Sequence stratigraphy of the Arab A to C members and Hith Formation, offshore Abu Dhabi

Abstract

The Upper Jurassic Hith Formation and Arab members A, B and C, in central and western offshore Abu Dhabi, consist of 450 to over 600 feet of massive to interbedded anhydrites with varying proportions of limestones and dolomites. A high resolution sequence stratigraphic framework for this important petroleum reservoir interval was developed from core and well log data, and various inorganic geochemical analyses. This data was acquired from wells located at 3 locations spread over 100 kilometers. Nineteen shallowing-upward parasequences, corresponding to fourth and possibly fifth-order cycles, were recognized for the Arab members as follows: A (7 cycles), B (5 cycles), and C (7 cycles). Five parasequences were recognized for the Hith Anhydrite Formation. The Arab parasequences are arranged in a layer-cake stacking pattern and vary in thickness from 6 to 30 feet. These are interpreted to correspond to transgressive-regressive episodes which are driven by low-amplitude sea-level fluctuations (eustacy). The typical parasequence consists of shoal grainstones, representing transgressive system tracts, that pass upward into thin-bedded lagoonal burrowed mud/wackestones, representing the maximum flooding surface. These are overlain by coarse bioclastic grainstones capped by algal laminites and culminate into supratidal anhydrites, which pinchout eastwards. In the west offshore Abu Dhabi the parasequences are thicker and consist of intertidal pack/grainstones overlain by anhydrites.