SSC: Bathos P-101 Production 8-1

Bathos P-101 Production

Overview

Chapter 8 is a case modeled after a South Texas well. The Bathos P-101 well produces a light oil (API 41) with an associated gas. The reservoir is a calcite-cemented sandstone at moderate temperature/pressure (90C, 350 atm). The produced water contains about 50,000 mg/l TDS. The reservoir requires water injection, and a tertiary aquifer water with moderate incompatibility is currently the best choice. The injection and mixing scenario is also simulated.

Setting up the OLI Studio File

✓ Start the OLI Studio and start working from a new file

This chapter uses English units and you need to change the file units to Scale English, specifically the Saturation and Scale Scenario

✓ Before adding any objects, click on the top-level object in the navigator -

✓ Click on the units manager button in the toolbar -

✓ Change the Object type to Brine and set the default units to English-batch-conc

✓ Continue with the remaining objects

Object Default Unit

Brine English Batch Conc

Oil English Batch Mole Frac

Saturator Scale-English Flowing Conc

Scale Scenario Scale-English Flowing Conc

Mixing Scale-English Flowing Conc

SSC: Bathos P-101 Production 8-2

✓ Name the file Bathos-GS Scenario, then press Save

Task 1 – Create the Bathos P-101 Brine

The brine’s composition is in the table below.

Bathos P101 Brine Analysis

Cations mg/L Anions mg/L Neutrals mg/L Measured Properties

Na+1 15260 Cl-1 24500 B(OH)3 107 Temperature 25C

K+ 180 SO4-2 160 SiO2 60 Pressure 1 atm

Ca+2 850 HCO3-1 (see alk) pH 6.7

Mg+2 135 Acetate (-1) 386 Alkalinity 673

Sr+2 65 Density 1.026

Ba+2 1.3 Econd (mho)

Fe+2 2.1 TDS (mg/l)

✓ Add a Brine Analysis and rename it Bathos P101

✓ Enter the composition from the table above in the Data Entry grid

✓ Select the Show Non-zero Only box

✓ Look in the lower right of the Summary box and note the charge balance output.

The software added approximately 799 mg/L of Na+1 to balance the charge imbalance of -0.023 eq. Notice in the Data Entry grid that the balanced Cl-1 concentration is 25299.5 mg/l.

✓ Select the Reconcile tab

✓ Enter the measured pH (6.7), alkalinity (673), and density (1.024)

The calculated results are 6.6 pH and 186 mg/l of HCO3 in total alkalinity. A bicarbonate concentration was not entered, because a total alkalinity was measured, and no inorganic carbon was reported. Therefore, is is straightforward to reconcile the alkalinity values.

SSC: Bathos P-101 Production 8-3

The two options for adding/removing bicarbonate alkalinity is to either use the Measured pH & Alkainity

calculation option – this is the automatic approach. The second way is to simply enter an alkalinity value in

the Data Entry table. The estimated amount needed is 673-186=487 mg/l HCO3 (measured-calculated

alkalinity).

✓ Return to the Data Entry tab, deselect the Show Non-Zero only box, and enter 487 mg/l HCO3-1

✓ Return to the Reconcile tab, Calculate, and review the calculated pH and alkalinity

The alkalinity did not reach 673 mg/l as expected. The reason is because the waters salinity affects species activity, that is, the elevated salt concentrations change the properties of the water and the other ions, and as a result, the alkalinity-per-mass property of bicarbonate is lower than what it would ideally be if no salt were present.

✓ Change the bicarbonate to 506 mg/l and recalculate

SSC: Bathos P-101 Production 8-4

The alkalinity is now consistent with the measured value. Now however the computed pH is greater than reported and the required Cl-1 to balance charge decreased to 505.5 mg/l.

The pH is also higher, 7.3. The alternative to balancing alkalinity with HCO3-1 addition resolved one

imbalance. This however, does not reconcile the pH. If both need to be matched, then the Measured pH

and Alkalinity reconcile options would be preferred.

Task 2 – Create the Bathos P101 Crude Oil

You will create an oil analysis using assay data. The Oil Analysis’s Design menu has four screens noted by a colored tab: Combined (pink) tab, Pseudocomponents (blue tab), Assay (red tab), and Reconcile (teal tab).

✓ Add an Oil Analysis and name it P101 Crude.

✓ Click the red Assay tab

The Assay screen contains three data entry grids: Component, Distillation Data, and Entry Options. The appendix at the end of this chapter explains assay options in further detail.

The data to be entered is shown in the two tables below. The first table contain the assay specifications, name, fraction, measurement type, etc. The second table contains the experimental data.

SSC: Bathos P-101 Production 8-5

Ass

ay

Da

ta

Name ASSAY

Dis

tilla

tio

n d

ata

Volume% Temperature(°C)

Mole% 98.4 1 26

Entry Options 5 41

(experiment) Type ASTM D86 10 65

Thermo Method API-8 20 88

Density value 41 30 102

Density units API Gravity 40 129

No. of Cuts 12 50 167

60 208

70 241

80 279

90 342

95 358

100 397

✓ Type the name ASSAY in the <Enter Assay Name> cell. Press the <Tab> key to move to the next cells

✓ Enter the value, 98.4 in the mole% cell

This instructs the software that the assay represents 98.4% of the total hydrocarbon mass. The remaining 1.6% are inorganic gases.

✓ Change the Analysis type to TBP Curve

✓ Keep API-8 as the Thermo Method

✓ Enter the value 41 in the Density box

✓ Select API Gravity

✓ Change the number of cuts to 12

✓ Enter the volumes and temperatures from the bottom right table in the Distillation Data grid

✓ Click on the Display Assay Cuts button

The Assay cuts are pseudocomponents. They combine to represent the overall crude oil. Each

pseudocomponent has a name: “Assay_nbpK”, which is the name Assay you entered plus the normal

boiling point in Kelvin. The next three columns are the molecular weight, boiling point, and specific gravity

computed using the distillation data and the experimental type specification. The remaining columns are

four key critical properties. There are a total of fourteen critical properties generated, and these are found

in the individual tabs at the bottom of the table

SSC: Bathos P-101 Production 8-6

The next step is to add the inorganic data

✓ Click on the Combined tab

✓ Enter the N2 and CO2 concentrations

Component Mole%

N2 0.5

CO2 1.1

✓ Click on the Show Non-zero Only box

When done, the combined grid should look like the one below

Task 3 – Add a Saturator

You will combine the brine and oil analysis at reservoir conditions, and saturate the combined fluid with CaCO3.

P101 Saturate

Type Name Flow

Brine (bbl/day) Bathos P101 850

Oil (std bbl/day P101 Crude 2200

✓ Add a Saturator and name it P101 Current Reservoir

✓ Select the Design tab and enter the following inputs

✓ Enter the current Reservoir conditions of 200°F and 3200 psia

SSC: Bathos P-101 Production 8-7

✓ Check the Calculate Alkalinity box just below the Calculate button

✓ Select the Solid tab and place a check in the Standard solids box

You will calculate the CaCO3 scale tendency before saturating, to see how close it is to saturation.

✓ Calculate

✓ Click on the report tab and review the Scale Tendencies table

Calcite is about 73% of saturation. All other minerals are subsaturated. Barite is close, at about 67%, which

is slightly farther from saturation than calcite. And so it is reasonable to set this mineral to saturation for

maximum risk conditions.

You were instructed to calculate alkalinity. This is because if calcite will be reservoir-saturated then the composition effects on properties should be monitored.

✓ Record the calculated alkalinity in the Phase properties tab

✓ Return to the design tab and saturate calcite by adding CaCO3 inflow

✓ Calculate and review the top table in the report (Saturation Details).

According to the calculation, 68.7 mg/l CaCO3 is added to saturate calcite mineral. This converts to 27.5

mg/l Ca+2 and 41.3 mg/l CO3-2.

SSC: Bathos P-101 Production 8-8

The overall change is nominal to total dissolved Ca+2. It increases about 3% to 877 mg/l. Carbonate, on the other hand, increases by 41.4 mg/l, which increases the alkalinity by 13%, from 671 to 755 mg/l as HCO3

-1. The calcium change is small, and perhaps within the sampling, experimental, and fluid representation uncertainty. A Similar argument for the total alkalinity is less tenable.

The next analysis is to review the hydrocarbon tables, to review the data provided, including the water and CO2 content.

✓ Scroll down to the Oil Composition table.

The water content is 0.51 mole% and the dissolved CO2 is 0.98%. This water mass was transferred from the brine phase and the reduced CO2 (from 1.1% entered). The CO2 transferred to the brine phase.

✓ Lastly, check the brine volume (at standard conditions) and compare the values to the 850 bwpd inflows.

The difference is 0.7 bbl, and so this is the amount of missing water.

Task 4 – Add a Scale Scenario

As has been done in previous chapters, the final task is to calculate scaling tendencies.

✓ Add a Scale Scenario and name it P101 Scale Scenario

✓ Enter the Whole Fluid, P-101 Current Reservoir, and <automatic>

The grid should look like the one below.

✓ Select the Conditions tab, and enter the following information:

SSC: Bathos P-101 Production 8-9

P101 Scale Scenario Locations

Location Temp ( F) Press (psia)

Original Reservoir 200 3200

Current Reservoir 200 2300

Flowing Reservoir 200 2200

Bottomhole 200 2150

2600’ 190 1700

1300’ 180 1200

Welhead 170 800

Flowline 150 500

Separator 140 150

The screen should look like the one below:

✓ Select the Solid tab and select the Standard checkbox

✓ Calculate or press the <F9> key

✓ Select the Plot tab

✓ Open the Variables window and check all the boxes at the bottom of the window

✓ Close the window and review the results

SSC: Bathos P-101 Production 8-10

✓ Change the Y1-axis variables to Dominant Solids

✓ Save the file

SSC: Bathos P-101 Production 8-11

Summary

This is another typical well, with similar procedures to previous chapters. The difference is that this chapter introduced the oil analysis object. There are a few errors that were overlooked, including the missing water in the oil analysis and the missing dissolved CO2 in the water. This could have been resolved by adjusting the two analyses, or by creating a makeup water or CO2 stream. Both options will be considered in the advanced section of the ScaleChem training manual.

Appendix: Assay Entry Options

There are four Assay types. These are experimental methods used to create distillation curves.

ASTM D86 runs at atmospheric pressures and is used for all oil types. ASTM D1160 runs at vacuum pressures and is used for heavy oils. ASTM D2887 runs on a gas chromatograph and is used for light oils. TBP CURVE refers to true boiling point curve.

There are four methods for calculating thermodynamic properties, API, Cavett and Lee-Kessler.

API-8 and API-5 are methods that use specific gravity to determine critical parameters. Cavett is a method to determine critical parameters using the API gravity. Lee-Kessler is a method to determine critical parameters by using the Watson K. There are three average bulk density options, Specific Gravity, API Gravity, and Watson K.

Specific Gravity is the ratio of the material density to water. Studio ScaleChem requires specific gravity to be between 0.228 and 1.6

API Gravity is defined by the following equation:

API Gravity =141.5

sg− 131.5

Watson K is a method that relates density to boiling point.