Obtaining high resolution, quality formation evaluation data is still only possible with wireline logging. However, with the continued push into deeper and more complex drilling environments, many challenges have been placed in the way of wireline logging, including high tension, high deviation, and increased differential pressure. These factors contribute to an increased risk of tool sticking incidents and lost-in-hole scenarios. Several methods of mitigating these issues on surface (powered capstans, pipe conveyance, etc) have been implemented in the past, but none have been successful in reducing or eliminating the risk downhole without introducing further drawbacks. This paper describes how a new wireline conveyance system has eliminated these issues. The conveyance system consists of wheeled carriages that carry the toolstring off-centre. The mass of the toolstring acts as a counterweight to ensure correct tool orientation in the wellbore. This orientation feature also enables a "guide" device to help navigate ledges and washouts. Such a system eliminates toolstring hold ups, allows access to highly deviated wells without pipe conveyance or tractors, and significantly mitigates differential sticking hazards, while also offering additional benefits in operational efficiency and data quality. A case study from a particularly difficult well in New Zealand is presented. Data acquisition in this well was fraught with challenges: In addition to the 2000m tangent section at 67° deviation, well had severe borehole breakouts. Previous experience in similar scenarios with conventional data acquisition methods yeided poor results. The wheeled carriage system was deployed in multiple innovative configurations resulting in the acquisition of excellent quality data from five wireline descents in hole. This wireline conveyance system has been routinely deployed on multiple deepwater operations in the Gulf of Mexico. One such operation is presented where large gains in logging efficiency have been realised, particularly with the elimination of differential sticking risk and time-consuming pipe conveyed logging. The new technology takes a holistic approach to wireline tool conveyance: Prevent sticking issues using wheeled carriages and mitigate fishing risk using ultra-high strength wireline cables. Wheeled carriages greatly reduce the tool-borehole contact area, preventing the incidence of tool sticking. In addition, wheeled carriages reduce drag while ensuring optimum data quality by sensor position and orientation within the wellbore. Ultra-high strength cables provide ability to log at very high tensions and at the same time provide high overpull capability. The result is a safe, efficient, cost effective and complete Wireline data acquisition.
Flow assurance is a vital challenge that affects the viability of an asset in all oil producing environments. A proper understanding of asphaltene precipitation leading to deposition lends itself to reliable completions planning and timely remediation efforts. This ultimately dictates the production life of the reservoir. The Wireline Formation Tester (WFT) has traditionally aided the understanding of asphaltene composition in reservoir fluids through the collection of pressurized fluid samples. Moreover, the use of Downhole Fluid Analysis (DFA) during a fluid pumpout has augmented the understanding of soluble asphaltenes under in-situ flowing conditions. However, an accurate and representative measurement of Asphaltene Onset Pressure (AOP) has eluded the industry. Traditionally, this measurement has been determined post-acquisition through different laboratory techniques performed on a restored fluid sample. Although sound, there are inherent challenges that affect the quality of the results. These challenges primarily include the need to restore samples to reservoir conditions, maintaining samples at equilibrium composition, and the destruction of fluid samples through inadvertent asphaltene precipitation during transporting and handling. Hence, there is a need for WFT operations to deliver a source of reliable analysis, particularly in high-pressure/high-temperature (HP/HT) reservoirs, to avoid costly miscalculations. A premiere industry method to determine AOP under in-situ producible conditions is presented. Demonstrated in a Gulf of Mexico (GOM) reservoir, this novel technique mimics the gravimetric and light scattering methods, where a fluid sample is isothermally depressurized from initial reservoir pressure; simultaneously, DFA monitors asphaltene precipitation from solution and a high-precision pressure gauge records the onset of asphaltene precipitation. This measurement is provided continuously and in real time. An added advantage is that experiments are performed individually after obtaining a pressurized sample in distinct oil zones. Therefore, the execution of this downhole AOP experiment is independent of an already captured fluid sample and does not impact the quality of any later laboratory-based analysis. Once the measurements are obtained, these can be utilized in flow assurance modeling methods to describe asphaltene precipitation kinetics, and continuity of complex reservoirs. For the first time in literature, this study applies these modeling methods in combination with the AOP data acquired from a downhole WFT This approach has the potential to create a step change in reservoir analysis by providing AOP at the sand-face, along with insight that describe performance from asphaltene precipitation. The results of which have tremendous economic implications on production planning.
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