In the oil and gas industry, 3-D reservoir modeling involves the construction of a computer model of a petroleum reservoir, for the purposes of improving estimation of reserves and making decisions regarding the development of the field, predicting future production, placing additional wells, and evaluating alternative reservoir management scenarios.


Reservoir models typically fall into two categories:

  1. Geological models are created by geologists and geophysicists, and aim to provide a static description of the reservoir, prior to production.

  2. Reservoir engineers create reservoir simulation models and use finite difference methods to simulate the flow of fluids within the reservoir, over its production lifetime.


The role of the geologist is to provide a geological framework of the structure and reservoir architecture from seismic data and well logs. In such a static reservoir model, required by many Operators, all reservoir characterization data, such as reservoir distribution (porosity, internal baffles, facies), hydrocarbon saturation, fault connectivity, are integrated. The static model is used as input for the following modeling phase: dynamic simulation. Upon completion, the static model is handed over to the Reservoir Engineer for the dynamic simulation.


Reservoir Simulation is an area of reservoir engineering in which computer models are used to predict the flow of formation fluids (typically oil, gas and water) through a porous medium. In more detail this means forecasting reservoir performance, flow rates, water break-through, reserves, history matching and understanding of flow mechanisms. Simulation studies performed at early stages of field development are done to estimate parameters such as optimal well spacing. At later stage, on producing fields, simulation is performed for infill well planning or secondary recovery.


OPS OES Thailand provides Reservoir Engineers who are familiar with most industry standard simulation packages. Our dedicated teams work closely together in Client’s premises, and are as a rule, closely interacting with Client’s project geologist, who is familiar with the geological setting of the modeled reservoir. This cooperation gives the best possible outcome and the best chance to meet Client’s objectives of optimum or increased hydrocarbon recovery. In the (infill) well planning process on a producing field, reservoir modeling is a powerful additional tool for the development geologist, but commonly not accepted by management as a stand-alone tool.



Well correlations at scale of individual reservoir layers


Since the static reservoir model forms the basis for the dynamic modeling by the engineer, it is of key importance that the reservoir correlation between wells is as accurate as possible at the smallest possible scale; the individual reservoir bed. This could reveal the presence of internal reservoir baffles, critical for the dynamic modeling.


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Example of high-resolution stratigraphic correlations from a field in Qatar. The vertical scale bar indicates how thin some of the reservoir beds are.

Review and updating of existing reservoir models


Over time, Client’s project geologists have built reservoir models and applied these in their day-to-day work. Before the geological modeling specialist can start, he and the project geologist must agree on the existing model. In many cases, subtle changes in the existing model can have dramatic consequences in the later dynamic modeling. Two examples are from two fields, formerly operated by Unocal/Chevron. The reservoir in the Halfweg Gas Field in the Dutch North consists of Rotliegendes aeolian sands, a thick section of clean sands. However, it contains multiple foresets and bottomsets, forming interdune beds acting as permeability barriers and baffles. In the initial model, this was ignored, but after incorporating these in the reservoir model, the dynamic modeling all over sudden made sense. 


Static Reservoir Modeling


Once there is consensus on the geological framework of structure and reservoir architecture, the modeler starts constructing the static model by creating an array of discrete cells, delineated by a grid, which may be regular or irregular (see examples from the Niger Delta; the upper diagram showing modeled porosity, the lower diagram the modeled water saturation). The array of cells is usually three-dimensional, although 1D and 2D models are sometimes used.

All reservoir parameters/properties are integrated in the model: reservoir distribution (porosity, permeability, facies, internal baffles), HC saturation, fault connectivity, all derived from seismic- and well data. All these values are geostatistically attributed to each cell, whereby a specific property or attribute is applied uniformly throughout a specific cell. Commonly, these models are constructed at a relatively high (fine) resolution.


The static model is subsequently handed over to the reservoir engineer for the dynamic simulation.

Dynamic Reservoir Simulation

As mentioned here fore, reservoir dynamic simulations are performed for reservoir management through forecasting of reservoir performance; improving reservoir description through history matching and understanding of flow mechanisms.

Uncertainty in the true values of the reservoir properties is sometimes investigated by constructing several different realizations of the sets of attribute values. The behavior of the resulting simulation models can then indicate the associated level of economic uncertainty. The outcome of different runs in simulation is a reality check of the validity of the static model. In particular, when the reservoir engineer is not able to reach a decent history match, it will tell us changes must be made to the static model. Workflows for integrated reservoir modeling are illustrated in the below diagram.


Source: Oil & Gas portal; Reservoir Management.

Team Work


OPS OES Thailand dedicated GL/RE teams work closely together in Client’s premises. They are, as a rule, closely interacting with Client’s project geologist. During the modeling, all available data will be reviewed and integrated in order to give the optimum outcome and the best chance to meet Client’s main project objectives, which is to increase HC recovery from the reservoir