Petroleum reservoir

About: Petroleum reservoir is a research topic. Over the lifetime, 5403 publications have been published within this topic receiving 83535 citations. The topic is also known as: petroleum deposit.

Recognition and Delineation of Paleokarst Zones by the Use of Wireline Logs in the Bitumen-Saturated Upper Devonian Grosmont Formation of Northeastern Alberta, Canada

Abstract: The Upper Devonian Grosmont Formation in northeastern Alberta, Canada, is a shallow-marine carbonate platform complex that was subaerially exposed for hundreds of millions of years between the Mississippian(?) and Cretaceous. During this lengthy exposure period, an extensive karst system developed that is characterized by an irregular erosional surface, meter-size (several feet) dissolution cavities, collapse breccias, sinkholes, paleosols, and fractures. The karsted Grosmont Formation, which contains giant reserves of bitumen, subcrops beneath Cretaceous clastic sediments of the giant Athabasca tar sands deposit. The paleokarst in the Grosmont Formation can be recognized on wireline logs in relatively nonargillaceous carbonate intervals (<30 API units on the gamma-ray log) as excursions of the caliper log, off-scale neutron-density porosity readings, and severe cycle skipping of the acoustic log. The paleokarst is more prevalent in the upper units of the Grosmont Formation, and the effects of karstification decrease toward stratigraphically older and deeper units. The paleokarst usually occurs within 35 m (115 ft) of the erosional surface. The reservoir properties of the Grosmont Formation (e.g., thickness, porosity, permeability, and seal effectiveness) are significantly influenced by karstification. Depending upon the location, karstification has either benefited or degraded the reservoir characteristics. Benefits include porosity values greater than 40% (up to 100% in caverns) and permeability values of 30,000 md in severely fractured intervals. Detrimental reservoir characteristics include erosion, porosity and permeability reduction, and seal ineffectiveness.

Prevention of Carbonate Cementation in Petroleum Reservoirs

Abstract: By the time a carbonate unit has been buried to the depths of most petroleum reservoirs, the significant question is often not how did the pores originate but rather, why are they still there. Preservation of porosity, regardless of its origin, is a consequence of one or more of the following mechanisms: (1) minimal burial; (2) reduced burial stress, generally due to overpressured pore fluids; (3) increased framework rigidity, which prevents compaction; (4) exclusion of pore waters by petroleum entry; (5) stable mineralogy; (6) permeability barriers, isolating porous intervals from diagenetic fluids; and (7) pore resurrection, a consequence of the temporary filling of pores with cement that is subsequently removed. Examples from the stratigraphic record demonstrate that each of these pore-preserving mechanisms may control reservoir quality.

Origin and reservoir rock characteristics of dolostones in the early triassic feixianguan formation, ne sichuan basin, china: significance for future gas exploration

Abstract: Major discoveries of natural gas have recently been made in the oolitic dolostones of the Early Triassic Feixianguan Formation in NE Sichuan Province, Southern China. These dolostones were formed by three facies-controlled dolomitization processes: (i) meteoric mixing zone dolomitization with dolomites having a relatively high degree of crystalline order (δ13C:−1.0 to 2.5%PDB; δ18O:−6.5 to −2.5%PDB); (ii) seepage-reflux dolomitization associated with evaporative brines; the corresponding dolomite crystals are relatively ordered and were formed in tidal flat environments and platform-margin oolitic shoals adjacent to lagoons; (iii) burial dolomitization (shallow to moderate burial depths, ca. 1,000 to 4,000m), whereby seawater-derived brines were present in the host rock and the resultant water/rock reactions played a major role in dolomitization. The three dolomitization processes were controlled by the arid climate prevailing during the Early Triassic, and also by fourth-order relative sea-level changes, especially with respect to the reflux dolomitization. Burial dolomitization, which is of second-order of importance for porosity development, was strongly dependant on the presence of sufficient original porosity to facilitate water-rock reactions within the carbonates. The best reservoir rocks formed as oolitic banks and bars in the vicinity of evaporative lagoonal-tidal complexes which experienced optimal conditions for dolomitization. Dolostones with a dolomite content of 80% to 90% form good vuggy reservoir rocks at the present day, indicating that the intensity of dolomitization influences the quality of reservoir rocks. According to our results, future gas exploration in the Feixianguan Formation dolostone reservoirs should focus on locating oolitic banks associated with evaporative lagoon and tidal flat complexes and delineating the best structural/lithological traps.

Hydrocarbon habitat of the west Netherlands basin

Abstract: The traditional hydrocarbon charge model for the West Netherlands Basin was that the Carboniferous coal measures have generated only gas, and the Jurassic Posidonia Shale only oil. However, it is now concluded that both have generated oil and gas, and that an additional possible source rock for oil occurs in the lower part of the Lower Jurassic Aalburg Formation. Geochemical ’fingerprints’ have been established to distinguish the different groups of gas and oil, the occurrence of which is consistent with their geological setting and possible migration routes. The main phase of hydrocarbon generation and expulsion occurred prior to the mid-Cretaceous and the occurrence of biodegraded oils indicates that significant amounts of hydrocarbons were already in place at the onset of the Tertiary. Previously, it had been considered that charge ended during the Late Cretaceous inversion. However, recent modelling studies indicate that along the south-west margin of the basin and in the lows between inversion highs, charge continued during the Tertiary at rates that should have been sufficient to at least compensate for any loss of hydrocarbons through imperfect seals. The distribution of biodegraded oils in Jurassic and Cretaceous reservoirs suggests that biodegradation must have occurred during the earliest Tertiary, when meteoric fresh waters had access to the reservoirs. Significantly, reservoirs that were at that time so deeply buried that temperatures exceeded 70 to 80 °C, and that were thus at levels where bacteria cannot survive, do not contain biodegraded oils. For the fault-bounded traps in Triassic reservoirs, juxtaposition with Triassic and Jurassic sandstones and shales is the principal control of trap integrity and determines the spill point. Traps bounded by faults that have been reactivated during the Tertiary have clearly been breached. Traps at Upper Jurassic and Cretaceous levels are usually faulted dip-closures and have always been found to be full to their spill points within the limits of seismic resolution.