Congenital Reservoir Rock Characterization of Weak Hydraulic Properties

Abstract

Weak hydraulic units occur frequently in many Niger Delta fields. This makes the characterization of reservoirs in such fields quite challenging. In this work the interpretation procedure, adopted model and algorithm were chosen such that each unit is treated separately to make the evaluation process as detailed as possible. Also, a conscious effort was made to incorporate functions in our adopted model that take care of the factors responsible for the weak hydraulic units in the reservoir. The application of cut-offs was done in a manner that blocked properties and predictive algorithm only relate to intervals that will contribute to production. This approach is necessary to improve the precision and predictive algorithm of porosity, permeability and water saturation that form part of the reservoir evaluation process. Usually the inclusion of units with weak hydraulic properties in the evaluation of hydraulic storage at the onset will decrease and weaken the precision of the evaluation process if cut-off were not applied. Also, the approach resulted to a construction of the simplest dynamic model that is compatible with the static model which is the objective of every reservoir characterization. The prime aim of this approach is a more precise reservoir characterization as against a mere approximate. Introduction Most reservoirs formed within a progradational to retrogradational parasequence have rock units that are of weak hydraulic properties which are typified in many Niger Delta fields. The description of such reservoir needs to be precise to reduce the amount of hydrocarbon left behind pipe. It is therefore expedient to develop appropriate methodology and algorithm in the description of such reservoirs. Hydraulic units have previously been defined as the representative elementary volume of total reservoir rock within which geological and petrophysical properties that affect fluid flow are internally consistent and predictably different from properties of other rock volumes1. When such units are of small transmissibility they are said to be weak. Geologically the weak hydraulic units form part of the reservoir succession (congenital), but they do not contribute significantly to the evaluation of the hydrocarbon in place or the estimation of reserves2. This is due to the poor storage capability of these units. The permeability values of these units are also very low; hence the transmissibility is also invariably small compared to the other successions in the reservoir rock.

A Robust Approach to Flow Unit Zonation

“…With layers far apart sharing similar petrophysics, while adjacent ones differ significantly, we conclude that flow units do not necessarily depend on depth ordering. Furthermore, the dominance of the least quality zone (zone 1) supports the argument that weak hydraulic units are typified in many Niger Delta fields (20) . Tables 10 and 11 show inter-Well discrimination, with the uniform zones highlighted, and Fig.…”