TECHNICAL ASSESSMENT Petapahan-Kotabatak Pipeline Flow Assurance
SLO Capital Project Facility Engineering - Heavy Oil Chevron Pacific Indonesia 2015 Rev
Date
0
Oct 2015
Pages
Description
Prep’d
Chk’d
PEATRICE
HANS
RAMDANI
App’d
Petapahan Kotabatak Pipeline Flow Assurance Report
Executive Summary The objective of this study is to assess opportunity on reducing water transfer for Petapahan oil wet shipment to Kotabatak GS. Currently Petapahan GS sends ~90,000 BFPD (~15,000 BOPD and ~75,000 BWPD) as wet shipment to Kotabatak through ~20 km Petko Pipeline. Wet shipment is done because of waxy oil characteristic and Petko pipeline integrity issue. Old Petko pipeline has corrosion in several spots and thinner wall thickness which has limited the operating pressure on the pipeline. However, pipeline integrity issue will be alleviated by on-going Petko Pipeline Replacement project.
To evaluate the minimum water required to transfer oil to Kotabatak, the proposed new condition will be evaluated based on minimum velocity and temperature profile along the pipeline. Minimum fluid velocity is 3 fps (based on API RP 14E), which equals to 75,000 BFPD flow through 18” the pipeline. As per production forecast, oil transfer from Petapahan to Kotabatak will be ~20,000 BPD. Therefore, the minimum water to satisfy minimum velocity requirement will be ~55,000 BPD. This will change the water to oil ratio for wet shipment from 5:1 to 2.75:1.
Based on the new proposed water to oil ratio for wet shipment, a Pipephase simulation has been performed to model temperature profile along PetKo pipeline at various ambient condition. At the average ambient temperature,
mixture temperature at
Kotabatak GS is only slightly higher than Petapahan oil Wax Appearance Temperature (WAT) (140.6 F vs 137 F). At minimum ambient temperature, mixture temperature at end point (Kotabatak GS) is almost the same as WAT (139F vs 137F), hence congealing issue has just started to appear.
SLO Capital Project – FE – HO – CPI 2
Petapahan Kotabatak Pipeline Flow Assurance Report
1. Objective The objective of this study is to assess opportunity on reducing water transfer for Petapahan oil wet shipment to Kotabatak GS. Modelling and analysis was developed using the following information source and tool:
Scope : PetKo Pipeline Tool : PipePhase V9.5 Daily report : September 2015
2. Input Data Oil properties is taken from Petapahan oil analysis performed by TS Lab:
Faci li ty Uni t
Sampl ing Poi nt
Pour Viscosity at Viscosity at Viscosity at Viscosity at Viscosity at Viscosity at Viscosity at Viscosity at Viscosity at Viscosity at Viscosity at Viscosity at Point (F) 110 °F, SUS 110 °F, cP
WASH TANK
INCOMING FROM FIE LD 103
WASH TANK WASH TANK
OUTLET
110 °F, cSt 130 °F, SUS 130 °F, cP
130 °F, cSt 150 °F, SUS
150 °F, cP
150 °F, cSt 180 °F, SUS 180 °F, cP
180 °F, cSt
INCOMING FROM WEST 109
128 248.6
23.1 47
26.9 53.8
82.4 127.6
14 23.4
16.2 26.8
63.8 91.4
10 16
11.6 18.4
52 67.6
7.3 11
8.5 12.6
105
139.2
25.3
29.4
86.6
14.8
17.2
67.3
10.8
12.5
53.6
7.7
8.9
From the oil analysis, pour point for Petapahan oil is 105 F. For ambient temperature, the reference data is taken from BMKG (Meteorology Agency) for monthly average ambient temperature at Pekanbaru in 2014.
Figure 2.1 Monthly average temperature at Pekanbaru in 2014
SLO Capital Project – FE – HO – CPI 3
Petapahan Kotabatak Pipeline Flow Assurance Report Kotabatak Shipped Oil Character Wax Content, %WT 15.19 137
WAT, F
Wax Appearance Temperature (WAT) for Petapahan oil is assumed to be the same as Kotabatak since currently there is no specific data for Petapahan. WAT for Kotabatak oil is obtained from HCT study on flow assurance of its shipping line. The bases of this assumption are: 1. These two fields are close. The precipitation age and hydrocarbon fluid source is relatively the same. 2. Reservoir properties such as permeability, temperature, and porosity is also similar Therefore WAT for Petapahan oil is assumed to be 137F.
3. Analysis Wet shipment flow rate will be evaluated on the basis of minimum velocity. Minimum flow rate will be evaluated for its temperature profile along the pipeline and compared against pour point temperature and wax appearance temperature to evaluate whether congealing issue will present or not.
3.1 Velocity Flow velocity is calculated from fluid flow rate through that pipeline divided by crosssectional area of the pipeline. v = Q/A = 0.03744Q/πD2 v = fluid velocity (fps) Q = fluid flow rate (bpd) D = pipeline inside diameter (inch)
SLO Capital Project – FE – HO – CPI 4
Petapahan Kotabatak Pipeline Flow Assurance Report
Using the above formula, the minimum flow rate will be determined based on assumed minimum fluid velocity permitted. At a lower fluid velocity in the pipeline, solids have a tendency to separate out from the liquid phase. On Material and Design of Liquid Pipeline CES PP DU-5023-B, the sizing criteria for off-plot facility are as follow: 1) Unless limited otherwise, maximum line velocity in pipeline shall be governed by factors such as erosion and noise 2) Apparent velocities of pure liquid or vapor-liquid shall not exceed the following:
=
, √
where v = velocity (fps) C = value based on fluid characteristic
= density (lb/sf) Recommend values of C shall be as per the table below: Fluid Two Phase Liquid Liquid with sand Liquid with silt Liquids - Minimum
Recommended C 100 155 130 100 20
3) Surging in two-phase mixture (e.g vapor-liquid) lines shall be prevented 4) Vertical risers shall be avoided or minimized and shall not be pocketed 5) Unless otherwise specified, line size should be in accordance with API RP 14E SLO Capital Project – FE – HO – CPI 5
Petapahan Kotabatak Pipeline Flow Assurance Report
However, PP DU-5023-B does not specify about minimum velocity but stated API RP 14E can be used as reference if no specific criteria are set forth.
Using API RP 14-E (Recommended Practice for Design and Installation of Offshore Production Platform Piping Systems) as reference, flow velocity should not be less than 3 feet/second (fps). Using the above formula, for Petko pipeline (18” outside diameter, 17.25 inch inside diameter), minimum fluid flow rate that satisfy this minimum fluid velocity is 75,000 BFPD. Based on the information that future oil production from Petapahan will be 20,000 BPD, and then the minimum water required for wet shipment is 55,000 BWPD.
3.2
Temperature Profile
Simple simulation is performed using PipePhase V9.5 to model the temperature profile along Petko pipeline. Soave-Redlich Kwong EOS is used as fluid package and Beggs and Brills with Moody as the pressure drop calculation method. Crude oil contains n-paraffin waxes that tend to be separated from oil when the temperature of crude oil falls below the wax appearance temperature. With decreasing temperature, the waxes generally crystallize thereby entrapping the remaining liquid fuel in cage-like structures. When the temperature approaches the pour point, the oil may gel completely causing the cold flow problems such as blockage of flow pipes or production lines. The pour point is the lowest temperature at which oil will flow freely under its own weight. Changing on ratio volume rate fluid from Petapahan GS will change the heat transfer capacity and eventually the fluid temperature profile along Petko pipeline. The temperature profile will also impacted by the ambient temperature at a given time. The Petko pipeline schematic in PipePhase is shown in figure below:
SLO Capital Project – FE – HO – CPI 6
Petapahan Kotabatak Pipeline Flow Assurance Report
Steady state hydraulic simulation was performed with the following basis: 1. Fluid composition based on oil analysis and oil and water volume rate transferred to Kotabatak
*Source: TS IBU (Indo Asia Bussiness Unit) Laboratory Data (analyzed on 4 April 2011)
2. Destination pressure at Kotabatak GS (pig receiver) is set at 25 psig 3. Operating temperature at Petapahan GS is taken as average temperature fluid sent (oil from shipping tank is 152F and water from surge tank is 150 F) 4. Pipe segment (length, elevation change, elbow, valve, fitting, etc) is based on PetKo Pipeline drawing: Pipeline Overall Layout and Key Plan (MD-OPFO-KTBT-PP00001) 5. Pipe inside roughness is assumed as new pipeline from carbon steel (roughness coefficient = 0.0018) 6. Based on IPSO 2015, oil transferred from Petapahan to Kotabatak is around 20,000 BOPD. SLO Capital Project – FE – HO – CPI 7
Petapahan Kotabatak Pipeline Flow Assurance Report
Temperature profile along pipeline will be compared against pour point and WAT of Petapahan oil. Heat loss will occur along pipeline because of the difference between fluid temperature inside the pipeline and the ambient temperature.
WAT Pour point
Figure 3.1 Temperature profile at average ambient temperature
At average ambient temperature (77F), by wet shipping 20,000 BOPD Petapahan oil with 55,000 BPD of water, minimum temperature fluid (when reaching Kotabatak GS) is estimated to be 140.6 F. This temperature is still above both Petapahan oil pour point temperature (105F) and also Wax Appearance Temperature (137F).
SLO Capital Project – FE – HO – CPI 8
Petapahan Kotabatak Pipeline Flow Assurance Report
WAT Pour point
Figure 3.2 Temperature profile at minimum ambient temperature
As worst case scenario, similar simulation is performed at minimum ambient temperature, (72 F). Wet shipping 20,000 BOPD Petapahan oil with 55,000 BPD of water, minimum temperature fluid (when reaching Kotabatak GS) is estimated to be 139.9 F which is still above Petapahan oil pour point temperature (105F) but only slightly above its Wax Appearance Temperature (137F). It showed that this condition (wet shipping 20 MBPD of oil with 55,000 BPD of water) is the minimum water to oil ratio that can be applied without congealing issue.
4. Conclusion and Recommendation a. Minimum fluid delivered through Petko Pipeline is ~75,000 BFPD. b. For future wet shipment (after PetKo pipeline replacement is completed), water can be reduced to 55,000 BWPD for wet shipping 20,000 BOPD based on the evaluation of temperature profile and oil characteristic (pour point and WAT).
5. Attachments
PipePhase v9.5 Model SLO Capital Project – FE – HO – CPI 9
Petapahan Kotabatak Pipeline Flow Assurance Report
6. References a. CES Material and Design of Liquid Pipeline PP DU-5023-B b. API RP 14E Recommended Practice for Design and Installation of Offshore Production Platform Piping Systems c. Petapahan Pipeline Overall Layout and Key Plan (MD-OPFO-KTBT-PP0-0001)
SLO Capital Project – FE – HO – CPI 10
