Mishrif Formation (mA, mB1-1, mB1-2, mB2-1and mB2-2).

These units characterized by a high total porosity located within shoal, shallow open marine and rudist biostrom facies.

The reservoir facies of good oil prospects that have been diagnosed are: mud dominated Wackst one, grain dominated, bioclas ticpelloidal and / or pelloidal Grainst one micro facies, Bondstone, rudist Pack stone, coralline algal Wicks one packs one micro facies and dolomitic Lime Mudstone-Wicks one micro facies.