# Difference between revisions of "Reservoir simulation"

"A reservoir model contains the permeable rock formation. The color specifies the oil saturation (more red, more oil)."[1].

In general, simulation is a theoretical or a physical representation of an operation and an imitation of its system/processes in real-life. Reservoir Simulation is a field developed in petroleum engineering where it utilizes porous media in computer modeling to estimate the fluids dynamics, its goal is to predict the field performance under varies producing strategies. Reservoir Simulation is grounded on recognized engineering equations, engineers started calculating reservoir engineering with basic mathematical model long before the emergence of modern technology. Although Reservoir simulation is not new to the industry, it has become more efficient than before due to the advanced capabilities provided by modern day technology. Proficiency, efficiency and effectiveness are the reasons why many engineers became a competent to the model and its development. [2]

## Reservoir Simulation Basic Analysis

Material balance equation (MBE) methods are used to calculate if a reservoir is homogeneous and to predict its production behavior by providing values of its properties and describing its average time, pressure,porosity and other properties under a solution gas drive. (Cumulative net withdrawal in STB) = (Original oil in place in STB) - (Oil remaining in place in STB) "1". One of the representations of reservoir models is called the Tank Model, is also called "the building block of reservoir simulators", it is a zero dimensional model, because just like in the example of the oil MBE equation, the difference between the initial oil and the final oil entering the reservoir is the Cumulative net withdrawal. The tank model takes the average values for the whole properties of the reservoir by assuming that there is no oil entering the reservoir. However, the tank model cannot represent sandbars and average them out as a whole due to variation of lithology, but instead it can average out the components within. In this case, because of the expansion of fluids complications, the MBE equation together with Darcy's Law are used to describe the behavior of each component. This new model is a one- dimensional simulator because it has more than one component in one direction and one component in the other two directions. Another models were extended and modified because lithologies vary in more than one dimension, like two-dimensional and three-dimensional simulators. Moreover, deep understandings of the characteristics of the reservoir and extensive data gathering and testing are required before choosing a simulator. However, the two dimensional simulator is the most commonly used, it has different common geometries, respectively, the horizontal (x-y) geometry, the vertical (x-z) geometry and the radial (r-z) geometry. [3]

## Uses

Reservoir Simulation tool is an amazing product of an integrated effort of geosciences, reservoir and production engineering, petrophysics, computer science and economics. Reservoir simulation is a widely used method by oil and gas companies to expand and develop new methods, recovery projects and locations of infill wells.[4]

### Geological Model

The geologic model (Geocellular model) is built as a numerical/mathematical imitation of the reservoir. It offers seismic structural interpretation, well petrophysical data with known depositional characteristics and 3D volume (porosity, permeability and water saturation) model. It consists of over 50 million cells on large complex reservoir, which enabled the industry to simulate equal number of this large magnitude of cells in a reservoir simulator.

### Flow Model

The geological model is large and contains lithology, facies, major faults and pinchouts. Therefore, the model is upscaled in vertical and areal directions introducing new methods including local flow-based methods and global flow methods to calculate transmissiblities. Faults and pinchouts upscaled models have been developed by knowing the general information of faults and calculated transmissibilities. The inclusion of faults became an important factor in reservoir information and modelling.

### Gridding

Complex geometries in reservoir simulation studies use Cartesian or corner point structured grids. The 3D System in a grid allows a better examination of infill well locations and water/gas calculations.

### Nonconventional wells

Nonconventional wells are utilized to enlarge production rates and recovery in petroleum industry. There are several steps to simulate nonconventional wells that will help the well to have a uniform inflow that are in use today in the industry.

### Integrated reservoir models and multiple reservoirs

Enhancement of reservoir management, this connects multiple wells from different fields (ex. Subsurface and surface fields) and simulates their integration which enhances recovery and developments.

### Use of larger models

As a result of the gigantic increase in computer hardware industry, the maximum model size has increased. Which, resulted in an unprecedented change in the simulating industry.

### Subsurface Modeling

"Structural model created with JewelSuite 6 Subsurface Modeling" [5]

Assembling precise 3D models of complex structures. New reservoir and geological information can be updated and combined with new data sets. This software provides operators a better knowledge of the subsurface which will improve production planning reserves estimation and well placement.

### Geomechanics

"GeoMechanics Technologies is applying advanced techniques to design multi-stage fracturing and simulate subsequent production from unconventional resources" [6]

In reservoir simulation, rock mechanics are connected with fluid flows through two elements: the change of the Permeability of the media and porosity. Software prevent rock mechanical challenges to enhance well planning by minimizing high risks.

### Hydraulic Fracturing

"Unstructured grid created used to simulate production effects over time in multiple hydraulically fractured wells."[7]

Hydraulic Fracturing is the process of pumping fluid into a wellbore at an injection rate that is too high for the formation to accept without breaking.” (Hydraulic Fracturing, petrowiki) Using the right software provides a clear imitation of the distribution and geometries of complex hydraulic fractures to seek the most effective areas and interpret fracture solutions in reservoir simulation.

### Fluid Analysis and Characterization

Accurate PVT modelling and analysis to help engineers characterize fluid phases easily, it provides high calculations speed, varies modelling equations, numerous workflows to measure data and good quality lines at specified intervals and periods to calculate fluid properties.

### History matching and production forecasting

The construction of reservoir simulation models are saved and used to present a performance of a field of similar past system conditions. The ratio between the calculated performance and the stated performance provides a better understanding for decisions made to cut down the error percentage to enhance future predictions.

## Common Software

### Commercial

CMG: Industry-standard black oil simulator IMEX, compositional simulator GEM and a thermal compositional simulator STARS.

"Results 3D image of a large conventional field. Gas is indicated by pink, oil by green, and water by blue." [8]

Schlumberger Eclipse: Industry-standard reservoir simulator developed by Exploration Consultants Limited and currently owned by Schlumberger.

"Fluid Saturation from a full-field Eclipse Simulation." [9]

Landmark Nexus: A simulator developed by Amoco, and currently owned by Landmark graphics.

"3D visualization in Nexus View TM software." [10]

RFD tNavigator: A high performance reservoir simulator.

Schlumberger Intersect: A high performance reservoir simulator jointly developed by Schlumberger, Chevron and Total. Commercial rights owned by Schlumberger.

Stone Ridge Technology Echelon: A full-GPU, high performance reservoir simulator jointly developed by Stone Ridge Technology (SRT) and Eni. Commercial rights owned by SRT.

Meera Simulation: AI-Physics hybrid reservoir simulation production forecasting tool for operation planning and budgeting by Target solutions LLC.

Merlin Simulator: Very simple to use, black oil, applied reservoir simulator. Trusted by the US government, simple workflow can build large model in minutes.

### Open Source

MRST: The MATLAB Reservoir Simulation Toolbox, provides new methods and concepts on unstructured grids, can be applied to large and complex systems.

BOAST: Black Oil Applied Simulation Tool, it is a numerical simulator to estimate the pressure destitution for a certain time to calculate the saturation destitution. Good for educational purposes.

OPM: The Open Porous Media, provides methods and tools to simulate flow of fluid in porous media.