Diagenetic factors controlling reservoir quality in the Faraghan Formation (Lower Permian), Darang Field, Southern Iran

The role of diagenesis in affecting (reduction or enhancement) reservoir quality in the Faraghan Formation in Darang #1 well was investigated. The Faraghan Formation is mainly composed of sandstone facies along with minor mudstone and siltstone and grades upward into mixed carbonate –siliciclastic facies and then to Dalan Formation carbonates. Depositional environment of this formation comprises various sub-environments of a delta setting in the lower part of the formation which grades upward into a shallow marine clastic environment in the upper part. The processes enhancing reservoir quality include dissolution of carbonate grains and cements and alteration of feldspar grains. Burial history diagram shows that after deposition during Lower Permain, the formation underwent a rapid burial up to 1000 meters below sea level in Upper Permian. Then a slight uplift (about 100 meters) and gradual burial followed up to Mid- Jurassic. Afterwards the formation experienced a series of rapid and moderate uplift from Mid-Jurassic to Tertiary when the formation uplifted to around 2500 meters above sea level. The suitable conditions resulting in dissolution took place in shallow buried sandstones. These conditions occurred two times during burial history: at the early stages of eodiagenesis and during telodiagenesis. The major processes deteriorating reservoir quality include compaction and cementation. Major cement types include carbonate cements (dolomite, siderite), clay cements (kaolinite, sericite, chlorite), silica cement and pyrite cement. The most abundant cement is the carbonate cement especially dolomite. The dolomite cement occurs as intergranular and poikilotopic forms. The most frequent clay cement is sericite which dominates in sitstones and lithicarenites. Silica cement, where present, fills all the pore spaces. The least frequent cement type is pyrite which is found in two forms of poikilotopic and framboidal. Where it is found in the form of poikilotopic cement, it massively fills the pore spaces and deteriorates the porosity and permeability of the sandstones

Orbital obliquity evolution during the late Paleozoic ice age across the northeastern gondwana: Implications for regional sea-level change trigger and reservoir quality assessment

Orbitally-induced cycles build stratigraphic sequences on time spans ranging from several thousand to several million years by altering depositional conditions. Previous works have shown that the gas-bearing Faraghan Formation (Cisuralian) has been impacted by orbitally-forced climatic change, resulting in the development of sedimentary sequences on astronomical cycle timescales. Obliquity evolution has been observed in the Faraghan Formation, with ∼1.2 Ma and ∼173 ka modulation cyclicities recorded. We attribute a strong sedimentary noise observed in the Faraghan Formation, which is distinct from the other noises, to a transregional sea-level rise, most likely correspond to MFS P10. The prolific gas zones (PGZ) in the Faraghan Formation are in consistent relationship with obliquity maxima and depositional noise events, which are associated with high obliquity power. This constant offers the hypothesis that obliquity altered the sedimentary regime in such a way that favorable conditions for reservoir quality development occurred. The ∼173 ka obliquity modulation cycle is recorded from the Late Paleozoic. It is postulated that this periodicity was the causal mechanism for the creating of the Faraghan Formation's fifth-order sequences. The reconstructed sea-level patterns from sedimentary noise modeling (DYNOT) confirm the three third-order sequences proposed for the Faraghan Formation by displaying three different sedimentary noises. The detected ∼1.2 Ma obliquity modulation cycles match the ∼1.2 Ma periodicities filtered from the DYNOT median values, indicating that the ∼1.2 Ma orbital cycle is one of the primary drivers of regional sea level. ∼1.2 Ma obliquity modulation cycles are correlated with third-order sequences, implying that the aforementioned cycle was one of the key mechanisms causing the creation of these third-order sequences