Large scale (6") flow experiments have been performed to determine the flow induced forces on a 1.5D horizontal bend in single and multiphase conditions. Multiphase experimens were performed between vsg = 1 – 45 m/s and vsl, =0.004 – 4 m/s at near atmospheric air-water conditions, resulting in a wide range of flow regimes. The bend was fully instrumented with dynamic pressure sensors, force sensors and strain (static and piezo) gauges, upstream and downstream tomography and upstream and downstream video section. Three configurations were evaluated: single bend and upstream Ubend configuration (horizontal and vertical). For the single bend, the upstream holdup characteristics with respect to frequency and wave/slug velocities corresponded well to literature data, indicating developed flow. The force measurements reproduced via F(t)=(p(t)+ρ(t)vwave,slug2)A, in which for the pressure and density the upstream conditions were used. The wave and slug velocity were detetermined via a cross correlation between the upstream and downstream holdup signals. The total force can be estimated via Frms = C(ρl vm2A)We-0.4, with C ~ 25. This is in line with literature data for larger ID pipes but higher than C ~10 for smaller ID tubes. The measured PSD of the force does have the same width as stated in literature.
With an increasing number of smart well applications being installed in the field, more knowledge is required to optimize their operation. This paper compares the benefits of various wellhead gas coning control strategies to optimize production of a thin oil rim. This study is performed within the "Integrated System Approach Petroleum Production (ISAPP)" knowledge center of TNO, TU Delft and Shell. For this study a field case model is used, which has been validated with field data. The field case is a thin oil rim with a horizontal well. Due to the location of the horizontal well in the oil rim, the well is particularly susceptible to gas coning. Besides gas coning, wax precipitation is a second production constraint. This makes this well challenging to operate. Different production strategies are investigated and compared against each other: intermittent production and continuous production with pressure differential control. The results of the different production strategies are presented by analyzing the advantages and disadvantages for the different gas coning control strategies, satisfying the given constraint of gas influx. This study reveals the difference in the cumulative production between the two strategies. The use of a closed loop control strategy can lead to a larger oil production in the same amount of time. This paper shows the viability of using dynamic simulation models to quantitatively assess the benefits of various production optimization strategies. This allows operators to compare emerging smart well technologies, and increase trust in specific technologies that could be of an added value to their operation. Even though much has been published about the potential benefits of a smart field philosophy, few published field cases are available. This paper offers a field case testimony of the comparison of various feedback control strategies for purpose of production optimization. Introduction With increasing knowledge and improving technologies, more complex reservoirs (with respect to location and dimensions) can be explored and produced. This brings new challenges in exploration, drilling and production. Furthermore, existing reservoirs require new insights to be able to increase ultimate recovery. Dedicated simulation software tools can offer these new insights by helping to understand production instabilities and test new control strategies to avoid instabilities and to optimize production. The field under investigation has most of its wells drilled with long laterals in a thin oil rim, making them particularly susceptible to gas coning. Gas coning is a phenomenon where the gas oil contact of a reservoir slowly moves towards a well as a result of high drawdown. Eventually, the free gas is being drawn into the well, see Figure 1. Furthermore, the reservoir temperature is low enough to cause wax deposition. At high production rates, a well will suffer a large gas influx, which cannot be handled by the topside equipment. For low production rates, a well will suffer increased wax deposition due to the lower fluid temperature [Nennie, 2008]. Therefore, due to gas coning and wax deposition, some of the wells are operated intermittently. Goal of this study is to determine whether instead of the intermittent production continuous production is more beneficial and if so, quantifying the difference between these control strategies.
A strong increase in gas inflow due to gas coning and the resulting bean-back because of Gas to Oil Ratio (GOR) constraints can severely limit oil production and reservoir drive energy. In this paper we will use a coupled reservoir-well model to demonstrate that oil production can be increased by using controlled inflow from a gas cone as a natural lift. This model was developed in the knowledge centre Integrated System Approach Petroleum Production (ISAPP) of TNO, TU Delft and Shell, and is based on a commercially available dynamic multiphase well simulation tool (OLGA) and a dynamic multi-phase reservoir simulator (MoReS). In order to give a proof of principle we have implemented a PID feedback controller, which controls the gas fraction in a well by changing its wellhead choke or inflow control valve (ICV) settings, on a realistic test case. We introduce a strategy to find an optimal production set point for this controller and the benefits of using downhole ICVs in comparison to the wellhead choke are investigated. Simulation experiments show that a PID controller is an effective means to prevent a full gas breakthrough and, moreover, can be used to increase the produced oil rate by tuning ICV settings to achieve an optimal well gas fraction. Results show that the coupled simulations could be significantly more accurate in comparison to stand-alone well or reservoir simulations. In current operations ICVs are mostly used to completely shut down well segments that experience gas coning. We show that by keeping these ICVs open in a controlled way the - otherwise undesirable - phenomenon of gas coning can be used to increase oil production. Introduction: Gas Coning Control Gas coning is a phenomenon where the gas-oil-contact (GOC) of a reservoir slowly moves towards a well as a result of oil drawdown. In case of horizontal or deviated wells this is often a zonal phenomenon, which occurs at a limited amount of perforations, and is referred to as 'cresting' (Figure 1). At a certain moment in the production life of a gas coning well the gas-oil-contact will reach the well and a gas breakthrough will occur. Upon breakthrough the well will experience a high gas inflow. Largely for three reasons this is an undesired phenomenon. Firstly because the gas phase may start to dominate production, which will deem the well to be uneconomical. Secondly, the inflow of gas may damage topside equipment that is not designed to process large quantities of this phase. Thirdly, after breakthrough the gas cap of the oil reservoir will be depleted fast, taking away its drive energy. The difficulty of containing these three negative consequences lies in the relative speed of a gas breakthrough - typically expressed in hours. Unfortunately the industry is increasingly faced with these hard to contain consequences because many mature fields experience gas coning. Also, oil is increasingly produced from reservoirs like thin oil rims that tend to cone easily.
In this paper details of the measurement results of the forces on the bends in a 4″ setup are compared to two models. The first model is a simple analytical model and is used to estimate the forces. In the second model, CFD is used. In the experiments only resulting forces, including upstream and downstream bends and mechanical resonance and interaction is measured. The goal of the CFD was to discriminate between flow and mechanics and to evaluate the influence of a flow disturbance as a result of a bend on the force on a downstream second bend. For the simplified analytical model the amplitudes are underestimated, but the frequency spectra look very reasonable in case of the slug flow regime. The main advantage of the simplified analytical model is that the computational time is in the order of seconds, but the accuracy is still reasonable for the use in an engineering approach of determining the structural integrity of the complete pipe system. For the CFD the shape of the force function is similar to the experiments. The CFD results indicate that the forces on the second downstream bend are also measured on the first upstream bend. The accuracy of the CFD simulation is the advantage of this model, but the computational time is very long, especially if the multiphase flow simulation is coupled to the structural model.
A current trend in the oil and gas industry is to use compact so called inline separators (ILS). Unlike their large conventional counterparts, the operation of these separators is very sensitive towards variations in the multiphase flow to be separated. This sensitivity easily results in operational problems and economic loss and may prohibit the application of ILS, in particular as many current production operations are facing large slug flow type of variations. One way to reduce the ILS sensitivity towards flow variations is via improved control. Here, motivated by the industrial need for cost-effective compact separators with sufficient flow variation handling capabilities, a model based approach is pursued to obtain this improvement. More specific, as a first main contribution, a new approach to control oriented modeling of gas/liquid (G/L) ILS is proposed which, in contrast to currently available such modeling approaches, allows for a comprehensive evaluation and design of G/L ILS control strategies. As an example application of the models resulting from this approach and as a second main contribution of this paper, a new model and feedforward control based method for fastly approximating the closed-loop performance limits of a G/L ILS is proposed. The motivation for pursuing this method is an acceleration in overall G/L ILS design speed. The merits of the method are demonstrated through a simulation based application on a commercially available G/L ILS.
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