Reduce probability for Lost circulation.
Environmental impact (17 ½ and 12 1/4 sections). Not HTHP.
| WBM | OBM | |
|---|---|---|
| Emissions | Yes | No (vessel transport to shore) |
| ROP | 1 | 1.2 |
| Consumption | X2.5 | x1 |
| Transport to/from rig | X2.5 x 1.3 = 3.25 | X1 x 1.65 = 1.65 |
| Production of slop | No | Yes |
| Effect on the working environment | -1 | -2 |
| Harmful external environment | 1 | 2 (Norwegian Continental shelf) 3 (UK sector) 4 (Africa) |
A horizontal drilling operation might result in poor hole cleaning. To overcome the hole cleaning issue, traditional procedure is to circulate mud with no drilling progression (ROP=0). This results in additional time spent in drilling operation.
With a pump flow of approx. 1 m/s on depth 3600m, it will take one hour to circulate the complete well, and 4 circulations is necessary to clean the hole, resulting in 4 hours circulation time, with no drilling progression.
This circulation procedure needs to be repeated 3 – 15 times per section. For drilling a hole with 3 sections, the total time is 36 – 180 hours. With a hourly rate of NOK 200.000, the cost will be NOK 7,2 mill – 35 mill) for the drilling operation.
For a horizontal well, MudSim makes it possible to drill the well and circulate drilling fluid simultaneously, with acceptable hole cleaning performance. This is achieved by adjusting drilling fluid parameters, especially viscosity and pump flow rate, continuously during drilling.
Traditionally, selection of Oil Based Mud (OBM) can be a challenge (source: SPE 184661 and SPE 150714).
Case: During drilling, large amount of cavings resulted in severe overpull and almost stuck pipe. Due to high concentration of KCL exposed to the formation over long time.
Result: Poor wellbore state was plugged back. Entire new 17 ½” section was drilled with OBM. Actual time used on the well was 132 days compared to planned 98 days (the total length 5200 m Measured Depth), which is an extra 34 days compared to planned.
Learning: Some overburden claystone, siltstone and interbedded sandstones can have cavings/unstable wellbore if wrong KCL when wellbore is exposed to the drilling fluid for several days.
Corrective action: Rock mechanical analysis could identify optimal KCL concentration in the drilling fluid changes with depth and sensitivity on the borehole inclination.
Cost savings: MudSim could have predicted that the formation had a potential for unstable wellbore/cavings. Potential cost reduction could have been achieved by eliminating 34 extra days of drilling. Anticipating a daily rig-rate of MNOK 4,8 /day, the result is a total saving of NOK 163 mill.
Environmental impact: The drilling of the section was decided to continue with OBM due to the unexpected problems with instability. Pre-drilling analysis identified WBM, with the right KCl concentration, could have been used. A MudSim simulation can identify WBM as an alternative instead of OBM in the 17 ½” section. No dangerous goods, less use of support vessel, less fee for final disposal of environmental hazardous waste.