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The parasitic blood flukes Cardicola forsteri and C. orientalis are an ongoing health concern for Southern Bluefin Tuna Thunnus maccoyii (SBT) ranched in Australia. In this study we compared the effect of treatment, company, and ranching year on blood fluke infections in ranched SBT. SBT were sampled during the 2018 and 2019 ranching seasons from praziquantel (PZQ) treated pontoons and untreated pontoons managed by two companies. Severity of infection was diagnosed by several criteria including adult fluke counts from hearts, egg counts from gill filaments and the use of specific quantitative polymerase chain reaction (qPCR) for detection of C. forsteri and C. orientalis ITS-2 DNA in SBT hearts and gills. PZQ treatment remains highly effective against C. forsteri infection. Prevalence and intensity of Cardicola spp. infection was lower in 2019 than 2018 for Company A in treated pontoons at week 12 and week 17 of ranching, and lower for Company A than Company B in untreated pontoons at month 5 of ranching. Results indicate re-infection may be less likely in the environment near Company A pontoons, and consistent years of treatment may have lowered the parasite load in the environment. qPCR demonstrated higher sensitivity when comparing diagnostic methods for C. forsteri in heart, and higher specificity when comparing diagnostic methods for Cardicola spp. in gills. Continuing to monitor blood fluke infections in ranched SBT can help to detect changes in drug efficacy over time and help industry to develop a best practice for treatment.

Melanomacrophage centres (MMCs) are aggregates of macrophages accumulating various pigments. They have been proposed as an indicator of fish immune response. Blood flukes are common parasites in farmed fish. Two cohorts of wild Southern Bluefin Tuna (Thunnus maccoyi) were examined at transfer, before treatment against blood flukes (pre-treatment) and at harvest. MMCs were assessed in histological sections using image analysis, while Cardicola forsteri and Cardicola orientalis infection severity was determined using qPCR, count of adult flukes in heart flushes and count of eggs in gill filaments. Fish from both cohorts showed the same pattern in the changes in the surface area of MMCs. The surface area of splenic MMCs increased over the ranching duration and was positively correlated to the PCR determined copy numbers of Cardicola forsteri ITS2 rDNA in the gills of those fish. However, the infection with blood fluke was more variable, both between cohorts and individuals within the same cohort. Eggs of blood fluke were detected in renal MMCs using histology. Cardicola forsteri had a higher prevalence than Cardicola orientalis. This study contributes to our understanding of blood fluke infections in Southern Bluefin Tuna and their interactions with MMCs.

While abandoning a well from a light well intervention vessel (LWIV), and with no ability to run a mechanical cement-setting tool, a fluid barrier spacer was needed to provide a base for the cement. This barrier required a sufficient rheology to hold a 16.0 lb/gal cement slurry and to limit commingling of the cement and the fluid base, which could prevent the cement from setting and risk an inadequate cement barrier length required for abandonment regulations. Two approaches were investigated: a thixotropic water-based barrier spacer and a high viscosity spacer. Laboratory testing indicated that only the thixotropic barrier spacer maintained good separation between the 13.3 lb/gal calcium chloride/calcium bromide brine (the current annular fluid) and the cement. This testing was repeated with 8.7 lb/gal seawater, and the thixotropic barrier again showed excellent separation. Neither spacer could be weighted with barite because of limited deck space; both pills were built at 8.7 ppg. The thixotropic water-based spacer was selected for this application. The annulus was circulated to seawater, and the spacer was mixed in a cement batch tank on the vessel. This tank was then used for the cementing operations; there was no requirement to clean the tanks between mixing the cement setting spacer and the cement spacer used to cement the plug. After the pill was mixed, the tubing was punched at 4,100 ft, and a 500 ft thixotropic water-based pill was set in the annulus and outside of the punched tubing. The tubing was punched at 3,600 ft. A cement job was performed with 16 ppg cement; after the wait-on-cement time elapsed to verify the barrier, the top of cement was tagged at 2,669 ft and successfully pressure tested. The regulatory required length of the cement barrier was successfully set with the thixotropic spacer fluid as a setting base. The thixotropic spacer successfully demonstrated sustained separation and a viable fluid base for setting cement. The result is a reliable method to set cement. This method does not require the mobilization of mechanical cement setting tools; the use of the fluid as the cement base enabled the use of a LWIV and negated the expensive need of mobilizing rig barriers to be set in place.

Successfully spotting an Off-Bottom Cement Plug (OBCP) has been problematic in the oilfield for decades. The use of high viscosity support spacers below the cement plug has been an attractive method to support the cement. These isolation spacers have traditionally been formulated with either biopolymers or bentonitic clays, but they too often fail to support the cement plug due to inadequate viscosity or poor placement. The result is that the cement slumps below the desired location in the wellbore, requiring some remedial action such as spotting an additional spacer and OBCP. One response to this challenge has been the use of a packer to support the plug, but this entails the additional cost of the packer plus the rig time required to place it. A better method was needed to increase OBCP success while reducing costs. A new isolation spacer technology was adapted to meet this challenge, and the resulting field applications are described in this paper. Developmental lab testing will be detailed along with an initial trial well where the spacer was used to isolate a retrievable packer from workover debris. After success there, the same spacer technology was used to successfully support an OBCP on a rigless well abandonment.

An engineered dual-purpose drilling and screen-running fluid was required to achieve optimum oil production with increased operational efficiency in a tight pressure window environment. The fluid needed to pose minimal formation damage risk while drilling and avoid completion damage through plugging of the standalone sand screen. This required a balance between bridging material content and particle size distribution (PSD), and a low fluid rheology to minimize the equivalent circulating density (ECD). The wide temperature profile and predicted restrictive narrow pressure margin in the well favored the use of a low ECD Non-Aqueous-Fluid (NAF). An organoclay-free NAF solution was selected. To reduce solids loading and ECD further, the fluid was designed with a brine phase that was high-density calcium bromide. Sized ground marble was selected to bridge the largest pore throats (42-μm) in the reservoir sand and still be screened quickly to avoid plugging of the 150-μm 6 5/8-in. standalone sand control production screens. Fluid optimization was achieved through rheology, stability, and formation-damage testing. The return permeability on cores/matched sandstone of >97%, indicated minimal formation damage risk when drilling and after production flowback/solids removal. In the field, the reservoir was drilled without major issue (i.e. no differential sticking, no down-hole losses) and the fluid quickly reached production screen test (PST) specifications prior to running screens. The sand screens were installed without issues. Although the sand section was significantly shorter than planned, the production from ~160 ft of net pay when the well was initially flowed produced as expected. After subsequent tie-in to the host floating production storage and offloading (FPSO) unit and upon choke opening, a gradual drop in production was observed. An acid job was performed via a subsea vessel-based operation and the planned production target exceeded the original clean-up well productivity.

The aporocotylids Cardicola forsteri and C. orientalis are considered one of the most significant health concerns for Southern Bluefin Tuna (SBT) ranched off Port Lincoln, South Australia. In this study we compared the effects of different treatment strategies on blood fluke infections in ranched SBT by sampling from one untreated and two praziquantel treated pontoons progressively throughout the 2018 season. Severity of infection was assessed relative to a number of criteria including adult fluke counts from hearts, egg counts from gill filaments and the use of specific quantitative polymerase chain reaction (qPCR) for detection of C. forsteri and C. orientalis ITS-2 DNA in SBT hearts and gills. Cardicola forsteri was the dominant species detected in this study, and intensity of C. forsteri infection in SBT was significantly higher in the untreated pontoon than the two treated pontoons from week 8 of ranching. Cardicola orientalis in SBT was rarely detected, and no significant differences were seen in mortalities or condition of SBT between pontoons. Comparing diagnostic methods for C. forsteri in SBT heart demonstrated qPCR as the gold standard. This study provides important insights into the continued efficacy of praziquantel on blood fluke infections in ranched SBT.