Petrographic and geochemical characteristics of different dolomite types, and their textures and fabrics in Asmari reservoir,Shadegan Oil Field

Authors

1 National Iranian South Oil Company (NISOC), Ahvaz, Iran

2 Dept., of Sedimentary Basins and Petroleum, Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran

3 Prof., Dept., of Geology, Ferdowsi University of Mashhad, Mashhad, Iran

Abstract

The Oligocene – Miocene Asmari reservoir with 400 meters thickness in the Shadegan Oil Field consists of limestones and porous dolostones associated with sandstones, and shales. Dolomitization, as the most important diagenetic process, affected the Asmari reservoir and thus played a major role in the formation of the pore spaces structure, final flow capacity and heterogeneity of the Asmari reservoir. Dolomite types based on geochemical and textural characteristics, especially crystal size and shape includes: (i) very finely-crystalline, fabric-retentive dolomite (D1), (ii) fine to medium-crystalline, fabric-retentive dolomite (D2); (iii) medium to coarse-crystalline, fabric-destructive dolomite (D3); and (iv) very coarsely-crystalline, non-planar saddle dolomite (D4).Two types of fabric named fabric selective dolomitization and pervasive dolomitization were identified in dolomite crystals. Based on textural classification, 6 different textures including idiotopic, hypidiotopic or (idiotopic-S), xenotopic or non-planar-A (anhedral), idiotopic-C or planar-C (cement), porphyrotopic and poikilotpoic texture for dolomite crystals is identified.
The mean concentration of strontium in dolomite samples is 483 ppm and the mean concentration of sodium is 1618 ppm which indicates the enriched amounts of strontium and sodium in these samples. The mean values of iron in dolomite samples are 3111 ppm and the mean concentration of manganese is 111 ppm. Dolomites (D1) with low Fe and Mn content may have formed during the early stages of diagenesis in an oxidizing environment. High amounts of iron and manganese in D3 and D4 dolomites indicate deposition in a reducing environment during shallow to relatively deep burial.

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History

  • Receive Date: 10 October 2023
  • Revise Date: 10 December 2023
  • Accept Date: 16 December 2023

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