Determining Individual Characteristics of a Two- Layered Reservoir Using the Tds Technique
Determining Individual Characteristics of a Two- Layered Reservoir Using the Tds Technique.
Abstract
The first part of this study discussed in details the two major model that was developed for the study of a multilayer reservoir system.
They are the Dual permeability model proposed by Bourdet and the semi permeability wall model proposed by Gao.
The pressure response of a crossflow system is observed in three stages; it behaves as a commingled system in the early stage and then as a single layer homogenous system in the late stage.
There is a transition stage, which connects the early and late stages. The effect of some reservoir parameters such as the permeability thickness ratio, the storativity ratio, and the semi permeability was studied.
The second part of this study focused on a two-layer reservoir system with crossflow when only one layer is perforated and tested.
The pressure response for this test method was observed to have two infinite acting straight line on which the TDS technique was developed to determine the individual layer parameters such as permeability thickness for both layers, wellbore storage and skin effect for the perforated layer.
Introduction
Many reservoirs consist of two or more layers with non-permeable or low-permeability shales between them. Over the years, well test data has often been interpreted with the assumption that the reservoir is homogenous and of a single layer (C. Gao, 1987).
Pascal, in 1992 pointed out in his study of pressure and rate transient data from wells in multilayered reservoirs, that there is geological evidence (logs, core analysis) which substantiate the fact that numerous reservoirs have strong heterogeneous characteristics with respect to the vertical direction, which indicates that they are multi-layered reservoirs.
It has been observed that pressure transients in multilayered reservoirs often show a significant deviation from the response that would be obtained in a single layer homogeneous reservoir having equivalent thickness-averaged properties (Pascal, 1992).
Most oil and gas reservoirs are layered (stratified) to various degrees because of the sedimentation process over long geological time (Kucuk, 1986).
Layered reservoirs are composed of two or more layers that may have different formation properties and fluid characteristics. Wells in such reservoirs may produce from more than one layer (Kucuk, 1986).
Pressure behavior in this kind of vertically heterogeneous system is not necessarily like that of a single-layered system; it reveals only the average properties of the entire system.
To identify the characteristics of the individual layers is important, especially if water flooding or an enhanced recovery scheme produces the reservoir fluid. (Horne, 1989)
The deviation of the pressure transient observed in multilayered reservoirs from that of a vertically homogeneous reservoir, became particularly obvious with the advent of high resolution, downhole electronic gauges, allowing very accurate pressure measurements.(Kucuk, 1986).
References
Ahmed Aly, et al. “A New Technique for Analysis of wellbore Pressure From Multi-layered Reservoirs With Unequal Initial Pressures To determine Individual Layer”. Society of Petroleum Engineers Journal, (1994).
Barenblatt, G.I, Zeltov, Ju.P. and Kocina, I.N,: “Basic Concepts in the theory of Seepage of Homogenous Liwuids in Fissured Rocks (Strata)”, Soviet J. App. Math. and Mech.,1960.
Bourdet, D. “Pressure Behavior of Layered Reservoirs With Crossflow”. Society of Petroleum Engineers Journal, (1985).
Coats, K.H., Dempsey, J.R., and Henderson, J.H.: “The use of vertical Equilibrium in two-Dimensional simulation of Three-Dimensional Reservoir Performance,” Society of Petroleum Engneers journal (March 1971) 63-71; Trans., AIME, 251
Ehlig-Economides, C. A., & Joseph, J. “A New Test for Determination of Individual Layer Properties in a Multilayered Reservoir”. Society of Petroleum Engineers Journal, (1985).
Gao and Dean, “Single-Phase Flow in a Two-Layer Reservoir with Significant Crossflow- Pressure Drawdown & Buildup Behaviour When Both Layers are Completed at a Single Well’. Society of Petroleum Engineers Journal, (1984).
