Title : A novel approach to enhance well design using minimum horizontal stress estimation by different methods: A case study from WDDM concession, Mediterranean sea, Egypt.
Abstract:
1. Introduction:
The west Delta Deep Marine Concession is located on the northwestern margin of the Nile Delta,
approximately 90km offshore. Since 1998, +90 successful E, A&P wells were drilled. The wells have discovered and developed significant quantities of gas in a number of fields named Scarab, Saffron, Simian, Sienna, Sapphire, Sequoia, Saurus and Serpent. In addition to a number of smaller satellites around these fields. The gas discoveries in WDDM are all classified as Pliocene, Deep marine clastic turbidites that were deposited on upper-middle-lower slope setting except Mina which is Messinian, fluvio-marine clastic.
Fracture pressure and minimum horizontal stress estimation is a key factor to design a proper mud weight window (MW). In case where the MW exceeds the fracture pressure, the formation breaks and cause complete losses.
2. Well Story:
SSc-Da well original hole was drilled with MW 13.5ppg, total losses, pack-off then plug and side track the
well! Side Track-1 which was drilled with MW 13.5ppg, but again several tight spots encountered and differential stuck, then side track-1 was plugged back and drill Side Track-2 which was wisely managed and drilled with the previous MW 13.5ppg till certain depth and then set a casing and decrease MW to 11.5ppg and continue drilling until the target was safely reached
3. Objectives
In this study different methods applied on a real case in WDDM, SSc-Da well, where the MW exceed the fracture pressure and Shmin and break the formation and accordingly drilling challenges, to enhance well design using the most accurate method Of Fracture pressure and minimum horizontal stress estimation and applying lessons learnt for previous wells to the next drilling campaign safety recorders, NPT and cost would be enhanced.
4. Minimum Horizontal Stress Prediction Methods
Jaeger & Cook
- Method 1: depend on overburden & pore pressure using a constant friction coefficient.
- Method 2: depend on overburden & pore pressure using the measure friction coefficient.
Horsrud
- Method 3: depend on overburden & pore pressure using the sand friction angle.
- Method 4: depend on overburden & pore pressure using the shale friction angle.
Matthews & Kelly
- Method 5: Depend on the overburden and pore pressure using the low-bound of measure effective stress coefficient.
Hubbert & Willis
- Method 6: Depend on the pore pressure only
5. Fracture Prediction Methods
Matthews & Kelly
- Method 1: Depend on the overburden and pore pressure using the average-bound of measure effective stress coefficient.
Eaton
- Method 2: Depend on the pore pressure & the Poisson's ratio.
6. Conclusion & Recommendation:
“Mathews & Kelly” method using the average trend of effective stress coefficient, showed reliability in estimating the fracture pressure which is matched with the actual well events. While the other method like “Eaton” did not show match with well events. Also the method showed reliability in minimum horizontal stress estimating; “Horsrud” method by using the shale friction angle and “Jaeger & Cook” method by using the calculated friction coefficient of actual data for 20 wells in WDDM. While the other methods like “Hubert & Willis” did not show match with well events. By using “Mathews & Kelly” method in fracture estimation and “Jaeger & Cook” in minimum horizontal stress estimation and applying lessons learnt for previous wells to the next drilling campaign safety recorders, NPT and cost would be enhanced.
