Maersk (Qatar)

Conservation and management of marine biodiversity depends on biomonitoring of marine habitats, but current approaches are resource‐intensive and require different approaches for different organisms. Environmental DNA (eDNA) extracted from water samples is an efficient and versatile approach to detecting aquatic animals. In the ocean, eDNA composition reflects local fauna at fine spatial scales, but little is known about the effectiveness of eDNA‐based monitoring of marine communities at larger scales. We investigated the potential of eDNA to characterize and distinguish marine communities at large spatial scales by comparing vertebrate species composition among marine habitats in Qatar, the Arabian Gulf (also known as the Persian Gulf), based on eDNA metabarcoding of seawater samples. We conducted species accumulation analyses to estimate how much of the vertebrate diversity we detected. We obtained eDNA sequences from a diverse assemblage of marine vertebrates, spanning 191 taxa in 73 families. These included rare and endangered species and covered 36% of the bony fish genera previously recorded in the Gulf. Sites of similar habitat type were also similar in eDNA composition. The species accumulation analyses showed that the number of sample replicates was insufficient for some sampling sites but suggested that a few hundred eDNA samples could potentially capture >90% of the marine vertebrate diversity in the study area. Our results confirm that seawater samples contain habitat‐characteristic molecular signatures and that eDNA monitoring can efficiently cover vertebrate diversity at scales relevant to national and regional conservation and management.

Data on the occurrence of whale sharks, Rhincodon typus, in the Arabian Gulf and Gulf of Oman were collected by dedicated boat surveys and via a public-sightings scheme during the period from 2011 to 2014. A total of 422 individual whale sharks were photo-identified from the Arabian Gulf and the northern Gulf of Oman during that period. The majority of sharks (81%, n = 341) were encountered at the Al Shaheen area of Qatar, 90 km off the coast, with the Musandam region of Oman a secondary area of interest. At Al Shaheen, there were significantly more male sharks (n = 171) than females (n = 78; X2 = 17.52, P < 0.05). Mean estimated total length (TL) for sharks was 6.90 m ± 1.24 (median = 7 m; n = 296). Males (7.25 m ± 1.34; median = 8 m, n = 171) were larger than females (6.44 m ±1.09; median = 7 m, n = 78; Mann-Whitney U test, p < 0.01). Of the male sharks assessed for maturity 63% were mature (n = 81), with 50% attaining maturity by 7.29 m and 100% by 9.00 m. Two female sharks of >9 m individuals were visually assessed as pregnant. Connectivity among sharks sighted in Qatari, Omani and UAE waters was confirmed by individual spot pattern matches. A total of 13 identified sharks were re-sighted at locations other than that at which they were first sighted, including movements into and out of the Arabian Gulf through the Strait of Hormuz. Maximum likelihood techniques were used to model an estimated combined population for the Arabian Gulf and Gulf of Oman of 2837 sharks ± 1243.91 S.E. (95% C.I. 1720–6295). The Al Shaheen aggregation is thus the first site described as being dominated by mature males while the free-swimming pregnant females are the first reported from the Indian Ocean.

Abstract In this work, we present the study of an efficient method of separating “contaminants” from water produced from oil reservoirs, using magnetic nanoparticles (MNPs). Micron-scale, highly stable oil droplets as well as divalent cations such as Ca2+ can be removed from the produced water through the adsorption onto functionalized MNPs. The method employs MNPs to initially attach to the oil droplets or to the cations, and then to separate them from the liquid phase using a magnetic field. After separating out the “contaminant”-free water, the MNPs can be regenerated and re-used. As the collection of the contaminant-attached MNPs by the application of magnetic field gradient is a critical step for the process, we developed a 1D mathematical model for the description of the dynamics of the MNP collection in the framework of the sedimentation theory. The conservation equation for MNPs is coupled with the flux function, which accounts for not only gravity force but also magnetic force and Brownian interaction. The model describes both the behavior of colloidal particles during settling and the enhancing effects of the magnetic field due to attraction of MNPs towards a magnet. Simulations were compared with measurements from settling tests of a suspension of MNPs.

Cured poly(dimethyl siloxane) microspheres are prepared by an emulsion polymerization reaction of silicone droplets in a continuous aqueous phase. The commonly used PDMS elastomer, Sylgard 184 from Dow Corning, is used as the dispersed phase. PDMS is polymerized and cross‐linked by reacting vinyl end‐terminated poly(dimethyl siloxane) oligomers with dimethylmethylhydrogen siloxane cross‐linkers via the hydrosilylation reaction using platinum catalyst and heat. Weight ratios of 10:1, 20:1, and 25:1 of the PDMS mixtures are used and emulsified in water using two water‐soluble surfactants as stabilizers (sodium dodecyl sulphate and polyvinylalcohol). The temperature is subsequently increased to accelerate the rate of cross‐linking and prevent the prepolymer droplets from coalescing. The particle size distribution of cured PDMS microspheres is determined by Mastersizer (laser diffraction). Finally, cured PDMS microspheres are coated with poly(methyl methacrylate) using a chemical process (solvent evaporation technique). Three solvents are used in three different experiments: dichloromethane, tetrahydrofuran, and acetone. The composition and morphology of the cured PDMS microspheres and PMMA coated cured PDMS microspheres are characterized by differential scanning calorimetry, Fourier transform infrared spectroscopy in attenuated‐total‐reflection mode, optical microscopy, and thermogravimetric analysis. Curing profiles of PDMS elastomer with different ratios between the silicone elastomer base and the silicone elastomer curing agent are obtained. The reactivity of cured PDMS microspheres and PMMA coated cured PDMS microspheres are measured by rheology to evaluate the efficiency of the PMMA coating.

Abstract The use of water tracers to better understand and improve water flood performance has long been part of the reservoir management toolbox. Its use is even more relevant when applied to complex and heterogeneous reservoirs. This paper describes the planning and implementation phases of a chemical tracer injection pilot in the Al Shaheen oil field, offshore Qatar. In Al Shaheen injection water has historically been used as natural tracer to identify inter-well communication in the field by analysis of the salt and ionic content of produced water. However, this approach has become less effective over time. Identification of short-circuits is getting more complex with the increasing number of wells completed. A tracer pilot including chemical water tracers was designed to identify inter-well communication and flow paths of injected water in a complex area of the field. The geology of this area is highly heterogeneous, with a stacked sequence of carbonate and clastic reservoirs. Numerous features were identified as the possible cause of these inter-well communication paths, including faults and fractures, thief zones, permeable shale and/or absence of shale. The pilot includes two water injection wells completed in two different reservoirs and twenty six oil production wells. This paper reviews the selection of the candidate wells, the operational constraints as well as the detailed analysis and interpretation of the results. Based on this pilot, interwell connection has been proven in most of the area of interest. Tracers have been detected in six of the twenty six wells, with breakthrough times ranging from three to seventy days. Communication between the carbonate and clastic reservoirs was confirmed in two wells. For some of the early samples, anomalous results were obtained. This has been attributed to contamination during sampling at the platform, and was remediated by improving the quality control during sampling. This water tracer pilot paves the way for further application across the field. Ultimately the tracer results will be used in combination with other surveillance techniques to identify by-passed oil and design fit-for-purpose solutions to target higher recovery.

The vast majority of surfactant flood applications to date have been targeted to high permeability sandstone reservoirs containing formation brine with moderate salinity and hardness. Surfactant flooding in oil-wet, low-permeability carbonate rock is only reported sparsely throughout the literature. In the present work we aimed at identifying an efficient enhanced oil recovery strategy using a dilute surfactant solution. The dilution is highly beneficial in order to reduce not only chemical costs but in particular the environmental footprint. The work contains results from laboratory core flood tests performed on a highly oil-wet, low permeable carbonate reservoir rock material. The rock material investigated had approximately 30% porosity and 5 mD permeability, whereas the formation brine had a high salinity of about 120,000 ppm with a hardness of about 10,000 ppm. Initial combinations of several commercial surfactants, co-surfactant and alkalis were tested for brine compatibility and from these tests two cost-effective surfactant systems were identified. The first system, denoted ITR, was capable of reducing the interfacial tension below 0.001 mN/m at reservoir salinity and hardness. The second system, referred to as WA, altered the wettability from strongly oil-wet to intermediate-wet without altering the interfacial tension. Adsorption of the surfactants was measured to be low for both systems. No mobility control agents, such as polymers, were used in any of the systems because of low rock permeability. Both surfactant systems yielded significant incremental oil, when injected in tertiary as well as in secondary mode. The ITR system recovered almost 95% of OIIP but required many pore volumes since the cores remained oil-wet. Strikingly the WA system recovered approx. 85% of OIIP in secondary mode but achieved this with much fewer pore volumes using a very low concentration of surfactant. The promising WA system was subjected to extensive analysis involving relative permeability function estimation and flooding simulations using UTCHEM. In summary, we have designed an efficient surfactant system capable of recovering significant amounts of oil from low-permeability carbonate reservoir rock material. Wettability alteration of highly oil-wet rock using dilute surfactant solutions may assist in unlocking significant volumes of additional oil from a variety of carbonate reservoirs.

Abstract Chemical radioactive sources are commonly deployed in logging-while-drilling (LWD) assemblies to measure formation bulk density and neutron porosity. These measurements are widely used in porosity evaluation, lithology determination, clay volume estimates and fluid identification. Deploying logging tools with chemical sources poses Health, Safety and Environment (HS&amp;E) risks requiring specific procedures throughout the entire process of planning, logistics and execution of well construction. Obtaining similar, identically equal or better formation bulk density and neutron porosity measurements without chemical sources has many advantages, particularly from the HS&amp;E perspective in both standard and high-risk developments. Advances in LWD technology have enabled the neutron porosity measurement to be obtained by employing an electronic neutron generator instead of a chemical source. These electronic neutron generators have been used for many years in different wireline tools and are now also available in LWD tools. The bulk density measurement has, until recently, only been measured utilizing a chemical source. Recent developments use the gamma rays induced by the interaction of high-energy neutrons (from the electronic neutron generator) with the formation as an "in-situ" source for subsequent derivation of bulk density. Studies of the sourceless neutron-gamma-density (SNGD) data acquired in 15 to 20 horizontal and vertical wells have shown the accuracy obtained is within the specified limits, as compared to the traditional gamma-gamma-density (GGD) data. The typical density differentials observed in these environments are in the 0.01 to 0.02 g/cm3 range, which results in a porosity and saturation "error" in the order of 0.002 to 0.004 V/V. This level of accuracy is probably acceptable in a number of applications (e.g., infill drilling in mature fields), but may not be acceptable in other scenarios (e.g., more complex lithologies, extremely tight reservoirs), unless the HS&amp;E considerations are overriding. The HS&amp;E benefits are important to keep in focus as they have a direct human benefit through the entire process of equipment preparation, transportation, wellsite operation and potential bottomhole assembly abandonment. Associated with this there is also the economic benefits related to less rig time required for source handling, and the potentially large savings in a lost-in-hole (LIH) abandonment scenario, in the locations where this is applicable. All these different aspects, HS&amp;E, financial and technical, associated with the SNGD system need to be evaluated from a holistic viewpoint to ensure the most appropriate, fit-for-purpose acquisition program is selected in each case.

Summary An accurate minimum miscibility pressure (MMP) is one of the key factors in miscible-gasflood design. There is a variety of experimental and analytical methods to determine the MMP, but the most-reliable methods are slimtube experiments, 1D slimtube simulations, mixing-cell models, and the fast key-tie-line approach using the method of characteristics (MOC). Direct comparisons of all these methods generally agree well, but there are cases in which they do not. No explanation has yet been given for these anomalies, although the MMP is critically important to recovery. The focus of this paper is to explain when current MOC results assuming that shocks exist from one key tie line to the next may not be reliable, and how to identify when this is the case. We demonstrate, using fluid characterizations from Middle East oils, that the MMPs using this MOC method can be more than 6,500 psia greater than those calculated using a recently developed mixing-cell method. The observed differences in the MMP increase substantially as the API gravity of the oil decreases, likely the result of the onset of L1-L2-V behavior. We show that the key tie lines determined using this MOC method do not control miscibility for such cases. We explain the reasons for these differences using simplified pseudoternary models and show how to determine when an error exists. We also offer a way to correct the MMP predictions using the MOC for these complex gas/oil displacements without solving for the complete compositional path.

Abstract This paper describes a case study of planning, drilling, completing and production of an extended reach horizontal infill well in the giant Al Shaheen oil field, offshore Qatar. The completion has been designed with three surface controlled zones. The completion is supplemented by a straddle on mechanical open hole packers to isolate a section which has higher risk of pre-mature water breakthrough. This completion provides flexibility for selective production, production testing and performance monitoring.Seven infill wells were planned in the Shuaiba formation for optimization of oil recovery. The first wells were brought online with higher than expected water cuts. A completion was designed for the fourth well in the area to improve reservoir management and liquid handling.The well was successfully drilled with a long step out in order to avoid installing a cemented liner for well spacing purposes in the inner section. The completion was designed based on the downhole logs and record of mud losses while drilling and was installed to 15,000ft. The completion consists of surface controlled sliding sleeves and a ball valve complemented by a pressure gauge and chemical injection. The completion was installed inside a predrilled liner which separated the liner section into zones by timer set mechanical open hole packers. In addition a straddle was installed to isolate a natural fracture zone in the outer part of the well.The completion was run and installed successfully and selective production testing has been conducted. The results show that the three zones have water cuts ranging from 5 to 50%. Selective control of the completion helps to optimise oil production and minimise water production as an integral part of an intelligent field management strategy. Net gain from this completion amounts to some 4,000 stb/day.