Estimating Oil in Place with Hampson-Russell Software By Gary Thorpe

Estimating the oil in place for a prospect is a complex task. In this article, we would like to show you a quick and easy way you can create an approximate “oil thickness” map. This will allow you to get a feel for the potential hydrocarbon reserves in your study area. This example demonstrates the use of the Map Maths utility and the new contouring functionality within Hampson-Russell software. Required data: Porosity volume, easily created in EMERGE Sw or Soil , also easily created in EMERGE Top and base reservoir horizon picks Processing velocities for the area Original Oil In Place (OOIP) refers to the total volume of hydrocarbon stored in a reservoir prior to production. It may be referred to as Stock Tank Oil Initially In Place, or STOIIP.

( )oi

wb

BSV

N−

=17758 φ

For English units giving stock tank barrels (bbl)

( )oi

wb

BsV

N−

=1289808.6 φ

For metric units giving stock tank barrels

( )oi

wb

BsV

N−

=1φ

For metric units giving cubic meters.

where: N = OOIP (barrels or m3) Vb= Bulk rock volume (acre-feet or m3) Φ = porosity (fraction) from log or core data Sw = connate water saturation (fraction) from log or core data Boi = formation volume factor for oil at initial conditions. This compensates for the volume change in the oil at standard conditions at the surface.

The constant 7758 converts acre-feet to stock tank barrels (bbl) and 6.289808 converts cubic meters to barrels. Notes: We use the current SPE (Society of Petroleum Engineers) standard conditions (100.00kPa and 15°C) and that the scientific community instead uses 0°C as standard temperature. So check which standard conditions your equations are using as older documents also may use 101.325 kPa. Some documents use FVF to represent Boi.

Petroleum engineer shrinkage is oiB1

and is sometimes used in equations instead of Boi, and multiplied against the volume instead of dividing into it. Also, there is an alternative shrinkage definition that is equal to (1 - shrinkage) as defined above. We recommend using the Formation Volume Factor as it is always consistently defined. Note that Vb is sometimes shown as A*H, where: A = Area of reservoir (acres or m2) from map data H = Average height of thickness of pay zone (ft or m) from log data We have not included a "recovery factor" since we are calculating oil in place, not recoverable oil. Example: Figure 1 is a base map showing the distribution of wells that contain logs including porosity and oil saturation. Combined with a seismic and an inversion volume in this area there is more than ample information to use EMERGE to predict both porosity and oil saturation volumes for this project area. Figure 1: Well Basemap

Figure 2: Section of EMERGE computed porosity volume

Figure 3: Section of EMERGE computed oil saturation volume

In our latest software (CE8) we are able to insert contours on to maps and slices, improving the clarity of these displays. The contouring functionality allows the user to include contours at major and minor intervals, and can be at automatically or user

specified intervals. This is achieved by using View > Display Options from the displayed slice. You can use the View>Regrid option if you wish to smooth the slice display. In this example, the area of interest is a channel that runs east-west from well 01-08 to well 01-17. Figures 4 and 5 depict slices through porosity and oil saturation volumes respectively. The slices are extracted over the reservoir interval as defined by the horizons. Figure 4: Porosity slice between horizons

Figure 5: Oil Saturation slice between horizons

In figure 5 you can see that the oil saturation is high in the channel area. In order to complete our calculation, we need to know the reservoir thickness (isopach). One way we can compute this is to first of all convert the seismic data and/or horizons into the depth domain. If your input data is in the time domain and you have velocities in the same area, then you can use the HR Process > Utility > Time to Depth Conversion to convert the data. In addition to converting the seismic, you may use this tool also to convert any time horizons in the project.

Figure 6: Isopach between horizons

To calculate oil in place we use:

Oil in Place = Rock Volume * Porosity * Oil Saturation Note that in this example, we use the isopach to give us the rock volume in the depth domain (Z direction) only. We have also not converted to Stock Tank Barrels. We use our Map Maths utility to multiply our slices to find the oil thickness (though the oil could be spread through the zone). The Map Maths functionality is found under the Process menu (Figure 7). Figures 8 to 10 show the Map Maths menus set up for the oil thickness computation. In particular, figure 10 shows the Map Maths script needed to complete the simple multiplication of the three slices. Inputs to Map Maths can be data slices of any type created in or imported into Hampson-Russell. You can use horizons in depth or time domain. Simple map calculations involving just two maps can be performed using Map Operations.

Figure 7: Map maths option

Figure 8: Choose input maps/slices

Figure 9: Output type options

Figure 10: Map Maths

Figure 11: Oil thickness map

Figure 11 therefore shows you the estimated “thickness” of the oil in between the two horizons at each point on the map. Compared to the isopach map (figure 6), this map gives you a representation of which areas may have high oil content. In order to get to the actual OIP number, it is necessary to sum these results over a defined area, such as within a contour. Summing values in contours (planimetering) is a functionality that we are currently considering for inclusion in our development plans for our next major software update (CE9). However, there are further steps you can take with the current Map Maths. To better constrain the interpretation you can make use of map zones in Map Maths.

Figure 12:

As shown in figure 13, you can draw a zone interactively on the data slice. Figure 13: Polygon zone on slice

In Map Maths, choose the restricted zone option:

Figure 14: Map Maths Zone option

As in figure 15 choose the slice you are editing as your output.

Figure 15: Map Maths

Figure 16: Slice of zone area

Then you can use View>Display Statistics to view statistics just of that zone.

Figure 17: Zone statistics

From these statistics we can then estimate Oil in Place for the whole zone. Estimated Oil Volume = Sum * (Number of valid values -1) * bin spacing e.g. Oil volume = 166 * 523 * 1 = 86,818 m cubed of oil in the zone. We then have a quantitative result from our analysis. Note Our Pro4D time-lapse software has an excellent volumetrics tool which enables the estimation of hydrocarbon volumes based on maps including area, thickness, porosity and saturation. This example was run using CE8R1.2 software.