MatBal™ - Material Balance Modeling of Hydrocarbon Reservoir Systems

Quick Links to Information Below

• MatBal Overview
• Typical Applications for MatBal
• Why MatBal?

• Key Technical Features of MatBal
• MatBal Technology Overview
• Modes of Operation for MatBal
• A Working Example of MatBal

PDF Documents

• EPS Software Brochure
• EPS Products At-A-Glance

MatBal Overview

MatBal is a software package designed for reservoir analysis and reservoir-centered production forecasting based on a material balance approach.

For engineering applications, MatBal provides a quick and easy alternative to a full reservoir simulation study. Additionally, MatBal provides one important way of building an understanding of reservoir behavior, reservoir connectivity, and key reservoir parameters. If required, MatBal models can also form the basis on which a more comprehensive reservoir simulation study can be built.

Typical Applications for MatBal

Commercial Viability

MatBal’s history matching capability uses initial appraisal data to estimate key reservoir parameters. From this the user can gain an understanding of the size of reserves and subsurface connectivity between reservoirs and aquifer to assess the commercial viability of a new development.

Reserves Estimation and Reporting

Use the reservoir’s reported production history and MatBal’s history matching capability to estimate fluids in place and other key reservoir parameters for ongoing reserves estimation and reporting.

Field Development Planning

Use MatBal’s forecasting capability to produce a first-pass field development plan for green and brown fields including drilling schedules, well workovers, and well abandonment planning. Such plans can form the basis for a later more sophisticated analysis using field development optimization by ReO Forecast or full reservoir simulation.

Model building.

All tabular data can be plotted with upgraded graphing tool.

Why MatBal?

Flexibility and Accuracy

Unlike many material balance based software applications, MatBal allows the user to build sub-surface models containing several aquifers and reservoirs with complex connectivity. This makes MatBal applicable to a greater range of subsurface modeling needs and enhances the accuracy of model predictions and any management decisions based on them.

Speed

MatBal models are quick to build and fast to run, especially when compared with the engineering effort and computation time required to build and run equivalent full-reservoir simulation models.

Ease of Use

MatBal’s intuitive user interface and comprehensive help system allow engineers to familiarize themselves with the application quickly and efficiently. This minimizes engineering time lost during the familiarization phase.

Integration

MatBal is seamlessly integrated with ReO and ReO Forecast applications to allow accurate production forecasting and optimization from reservoir to delivery point.

Reporting–selection of model data, history match, and forecasts for output.

Key results are plotted as forecast progresses.

Key Technical Features for MatBal

• Full history matching and reservoir production forecasting capabilities
• History matching using linear regression (straight line fits to the classic material balance equations) or non-linear regression
• Reservoir production forecasting at reservoir or well level., production can be controlled using a choice of rate or pressure schedules at reservoir, well or manifold level
• Suitable for oil, condensate, dry/wet gas, and volatile oil reservoirs
• Choice of aquifer geometries and models
• Tabular PVT data for each reservoir
• Well modeling based on inflow performance relationships (IPRs) and vertical flow performance (VFP) tables
• Well modeling and PVT data can be imported from WellFlo, alternatively, this data can be supplied from other applications
• Integration with ReO and ReO Forecast for asset wide production forecasting and optimization
  

  Linear history match–classic straight line fit to data (left); simultaneous display of diagnostic plots (right).

  Non-linear history match.

MatBal Technology Overview

MatBal allows analysis, evaluation and prediction of the response of hydrocarbon reservoir systems using fundamental material balance principles.

This new application from eP is easy to use and allows users to get more value from their investment in other eP applications.

Material balance techniques are widely used throughout all phases of field development, providing engineers with a dynamic measure of hydrocarbon volumes and a critical estimate of key reservoir parameters. The ease with which material balance techniques can be applied results in an efficient and cost-effective alternative to more complex and expensive simulation techniques.

(Click icon to change Reservoir Type)

Using these techniques engineers can:

• Estimate the volume of fluids initially present in the reservoir.
• Examine the effects of changes resulting from produced and injected fluids.

MatBal helps the reservoir engineer to perform each stage of a material balance study quickly and efficiently:

• Building an appropriate material balance model
• Matching to historical data
• Generating production forecasts

MatBal provides all the functionality required within an up-to-date interface, designed to streamline all stages of the process. Integrated well Modeling is provided by WellFlo (part of the WellFlo suite), but MatBal is also compatible with well performance data generated by other means, or other software.

Modes of Operation for MatBal

History Match Mode

The field model can be calibrated against observed data using a combination of linear and non-linear regression methods in conjunction with diagnostic plots for Water Influx and Pressure Comparison.

Workflow Illustrating MatBal Operation

Forecast Mode

The history matched field model can be used as a basis for forecasting future reservoir performance and potential through estimated off-take and tubing-head pressure schedules. Three basic forecasting models are available:

Rate Controlled (Field Model):

User-defined field oil production and injection rates. MatBal calculates reservoir pressures, saturation and secondary phase rates and cumulative production.

Rate Controlled (Well Model):

Depending on the options selected the user can specify oil production, reservoir and gas lift injection rates, water injection rate and constraints (minimum and maximum production manifold pressures). MatBal determines reservoir pressure, saturations, rates, cumulative production, manifold pressures, manifold status with respect to manifold constraints, injection rates and cumulative injection. Individual well parameters are also calculated, including well status, tubing head pressure, bottom hole pressure, drawdown, productivity index, production rates and cumulative production for all phases, injection rates and production of secondary phases. MatBal also determines the optimum allocation of lift gas to individual gas lifted wells subject to user-defined constraints such as maximum lift gas rate, maximum water production etc.

Pressure Controlled (Well Model):

This is similar to the Rate Controlled (well model) option but in this case the user defines production and injection manifold pressures and fluid rate constraints.

MatBal Forecast Results for Manifold/Reservoir

A Working Example of MatBal

History Matching and Forecasting for A Gas-Lifted Field

This example illustrates how to generate forecasts for a gas-lifted black oil reservoir with an aquifer.    The field has been producing for four years with three gas-lifted wells and MatBal will be used to examine the impact on field performance of drilling additional wells and applying water injection. History Matching will be used to determine the aquifer size.

This example will be divided into four principal stages:

1) Data Input which comprises entry of:

• Hydrocarbon and Water PVT.
• Reservoir and Aquifer properties.
• Production Data - in this case production data will be specified on a Well by Well basis.

2) History Matching to determine the aquifer size.

3) Forecasting of future field performance for the following scenarios:

• Scenario A: Three additional production wells coming on-line in 2008, 2009 and 2010.
• Scenario B: In addition to the three new producers, a water injection well to be drilled and due to come on-line sometime between 2010 and 2015.

4) Results comparison.

Step1: Create New Project

The first step is to create a new project. Within the System Data dialog window, select Black Oil for the reservoir type and select the Aquifer Present? check box. For this example production will be specified on a Well-by-Well basis, so select that option in the Production History section.

MatBal System Data

Step 2: Reservoir Data

Next open the Reservoir Data dialog window by selecting the Reservoir hotspot button or Data Input/Reservoir menu item and enter the reservoir details shown below:

MatBal Reservoir Data

Step 3: Hydrocarbon and Water PVT

Open the Hydrocarbon PVT Data dialog window by selecting the Hydrocarbon PVT hotspot button or Data Input/Hydrocarbon PVT menu item and enter the hydrocarbon PVT data. For this example the PVT data has been saved in the spreadsheet called Example 3 PVT.xls and the data can be imported. In addition to the imported data the following data must also be entered manually:

• Bubble Point = 2164 psia
• Gas Gravity = 0.898
• Oil Gravity = 0.875

After selecting OK to validate and leave the Hydrocarbon PVT Data dialog, the warning shown below may be issued. If Yes is selected it will be necessary to insert a row of data at the pressure nearest to the bubble point, then add the PVT data for the bubble point pressure. If this action is not performed, the fluid parameters at the bubble point will be calculated by linear interpolation from the values lying on either side of the bubble point. Obviously, if these values are far removed from the bubble point, the interpolated values may exhibit a significant error. For this example, fluid properties at the bubble point have been provided.

MatBal PVT Data Warning

Next select and open the Water PVT Data dialog window via the Water PVT hotspot button or Data Input/Water PVT menu item and enter the water PVT data as shown below:

MatBal Water PVT Data

Step 4: Production Data

For this example, the Production Data is to be entered on a Well by Well basis rather than the field-wide Reservoir basis selected for Tutorial Examples 1 and 2.  The well production data has been saved as a set of Excel spreadsheets and this data can be easily imported into MatBal. To import the well production data:

• Select the Production hotspot button or Data Input/Production menu item to open the Wells dialog window.
• Select New and then type in Well 1 as the well name and check that the well type is Oil Producer.  Repeat this step for Well 2 and Well 3.
• Now highlight and select Well 1, then select the Edit button. This displays the Well Data dialog window for this well. Select the Production Data tab, then select Import.  Select the spreadsheet called Example 3 Well 1 Production.xls and then Open. Repeat this step for Well 2 and Well 3.
• The View Res. Production button option displays the total reservoir production for the selected production interval. For this example select a Monthly production interval from the drop-down menu and then select the View Res. Production button to display the reservoir production.

Step 5: Aquifer Data

Select the Aquifer hotspot button or Data Input/Aquifer menu item to open the Aquifer Data dialog window and enter data as shown below:

MatBal Aquifer Data

Step 6: History Matching

For this exercise it is assumed that the aquifer radius (Re), is the only parameter which will be adjusted in order to achieve a good match between the calculated and observed reservoir behavior.

The initial estimate of the aquifer radius entered in the Aquifer Data dialog was 13,000 ft. Operating in the History Match dialog window, select the Linear tab and choose the ( F-We vs E) plot from the iconic toolbar menu situated below the main menu at the top left corner and note that the observed data trends below the calculated response, which is characteristic of an overestimated aquifer response.

MatBal Regression Graph

• Using the Linear Regression option, adjust the aquifer radius (Re), until a good visual match is achieved.
• Refine the match using the Non-Linear Regression option with (Re) as the only regression parameter. A good match should be achieved with an aquifer radius of around 12,300 ft, giving a dimensionless aquifer radius of 1.7.
• Check the Aquifer Influx and Pressure Comparison plots to ensure that a good match has been obtained against the historical data.

Step 7: Forecasting

The tuned material balance model will now be used to evaluate the impact on field performance of drilling additional wells and the effect of adding water injection. Select the Forecast hotspot button option or the Forecast/Forecasting Model menu item to open the Forecasting Model dialog window.

It will be assumed that for the period of the forecast the production manifold pressure will be held constant at 300 psia and therefore the Pressure Control (well model) forecasting mode is the appropriate one. In this mode the manifold pressure is held constant and production is calculated on a Well by Well basis using the IPR and VFP data specified for each well.

• Select the Pressure Control (well model) forecasting option and a Quarterly reporting interval from the drop-down menu.
• Enter a Start date of 01/01/2005 and an End date of 01/01/2025.
• For the moment, leave the Injection Type section set at None (default), then OK from the dialog.

The individual well properties (i.e. inflow performance, IPR and vertical flow performance, VFP) for the three existing wells must now be defined and the first step is to import the relevant VFP tables into MatBal and assign each table to the appropriate well.

• Select the Tubing Performance hotspot button or Forecast/Tubing Performance menu item to open the Tubing Performance dialog window, then choose the Production tab. Select Add, then navigate to the MatBal\Data folder. Choose the *. vfp file type from the drop-down list at the bottom of the dialog, then select Well1.vfp and the Open button. Repeat for Well2.vfp and Well3.vfp.
• Select Well Data, highlight Well 1, then select Edit, which displays the Well data screen, and then click on the Forecast/Constraints tab.
• To assign the VFP table for this well select the Browse button next to Tubing Performance Table and then select Well1.vfp from the list of available VFP tables and then OK.

MatBal Tubing Performance

The IPR data for this well can now also be entered. This data can either be entered manually or imported directly from WellFlo. In this case, a WellFlo file applicable to each well is supplied for users who have WellFlo. For users without WellFlo, the IPR data relevant to each well is presented in the table below:

• Choose the IPR Data tab in the Well Data dialog.
• To import the IPR data into MatBal from a WellFlo file, select the Import from WellFlo button, select Well1.wfl and then the Open button.
• The above steps (i.e. IPR table assignment and IPR data entry/import) must be repeated for Well 2 and Well 3.

The next step is to enter the relative permeability data (i.e. Corey exponents and end-point saturations):

• Return to the Forecast dialog screen and select the Field Rel. Perm. button or Forecast/Field Rel. Perm. menu item, to open the Field Relative Permeabilities dialog window.
• Enter the data that appears below:

MatBal Field Relative Permeabilities

Finally, before a forecast can be run, a manifold schedule must be defined:

• Select the Manifold Schedule hotspot button or Forecast/Manifold Schedule menu item and enter a Start Date of 01/01/2005 and a Production Manifold Pressure of 300 psia. The right-most column in this table is entitled Maximum Gas Lift Injection Rate and if this is left blank a default value of 1000 MMscf/day is used, which effectively means that there is unlimited lift gas for this field.

Step 8: Generate Base Case Forecast

The data required to generate the base case forecast is now complete. This forecast will predict field performance for the period from 01/01/2005 to 01/01/2025 for a fixed production manifold pressure of 300 psia and determine the optimum allocation of lift gas to each well.

• Select the Forecast hotspot button or Forecast/Forecast menu item to open the Perform Forecast dialog window.
• Check that the forecasting model parameters are correct, then enter the Forecast ID as Base Case and select OK to perform the forecast.
• To review the results of the forecast, select the Results hotspot button or Forecast/Results menu item, then choose either the Field or Wells tab and select Plot.

The generated plot below shows that reservoir pressure declines from just under 2000 psia at the start of the forecast period to 975 psia at the end of the forecast period, for total oil production of 53 MMstb. The total lift gas requirement remains constant at 8.5 MMscf/day until 2009, then decreases as the natural lift provided by the gas produced from the reservoir increases.

The instantaneous GOR plotted in the figure below and shown in the Field and Wells results tables is calculated using only the gas produced from the reservoir and not the total gas (i.e. reservoir plus injected).

MatBal Forecast Results for Manifold/Reservoir

Step 9: Scenario A: Additional Wells

For this example it will be assumed that well data parameters for the three new wells will be identical to Well 3. These wells will also be introduced gradually, with Well 4 coming on-line on 01/01/2008, Well 5 on 01/01/2009 and Well 6 on 01/01/2010.

• To add the new wells select the Well Data hotspot button or Forecast/Well Data menu item, select Well 3, then select Copy and enter Well 4 for the well name. Repeat this copying process for Well 5 and Well 6.
• Select Well 4, then the Edit button and choose the Forecast/Constraints tab to enter the Start Date as 01/01/2008. Repeat this process for Well 5 and Well 6 with the appropriate start dates mentioned above.
• Select the Forecast hotspot button or Forecast/Forecast menu item and enter the Forecast ID as New Wells, then select OK to perform the new forecast.
• To review the results of the forecast, select the Results hotspot button or Forecast/Results menu item, then choose either the Field or Wells tab and select Plot.

Comparing the cumulative oil production and instantaneous oil rates for the two forecasts shows the predicted cumulative oil production with the additional wells is 56.6 MMscf/d , which compares with the 53 MMscf/ d for the base case. The step change in oil rate as each well comes on line is clearly seen in the oil rate plot, with maximum daily oil production peaking at just over 11,000 std / d in 2010.

MatBal Forecast Results for Manifold/Reservoir

The lift gas requirements for the two forecasts illustrated below, show as expected, that the overall lift gas requirement increases with the addition of the new wells, but then decreases because of the increased natural lift provided by the associated gas before rising again as the reservoir pressure drops.

MatBal Forecast Results for Manifold/Reservoir

Step 10: Scenario B: New Wells And Water Injection

In this scenario the impact on field performance through the addition of a water injector coming on-line between 2010 and 2015 will be investigated:    

• Select the Forecast Model hotspot button or Forecast/Forecasting Model menu item and select Water as the Injection Type, but leave the Forecast Type set to Pressure Control (well model).

The addition of the water injection well is carried out in the same manner as before with Wells 1, 2 and 3:

• Select the Tubing Performance hotspot button or Forecast/Tubing Performance menu item, then choose the Injection tab. Select Add, then select the vfp table called Injector.vfp in the MatBal/Data folder. Select OK to validate and close the Tubing Performance dialog.
• Select the Well Data hotspot button or Forecast/Well Data menu item to open the Wells dialog window, then select New to open the New Well sub-dialog, enter Water Injector as the well name, select Water Injector as the Well Type and then OK from the sub-dialog.
• With the water injection well highlighted in the Wells dialog, select Edit to open the Well Data dialog window for the injection well, choose the IPR tab, then either import the IPR data from the WellFlo model called Water Injector in the MatBal/Data folder or manually enter the data presented below:

• Choose the Forecast/Constraints tab and enter a Start Date of 01/01/2010.
• Whilst in the Forecast/Constraints dialog assign the correct vfp table to this well - click on the Browse button, select the Injection tab and then select the Injector.vfp file.

The water injection manifold pressure must now be defined. For this example it is assumed that the manifold pressure will be held constant at 500 psia.

• Return to the main Forecast dialog window and select the Manifold Schedule hotspot button or Forecast/Manifold Schedule menu item and enter 500 psia in the Water Inj. Manifold Pressure field.
• The data required for this forecast is now complete. Select the Forecast hotspot button or Forecast/Forecast menu item and generate a forecast with a Forecast ID entitled Injection in 2010.
• Generate additional forecasts for the commencement of water injection in 2012 and 2015 by editing the start date for the water injector.

Step 11: Comparison of Results

The figure below compares the cumulative oil production for the five forecasts; the effect of drilling the three new wells results in some gain in production, but only by introducing water injection at an early stage is there is a significant gain in oil.

 
MatBal Forecast Results for Manifold/Reservoir

The lift gas requirements for each scenario illustrated below, also indicate that as a result of the higher reservoir pressure obtained with water injection, the maximum lift gas injection rate increases from 11.5 MMscf/d to 18 MMscf/d.

MatBal Forecast Results for Manifold/Reservoir