地理(地质)专业英语作业

Lesson 53 Rservoir Heterogeneity It has been proposed that most reservoirs are laid down in a body of water by a long-term process, spanning a variety of depositional environments, in both time and space. As a result of subsequent physical and chemical reorganization, such as compaction , solution , dolomitization and cementation the reservoir characteristics are further changed . Thus the heterogeneity of reservoirs is , for the most part ,dependent upon the depositional environments and subsequent events.
The main geologic characteristic of all the physical rock properties that have a bearing on reservoir behavior when producing oil and gas is the extreme variability in such properties within the reservoir itself , both latterly and vertically , and within short distance . It is important to recognize that there are no homogeneous reservoirs , only varying degrees of heterogeneity.
The reservoir heterogeneity is then defined as a variation in reservoir properties as a function of space .Ideally , if the reservoir is homogeneous , measuring a reservoir property at any location will allow us to fully describe the reservoir . The task of reservoir description is very simple for homogeneous reservoirs. On the other hand, if the reservoir is heterogeneous ,the reservoir properties vary as a function of a spatial location. These properties may include permeability, porosity , thickness, saturation, faults and fractures, rock facies and rock characteristics. For a proper reservoir description , we need to predict the variation in these reservoir properties as
a function of spatial locations. There are essentially two types of heterogeneity：
(1) Vertical heterogeneity；
(2) Areal heterogeneity.
Geostatistical methods are used extensively in the petroleum ineustry to quantitatively describe the two types of the reservoir heterogeneity . It is obvious that the reservoir may be nonuniform in all intensive properties such as permeability , porosity , wettability , and connate water saturation. We will discuss heterogeneity of the reservoir in terms of permeability .
One of the first problems encountered by the production geology in predicting or interpreting fluid displacement behavior during secondary recovery and enhanced oil recovery processes is that of organizing and using the large amount of data available from core analysis . Permeabilities pose particular problems in organization because they usually vary by more than an order of magnitude between different strata. The engineer must be able then to：
(1) Describe the degree of the vertical heterogeneity in mathematical terms.
(2) Describe and define the proper permeability stratification of the pay zone .This task os commonly called the zoning or layering problem.
It is appropriate to be able to describe the degree of heterogeneity within a particular system in quantitative terms. The degree of homogeneity of a reservoir property is a number that characterizes the departure from uniformity or constancy of that particular measured property through the thickness of reservoir . A formation is said go have a uniformity coefficient of zero in
A specified property when that property is constant throughout the formation。