Production Issues in Unconventional, Tight Oil Formations: Interplay of fracture treatment, reservoir and completion

Transcription

1 Production Issues in Unconventional, Tight Oil Formations: Interplay of fracture treatment, reservoir and completion Hans de Pater, Fenix Consulting Delft Jeff Saponja (Triaxon Resources/Production Plus) DEVEX 2015 May 2015

2 Outline Horizontal Well Technology Facilitates Tight Oil recovery. Most Shale Oil is really from tight reservoirs, that have been produced from vertical wells. But what Challenges bring Horizontals? Frac-Well connection Tortuosity Overdisplacement Fracture initiation Fracture containment 2

3 Canadian Viking Reservoir: Water sensitivity May hamper effective stimulation Reservoir Model Correlation from Offset Well

4 Viking E Vertical Well Frac (5 m Pay) Vertical Well 5 meter Viking Oil Zone Contained Frac Height Growth - As Shown by Low Gas Rate - TVD(m) 2090 Layer Properties R... S... M... Up... P Concentration of Proppant in Fracture (kg/m²) Fracture Length (m) Propped Length (m) Total Fracture Height (m) Total Propped Height (m) Fracture Top Depth (m) Fracture Bottom Depth (m) Average Fracture Width (cm) Average Proppant Concentration (kg/m²) Equivalent number of multiple fractures Dimensionless Conductivity BFS Viki Ru... Viki Viki... Viki... Viki... Viki... Proppant Concentration (kg/m²)

5 Wellbore Schematic

6 The estimated postfracture production from just a single fracture, with an effective propped length of 30 m and a reservoir permeability of only 0.3 md over 5 meters, would have been around 2 m3/day at ~40 bar drawdown (natural flow). Single Fracture Estimated Production - X-link Treatment -

7 Failed Treatment The actual production from the entire well was only 1.5 m3/day, at even higher drawdown. Poor Connection due to Overdisplacement? Poor Conductivity? Downward growth and proppant falling out? Water Damage? 7

8 Well-Fracture Connection Tortuosity and Multiple Fractures Overdisplacement and Poor conductivity near the well Important because of flow convergence 8

9 High Breakdown Pressure Breakdown at a gradient of 30 kpa/m (overburden 24 kpa/m) Fracture may grow quickly out of thin zone Exacerbated since developing thinner zones, compared with historical vertical wells 9

10 Breakdown Pressure and Geometry Scaled Tests on Cement Viking: High Stress and Oblique Orientation s a s o o o s s / m

11 Breakdown Gradient - May exceed Overburden G br (kpa/m) 60 Range of Stress Orientation from Nearby Wells a ( o ) ( o ) 11

12 Effect of Overdisplacement XL Gel Frac For a crosslinked gel fracture treatment, overdisplacement leaves unpropped fracture at the wellbore Layer Properties Stress (psi) Modulus (... Poisson's TVD(ft) Concentration of Proppant in Fracture (lb/ft²) Will the fracture stay open anyway? What is the effect on production? Proppant Concentration (lb/ft²)

13 Failed Treatment: Good News After 6 months shut-in PI Improved: 20,000 m3/d gas and 5 m3/d oil Apparently, soaking helped to mitigate water block 13

14 W5 Re-Frac TVD(m) 2125 Rocktype BFS Viking E Sand Viking D Sand Layer Properties Stress (kpa) New Attempt: Viking E Zone Frac Geometry - Crude-Based Gel Frac - Permeability (m Concentration of Proppant in Fracture (kg/m²) Fracture Length (m) Propped Length (m) Total Fracture Height (m) Total Propped Height (m) Fracture Top Depth (m) Fracture Bottom Depth (m) Average Fracture Width (cm) Average Proppant Concentration (kg/m²) Equivalent number of multiple fractures Dimensionless Conductivity Viking C Sand Viking C Dirty 2150 Viking C Shale Viking B Sand Viking B Dirty Viking A Sand Viking A Dirty Shale Proppant Concentration (kg/m²) Fracture Half-Length (m) 79 Propped Half-Length (m) 45 Total Fracture Height (m) 56 Total Propped Height (m) 32 Depth to Fracture Top (m) 2110 Depth to Propped Fracture Top (m) 2115 Depth to Fracture Bottom (m) 2166 Depth to Propped Fracture Bottom (m) 2147 Equivalent Number of Multiple Fracs 1.0 Max. Fracture Width (cm) 0.20 Avg. Conductivity** (md m) 48.0 Avg. Fracture Width (cm) 0.50 Dimensionless Conductivity** 31.3 Avg. Proppant Concentration (kg/m²) 4.24

15 Post-Frac Production Match Initial flush production rate appears to be some kind of storage of frac oil in fissures\fractures. 100 m3 produced in first 4 days = re-frac volume Stabilized rate can be matched with Viking E or Viking D interval assuming very low GOR (100 scf/stb = 18 sm3/m3) Model rate

16 Forecast of Oil Production (Per Frac Stage) 4 years OPT: 1050 m3 OPT: 280 m3 Production after 4 years : Contained 20 stages: Uncontained 20 stages: 14,800 m3 3,480 m3

17 Stabilizing Gas Flow Improves Production HEAL System TM Technology Solves Root Problem Key Technology Attribute regulation and smoothening of f l o from the horizontal wellbore Well 1 Well 2 Gas Production Rates Before HEAL Gas Production Rates After HEAL Inconsistent f l o from horizontal Regulated consistent f l o from horizontal Downtime > 50% due to gas interference Downtime < 5%, with regulated consistent f l o HEAL system by Production Plus 17

18 Conclusions Significant differences exist between vertical and horizontal wells, that need to be addressed for tight oil recovery with multi-frac horizontals Near-wellbore issues: plan well path and ensure high conductivity near the well Water sensitivity is often not recognized: Especially in tight oil this may hamper fracture performance Proper diagnostics is needed, but trial of oil-based or propane gives direct evidence Stabilizing gas flow from horizontals can improve productivity 18