Deepwater Gas Well Testing: Methods for Predicting Hydrate Formation

1. Practical Methods for Predicting Hydrate Formation during Gas Well Testing in Ultra-Deep Water 10th September 2014 Alex Lowden Academic Supervisor: Alain Gringarten Industry Supervisor: Tim Whittle (BG Group)

2. Deepwater Oil & Gas Discoveries 2013/14 Block/prospect, Operator, Year, Water Depth > 3,000ft India Gas: Block CYD5, Cauvery Basin, Reliance – 2013/5,717 Cyprus Gas: Block 12 (Aphrodite), Noble – 2013/5,574 Canada Oil: Harpoon, Statoil – 2013/3,630 Oil: Bay Du Nord , Statoil – 2013/3,874 South China Sea Gas: Lingshiu 17-2, CNOOC – 2014/11,512 Cote d’Ivoire Oil: Block CI-100, Total – 2013/7,400 Malaysia Gas: Block SK318, Shell – 2014/6,963 Gulf of Mexico Oil: Shenandoa, Anadarko – 2013/ 5,800 Oil: Coronado, Chevron – 2013/6,127 Oil: Gila, BP – 2013/4,900 Oil: Dantzler, Noble – 2013/6,580 Oil: Block 525, Shell – 2014/7,479 Oil: Exploratus-1, Pemex – 2014/8,202 Oil: Maximino, Pemex – 2013/9,570 Israel Gas: Tamar SW. Noble – 2013/17,420 Gas: Karish Alon C, Noble – 2013/5,742 Brazil Oil: Block BM-S-50, Petrobras – 2013/6,183 Oil: BM-POT-17 Block, Petrobras – 2013/5,712 Gabon Gas: Diaba License G4-223, Total – 2013/5,673 Mozambique Gas: Area 4, Alguha, Eni – 2013/8,537 Gas: Area 4, Coral, Eni, 2013/6,676 Gas: Area 1, Orca, Anadarko – 2013/3,481 Tanzania Gas: Tangawizi-1, Statoil – 2013/7,544 Gas: Mronge-1, Statoil – 2013/8,200 Gas: Taachui-1, BG – 2014/3,270 Gas: Piri, Exxon – 2014/7,440 Gas: Ngisi-1, Mkizi 1-3, BG – 2013&2014 /4,600-5,900 Congo Oil/Gas: Marine 12, Eni – 2013/9,882 Angola Oil/Gas: Block 20, Sonangol, BP – 2014/12,703

3. Crystalline solid compounds • Stabilised by encapsulating a low molecular weight guest molecule • Growth occurs in the presence of water/gas • At low temperatures and elevated pressures What Are Gas Hydrates? http://i.ytimg.com/vi/nUluhIa-hzA/0.jpg. Accessed 01/09/14 http://i.ytimg.com/vi/nUluhIa-hzA/0.jpg. Accessed 01/09/14

4. The Problem:Hydrate formation during gas well testing in deep and ultra-deep water

5. The Problem:Hydrate formation during gas well testing in deep and ultra-deep water The Solution:To provide a fast and reliable method to predict gas temperatures during well testing

6. Presentation Workflow 1 The Deepwater Environment 2 Modelling temperature during a Shut-in Period Theory A) Programme Development and Testing B) 3 Modelling temperature during a Flowing Period Theory A) Programme Development and Testing B) 4 Field application

7. The Deepwater Environment 20 24 12 16 8 4 Sea Current Velocity, m/s Ocean Temperature, ͦC 0 0.4 0.2 0.5 0 0 500 1000 1500 Depth, mss 2000 2500 3000

8. Presentation Workflow 2 Modelling temperature during a Shut-in Period • Theory • Analytic solution A) Programme Development and Testing B)

9. Theory: Shut-in Period Sea Current Direction A solution for the temperature at any point in the riser as a function of shut-in time • As seawater flows around the riser: Boundary layer • Multi-layer composite cylinder • Transient heat conduction in the radial direction • Heat transfer to the surrounding ocean by forced convection Gas hydrate formation typically starts at a gas-water interface

10. Theory: Shut-in Period How is heat transferred from the gas to the surrounding ocean? 1. Production tubing and outer riser Multilayer conduction problem 2. Condensate water layer 3. Riser Annulus Gas + Condensate Water Condensate Water Layer • Using a Green’s function approach to derive a solution to this problem

11. Theory: Shut-in Period How is a solution obtained? Multilayer conduction problem Condensate water layer Annulus fluid Gas + Condensate Water Condensate Water Layer

12. Programme: Shut in Period Programme tested against transient data from a DST conducted in deepwater • Calculated temperatures are within +-5% of gauge data for all shut-in periods Within 4 minutes, a well test planner can predict gas temperatures for a shut-in operation

13. Presentation Workflow 3 Modelling temperature during a Flowing Period Theory A) • New approach to improve the accuracy of existing heat transfer calculations Programme Development and Testing B)

14. Theory: Flowing Period Hasan et al (2005) Analytic Solution • Methods of solving this equation in the literature make a number of assumptions • Solving this equation using numerical integration RK-4 Numerical Integration Can this numerical method be used to create a programme?

15. Theory: Flowing Period Approach: numerically solve for the fluid temperature and pressure • Run time for each temperature and pressure traverse is less than a minute 0 Hours 0.5 Hours 4 Hours 0.5 Hours 4 Hours 0 Hours Well test planners can use this programme to quickly check if operating conditions are within the hydrate formation region

16. Programme: Flowing Period • To test the programme, transient temperature profiles were calculated for flowing periods of the DST Gauge Depth • Comparison with dynamic multiphase flow simulator +-10% The accuracy of this programme is verified against field data and calculations from OLGA

17. Presentation Workflow 4 • Field application • Gas hydrates formed during a flowing period of the DST

18. Gas Hydrate Formation Well Configuration • Flowing gas temperatures over the length of the well: 5 Hours 2 Hours 1 Hour

19. Summary