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.

Effect of Reservoir Depletion And Pore Pressure Drawdown On In Situ Stress And Deformation In the Ekofisk Field, North Sea

Abstract: Knowledge of in situ stress and how stress changes with reservoir depletion and pore pressure drawdown is important in a multi-disciplinary approach to reservoir characterization, reservoir management, and enhanced oil recovery projects. Over 20 years of petroleum production from the Ekofisk field has resulted in a 21-24 MPa reduction in reservoir pore pressure. The effect of pore pressure drawdown on the minimum horizontal in situ stress in the Ekofisk field has been determined from shut-in pressure data of 32 hydraulic fractures. The effective stresses in the reservoir increase linearly with pore pressure drawdown, but at different rates. The ratio of the change in effective minimum horizontal stress to the change in effective vertical (overburden) stress is approximately 0.20. Laboratory experiments, which simulate the stress path followed by reservoir rock during the production history of the Ekofisk field, clearly indicate that shear failure has occurred during compaction of high porosity chalk as the shear stress increased with pore pressure drawdown. It is suggested that shear failure during primary production has increased fracture density and reduced matrix block dimensions, and has therefore maintained reservoir permeability, which may account for the continued good producibility of the Ekofisk field, in spite of compaction. 9more » refs., 5 figs.« less

Effects of wettability on three-phase flow in porous media

Abstract: We study the effects of rock wettability on the flow of oil, water, and gas in hydrocarbon reservoirs. We describe the three-phase fluid configurations and displacement processes in a pore of polygonal cross section. Initially water-filled, water-wet pores are invaded by oil, representing primary oil migration. Where oil directly contacts the solid surface, the surface will change its wettability. We then consider water injection followed by gas injection for any possible combination of oil/water, gas/water, and gas/oil contact angles. We find the capillary pressures for the different displacement processes and determine the circumstances under which the various fluid configurations are stable. Using empirical expressions for the phase conductances, we find three-phase relative permeabilites for a bundle of pores of different sizes with constant triangular cross sections. For gas injection, we show that the oil remains connected in wetting layers down to low oil saturation with a characteristic layer drai...

Geological Applications of Capillary Pressure: A Review

Abstract: Capillary pressure concepts can be used to evaluate reservoir rock quality, expected reservoir fluid saturations and depths of fluid contacts, thickness of transition zone, seal capacity, and pay versus nonpay, and to approximate recovery efficiency. Mercury-injection capillary pressure is typically favored for geological applications, such as inferring the size and sorting of pore throats. The differences between mercury injection and withdrawal curves can provide information on recovery efficiency. The height above free water level can be determined by comparing capillary pressure data to hydrocarbon shows and measured fluid saturations. Capillary pressure data can also be used to distinguish reservoir from nonreservoir rocks and pay from nonpay on the basis of nonwetti g-phase saturations. Other applications of capillary pressure data include relating capillary pressure to absolute and relative permeabilities, and using porosimetry to investigate pore-level heterogeneity. This paper reviews geological applications and interpretation of capillary pressure in reservoir studies.

Diagenesis and Fluid Evolution of Deeply Buried Permian (Rotliegende) Gas Reservoirs, Northwest Germany

Abstract: Depositional environment and tectonic setting were important in the diagenesis and evolution of reservoir properties in the Rotliegende sequence of the North German Basin. Facies belts paralleling the edge of a central saline lake controlled the distribution of early and shallow burial cements. Lake shoreline sands with radial chlorite cement show the best reservoir properties in the study area. Juxtaposition of Rotliegende deposits against either Carboniferous Coal Measures or Late Permian (Zechstein) evaporites by faulting resulted in cross-formational fluid exchange. The introduction of fluids from Carboniferous Coal Measures into Rotliegende reservoirs produced intense clay cementation, significantly reducing rock permeabilities. Influx of Zechstein fluids favored pre ipitation of late carbonate and anhydrite cements. Cross-formational and fault-related fluid flow was enhanced during periods of fault activity.

Small-Scale Fracture Density in Asmari Formation of Southwest Iran and its Relation to Bed Thickness and Structural Setting

Abstract: Knowledge of the distribution of rock fractures in the Asmari limestone reservoir rock of the prolific Khuzestan oilfield belt of southwest Iran provides for a better understanding of the production mechanism. Though the high productive capacity of wells in this area has been ascribed predominantly to fracturing of the reservoir rock, quantitative work on this topic has been neglected in the past. Details of small-scale fracturing have been investigated locally on individual anticlines and regionally in Asmari limestone outcrops over an elongate area of about 2,000 sq mi (5,180 sq km) of the Zagros Mountains foothills. Fracture density has an inverse logarithmic relation to bed thickness, but it is independent of structural setting. Such findings make necessary the rejection of a theory involving a genetic relation of fractures of this scale to the folding process, at least in the area studied. The early formation of fractures is such that their orientations are related to localized irregularities, and their initiation by shock waves is suggested. Specific values for average fracture spacing in the Asmari limestone beds provide valuable data for the reservoir engineer. Fold formation by the exploitation of appropriate preexisting fracture sets enhances reservoir porosity and permeability in preferred directions.