Benthos response following petroleum exploration in the southern Caspian Sea: Relating effects of nonaqueous drilling fluid, water depth, and dissolved oxygen

Abstract

The effects of linear alpha olefin (LAO) nonaqueous drilling fluid on benthic macrofauna were assessed over a six year period at a southern Caspian Sea petroleum exploration site. A wide-ranging, pre-drilling survey identified a relatively diverse shelf-depth macrofauna numerically dominated by amphipods, cumaceans, and gastropods that transitioned to a less diverse assemblage dominated by hypoxia-tolerant annelid worms and motile ostracods with increasing depth. After drilling, a similar transition in macrofauna assemblage was observed with increasing concentration of LAO proximate to the shelf-depth well site. Post-drilling results were consistent with a hypothesis of hypoxia from microbial degradation of LAO, supported by the presence of bacterial mats and lack of oxygen penetration in surface sediment. Chemical and biological recoveries at ≥200m distance from the well site were evident 33months after drilling ceased. Our findings show the importance of monitoring recovery over time and understanding macrofauna community structure prior to drilling.

Differential impact of anthropogenic pressures on Caspian Sea ecoregions

“…Some of the respective compounds might be biologically magnified along the food chain, causing physiological impairments (Bickham et al, 1998;Moore et al, 2003;Wilson et al, 2014). Thus, chemical pollution may be of particular concern for endemic species in the deeper parts of the Caspian Sea (Parr et al, 2007;Tait et al, 2016) and could, for example, explain the strong decline of mollusks species in the profundal zone (Wesselingh et al, 2019).…”

A novel control system design for automatic feed drilling operation of the PLC-based oil rig

“…It is not as easy as it looks to establish the time-delay, timevarying and non-linear mathematical models. Therefore, even if the closed-loop control features certain accuracy, stability and fastness, this conventional control method cannot effectively overcome the large-scale variation of load parameters and the nonlinear effects, being unable to achieve more accurate and stable control [6][7][8].…”