Eco-friendly water deoiling systems for effective water treatment presents a significant operational and environmental challenge during exploration and development well testing and clean-up operations in offshore environments. As an alternative to traditional storage, transport, and disposal onshore, some offshore operations have attempted to use mobile water treatment systems to reduce the oil-in-water content from the produced water to an acceptable level, before safely discharging overboard in accordance with the local regulatory permitted environmental limits. When this can be routinely and effectively performed, offshore water treatment units may provide an efficient and cost effective alternative to conventional approaches of onshore treatment and disposal of aqueous effluents and waste streams. This paper outlines the operational envelopes and limitations of current commercially available water deoiling systems, and introduces a relatively recently developed mobile light water treatment unit. This new generation light water treatment unit consists of a horizontal vessel containing five coalescing beds evenly distributed along the vessel length and inlet centrifuge for solids removal. The vessel combines both coalescing and gravity separation techniques that is capable of reducing oil-in-water (OIW) concentration to less than 20 ppm. The primary coalescing material is a reusable petroleum absorbent polymer that can be regenerated through centrifugation onshore. Therefore, unlike more traditional water filtration and deoiling systems, it generates no additional waste or by-products. The field applications highlighted in this paper demonstrate the results and lessons learned from successful deployments of this new generation light water treatment unit in firstly offshore well test operations and subsequently the inspection and dewatering of subsea pipelines in environmentally sensitive areas.
Accurate, reliable, and repeatable flow rate measurements during well testing are critical for appropriate reservoir characterization. Recently, well tests have become shorter and more challenging, with the application of new interpretation techniques heightening the need for high resolution and more accurate flow rate measurements. Although conventional well test separators have seen significant improvements over the last few decades in separation efficiency, flow rate measurement accuracy, reliability and repeatability have remained immutable. Historically, the liquid outlets of most conventional well test separators were equipped with positive-displacement or turbine-type flow meters which are not typically tolerant of debris or solids in completion or produced fluids. This results in separators being bypassed during the initial clean-up or well-flow stages, creating gaps in flow rate histories. Additionally, flow rate measurements were greatly influenced by wellsite meter factor measurements (correction coefficients), which usually did not consider fluid type or separation efficiency. Coriolis mass flow rate meters can overcome these challenges. These meters are widely used in process facilities and highly regarded for their precision, accuracy, and simultaneous measurement of true mass flow and fluid density. However, their use in mobile and conventional well testing is still considered to be in its infancy, lacking an extensive track record and field operation experience. This paper will summarize the benefits and lessons learnt from using new-generation Coriolis-equipped well test separators in the North Sea over the past five years. Furthermore, a series of case studies are presented, in which data provided by these flow meters was critical for successful well test operations.
The Caspian offshore is a promising area for hydrocarbon accumulation. Since it is an offshore, it is a challenging area in terms of strict environmental regulations and safety. At the early stage of the project it was clear, that reservoir properties of the exploration well require artificial lift assistance to produce during well testing. Therefore, designing proper DST string with artificial lift was crucial to the success of well testing. This paper describes the methodology to select the artificial lift solution for well test. It shows the unique combination of technologies and techniques that enabled a DST with ESP in combination with the Y tool, that provides capabilities to run thePLT below the pump. Also, one of the main challenges of well testing operation was to handle heavy oil fluid at surface. Being in environmentally sensitive area, designing a surface well testing equipment in a limited footprint, that enables efficient separation and disposal of heavy oil was very critical. Another challenge was unconsolidated formation with the high risk of sand production under drawdown, therefore downhole testing string and ESP pump supposed to withstand large quantity of solids during the production. The key technology that enabled testing was a new generation of abrasion resistant ESP pumps, that are designed to handle extensive solids production. The heavy oil also posed a number of risks. The surface equipment was specifically designed to heat oil in the tanks and if required to mix with diesel before flaring operations. Local regulation does not permit production during the night time and allows limited number of days for well testing. Therefore, well testing design must enable to acquire all necessary information within short period of test duration. The real-time data transmission and interpretation was a key to achieve main goal of the testing in exploration well - to accurately characterize the reservoir. This was the first successful ESP-DST in Caspian Sea. Despite of many challenges, the technologies that were selected for well testing operation was proven to be reliable. This allowed Operator to untap previously not accessible hydrocarbon reserves.
Fractures are common features of many carbonate reservoirs. Given complex flow network that they create, characterization of dynamic behavior of these reservoirs is often complicated and becomes important, especially, if fractures provide primary pathways of fluid flow. In this paper a novel semianalytical simulator was used to understand the pressure behavior of naturally fractured reservoir containing a network of discrete and/or connected finite and infinite-conductivity fractures. In this study an integrated interpretation methodology is applied to analyze well test data acquired in open hole section of exploration well drilled into highly fractured carbonate reservoir of Lower Eocene - Upper Cretaceous sediments on Patardzeuli field of Block XI-B, Republic of Georgia. The main steps consisted of explicitly modeling fractures - both wellbore-intersecting fractures and fractures located away from wellbore - using formation microimager data and calibrating the model to actual well test response using a unique novel mesh-free semi-analytical simulator designed for fractured reservoirs. Study presents the results of well test of one zone performed in highly fractured carbonate reservoir drilled in Patardzeuli field. The pressure-transient response confirmed the complexity of reservoir and dominant contribution to flow regimes from fractures. It is shown in this paper that there are many factors that dominate transient behavior of a well intersected by natural fractures, such as fracture conductivity, length, intensity and distribution, as well as whether fractures intersect the wellbore or not. Moreover, it was demonstrated that presence or absence of damage on wellbore-intersecting fractures in vicinity of wellbore will impact the pressure- transient behavior of reservoir and shape overall productivity of the well. The novelty of the approach is the analysis of the dynamic behavior using a unique semi-analytical pressure transient simulator for fractured reservoirs. The simulator can be used to obtain a response for arbitrarily distributed infinite and/or finite conductivity natural fractures within the reservoir by modeling them explicitly. In this study, it allowed to maximize the value of well tests by assessing the effect of fractures on reservoir dynamic behavior and obtain matrix and fracture parameters where conventional well test interpretation tools would be deemed unviable.
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