Bottomhole sampling is, without dispute, the most effective technique for the representative sampling of reservoir fluids, where reservoir flowing conditions permit. A good quality sample will increase the accuracy of and confidence in the PVT data, the interpretation of which can make or break a field development project. The cost benefits to the customer of obtaining quality samples far outweigh the direct cost of the sampling operation. Until recently the world-wide use of bottomhole sampling tools has been limited by a reputation for unreliability. This has led to a reluctance by both service companies and operators alike to invest in the time or equipment to perform this vital service. The transfer of samples from early tools necessitated the handling of large volumes of mercury in the field which was hazardous to personnel, time consuming and environmentally unacceptable. The unpopularity of this task with field engineers certainly contributed to early failures.The introduction of mercury-free bottomhole sampling in the North Seas led to an improvement in service reliability and client confidence. As oil companies began to see the benefit of the improved results, demand for sampling services increased and Oilphase was formed to introduce a new generation of mercury-free bottomhole sampler, the Single-phase Reservoir Sampler (SRS). The introduction of this pressure compensated positive displacement sampler was a resounding success, providing clients with the opportunity to perform studies not previously possible without a monophasic sample. A high pressure (15,000 psi) version of the SRS has been designed and this second generation monophasic sampler has since demonstrated a success rate of over 98% in recovering samples at pressures and temperatures unequalled by any other tool.
Surface sampling of reservoir fluids from the wellhead, separator and stock tank is performed routinely during most well tests and is occasionally required from production process lines. Separator recombination samples are frequently the only route to representative samples. In these circumstances the accuracy of the separator flowrate measurements and stability of separation conditions are critical to the accurate determination of reservoir phase behaviour from the recombined fluids. The Oilphase service includes experienced well test engineers with specific training in reservoir fluids behaviour who are capable of advising the client on sampling and subsequent validation of all types of samples. Advanced methods of sampling are available to determine the amount of liquid carryover in the separator gas line when conditions are stable but separation efficiency is poor. This is particularly the case during high flowrate testing of gas condensate reservoirs where standard methods can produce misleading results.
The interval between exploration or appraisal drilling and the fabrication of production process plant is becoming ever shorter as oil companies seek to exploit their assets with increasing efficiency. A complete understanding of the fluid stream composition and phase behaviour is critical in the selection of materials for completion and process design. Trace elements of highly corrosive or potentially hazardous elements can have an enormous cost impact of the process plant if their presence is unknown or measured inaccurately at the time of plant design. Oilphase offers a comprehensive wellsite analytical service providing sample qualification, fluid property measurement and fluid characterisation. This also includes trace element analysis and monitoring for environmental hazards.