INTEGRATED RESERVOIR CHARACTERISATION

Sh.R.P.Verma Dr. A.K.Nagar Dr. A.K.Manchanda Sh. Anand Prakash

OverviewDefinitionThe term characterisation means that we should drive out or describe the properties of the entity in such a way that with the driven out quality and quantity of information of the entity we should be in a position to synthesize it. In our case this entity is the reservoir.

ComponentsWe perceive the information on three scales: The microscopic scale: Electron and optical microscopy, mineralogical analysis and core study The mesoscopic scale: Log analysis

The megascopic scale: Seismics

Stability Field of Triangle of Perception, The Scale Problem

This understanding of scale problem has brought out two definitions. The information between mesoscopic and microscopic fields of a reservoir is termed as Reservoir Characterisation while the information between mesoscopic and megascopic fields is called Reservoir Description.

ProblemThe lack of object oriented modelling:Instead of preparing a high definition reservoir model we fragment the available gross geological model which does NOT has the desired microscopic level information.

ApproachTwo alternatives:Translate information from microscopic to megascopic scale through mesoscopic scale Prepare different models for different purposes. The model required for OOIP calculation and for simulation should be prepared separately : Process is slow Generate a reservoir model with downscaled data itself.

Reservoir Architecture

Layer cake Jigsaw puzzle Labyrinth types

Layercake (Continuous)

Brick work (Stochastic, Random)

Labyrinth (Stochastic, Random)

Reservoirs are the conglomeration of flow units and the flow baffles or permeability barriers. These barriers can be:Faults Facies boundaries Non-lithic boundaries Fluid boundaries : : : : Logs, Seismics 3D-3C Well Tests, FU Analysis AVO (gas reservoir), Logs

Reservoir characterisation can be divided into two classes Static Reservoir Characterisation Dynamic Reservoir Characterisation

Static Reservoir CharacterisationThis helps in the static modelling of the reservoir. This is performed in two stages.

1. At control points (wells) 2. Away from control points

At Control pointsThe data received at wells is used for this class of characterisation it involves 1. Lab study of core and fluid. 2. Log Analysis Determination of vertical limits by well picks and lateral limits by log correlation of reservoir facies.

1. Basin analysis 2. Petrophysical properties

3. Well Test analysis

Pressure study at wells

1. Reservoir energy, 2. Identification of a fault 3. Health of well 4. Average petrophysical properties around well

Away from Control points Interpolation & Extrapolation 1. Geostatistics 2. Seismics

Tools:1. Attribute Analysis 2. Well Test Analysis 3. Inter-well Tomography 4.Tracer Survey Technique

Dynamic Reservoir Characterisation1. Log Analysis : Movement of Fluid contacts

2. Reservoir monitoring: Time wise GOR, isobar, iso-watercut & iso-temperature maps 3. 4D Seismics: - Preferred orientation of permeability zones - Preferred movement of reservoir or injected fluid or thermal fronts -The amount of change in fluid saturations. - Uncertainty Analysis

4. Numerical simulation: