Publications

Four exploration wildcat wells were drilled in the deepwater Makassar Strait: R-1 (Surumana PSC), S- 1, K-1 and K-1 ST (Mandar PSC). Because of the near absence of offset well control, site investigation work consisted of detailed mapping of shallow seismic markers, complemented by a geotechnical and geochemical program. This paper gives an overview of potential geohazards and mitigations related to this challenging deepwater environment, by presenting examples from each of the wells.Sea surface morphology was constrained by 2D-HR seismic, supplemented by Site Surveys over the R-1 lead in the Surumana PSC. In the Mandar PSC, a block-wide 3D short offset (3Dso) was used to image seafloor geometry and potential hardgrounds associated with surface hydrocarbon seeps. In the near-subsurface, a high potential for gas hydrates was identified by mapping a bottom simulating reflection (BSR) and recovering solid methane gashydrate crystals from one of the Mandar leads. Specific subsurface hazards and constraints consisted of shallow gas, locally trapped in stacked turbidite sands with distinct slump features over the R-1 prospect. A polygonal pattern of normal compaction faults potentially impacting casing shoe integrity was imaged on the 3Dso seismic around the S-1 prospect, exhibiting polygonal, radial and linear fault patterns. Dispersed gas related to surface hydrocarbon seeps is present in the entire overburden section around the Mandar prospects and formed a constraint in terms of mud aeration. A gas chimney causing signal attenuation below the surface seep near the K-1 well location was delineated by 3D seismic and allowed detailed positioning of the wellbore, avoiding high nuisance gas flow.Integration of different marine site investigation techniques lead to the successful implementation of mitigation efforts and safe drilling of the challenging shallow section. A superior product was delivered for use in broader well planning, seal integrity and prospect maturation because of the focus on regional understanding of these deepwater prospects.Keywords: Shallow hazards, BSR, gas chimney, polygonal faulting, geohazard