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Innovations in drilling and completion technology has opened a new era in the oil and gas sector revitalizing old fields either to tap bypassed pockets of hydrocarbons or enhance the recovery factor with re-entry wells. Now enhancing production from aging fields has become a major activity for oil and gas companies. However, this is not a straight-forward decision and often the oil companies are challenged with the casing integrity, inadequate or missing log data and being able to complete the well economically. The history of re-entry wells goes back to 1950's but it is only recently that the industry is seeing more medium and short radius wells to improve operational efficiency and to make the projects more economical. Slim borehole, complex geometry and high dogleg severity are the common attributes of such re-entry wells. Unequivocally, these complex wellbore geometries will improve recovery of reserves and maximise the net present value (NPV); however the real challenge lies with the acquisition of formation evaluation data. In these challenging conditions conventional Wireline or LWD techniques cannot provide adequate solutions to obtain much needed formation evaluation data. It was one of the reasons why most of the challenging re-entry wells in the past were not logged. Saudi Aramco faced similar challenges in one of their re-entry aging wells. The well was drilled in 1968 as a vertical open-hole producer. A series of work-overs were performed over the life of the well and in 2002, the well was side-tracked and a short radius trajectory was chosen to drill a horizontal section. During drilling the operator encountered a total loss circulation zone and was forced to plug the zone blindly without being able to log and investigate the cause. Memory logging and slim tools have been introduced in the last decade. The operator planned to carry out another work-over in 2014.
Innovations in drilling and completion technology has opened a new era in the oil and gas sector revitalizing old fields either to tap bypassed pockets of hydrocarbons or enhance the recovery factor with re-entry wells. Now enhancing production from aging fields has become a major activity for oil and gas companies. However, this is not a straight-forward decision and often the oil companies are challenged with the casing integrity, inadequate or missing log data and being able to complete the well economically. The history of re-entry wells goes back to 1950's but it is only recently that the industry is seeing more medium and short radius wells to improve operational efficiency and to make the projects more economical. Slim borehole, complex geometry and high dogleg severity are the common attributes of such re-entry wells. Unequivocally, these complex wellbore geometries will improve recovery of reserves and maximise the net present value (NPV); however the real challenge lies with the acquisition of formation evaluation data. In these challenging conditions conventional Wireline or LWD techniques cannot provide adequate solutions to obtain much needed formation evaluation data. It was one of the reasons why most of the challenging re-entry wells in the past were not logged. Saudi Aramco faced similar challenges in one of their re-entry aging wells. The well was drilled in 1968 as a vertical open-hole producer. A series of work-overs were performed over the life of the well and in 2002, the well was side-tracked and a short radius trajectory was chosen to drill a horizontal section. During drilling the operator encountered a total loss circulation zone and was forced to plug the zone blindly without being able to log and investigate the cause. Memory logging and slim tools have been introduced in the last decade. The operator planned to carry out another work-over in 2014.
Post-drilling open-hole log measurements made by wireline tools are most commonly transmitted to surface via wireline, but the trend is towards increased use of memory-capable tools with greater operational flexibility. The primary purpose of the original memory tools was to operate on wireline in intermediate and TD sections while offering a low-risk alternative to conventional tools in horizontal wells, bad hole conditions and other challenging well scenarios. This wide operational envelope required the tools to be small-diameter to allow protected conveyance inside drill pipe, but it also required that measurement performance and associated environmental characterization be on a par with conventionally sized tools that generated the majority of the historical record. The extent to which these goals have been achieved, using evidence from the over 150,000 wells logged with the most highly developed of the small-diameter tool types, is reviewed. Standard response modelling is essential but insufficient to ensure optimum measurement performance. Findings from the performance in thousands of wells have been used to refine models, hardware designs and processing algorithms, including more precise control on the position of tools in the wellbore. Log data from test wells and commercial wells are provided showing the measurement quality from small-diameter tools matches that from conventionally sized tools for the large majority of operations. Log data is also provided from wells that had presented insurmountable challenges for traditional logging tools which demonstrate the conveyance flexibility and the reduced acquisition risk in using the small-diameter tools. The significance of the findings is that the performance of the most highly developed small-diameter tools has evolved to the point where measurement quality is not a differentiating factor for the large majority of operations, allowing job planning to be driven by the other considerations, in particular the minimization of acquisition risk.
Determining reservoir pressure and confirming fluid type in development wells is of major interest to many reservoir engineers. Because of the high costs and operational risks of having a wireline formation tester (FT) stuck downhole, operators seek reliable technologies that not only deliver the information they need but also mitigate the chances of losing the tool downhole. A new generation of slim, light-weight FT technologies can help make production-management decisions, especially in the often complex geometry of development wells. The Sirikit field Onshore Thailand is an extensively faulted and heterogeneous reservoir, therefore continuously updated pressure profiles have become the key in refining reservoir models. Productive zones are typically thin, but highly permeable. Traditional open hole (OH) log evaluation is insufficient to distinguish fluid types and formation fluid identification (FID) is required in every zone before completion. Because wireline FTs often have thick bodies which are pressed against the borehole wall and sampling takes at least one hour of pump out, they present an increased risk of getting stuck. A smaller diameter FT was evaluated whose body equally centralized in the well during a test in order to dramatically reduce the risk of differential sticking. However it was not clear whether the new tool could similarly distinguish between hydrocarbons and water in a synthetic based mud (SBM) environment using capacitance and resistivity sensors. Four wells with various trajectories and fluid types were selected to benchmark the new tool. Both traditional and new slim FTs were run in the hole (RIH), monitored in real time and the capabilities of the two tools were cross-checked against each other. The results showed that both tools required a similar pump out volume to reach a clean sample. Despite the oil-base mud environment, the slim tool was able to distinguish the transition from mud filtrate to formation hydrocarbons, and in wells where water-base drilling fluids were used, formation water could be similarly recognized. All water samples were directly drained at surface to verify the in-situ real time measurements and oil samples were sent to the lab. The results showed a remarkable consistency in most cases and during trial tests the slimmest sampling tool exhibited a tremendous value in the first stage of field development and it is continuously used nowadays in newly drilled wells. A slim testing and sampling tool shows good reliability for basic fluid identification and is especially suitable for wells with differential sticking issues. Globally, this tool may provide a solution of future wireline pressure and sampling, which can help operators to make proper reservoir-management decisions, especially in complex geometry wells or challenging geological formations.
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