Modern Drilling Organization

Dugong Appraisal 5 min well review

During 2020, Neptune received NPD approval to drill the Dugong Tail prospect in the license PL882. Two wellbores were planned, the vertical 34/4-16 S (drilled and currently suspended) and a side-track down-dip to the north. These wellbores will be followed by the Dugong appraisal 34/4-17. The purpose of this appraisal well is to drill through the sandstone formations Draupne (Viking Gp) and Rannoch (Brent Gp) and obtain data on the hydrocarbon potential and thus contribute to increased volume for the Dugong license. A well test (DST) will be performed to evaluate the dynamic reservoir deliverability.

Screenshot 2021 07 11 at 03 17 29

How to use previous experiences from offset wells?

Near field exploration is a valuable business. You can tie-in to existing infrastructure for production and you have lots of offsets to work on. Within 8 kilometres of the planned well location (61°33'46.09''N, 02°01'57.74''E), we find 8 wellbores without considering the latest already drilled since the last year (34/4-15 S, 34/4-15 A and 34/4-16 S) and the planned side-track 34/4-16 A.

A quick look at the Geology

The discovery well 34/4-15 S and the down-dip sidetrack 34/4-15 A proved oil in the Viking and Brent Groups of the Dugong prospect, which consists of two reservoirs that lie at a depth between 3,250 – 3,400 metres.

Screenshot 2021 07 11 at 03 20 52

Draupne as seal and Heather as seal/trap from Viking Gp are presented in offsets together with Brent Gp as additional hydrocarbon trap, these at depths between 3,450-4,169 mTVD. Northwestern (almost North) wells reach the same groups some hundreds of metres deeper.

Screenshot 2021 07 11 at 03 28 58

The planned trajectory is expected to reach Utsira and Lark formations, at approximately 1,000 m depth. Shetland Gp would be reached later at around 2,000 m depth and Intra Draupne and Heather formations (Viking Gp) below 3,350 m. Then Brent Gp would be the main target, where it is planned to conduct the Drill Stem Test (DST).

Screenshot 2021 07 11 at 03 30 40

Defining hole sizes and drilling mud program

The upper hole sections of 42”x36” are planned to be drilled with seawater and bentonite and drilled down to 457 m MD. Water-based drilling fluid (WBM - Glydril) will be used in the 26" section together with foam cementation to the seabed. A 17 ½” hole is drilled down to 1,983 m MD with an oil-based drilling mud (OBM). OBM is used for the 12 ¼” section down to 3,311 m MD, and the deepest hole section of 8 ½” is planned to be drilled with OBM down to a depth of 3,800 m MD. The nearby wellbores 34/4-8 and 33/6-2 provide valuable PPFG data to run a decent comparison and quick check.

Screenshot 2021 07 11 at 03 33 43

Screenshot 2021 07 12 at 09 22 07

The mud program is expected to involve values of around 1.03sg for the shallowest section (42” hole), 1.25sg approximately for 26” hole section, then from 1.30sg to 1.42sg for the 17 ½” hole and a range of 1.42sg to 1.52sg for the next 12 ¼” hole section. Finally, the last section will be drilled with 1.48sg OBM. Mud weight data available from the offset wells indicate these are good enough ranges for this design.

Screenshot 2021 07 12 at 09 23 21

A better look at the wellbore sections

Screenshot 2021 07 12 at 09 24 55

A standard pattern is followed in designing the sections for the Dugong Appraisal. That becomes clearer by looking at some of the offset wells, including those latest drilled by Neptune.

Screenshot 2021 07 12 at 09 26 28

There are 36 "x 30" guide tubes to be run and foam cemented along their entire length. A 20” casing is set in the 26” hole with foam cementation to the seabed. Drilling cuttings and any excess cement are discharged from the rig using mud return to rig (RMR) without the use of risers. Followed by a 13 ⅝” casing in 17 ½” hole with top of cement (TOC) at 200 - 400 m above set depth, and 9 ⅝” casing for the 12 ¼” hole section, cemented 300 - 400 m above set depth. A 7” liner is considered for the last hole. In the case of a discovery, a well test (DST) will be performed and data collection will be carried out according to a separate program and then plugged back permanently.

Screenshot 2021 07 12 at 09 28 16

How does the well path look?

The trajectory for the planned wellbore will be vertical from surface down to 3,800 m MD/TVD (RKB), reaching Draupne (Viking Gp) and Rannoch (Brent Gp).

Screenshot 2021 07 12 at 09 29 34

How long does this project is expected to take?

The well is scheduled to be drilled in about 71 days. In the case of a dry well, the drilling time is estimated at 41 days and in the case of discoveries, a well test is carried out with a duration of approximately 30 days. The well will be permanently plugged back (NORSOK D-010, 2013).

Screenshot 2021 07 12 at 09 32 30

Once all the main design parameters (those previously mentioned) are covered, it’s time to take a look at further operational details. In the picture below, you can see an initial check through the relevant calculations for the current design. Run several calculations with just one click and Ta-Da!, get a lot of plots and the risk report on the right side panel shows clearly what needs to be reviewed (:

Screenshot 2021 07 12 at 09 35 52

Did you see the risks with red markers? Well, some casing properties need some attention. But, that could be for a next occasion (;

Best of luck!

What kind of data can you find at Pro Well Plan software?

Our platform allows us to easily integrate with any public or private database. We also create your reports and QC your data, so you can invest in analysing and improving your wells.

Screenshot 2021 07 12 at 09 37 35

Would you also be able to do well designs and offset reviews in hours instead of months? Feel free to reach us at our website or LinkedIn account.

Share this

Latest news