Petrel: Static & Dynamic Modeling

  • Geomodeling: Geological models are created for many different purposes, but common to all of them is a desire to build a representation of the subsurface. Geological models may be used to achieve accurate volume calculations or to test the effect of different depositional regimes against observed data.
  • Petrel Interface: Petrel is a software package, which is a product of Schlumberger that allows the user to build a reservoir model with properties to export to a simulator. Petrel is a Windows based software for 3D visualization, 3D mapping and 3D reservoir modeling and simulation. It was founded in 1996, and commercially released in 1998. It became part of the Schlumberger Information Solutions in January 2003.
  • Data Set: The Gullfaks data set has been released for commercial use by the Norwegian oil company Statoil. Gullfaks is one of the major oil fields in the North Sea and one of the largest oil producing fields on the Norwegian continental shelf, Fig. 3.1 Gullfaks is an oil and gas field in the Norwegian sector of the North Sea operated by Statoil Hydro. It was discovered in 1979, in block 34/10, at a water depth of 135 meters (442.913 foot). The initial recoverable reserve is 2.1 billion barrels, and the remaining recoverable reserve in 2004 is 234 million barrels. This oil field reached peak production in 2001 at 180,000 barrels per day.
  • Data Import: When starting a new project, Petrel organizes the input data in the Input pane. The input data includes: wells data, seismic data, well tops, fault polygons, fault sticks, isochores, etc.
  • 3D Seismic Data: The 3D seismic Horizons are read into Petrel in a specific General Lines/Points (ASCII) (*.*) format…
  • Seismic Interpretation: To import the seismic section to the project, click the insert menu command and choose New Seismic Main Folder….
  • Fault Data: In Petrel, fault data is presented in two formats: Fault Polygons and Fault Sticks as follows: fault polygons and fault sticks. Fault polygons are normally generated in the seismic interpretation station or in a mapping application, and are commonly defined by the hanging wall line and the foot-wall line for a given surface. Fault sticks may be created from within Petrel. Their files can be edited with any text editor such as Notepad.
  • Isochores: The isochore data is read into Petrel in a specific Zmap+ grid format.
  • Input Data Editing: There are few editing steps that must be completed before a 3D geological model is created.
  • Well Correlation: Petrel includes a tool for doing well correlation; The Well Section Window allows displaying well logs in a specified order, with the available logs and well tops.
  • Fault Modeling: Generations of fault pillars, known as Key Pillars, are lines defining the slope and shape of the fault. There are up to five, so called Shape Points along each of these lines to adjust the shape of the fault to perfectly match your input data. The Key Pillars are generated based on input data such as fault surfaces, fault sticks, fault lines, fault polygons, structural maps, interpreted seismic lines, etc.
  • Pillar Gridding: The generation of the structural model is done in a process called Pillar Gridding. Pillar Gridding is a unique concept in Petrel where the faults in the fault model are used as a basis for generating the 3D grid. Several options are available to customize the 3D grid for either geo-modeling or flow-simulation purposes. Pillar Gridding is the process of making the “Skeleton Framework”. The Skeleton is a grid consisting of a Top, a Mid and Base skeleton grid, each attached to the Top, the Mid and the Base points of the Key Pillars.
  • Vertical Layering: The final step in structural modeling is to insert the stratigraphic horizons into the pillar grid, honoring the grid increment and the faults, defined in the previous steps. The result after the Pillar Gridding process as a 3D grid consisting of a set of pillars connecting the Base, Mid and Top Skeletons. All the faults to be incorporated into the model have been defined, and the pillars have been placed along and between the faults.
  • Geometrical Property Modeling: Geometrical Modeling is the process where you can use some pre-defined functions to generate properties (e.g. Bulk Volume, Depth, Height above Contact, and more). This section will describe general things about the property modeling, such as using filters and the property player. The distribution of properties in 3D, based on up-scaled logs, will also be described in general. Geometrical properties are properties created by using pre-defined system variables such as Cell Height, Bulk Volume, Depth and Above Contact.
  • Upscaling: The scale up of well logs is an automatic process with some user settings available. When scaling up the well logs Petrel will first find the 3D grid cells that the wells penetrate. For each grid cell all log values that fall within the cell will be averaged according to the selected algorithm to produce one log value for that cell. The resulting 3D grid will only hold values for the 3D grid cells that the wells have penetrated.
  • Facies Modeling: The process of building a basic facies model conditioned to well observations using SIS. The variogram type, ranges, and azimuth for each facies are provided for you. These are normally designed to match observations of geologic ends (typically as observed in a Well Section) and require some experimentation to create the desired effects.
  • Petrophysical Modeling: When the well logs have been scaled up to the resolution of the cells in the 3D grid, the values for each cell along the well trajectory can be interpolated between the wells in the 3D grid. The result is a grid with Property values for each cell.
  • Fluid Contacts: After having built a Petrel 3D grid and prior to running the volume calculation, the various contacts should be defined in the Make Contacts process. Several sets of contacts can be defined and each Contact Set can contain a number of different contact types. All Contact Sets will be stored under a folder called Fluid Contacts in the Petrel Explorer Models tab. The Contact Set can be created based on a constant depth value or a surface.
  • Volume Calculations: Volumes are most commonly calculated in the Volume Calculation Process step. Volumes can be calculated exactly within zones, segments and user defined boundaries (e.g. License boundaries). The Contacts defined in the previous process (Make Contact) are used as input to the Volume Calculation process. Volume calculations can be performed using several hypotheses in one operation. Each hypothesis is called a run. The user has the option to include an uncertainty range for the contact level and create distribution functions based on this uncertainty range.
  • Simulation: To simulate fluid flow in a reservoir, we first need a  3D or 4D geological model of the reservoir.  This model will have to be described in such a way that the data can be used for numerical computations. This is done by “gridding” the reservoir, which divides the reservoir into a finite set of homogeneous grid cells. Each of these cells contains data for each of the geological parameters in that cell.
  • Rock Properties: There are  number of functions of saturation or pressure used in simulation that represent the physics of the fluids, the rock, or the interaction between rock and fluids. The Make fluid model process creates the functions that represent the physics of the fluids. The Make rock physics functions process is used to create functions that represent the physics of the rock and the interaction between rock and fluids, allowing users to make saturation functions and rock compaction functions. In future releases of Petrel the range of rock physics functions available within this process will be extended.
  • Fluid Properties: Making fluid model process allows you to generate black oil fluid models. These models are defined by specifying several properties such as viscosity, density and volume formation factors for each of the fluid phases. These properties are normally entered as tables that only depend on pressure. The most reliable way to obtain this information is from a reservoir fluid study using bottom hole or reconstituted fluid samples. If such data is not available, correlations can be used to estimate the oil, water and gas properties as well as the gas/oil relationships. Note that this process does not offer any support for creating ECLIPSE 300 compositional fluid models.
  • Saturation Functions: Saturation functions are tables showing relative permeability and capillary pressure versus saturation. Creating saturation functions using the Make rock physics functions process will also generate curves for gas-oil and water-oil capillary pressure versus saturation. These are set to zero by default. The relative permeability and capillary pressure curves are grouped together under a saturation function icon in the Rock physics functions folder.
  • Aquifer Models: Aquifer modeling is a method of simulating large amounts of water (or gas) connected to the reservoir whereby it is not essential to know how the fluid moves in it, but rather how it affects our reservoir. There are several aquifer models: numerical, Carter-Tracy, Fetkovich, Constant flux, Constant pressure (gas or water) and rainfall. Each aquifer model has its own set of parameters and can be connected to the grid in different directions: top down, bottom up, grid edges and/or fault edges.
  • Observed Data:
    1.     Open the Wells folder in the Input pane.
    2.     Right click on the Global Observed Data and choose import (on selection).
  • Well Completion: Well completion consists of sealing off a drilled well in preparation for production. After the drilling equipment has been removed from the borehole, the well is fitted with, as appropriate: liner, tubing, valves, and safety and flow-control equipment. It includes setting and cementing the casing, perforating it, and installing pumping equipment or a production tree, and stimulating or pumping.
  • Field Development Strategy: Development Strategies are used to describe to the simulator how a field will be developed – that is, which wells will produce or inject, what rates and pressures they will flow at, what operations will be carried out on the wells over time, and so forth. Development strategies make it easy to keep track of how the control of a field evolves with time: for example, as new wells are drilled, the target field rates change; wells are converted from producer to injector; new platforms and manifolds are added; and so on.
  • Define Simulation Case: Defining a simulation case consists of specifying the input properties, then selecting predefined initial conditions and fluids models, rock physics functions, and development strategies. You can select the results that the simulation should generate and the type of simulator. The completed simulation case will appear in the list in the Cases pane.
  • Well Path Design: The Well path design process is a tool which enables users to generate well trajectories based on reservoir properties, seismic attributes or any other data. Well trajectories can be manually digitized in the 3D window. The design points can be displayed in a spreadsheet and can be easily cut and pasted between Petrel and other windows software applications. Reservoir targets defined by the user can be used as input to the Well Optimizer. This feature will, given a set of reservoir targets and a cost model, find well trajectories and platform locations that minimize the total cost of the project.
  • History Matching: The History match analysis process is located under Simulation in the Processes pane. If no History Match Statistics sets have been created then the first time the panel is displayed users will only be able to select Create new match. A unique name for the match set will be calculated automatically, but it can be edited via the appropriate edit field in the panel. The Observed Data Set will contain a list of all the observed data sets previously loaded and will default to the first one found. If History Match Statistics sets have previously been generated then the default selected option is Edit existing match. If a History Match Statistic set has been selected in the Results Pane then it will be the default selection. The Observed Data Set shown will be the one that was used to create the History Match Statistic set. If you do not want to edit an existing History Match Statistic set, then simply select Create new match.