URL: https://geoscience.data.qld.gov.au/dataset/cr143511
Cased with 125mm uPVC casing from surface to 194.35m MDGL with a 125mm stainless steel well screen from 170-175m MDGL and 125mm uPVC sliding sleeve from 162-163m MDGL.
A gravel pack (Unimin 5/2) and bentonite annular seal were both installed in the annulus from 196.40-169 and 168-169m MDGL respectively.
Whilst attempting to hold 30psi inside the casing, returns were observed in the annulus.
A test pull on the casing showed no overpull and 71.10m of 125mm uPVC was recovered to surface.
Multiple fishing attempts were unsuccessful with the final documented top of fish (TOF) at 77.00m MDGL. The decision was made to plug and abandon Lauren GW1 and the rig was moved 4.75m WSW to spud Lauren GW1A.
The fish remaining downhole in Lauren GW1 is 123.25m in length, located between 77.00 and 194.35m MDGL and consists (base to top) of 3 joints of 125mm uPVC casing (19.35m), 125mm x/o, 125mm stainless steel well screen, 125mm x/o (total of 5m), 125mm uPVC casing (7m), 125mm uPVC
sliding sleeve (1m) and 90.9m of 12mm uPVC casing.
On the 23rd June 2011, Lauren GW1 was plugged and abandoned (P&A) by the TCL 1 rig.
The P&A operation has limited details in the daily drilling reports and drilling summary.
The well abandonment schematic (Figure 2) provides a diagrammatic representation of the likely subsurface and surface P&A configuration.
A 2bbl 5% bentonite cement slurry (cement plug number 1) was placed with a tremmie line in the open 8 1/2 inch hole from 66-75m MDGL, 2 meters above the TOF.
There is no documentation that; i) cement plug number 1 was placed on a stable base (i.e. hi-vis pill) to prevent slumping whilst the cement hardened, or ii) of a tag on the top of cement (TOC) plug number 1 after waiting on the cement to harden to confirm its depth.
As such, it is possible that cement plug number 1 may have slumped downhole to an unknown depth interval.
The drilling summary indicates that the 0-1m MDGL steel surface casing was removed and a 1m surface cement plug was placed from 0-1m MDGL in the open 12 1/4 inch hole.
The same slumping risk described above would apply to this surface cement plug. Excavation activity on the 23rd June 2023 to confirm the exact well location and presence of the surface cement plug, was successful in locating the Lauren GW1 well bore and confirming the presence of a circular 12 1/4 inch diameter gravel type plug material at about 0.60m MDGL (Appendix 4).
The subsurface and surface P&A configuration (Figure 2) is derived from all of the available data balanced with an appreciation of what the operational team / licensed water bore driller were attempting to achieve, the equipment available to them and the Minimum Standards for the construction and reconditioning of Water Bores that Intersect the sediments of Artesian Basins in Queensland (MSWBIAB) that was in-force in June 2011.
The limited documentation of the P&A operations conducted at Lauren GW1 resulted in a degree of uncertainty around the final subsurface and surface P&A configuration.
A risk assessment of this uncertainty and a range of potential downhole P&A configurations was conducted to evaluate the integrity of these P&A scenarios at Lauren GW1 as per the current "Code of Practice for the construction and abandonment of coal seam gas and associated bores in Queensland, Version 2, 16 December 2019".
The Westbourne Formation and Gubberamunda Sandstone are likely to be in communication, however it should be noted that the Westbourne Formation is classified as an aquitard, resulting in a low risk and probability of movement of fluids between the two formations.
The combination of cement plug number 1, natural backfill (i.e. collapse) of the open 8 1/2 inch hole above cement plug number 1 and the surface plug have filled the well bore from 77.00m MDGL to surface and are highly likely to ensure isolation of the Gubberamunda Sandstone and Westbourne Formation from the surface and subcropping Orallo Formation.
As such the risk assessment for the Lauren GW1 P&A is considered ALARP and compliant with relevant standards (i.e. to isolate aquifers).
A P&A ID plate was placed above the well at 0.60m MDGL and surface P&A signage was installed as per Section 37 of the "Petroleum and Gas (General Provisions) Regulation 2017" and "Code of Practice for the construction and abandonment of coal seam gas and associated bores in Queensland, Version 2, 16 December 2019" (Appendix 4).