Methods for early-phase planning of offshore fields considering environmental performance

Extraction and processing of oil and gas with current technologies is energy- and carbon-intensive as well as are the manufacture, transport and installation of the facilities needed for oil and gas production. Nowadays, there is a strong emphasis on reducing emissions and energy usage to help mitigate climate change. In this work, we demonstrate a method for decision-support in early-phase field planning based on proxy modeling and optimization. An optimization model is developed to determine drilling and production schedules, as well as the processing capacities of oil and gas that maximize a key performance indicator. The key performance indicator is a linear combination of the normalized net present value and environmental variables, the carbon footprint and carbon dioxide emissions. The weight of each variable in the objective function is adjusted by varying the value of the constants. An offshore field on the Norwegian Continental Shelf is used as a case study. Results show that there is a clear trade-off between economic and environmental performance. There are cases, however, where a modest improvement in field environmental performance can be achieved without significantly decreasing its economic value or requiring additional technologies. As a result of a 13% and 8% reduction in NPV relative to the maximum achievable reduction, the carbon footprint and CO2 emissions will be reduced by 30% and 35%, respectively. The paper offers comments and observations about the implementation and inclusion of environmental indicators into early-field development planning. In the near future, this study will be improved to include a more accurate analysis of the impact of environmental indicators and different low-emission technologies on the field development plan.publishedVersio

Pipe flow experiments of unstable oil-water dispersions with three different oil viscosities: Flow pattern, pressure drop and droplet size measurements

The transport of oil-water dispersions in petroleum production pipelines is difficult to predict and requires special attention since it affects the performance of the entire system. For future field developments it is required to generate accurate predictive models to guarantee an optimal field design. The purpose of this work is to present novel experimental data suitable for improving mechanistic flow models in future works. Oil-water pipe flow experiments were conducted in a stainless-steel flow loop with a L/D ratio of 3766, larger than any comparable setups reported in the literature and sufficient to obtain fully developed flow. A novel level of detail measurements included pressure gradients, density profiles and droplet size distributions. Three oils with different viscosities (oil A: 1.3 cP; oil B: 7 cP; oil C: 22 cP) and brine (3.5 wt% NaCl) as the water phase constituted the three fluid systems used. For each fluid system, several flow rates, and a wide range of water fractions were studied. The fluids were not stabilized by any type of chemical additives. The oil viscosity influences the dispersion behavior, especially for oil continuous flow. For higher oil viscosities the dispersion tends to be more homogeneous, and the pressure drop increases due to increasing wall friction. The droplet size decreases as the oil viscosity increases, presumably due to higher shear stress. Water continuous flows, on the other hand, are less affected by the oil viscosity. A strong drag reduction was found for dispersed flow of all three oils and both oil and water continuous flow. A simple model for the dispersion viscosity and drag reduction was developed based on additional bench scale characterization experiments. With this model the pressure drop could be predicted with good agreement. The data reported in this paper will facilitate the development and validation of mechanistic models for predicting oil-water flows. Previous modelling efforts have been hampered by a lack of detailed measurements, in particular droplet size measurements, hence we believe that this data will allow for significant advancements on the modelling side.publishedVersio

The Low Emission Oil and Gas Open reference platform—An off-grid energy system for renewable integration studies

The data that support the findings of this study are openly available in Zenodo at https://doi.org/10.5281/zenodo (7373223)This article introduces and describes the integrated energy system of the Low Emission Oil and Gas Open reference platform. It is a hypothetical case meant to represent a typical oil and gas installation in the North Sea. The aim of this detailed specification is to serve as an open reference case where all the information about it can be publicly shared, facilitating benchmarking and collaboration. The relevance of this reference case of an off-grid energy system is not limited to the oil and gas industry, since it can also be seen as a special kind of electrical micro grid. The remote offshore location makes it especially relevant for studying offshore wind power and ocean energy sources like wave power. The specification has an emphasis on the energy system and electrical configuration, but also includes a basic description of the oil field and processing system. The intention is that it will serve as a basis for energy system studies and relating power system stability analyses regarding the integration of renewable energy sources. This allows for comparisons of a base case with different design modifications, new operational planning methods, power management strategies and control concepts. Examples of possible modifications are the replacement of gas turbines by wind turbines, addition of energy storage systems, a more variable operation of loads etc. The last part of the article demonstrates the behaviour of the reference platform implemented in two software tools: one for operational planning and one for dynamic power system analyses.publishedVersio

Modelling of dispersed oil/water flow in a near-horizontal pipe

A gravity-diffusion model was implemented for predicting water concentration profiles in dispersed oil-continuous oil–water flows. In this model, the measured droplet size distributions were used instead of a droplet size closure law. The turbulent diffusion was modelled assuming single-phase flow while the gravitational drift was based on closure laws from the literature, including hindrance effects. The results showed that including the effect of turbulence on the drag force was important, where the turbulent fluctuations cause an increase in the average drag because of the non-linearity of the drag law. The model yielded a good match with the experimental data reported by Gonzales et al. (Gonzalez et al., 2022), especially at the highest flow rates. We also concluded that the following model simplification could be introduced without changing the results significantly: 1) The droplet size distributions could be replaced by the Sauter mean droplet size. 2) The diffusivity profile model could be replaced by a uniform diffusivity model.publishedVersio

Experimental investigation of transitional oil-water pipe flow

In this thesis transitional oil-water pipe flow is experimentally studied. Here the word transitional relates to two main topics. First, the study focuses on the investigation of transitional flow patterns and resultant flow phenomena which neither are well described by stratified flow nor by homogeneously dispersed flow. Second, flow development, which can be of extensive length for oil-water flow, is investigated with help of consecutive measurement devices arranged along the test section. The experiments were conducted in two different multiphase flow laboratories. Tap water and different mineral oils with viscosities up to 120mPa*s were used as test fluids. The well flow loop at the Institute for Energy Technology (IFE) in Kjeller, Norway, provides a transparent 25m test section with inner diameter D = 100mm, which is equipped with advanced technology for flow visualization. Gamma densitometry and X-ray tomography were used to obtain detailed measurements of local phase fractions and cross-sectional phase fraction distributions. Three FBRM-probes were installed to investigate droplet size evolution. A static inlet mixer was installed to disturb the flow and enable investigating development of premixed flow. The Multiphase Flow Laboratory at the Norwegian University of Science and Technology (NTNU) provides a transparent test section which is easy to modify. A 50m long modification with a simple ball valve installed as adjustable inlet mixer was used to investigate flow development in terms of changing flow patterns and pressure gradients. Onset of dispersion at considerably lower mixture velocities compared to other studies without inlet mixing was found. Settling and inflow separation downstream of the mixing devices was observed. The flow development was further measured in terms of changing droplet sizes and pressure gradients. A rather dense packed droplet layer in the upper part of the pipe was characteristic for higher input water fractions. The occurrence of the dense packed layer always goes along with a significant increase of the pressure gradient. A simple model for predicting the pressure gradient in dense packed layer flow was proposed. The model considers the dense packed layer as independent phase with its own mixture properties. Model predictions are in good agreement with the measurements while the twofluid model for stratified flow and the homogeneous flow model fail. Furthermore, a tool for the prediction of flow development and development lengths downstream of a mixing device was developed based on simplified settling theory. Applying the tool together with the pressure gradient model allowed for qualitatively reproducing the observed flow development. Locally measured pressure gradient values along the test section could be reproduced with good agreement for low mixture velocities. For higher mixture velocities too fast separation was predicted, as the model does not consider turbulent mixing and droplet break-up

Experimental study of dispersed oil-water flow in a horizontal pipe with enhanced inlet mixing, Part 2: In-situ droplet measurements

acceptedVersio

Experimental study of dispersed oil-water flow in a horizontal pipe with enhanced inlet mixing, Part 1: Flow patterns, phase distributions and pressure gradients

acceptedVersio

Methods for early-phase planning of offshore fields considering environmental performance

Extraction and processing of oil and gas with current technologies is energy- and carbon-intensive as well as are the manufacture, transport and installation of the facilities needed for oil and gas production. Nowadays, there is a strong emphasis on reducing emissions and energy usage to help mitigate climate change. In this work, we demonstrate a method for decision-support in early-phase field planning based on proxy modeling and optimization. An optimization model is developed to determine drilling and production schedules, as well as the processing capacities of oil and gas that maximize a key performance indicator. The key performance indicator is a linear combination of the normalized net present value and environmental variables, the carbon footprint and carbon dioxide emissions. The weight of each variable in the objective function is adjusted by varying the value of the constants. An offshore field on the Norwegian Continental Shelf is used as a case study. Results show that there is a clear trade-off between economic and environmental performance. There are cases, however, where a modest improvement in field environmental performance can be achieved without significantly decreasing its economic value or requiring additional technologies. As a result of a 13% and 8% reduction in NPV relative to the maximum achievable reduction, the carbon footprint and CO2 emissions will be reduced by 30% and 35%, respectively. The paper offers comments and observations about the implementation and inclusion of environmental indicators into early-field development planning. In the near future, this study will be improved to include a more accurate analysis of the impact of environmental indicators and different low-emission technologies on the field development plan

Pipe flow experiments of unstable oil-water dispersions with three different oil viscosities: Flow pattern, pressure drop and droplet size measurements

The transport of oil-water dispersions in petroleum production pipelines is difficult to predict and requires special attention since it affects the performance of the entire system. For future field developments it is required to generate accurate predictive models to guarantee an optimal field design. The purpose of this work is to present novel experimental data suitable for improving mechanistic flow models in future works. Oil-water pipe flow experiments were conducted in a stainless-steel flow loop with a L/D ratio of 3766, larger than any comparable setups reported in the literature and sufficient to obtain fully developed flow. A novel level of detail measurements included pressure gradients, density profiles and droplet size distributions. Three oils with different viscosities (oil A: 1.3 cP; oil B: 7 cP; oil C: 22 cP) and brine (3.5 wt% NaCl) as the water phase constituted the three fluid systems used. For each fluid system, several flow rates, and a wide range of water fractions were studied. The fluids were not stabilized by any type of chemical additives. The oil viscosity influences the dispersion behavior, especially for oil continuous flow. For higher oil viscosities the dispersion tends to be more homogeneous, and the pressure drop increases due to increasing wall friction. The droplet size decreases as the oil viscosity increases, presumably due to higher shear stress. Water continuous flows, on the other hand, are less affected by the oil viscosity. A strong drag reduction was found for dispersed flow of all three oils and both oil and water continuous flow. A simple model for the dispersion viscosity and drag reduction was developed based on additional bench scale characterization experiments. With this model the pressure drop could be predicted with good agreement. The data reported in this paper will facilitate the development and validation of mechanistic models for predicting oil-water flows. Previous modelling efforts have been hampered by a lack of detailed measurements, in particular droplet size measurements, hence we believe that this data will allow for significant advancements on the modelling side