Unsteady State Water Influx In Naturally Fractured Reservoirs

1988 ◽  
Author(s):  
Roberto Aguilera
Keyword(s):  
Fractured Reservoirs ◽  
Naturally Fractured Reservoirs ◽  
Unsteady State ◽  
Water Influx ◽  
Naturally Fractured ◽  
State Water

Unsteady-State Behavior of Naturally Fractured Reservoirs

1965 ◽  
Vol 5 (01) ◽  
pp. 60-66 ◽  
Author(s):  
A.S. Odeh
Keyword(s):  
Fractured Reservoirs ◽  
Naturally Fractured Reservoirs ◽  
Unsteady State ◽  
Fractured Reservoir ◽  
State Behavior ◽  
Naturally Fractured ◽  
Matrix Blocks ◽  
The Matrix ◽  
Porosity And Permeability ◽  
Bulk Volume

Abstract A simplified model was employed to develop mathematically equations that describe the unsteady-state behavior of naturally fractured reservoirs. The analysis resulted in an equation of flow of radial symmetry whose solution, for the infinite case, is identical in form and function to that describing the unsteady-state behavior of homogeneous reservoirs. Accepting the assumed model, for all practical purposes one cannot distinguish between fractured and homogeneous reservoirs from pressure build-up and/or drawdown plots. Introduction The bulk of reservoir engineering research and techniques has been directed toward homogeneous reservoirs, whose physical characteristics, such as porosity and permeability, are considered, on the average, to be constant. However, many prolific reservoirs, especially in the Middle East, are naturally fractured. These reservoirs consist of two distinct elements, namely fractures and matrix, each of which contains its characteristic porosity and permeability. Because of this, the extension of conventional methods of reservoir engineering analysis to fractured reservoirs without mathematical justification could lead to results of uncertain value. The early reported work on artificially and naturally fractured reservoirs consists mainly of papers by Pollard, Freeman and Natanson, and Samara. The most familiar method is that of Pollard. A more recent paper by Warren and Root showed how the Pollard method could lead to erroneous results. Warren and Root analyzed a plausible two-dimensional model of fractured reservoirs. They concluded that a Horner-type pressure build-up plot of a well producing from a factured reservoir may be characterized by two parallel linear segments. These segments form the early and the late portions of the build-up plot and are connected by a transitional curve. In our analysis of pressure build-up and drawdown data obtained on several wells from various fractured reservoirs, two parallel straight lines were not observed. In fact, the build-up and drawdown plots were similar in shape to those obtained on homogeneous reservoirs. Fractured reservoirs, due to their complexity, could be represented by various mathematical models, none of which may be completely descriptive and satisfactory for all systems. This is so because the fractures and matrix blocks can be diverse in pattern, size, and geometry not only between one reservoir and another but also within a single reservoir. Therefore, one mathematical model may lead to a satisfactory solution in one case and fail in another. To understand the behavior of the pressure build-up and drawdown data that were studied, and to explain the shape of the resulting plots, a fractured reservoir model was employed and analyzed mathematically. The model is based on the following assumptions:1. The matrix blocks act like sources which feed the fractures with fluid;2. The net fluid movement toward the wellbore obtains only in the fractures; and3. The fractures' flow capacity and the degree of fracturing of the reservoir are uniform. By the degree of fracturing is meant the fractures' bulk volume per unit reservoir bulk volume. Assumption 3 does not stipulate that either the fractures or the matrix blocks should possess certain size, uniformity, geometric pattern, spacing, or direction. Moreover, this assumption of uniform flow capacity and degree of fracturing should be taken in the same general sense as one accepts uniform permeability and porosity assumptions in a homogeneous reservoir when deriving the unsteady-state fluid flow equation. Thus, the assumption may not be unreasonable, especially if one considers the evidence obtained from examining samples of fractured outcrops and reservoirs. Such samples show that the matrix usually consists of numerous blocks, all of which are small compared to the reservoir dimensions and well spacings. Therefore, the model could be described to represent a "homogeneously" fractured reservoir. SPEJ P. 60ˆ

scholarly journals A Global Search Algorithm for Determining Water Influx in Naturally Fractured Reservoirs

Energies ◽  
2019 ◽  
Vol 12 (14) ◽  
pp. 2658
Author(s):  
Jiali Zhang ◽  
Xinwei Liao ◽  
Zhiming Chen ◽  
Nutao Wang
Keyword(s):  
Search Algorithm ◽  
Fractured Reservoirs ◽  
Flow Regimes ◽  
Global Search ◽  
Naturally Fractured Reservoirs ◽  
Gas Reservoir ◽  
Global Search Algorithm ◽  
Water Influx ◽  
Naturally Fractured

The determination of water influx in naturally fractured reservoirs is always a significant and difficult task in gas reservoir engineering. To improve this situation, this paper presents a new global search algorithm to determine water influx in the naturally fractured gas reservoirs. In the methodology, a dimensionless water influx derivative curve is first introduced in this paper. It is used to identify flow regimes of water invasion by combining with the water influx characteristic curve. Following that, a sensitivity analysis is performed to study the impacts of key factors on flow regimes. Finally, based on the sensitivity study and material balance equation, a global search algorithm is proposed to obtain water influx. Results show that there are two steps in the dimensionless water influx curve and a “V-shape” in the derivative curve. The smaller the aquifer and gas reservoir radius ratio is, the earlier and more obvious the “V-shape” appears. The smaller the storativity ratio is, the earlier the “V-shape” appears. The smaller the interporosity flow coefficient is, the more obvious the “V-shape” is. Results of the field application demonstrate the method applicability, which provide a good reference for further work about determination of water influx.

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