Thirty cores from the Late Jurassic uppermost Jubaila, Arab-D reservoir and Arab-D anhydrite in Hawiyah (Ghawar) and Harmaliyah fields, eastern Saudi Arabia were studied to document the detailed facies stacking and high resolution sequence stratigraphy. The Jubaila-Arab-D interval is a shallowing upward succession of two composite sequences, in which the Arab-D reservoir and overlying anhydrite have up to twelve higher frequency sequences. Both fields are strikingly similar in terms of facies, parasequences, and vertical stacking of facies. The direction of the progrodaion is east and northeast and that is supported by northeast thickening of the Arab-D reservoir and by the stromatoporoid and Cladocoropsis facies progrodation. This suggests that the Arab-D reservoirs in both fields may represent part of a single carbonate ramp with subtle syndepositional highs. The scarcity of exposure surfaces with caliche in the Arab-D reflects the relatively high subsidence rate (~6 cm/k.y.) relative to the small sea level oscillations that formed the succession coupled with the long term shallowing trend up through the section. Dolomites from the Arab-D reservoir zones 1 to 4, in both fields were studied to better understand their origin. The dolomites are dominantly fabric destructive medium to coarse grained types, and much less common fabric retentive finer grained dolomites in the uppermost Arab-D reservoir. The δ¹³C values are rock buffered while the δ¹⁸O values have been greatly shifted toward negative values relative to unaltered early dolomite, and dolomite crystal rims generally have lighter δ¹⁸O values than cores. The dolomites were initiated at different times during shallowing phases on the Arab-D platform, with the bulk of the fabric destructive dolomites forming under near normal salinities, while the fabric preserving dolomites formed as a result of dolomitizing aragonitic sediments from more evaporated waters. With increasing burial and increasing temperature, the early dolomites re-equilibrated with the increasingly warm basinal brines resulting in replacement of cores, and dolomite cementation by rim overgrowth. Progressive plugging of higher dolomites earlier, caused some of these to retain slightly heavier δ¹⁸O values and marine seawater Sr isotope values while those that remained permeable developed very light δ¹⁸O values and more radiogenic Sr values, shifting them toward the field of late stage baroque dolomite. / Ph. D.

The Late Jurassic Arab D Formation in Saudi Arabia hosts the some of the world’s largest hydrocarbon reservoirs including Ghawar, the world’s largest oil field, and Khurais, the world’s largest supergiant to come into production in the last 5 years. Despite the vast oil reserves within the Arab D, and the central role of this reservoir at Ghawar in making up short-falls in global production, our understanding of the much fundamental characterization work both in terms of modern sequence stratigraphic reservoir frameworks and linked structural/fracture characterization. This study of Arab D reservoir at Qatif, immediately to the north of Ghawar, provides one of the first looks at a modern sequence analysis of this producing interval and illustrates that porosity zonations, and ultimately flow unit architecture may be substantially different than currently in use. The Arab D of the Arabian Plate is a carbonate ramp system of exceedingly low angle (<1o) developed during a low-eustatic-amplitude greenhouse Milankovitch setting. Combined macroscopic and petrographic data analysis allowed recognition of nine depositional facies: 1) spiculitic wackestone, 2) Planolites-burrowed wackestone, 3) bioturbated skeletal-peloidal packstone, 4) pelletal packstone, 5) peloidal-skeletal grain dominated packstone, 6) peloidal-skeletal grainstone, 7) skeletal-ooids grainstone, 8) cryptalgal laminites and 9) anhydrite. The depositional facies defined are used to interpret three facies tracts from deep to shallow across the ramp profile: 1) low energy sub-storm wave base (SWB) dominated facies that may illustrate disaerobic tendencies, 2) high energy within-fair-weather-wave-base ramp-crest or mid-ramp facies including foreshore and upper shoreface oolitic and skeletal grainstones that define one of the key reservoir pay zones and 3) back-barrier tidal flats consisting of cryptalgal laminites, sabkha-type anhydrites, and salina-type anhydrites. Three high frequency sequences are defined: QSEQ 1 is asymmetrical, dominated by subtidal lithofacies; and QSEQ 2 and QSEQ 3 are symmetrical and record a complex history of the fill on an intrashelf basin. Detailed cycle-scale correlations using core-based cycles and wireline log patterns allowed a cycle-scale correlation framework to be established that illustrates a north to south progradation of the Arab D reservoir strata, building landward from the Rimthan Arch. Diagenetic features observed in the Arab D reservoir include fitted fabric (chemical compaction), dolomitization, and cementation. These features play a major role altering reservoir quality properties as they essentially control fluid flow pathways which ultimately alter primary porosity and permeability. / text

Sub-seismic meter-scale interwell depositional facies heterogeneity and microporosity are critical components behind properties and fluid flow heterogeneities of many Middle eastern giants and supergiants carbonate reservoirs. The Hanifa reservoir is one of the most petroliferous Arabian carbonate strata that hosts the notoriously heterogenous stromatoporoid/coral facies. Paradoxically, the 3D geometry, architecture, and subsurface implication of these facies are poorly understood or completely ignored in most studies. The lower part of the Arab-D reservoir is dominated by microporosity. However, studies that investigate the influence of microcrystals that host microporosity to petrophysical properties and upscale it to reservoir simulation grid-block scale are modicum. This dissertation aims to bridge this paucity by performing an advanced three-dimensional outcrop analog investigation and multiscale microporosity studies of these formations. We document the 3D morphology and spatial distribution of the stromatoporoid/coral facies part of the Hanifa reservoir outcrop analog in Wadi Birk, Saudi Arabia, using 3D drone-based digital outcrop model, cores, near-surface geophysical measurements, and deep-learning methodology. We construct a high-fidelity outcrop analog reservoir model from these observations and utilize it for dynamic simulation during waterflood. Further, based on the Upper Jubaila Formation outcrop analog in Wadi Laban, Saudi Arabia, we investigate the influence of microcrystals that host microporosity on petrophysical properties. We upscale the relationships and utilize seismic-derived acoustic-impedance data to arrive at reservoir grid block-scale microporosity distribution. Our results provide a novel and valuable insight into the growth morphology of the stromatoporoid/coral buildups and their relationship with subsurface fluid flow previously unknown for the Hanifa reservoir. The results demonstrate that sweep efficiency is greatly influenced by the interaction between the buildup clusters with the background strata. Our results also provide a practical method to integrate key sub-grid scale micro and macro heterogeneities into reservoir grid block-scale property models.